1 @c -*- mode: texinfo; coding: utf-8 -*-
2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-2016 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
8 This chapter describes a number of features related to the display
9 that Emacs presents to the user.
12 * Refresh Screen:: Clearing the screen and redrawing everything on it.
13 * Forcing Redisplay:: Forcing redisplay.
14 * Truncation:: Folding or wrapping long text lines.
15 * The Echo Area:: Displaying messages at the bottom of the screen.
16 * Warnings:: Displaying warning messages for the user.
17 * Invisible Text:: Hiding part of the buffer text.
18 * Selective Display:: Hiding part of the buffer text (the old way).
19 * Temporary Displays:: Displays that go away automatically.
20 * Overlays:: Use overlays to highlight parts of the buffer.
21 * Size of Displayed Text:: How large displayed text is.
22 * Line Height:: Controlling the height of lines.
23 * Faces:: A face defines a graphics style for text characters:
25 * Fringes:: Controlling window fringes.
26 * Scroll Bars:: Controlling scroll bars.
27 * Window Dividers:: Separating windows visually.
28 * Display Property:: Enabling special display features.
29 * Images:: Displaying images in Emacs buffers.
30 * Xwidgets:: Displaying native widgets in Emacs buffers.
31 * Buttons:: Adding clickable buttons to Emacs buffers.
32 * Abstract Display:: Emacs's Widget for Object Collections.
33 * Blinking:: How Emacs shows the matching open parenthesis.
34 * Character Display:: How Emacs displays individual characters.
35 * Beeping:: Audible signal to the user.
36 * Window Systems:: Which window system is being used.
37 * Tooltips:: Tooltip display in Emacs.
38 * Bidirectional Display:: Display of bidirectional scripts, such as
43 @section Refreshing the Screen
44 @cindex refresh the screen
45 @cindex screen refresh
47 The function @code{redraw-frame} clears and redisplays the entire
48 contents of a given frame (@pxref{Frames}). This is useful if the
51 @defun redraw-frame &optional frame
52 This function clears and redisplays frame @var{frame}. If @var{frame}
53 is omitted or nil, it redraws the selected frame.
56 Even more powerful is @code{redraw-display}:
58 @deffn Command redraw-display
59 This function clears and redisplays all visible frames.
62 In Emacs, processing user input takes priority over redisplay. If
63 you call these functions when input is available, they don't redisplay
64 immediately, but the requested redisplay does happen
65 eventually---after all the input has been processed.
67 On text terminals, suspending and resuming Emacs normally also
68 refreshes the screen. Some terminal emulators record separate
69 contents for display-oriented programs such as Emacs and for ordinary
70 sequential display. If you are using such a terminal, you might want
71 to inhibit the redisplay on resumption.
73 @defopt no-redraw-on-reenter
74 @cindex suspend (cf. @code{no-redraw-on-reenter})
75 @cindex resume (cf. @code{no-redraw-on-reenter})
76 This variable controls whether Emacs redraws the entire screen after it
77 has been suspended and resumed. Non-@code{nil} means there is no need
78 to redraw, @code{nil} means redrawing is needed. The default is @code{nil}.
81 @node Forcing Redisplay
82 @section Forcing Redisplay
83 @cindex forcing redisplay
85 Emacs normally tries to redisplay the screen whenever it waits for
86 input. With the following function, you can request an immediate
87 attempt to redisplay, in the middle of Lisp code, without actually
90 @defun redisplay &optional force
91 This function tries immediately to redisplay. The optional argument
92 @var{force}, if non-@code{nil}, forces the redisplay to be performed,
93 instead of being preempted if input is pending.
95 The function returns @code{t} if it actually tried to redisplay, and
96 @code{nil} otherwise. A value of @code{t} does not mean that
97 redisplay proceeded to completion; it could have been preempted by
101 Although @code{redisplay} tries immediately to redisplay, it does
102 not change how Emacs decides which parts of its frame(s) to redisplay.
103 By contrast, the following function adds certain windows to the
104 pending redisplay work (as if their contents had completely changed),
105 but does not immediately try to perform redisplay.
107 @defun force-window-update &optional object
108 This function forces some or all windows to be updated the next time
109 Emacs does a redisplay. If @var{object} is a window, that window is
110 to be updated. If @var{object} is a buffer or buffer name, all
111 windows displaying that buffer are to be updated. If @var{object} is
112 @code{nil} (or omitted), all windows are to be updated.
114 This function does not do a redisplay immediately; Emacs does that as
115 it waits for input, or when the function @code{redisplay} is called.
118 @defvar pre-redisplay-function
119 A function run just before redisplay. It is called with one argument,
120 the set of windows to be redisplayed. The set can be @code{nil},
121 meaning only the selected window, or @code{t}, meaning all the
125 @defvar pre-redisplay-functions
126 This hook is run just before redisplay. It is called once in each
127 window that is about to be redisplayed, with @code{current-buffer} set
128 to the buffer displayed in that window.
133 @cindex line wrapping
134 @cindex line truncation
135 @cindex continuation lines
136 @cindex @samp{$} in display
137 @cindex @samp{\} in display
139 When a line of text extends beyond the right edge of a window, Emacs
140 can @dfn{continue} the line (make it wrap to the next screen
141 line), or @dfn{truncate} the line (limit it to one screen line). The
142 additional screen lines used to display a long text line are called
143 @dfn{continuation} lines. Continuation is not the same as filling;
144 continuation happens on the screen only, not in the buffer contents,
145 and it breaks a line precisely at the right margin, not at a word
146 boundary. @xref{Filling}.
148 On a graphical display, tiny arrow images in the window fringes
149 indicate truncated and continued lines (@pxref{Fringes}). On a text
150 terminal, a @samp{$} in the rightmost column of the window indicates
151 truncation; a @samp{\} on the rightmost column indicates a line that
152 wraps. (The display table can specify alternate characters to use
153 for this; @pxref{Display Tables}).
155 @defopt truncate-lines
156 If this buffer-local variable is non-@code{nil}, lines that extend
157 beyond the right edge of the window are truncated; otherwise, they are
158 continued. As a special exception, the variable
159 @code{truncate-partial-width-windows} takes precedence in
160 @dfn{partial-width} windows (i.e., windows that do not occupy the
164 @defopt truncate-partial-width-windows
165 @cindex partial-width windows
166 This variable controls line truncation in @dfn{partial-width} windows.
167 A partial-width window is one that does not occupy the entire frame
168 width (@pxref{Splitting Windows}). If the value is @code{nil}, line
169 truncation is determined by the variable @code{truncate-lines} (see
170 above). If the value is an integer @var{n}, lines are truncated if
171 the partial-width window has fewer than @var{n} columns, regardless of
172 the value of @code{truncate-lines}; if the partial-width window has
173 @var{n} or more columns, line truncation is determined by
174 @code{truncate-lines}. For any other non-@code{nil} value, lines are
175 truncated in every partial-width window, regardless of the value of
176 @code{truncate-lines}.
179 When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in
180 a window, that forces truncation.
183 If this buffer-local variable is non-@code{nil}, it defines a
184 @dfn{wrap prefix} which Emacs displays at the start of every
185 continuation line. (If lines are truncated, @code{wrap-prefix} is
186 never used.) Its value may be a string or an image (@pxref{Other
187 Display Specs}), or a stretch of whitespace such as specified by the
188 @code{:width} or @code{:align-to} display properties (@pxref{Specified
189 Space}). The value is interpreted in the same way as a @code{display}
190 text property. @xref{Display Property}.
192 A wrap prefix may also be specified for regions of text, using the
193 @code{wrap-prefix} text or overlay property. This takes precedence
194 over the @code{wrap-prefix} variable. @xref{Special Properties}.
198 If this buffer-local variable is non-@code{nil}, it defines a
199 @dfn{line prefix} which Emacs displays at the start of every
200 non-continuation line. Its value may be a string or an image
201 (@pxref{Other Display Specs}), or a stretch of whitespace such as
202 specified by the @code{:width} or @code{:align-to} display properties
203 (@pxref{Specified Space}). The value is interpreted in the same way
204 as a @code{display} text property. @xref{Display Property}.
206 A line prefix may also be specified for regions of text using the
207 @code{line-prefix} text or overlay property. This takes precedence
208 over the @code{line-prefix} variable. @xref{Special Properties}.
212 If your buffer contains only very short lines, you might find it
213 advisable to set @code{cache-long-scans} to @code{nil}.
215 @defvar cache-long-scans
216 If this variable is non-@code{nil} (the default), various indentation
217 and motion functions, and Emacs redisplay, cache the results of
218 scanning the buffer, and consult the cache to avoid rescanning regions
219 of the buffer unless they are modified.
221 Turning off the cache speeds up processing of short lines somewhat.
223 This variable is automatically buffer-local in every buffer.
228 @section The Echo Area
229 @cindex error display
232 @c FIXME: Why not use @xref{Minibuffers} directly? --xfq
233 The @dfn{echo area} is used for displaying error messages
234 (@pxref{Errors}), for messages made with the @code{message} primitive,
235 and for echoing keystrokes. It is not the same as the minibuffer,
236 despite the fact that the minibuffer appears (when active) in the same
237 place on the screen as the echo area. @xref{Minibuffer,, The
238 Minibuffer, emacs, The GNU Emacs Manual}.
240 Apart from the functions documented in this section, you can print
241 Lisp objects to the echo area by specifying @code{t} as the output
242 stream. @xref{Output Streams}.
245 * Displaying Messages:: Explicitly displaying text in the echo area.
246 * Progress:: Informing user about progress of a long operation.
247 * Logging Messages:: Echo area messages are logged for the user.
248 * Echo Area Customization:: Controlling the echo area.
251 @node Displaying Messages
252 @subsection Displaying Messages in the Echo Area
253 @cindex display message in echo area
255 This section describes the standard functions for displaying
256 messages in the echo area.
258 @defun message format-string &rest arguments
259 This function displays a message in the echo area.
260 @var{format-string} is a format string, and @var{arguments} are the
261 objects for its format specifications, like in the @code{format-message}
262 function (@pxref{Formatting Strings}). The resulting formatted string
263 is displayed in the echo area; if it contains @code{face} text
264 properties, it is displayed with the specified faces (@pxref{Faces}).
265 The string is also added to the @file{*Messages*} buffer, but without
266 text properties (@pxref{Logging Messages}).
268 A format that quotes with grave accents and apostrophes @t{`like
269 this'} typically generates curved quotes @t{‘like this’}. In
270 contrast, a format that quotes with only apostrophes @t{'like this'}
271 typically generates two closing curved quotes @t{’like this’}, an
272 unusual style in English. @xref{Keys in Documentation}, for how the
273 @code{text-quoting-style} variable affects generated quotes.
275 In batch mode, the message is printed to the standard error stream,
276 followed by a newline.
278 When @code{inhibit-message} is non-@code{nil}, no message will be displayed
279 in the echo area, it will only be logged to @samp{*Messages*}.
281 If @var{format-string} is @code{nil} or the empty string,
282 @code{message} clears the echo area; if the echo area has been
283 expanded automatically, this brings it back to its normal size. If
284 the minibuffer is active, this brings the minibuffer contents back
285 onto the screen immediately.
289 (message "Reverting `%s'..." (buffer-name))
290 @print{} Reverting ‘subr.el’...
291 @result{} "Reverting ‘subr.el’..."
295 ---------- Echo Area ----------
296 Reverting ‘subr.el’...
297 ---------- Echo Area ----------
301 To automatically display a message in the echo area or in a pop-buffer,
302 depending on its size, use @code{display-message-or-buffer} (see below).
304 @strong{Warning:} If you want to use your own string as a message
305 verbatim, don't just write @code{(message @var{string})}. If
306 @var{string} contains @samp{%}, @samp{`}, or @samp{'} it may be
307 reformatted, with undesirable results. Instead, use @code{(message
311 @defvar inhibit-message
312 When this variable is non-@code{nil}, @code{message} and related functions
313 will not use the Echo Area to display messages.
316 @defmac with-temp-message message &rest body
317 This construct displays a message in the echo area temporarily, during
318 the execution of @var{body}. It displays @var{message}, executes
319 @var{body}, then returns the value of the last body form while restoring
320 the previous echo area contents.
323 @defun message-or-box format-string &rest arguments
324 This function displays a message like @code{message}, but may display it
325 in a dialog box instead of the echo area. If this function is called in
326 a command that was invoked using the mouse---more precisely, if
327 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
328 @code{nil} or a list---then it uses a dialog box or pop-up menu to
329 display the message. Otherwise, it uses the echo area. (This is the
330 same criterion that @code{y-or-n-p} uses to make a similar decision; see
331 @ref{Yes-or-No Queries}.)
333 You can force use of the mouse or of the echo area by binding
334 @code{last-nonmenu-event} to a suitable value around the call.
337 @defun message-box format-string &rest arguments
339 This function displays a message like @code{message}, but uses a dialog
340 box (or a pop-up menu) whenever that is possible. If it is impossible
341 to use a dialog box or pop-up menu, because the terminal does not
342 support them, then @code{message-box} uses the echo area, like
346 @defun display-message-or-buffer message &optional buffer-name action frame
347 This function displays the message @var{message}, which may be either a
348 string or a buffer. If it is shorter than the maximum height of the
349 echo area, as defined by @code{max-mini-window-height}, it is displayed
350 in the echo area, using @code{message}. Otherwise,
351 @code{display-buffer} is used to show it in a pop-up buffer.
353 Returns either the string shown in the echo area, or when a pop-up
354 buffer is used, the window used to display it.
356 If @var{message} is a string, then the optional argument
357 @var{buffer-name} is the name of the buffer used to display it when a
358 pop-up buffer is used, defaulting to @file{*Message*}. In the case
359 where @var{message} is a string and displayed in the echo area, it is
360 not specified whether the contents are inserted into the buffer anyway.
362 The optional arguments @var{action} and @var{frame} are as for
363 @code{display-buffer}, and only used if a buffer is displayed.
366 @defun current-message
367 This function returns the message currently being displayed in the
368 echo area, or @code{nil} if there is none.
372 @subsection Reporting Operation Progress
373 @cindex progress reporting
375 When an operation can take a while to finish, you should inform the
376 user about the progress it makes. This way the user can estimate
377 remaining time and clearly see that Emacs is busy working, not hung.
378 A convenient way to do this is to use a @dfn{progress reporter}.
380 Here is a working example that does nothing useful:
383 (let ((progress-reporter
384 (make-progress-reporter "Collecting mana for Emacs..."
388 (progress-reporter-update progress-reporter k))
389 (progress-reporter-done progress-reporter))
392 @defun make-progress-reporter message &optional min-value max-value current-value min-change min-time
393 This function creates and returns a progress reporter object, which
394 you will use as an argument for the other functions listed below. The
395 idea is to precompute as much data as possible to make progress
398 When this progress reporter is subsequently used, it will display
399 @var{message} in the echo area, followed by progress percentage.
400 @var{message} is treated as a simple string. If you need it to depend
401 on a filename, for instance, use @code{format-message} before calling this
404 The arguments @var{min-value} and @var{max-value} should be numbers
405 standing for the starting and final states of the operation. For
406 instance, an operation that scans a buffer should set these to the
407 results of @code{point-min} and @code{point-max} correspondingly.
408 @var{max-value} should be greater than @var{min-value}.
410 Alternatively, you can set @var{min-value} and @var{max-value} to
411 @code{nil}. In that case, the progress reporter does not report
412 process percentages; it instead displays a ``spinner'' that rotates a
413 notch each time you update the progress reporter.
415 If @var{min-value} and @var{max-value} are numbers, you can give the
416 argument @var{current-value} a numerical value specifying the initial
417 progress; if omitted, this defaults to @var{min-value}.
419 The remaining arguments control the rate of echo area updates. The
420 progress reporter will wait for at least @var{min-change} more
421 percents of the operation to be completed before printing next
422 message; the default is one percent. @var{min-time} specifies the
423 minimum time in seconds to pass between successive prints; the default
424 is 0.2 seconds. (On some operating systems, the progress reporter may
425 handle fractions of seconds with varying precision).
427 This function calls @code{progress-reporter-update}, so the first
428 message is printed immediately.
431 @defun progress-reporter-update reporter &optional value
432 This function does the main work of reporting progress of your
433 operation. It displays the message of @var{reporter}, followed by
434 progress percentage determined by @var{value}. If percentage is zero,
435 or close enough according to the @var{min-change} and @var{min-time}
436 arguments, then it is omitted from the output.
438 @var{reporter} must be the result of a call to
439 @code{make-progress-reporter}. @var{value} specifies the current
440 state of your operation and must be between @var{min-value} and
441 @var{max-value} (inclusive) as passed to
442 @code{make-progress-reporter}. For instance, if you scan a buffer,
443 then @var{value} should be the result of a call to @code{point}.
445 This function respects @var{min-change} and @var{min-time} as passed
446 to @code{make-progress-reporter} and so does not output new messages
447 on every invocation. It is thus very fast and normally you should not
448 try to reduce the number of calls to it: resulting overhead will most
449 likely negate your effort.
452 @defun progress-reporter-force-update reporter &optional value new-message
453 This function is similar to @code{progress-reporter-update} except
454 that it prints a message in the echo area unconditionally.
456 The first two arguments have the same meaning as for
457 @code{progress-reporter-update}. Optional @var{new-message} allows
458 you to change the message of the @var{reporter}. Since this function
459 always updates the echo area, such a change will be immediately
460 presented to the user.
463 @defun progress-reporter-done reporter
464 This function should be called when the operation is finished. It
465 prints the message of @var{reporter} followed by word @samp{done} in the
468 You should always call this function and not hope for
469 @code{progress-reporter-update} to print @samp{100%}. Firstly, it may
470 never print it, there are many good reasons for this not to happen.
471 Secondly, @samp{done} is more explicit.
474 @defmac dotimes-with-progress-reporter (var count [result]) message body@dots{}
475 This is a convenience macro that works the same way as @code{dotimes}
476 does, but also reports loop progress using the functions described
477 above. It allows you to save some typing.
479 You can rewrite the example in the beginning of this node using
483 (dotimes-with-progress-reporter
485 "Collecting some mana for Emacs..."
490 @node Logging Messages
491 @subsection Logging Messages in @file{*Messages*}
492 @cindex logging echo-area messages
494 Almost all the messages displayed in the echo area are also recorded
495 in the @file{*Messages*} buffer so that the user can refer back to
496 them. This includes all the messages that are output with
497 @code{message}. By default, this buffer is read-only and uses the major
498 mode @code{messages-buffer-mode}. Nothing prevents the user from
499 killing the @file{*Messages*} buffer, but the next display of a message
500 recreates it. Any Lisp code that needs to access the
501 @file{*Messages*} buffer directly and wants to ensure that it exists
502 should use the function @code{messages-buffer}.
504 @defun messages-buffer
505 This function returns the @file{*Messages*} buffer. If it does not
506 exist, it creates it, and switches it to @code{messages-buffer-mode}.
509 @defopt message-log-max
510 This variable specifies how many lines to keep in the @file{*Messages*}
511 buffer. The value @code{t} means there is no limit on how many lines to
512 keep. The value @code{nil} disables message logging entirely. Here's
513 how to display a message and prevent it from being logged:
516 (let (message-log-max)
521 To make @file{*Messages*} more convenient for the user, the logging
522 facility combines successive identical messages. It also combines
523 successive related messages for the sake of two cases: question
524 followed by answer, and a series of progress messages.
526 A question followed by an answer has two messages like the
527 ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
528 and the second is @samp{@var{question}...@var{answer}}. The first
529 message conveys no additional information beyond what's in the second,
530 so logging the second message discards the first from the log.
532 A series of progress messages has successive messages like
533 those produced by @code{make-progress-reporter}. They have the form
534 @samp{@var{base}...@var{how-far}}, where @var{base} is the same each
535 time, while @var{how-far} varies. Logging each message in the series
536 discards the previous one, provided they are consecutive.
538 The functions @code{make-progress-reporter} and @code{y-or-n-p}
539 don't have to do anything special to activate the message log
540 combination feature. It operates whenever two consecutive messages
541 are logged that share a common prefix ending in @samp{...}.
543 @node Echo Area Customization
544 @subsection Echo Area Customization
545 @cindex echo area customization
547 These variables control details of how the echo area works.
549 @defvar cursor-in-echo-area
550 This variable controls where the cursor appears when a message is
551 displayed in the echo area. If it is non-@code{nil}, then the cursor
552 appears at the end of the message. Otherwise, the cursor appears at
553 point---not in the echo area at all.
555 The value is normally @code{nil}; Lisp programs bind it to @code{t}
556 for brief periods of time.
559 @defvar echo-area-clear-hook
560 This normal hook is run whenever the echo area is cleared---either by
561 @code{(message nil)} or for any other reason.
564 @defopt echo-keystrokes
565 This variable determines how much time should elapse before command
566 characters echo. Its value must be a number, and specifies the
567 number of seconds to wait before echoing. If the user types a prefix
568 key (such as @kbd{C-x}) and then delays this many seconds before
569 continuing, the prefix key is echoed in the echo area. (Once echoing
570 begins in a key sequence, all subsequent characters in the same key
571 sequence are echoed immediately.)
573 If the value is zero, then command input is not echoed.
576 @defvar message-truncate-lines
577 Normally, displaying a long message resizes the echo area to display
578 the entire message. But if the variable @code{message-truncate-lines}
579 is non-@code{nil}, the echo area does not resize, and the message is
583 The variable @code{max-mini-window-height}, which specifies the
584 maximum height for resizing minibuffer windows, also applies to the
585 echo area (which is really a special use of the minibuffer window;
586 @pxref{Minibuffer Misc}).
589 @section Reporting Warnings
592 @dfn{Warnings} are a facility for a program to inform the user of a
593 possible problem, but continue running.
596 * Warning Basics:: Warnings concepts and functions to report them.
597 * Warning Variables:: Variables programs bind to customize their warnings.
598 * Warning Options:: Variables users set to control display of warnings.
599 * Delayed Warnings:: Deferring a warning until the end of a command.
603 @subsection Warning Basics
604 @cindex severity level
606 Every warning has a textual message, which explains the problem for
607 the user, and a @dfn{severity level} which is a symbol. Here are the
608 possible severity levels, in order of decreasing severity, and their
613 A problem that will seriously impair Emacs operation soon
614 if you do not attend to it promptly.
616 A report of data or circumstances that are inherently wrong.
618 A report of data or circumstances that are not inherently wrong, but
619 raise suspicion of a possible problem.
621 A report of information that may be useful if you are debugging.
624 When your program encounters invalid input data, it can either
625 signal a Lisp error by calling @code{error} or @code{signal} or report
626 a warning with severity @code{:error}. Signaling a Lisp error is the
627 easiest thing to do, but it means the program cannot continue
628 processing. If you want to take the trouble to implement a way to
629 continue processing despite the bad data, then reporting a warning of
630 severity @code{:error} is the right way to inform the user of the
631 problem. For instance, the Emacs Lisp byte compiler can report an
632 error that way and continue compiling other functions. (If the
633 program signals a Lisp error and then handles it with
634 @code{condition-case}, the user won't see the error message; it could
635 show the message to the user by reporting it as a warning.)
637 @c FIXME: Why use "(bytecomp)" instead of "'bytecomp" or simply
638 @c "bytecomp" here? The parens are part of warning-type-format but
639 @c not part of the warning type. --xfq
641 Each warning has a @dfn{warning type} to classify it. The type is a
642 list of symbols. The first symbol should be the custom group that you
643 use for the program's user options. For example, byte compiler
644 warnings use the warning type @code{(bytecomp)}. You can also
645 subcategorize the warnings, if you wish, by using more symbols in the
648 @defun display-warning type message &optional level buffer-name
649 This function reports a warning, using @var{message} as the message
650 and @var{type} as the warning type. @var{level} should be the
651 severity level, with @code{:warning} being the default.
653 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
654 for logging the warning. By default, it is @file{*Warnings*}.
657 @defun lwarn type level message &rest args
658 This function reports a warning using the value of @code{(format-message
659 @var{message} @var{args}...)} as the message in the @file{*Warnings*}
660 buffer. In other respects it is equivalent to @code{display-warning}.
663 @defun warn message &rest args
664 This function reports a warning using the value of @code{(format-message
665 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
666 type, and @code{:warning} as the severity level. It exists for
667 compatibility only; we recommend not using it, because you should
668 specify a specific warning type.
671 @node Warning Variables
672 @subsection Warning Variables
673 @cindex warning variables
675 Programs can customize how their warnings appear by binding
676 the variables described in this section.
678 @defvar warning-levels
679 This list defines the meaning and severity order of the warning
680 severity levels. Each element defines one severity level,
681 and they are arranged in order of decreasing severity.
683 Each element has the form @code{(@var{level} @var{string}
684 @var{function})}, where @var{level} is the severity level it defines.
685 @var{string} specifies the textual description of this level.
686 @var{string} should use @samp{%s} to specify where to put the warning
687 type information, or it can omit the @samp{%s} so as not to include
690 The optional @var{function}, if non-@code{nil}, is a function to call
691 with no arguments, to get the user's attention.
693 Normally you should not change the value of this variable.
696 @defvar warning-prefix-function
697 If non-@code{nil}, the value is a function to generate prefix text for
698 warnings. Programs can bind the variable to a suitable function.
699 @code{display-warning} calls this function with the warnings buffer
700 current, and the function can insert text in it. That text becomes
701 the beginning of the warning message.
703 The function is called with two arguments, the severity level and its
704 entry in @code{warning-levels}. It should return a list to use as the
705 entry (this value need not be an actual member of
706 @code{warning-levels}). By constructing this value, the function can
707 change the severity of the warning, or specify different handling for
708 a given severity level.
710 If the variable's value is @code{nil} then there is no function
714 @defvar warning-series
715 Programs can bind this variable to @code{t} to say that the next
716 warning should begin a series. When several warnings form a series,
717 that means to leave point on the first warning of the series, rather
718 than keep moving it for each warning so that it appears on the last one.
719 The series ends when the local binding is unbound and
720 @code{warning-series} becomes @code{nil} again.
722 The value can also be a symbol with a function definition. That is
723 equivalent to @code{t}, except that the next warning will also call
724 the function with no arguments with the warnings buffer current. The
725 function can insert text which will serve as a header for the series
728 Once a series has begun, the value is a marker which points to the
729 buffer position in the warnings buffer of the start of the series.
731 The variable's normal value is @code{nil}, which means to handle
732 each warning separately.
735 @defvar warning-fill-prefix
736 When this variable is non-@code{nil}, it specifies a fill prefix to
737 use for filling each warning's text.
740 @defvar warning-type-format
741 This variable specifies the format for displaying the warning type
742 in the warning message. The result of formatting the type this way
743 gets included in the message under the control of the string in the
744 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
745 If you bind it to @code{""} then the warning type won't appear at
749 @node Warning Options
750 @subsection Warning Options
751 @cindex warning options
753 These variables are used by users to control what happens
754 when a Lisp program reports a warning.
756 @defopt warning-minimum-level
757 This user option specifies the minimum severity level that should be
758 shown immediately to the user. The default is @code{:warning}, which
759 means to immediately display all warnings except @code{:debug}
763 @defopt warning-minimum-log-level
764 This user option specifies the minimum severity level that should be
765 logged in the warnings buffer. The default is @code{:warning}, which
766 means to log all warnings except @code{:debug} warnings.
769 @defopt warning-suppress-types
770 This list specifies which warning types should not be displayed
771 immediately for the user. Each element of the list should be a list
772 of symbols. If its elements match the first elements in a warning
773 type, then that warning is not displayed immediately.
776 @defopt warning-suppress-log-types
777 This list specifies which warning types should not be logged in the
778 warnings buffer. Each element of the list should be a list of
779 symbols. If it matches the first few elements in a warning type, then
780 that warning is not logged.
783 @node Delayed Warnings
784 @subsection Delayed Warnings
785 @cindex delayed warnings
787 Sometimes, you may wish to avoid showing a warning while a command is
788 running, and only show it only after the end of the command. You can
789 use the variable @code{delayed-warnings-list} for this.
791 @defvar delayed-warnings-list
792 The value of this variable is a list of warnings to be displayed after
793 the current command has finished. Each element must be a list
796 (@var{type} @var{message} [@var{level} [@var{buffer-name}]])
800 with the same form, and the same meanings, as the argument list of
801 @code{display-warning} (@pxref{Warning Basics}). Immediately after
802 running @code{post-command-hook} (@pxref{Command Overview}), the Emacs
803 command loop displays all the warnings specified by this variable,
804 then resets it to @code{nil}.
807 Programs which need to further customize the delayed warnings
808 mechanism can change the variable @code{delayed-warnings-hook}:
810 @defvar delayed-warnings-hook
811 This is a normal hook which is run by the Emacs command loop, after
812 @code{post-command-hook}, in order to to process and display delayed
815 Its default value is a list of two functions:
818 (collapse-delayed-warnings display-delayed-warnings)
821 @findex collapse-delayed-warnings
822 @findex display-delayed-warnings
824 The function @code{collapse-delayed-warnings} removes repeated entries
825 from @code{delayed-warnings-list}. The function
826 @code{display-delayed-warnings} calls @code{display-warning} on each
827 of the entries in @code{delayed-warnings-list}, in turn, and then sets
828 @code{delayed-warnings-list} to @code{nil}.
832 @section Invisible Text
834 @cindex invisible text
835 You can make characters @dfn{invisible}, so that they do not appear on
836 the screen, with the @code{invisible} property. This can be either a
837 text property (@pxref{Text Properties}) or an overlay property
838 (@pxref{Overlays}). Cursor motion also partly ignores these
839 characters; if the command loop finds that point is inside a range of
840 invisible text after a command, it relocates point to the other side
843 In the simplest case, any non-@code{nil} @code{invisible} property makes
844 a character invisible. This is the default case---if you don't alter
845 the default value of @code{buffer-invisibility-spec}, this is how the
846 @code{invisible} property works. You should normally use @code{t}
847 as the value of the @code{invisible} property if you don't plan
848 to set @code{buffer-invisibility-spec} yourself.
850 More generally, you can use the variable @code{buffer-invisibility-spec}
851 to control which values of the @code{invisible} property make text
852 invisible. This permits you to classify the text into different subsets
853 in advance, by giving them different @code{invisible} values, and
854 subsequently make various subsets visible or invisible by changing the
855 value of @code{buffer-invisibility-spec}.
857 Controlling visibility with @code{buffer-invisibility-spec} is
858 especially useful in a program to display the list of entries in a
859 database. It permits the implementation of convenient filtering
860 commands to view just a part of the entries in the database. Setting
861 this variable is very fast, much faster than scanning all the text in
862 the buffer looking for properties to change.
864 @defvar buffer-invisibility-spec
865 This variable specifies which kinds of @code{invisible} properties
866 actually make a character invisible. Setting this variable makes it
871 A character is invisible if its @code{invisible} property is
872 non-@code{nil}. This is the default.
875 Each element of the list specifies a criterion for invisibility; if a
876 character's @code{invisible} property fits any one of these criteria,
877 the character is invisible. The list can have two kinds of elements:
881 A character is invisible if its @code{invisible} property value is
882 @var{atom} or if it is a list with @var{atom} as a member; comparison
883 is done with @code{eq}.
885 @item (@var{atom} . t)
886 A character is invisible if its @code{invisible} property value is
887 @var{atom} or if it is a list with @var{atom} as a member; comparison
888 is done with @code{eq}. Moreover, a sequence of such characters
889 displays as an ellipsis.
894 Two functions are specifically provided for adding elements to
895 @code{buffer-invisibility-spec} and removing elements from it.
897 @defun add-to-invisibility-spec element
898 This function adds the element @var{element} to
899 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
900 was @code{t}, it changes to a list, @code{(t)}, so that text whose
901 @code{invisible} property is @code{t} remains invisible.
904 @defun remove-from-invisibility-spec element
905 This removes the element @var{element} from
906 @code{buffer-invisibility-spec}. This does nothing if @var{element}
910 A convention for use of @code{buffer-invisibility-spec} is that a
911 major mode should use the mode's own name as an element of
912 @code{buffer-invisibility-spec} and as the value of the
913 @code{invisible} property:
916 ;; @r{If you want to display an ellipsis:}
917 (add-to-invisibility-spec '(my-symbol . t))
918 ;; @r{If you don't want ellipsis:}
919 (add-to-invisibility-spec 'my-symbol)
921 (overlay-put (make-overlay beginning end)
922 'invisible 'my-symbol)
924 ;; @r{When done with the invisibility:}
925 (remove-from-invisibility-spec '(my-symbol . t))
926 ;; @r{Or respectively:}
927 (remove-from-invisibility-spec 'my-symbol)
930 You can check for invisibility using the following function:
932 @defun invisible-p pos-or-prop
933 If @var{pos-or-prop} is a marker or number, this function returns a
934 non-@code{nil} value if the text at that position is invisible.
936 If @var{pos-or-prop} is any other kind of Lisp object, that is taken
937 to mean a possible value of the @code{invisible} text or overlay
938 property. In that case, this function returns a non-@code{nil} value
939 if that value would cause text to become invisible, based on the
940 current value of @code{buffer-invisibility-spec}.
943 @vindex line-move-ignore-invisible
944 Ordinarily, functions that operate on text or move point do not care
945 whether the text is invisible, they process invisible characters and
946 visible characters alike. The user-level line motion commands,
947 such as @code{next-line}, @code{previous-line}, ignore invisible
948 newlines if @code{line-move-ignore-invisible} is non-@code{nil} (the
949 default), i.e., behave like these invisible newlines didn't exist in
950 the buffer, but only because they are explicitly programmed to do so.
952 If a command ends with point inside or at the boundary of
953 invisible text, the main editing loop relocates point to one of the
954 two ends of the invisible text. Emacs chooses the direction of
955 relocation so that it is the same as the overall movement direction of
956 the command; if in doubt, it prefers a position where an inserted char
957 would not inherit the @code{invisible} property. Additionally, if the
958 text is not replaced by an ellipsis and the command only moved within
959 the invisible text, then point is moved one extra character so as to
960 try and reflect the command's movement by a visible movement of the
963 Thus, if the command moved point back to an invisible range (with the usual
964 stickiness), Emacs moves point back to the beginning of that range. If the
965 command moved point forward into an invisible range, Emacs moves point forward
966 to the first visible character that follows the invisible text and then forward
969 These @dfn{adjustments} of point that ended up in the middle of
970 invisible text can be disabled by setting @code{disable-point-adjustment}
971 to a non-@code{nil} value. @xref{Adjusting Point}.
973 Incremental search can make invisible overlays visible temporarily
974 and/or permanently when a match includes invisible text. To enable
975 this, the overlay should have a non-@code{nil}
976 @code{isearch-open-invisible} property. The property value should be a
977 function to be called with the overlay as an argument. This function
978 should make the overlay visible permanently; it is used when the match
979 overlaps the overlay on exit from the search.
981 During the search, such overlays are made temporarily visible by
982 temporarily modifying their invisible and intangible properties. If you
983 want this to be done differently for a certain overlay, give it an
984 @code{isearch-open-invisible-temporary} property which is a function.
985 The function is called with two arguments: the first is the overlay, and
986 the second is @code{nil} to make the overlay visible, or @code{t} to
987 make it invisible again.
989 @node Selective Display
990 @section Selective Display
991 @c @cindex selective display Duplicates selective-display
993 @dfn{Selective display} refers to a pair of related features for
994 hiding certain lines on the screen.
996 @cindex explicit selective display
997 The first variant, explicit selective display, was designed for use in a Lisp
998 program: it controls which lines are hidden by altering the text. This kind of
999 hiding is now obsolete; instead you can get the same effect with the
1000 @code{invisible} property (@pxref{Invisible Text}).
1002 In the second variant, the choice of lines to hide is made
1003 automatically based on indentation. This variant is designed to be a
1006 The way you control explicit selective display is by replacing a
1007 newline (control-j) with a carriage return (control-m). The text that
1008 was formerly a line following that newline is now hidden. Strictly
1009 speaking, it is temporarily no longer a line at all, since only
1010 newlines can separate lines; it is now part of the previous line.
1012 Selective display does not directly affect editing commands. For
1013 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
1014 into hidden text. However, the replacement of newline characters with
1015 carriage return characters affects some editing commands. For
1016 example, @code{next-line} skips hidden lines, since it searches only
1017 for newlines. Modes that use selective display can also define
1018 commands that take account of the newlines, or that control which
1019 parts of the text are hidden.
1021 When you write a selectively displayed buffer into a file, all the
1022 control-m's are output as newlines. This means that when you next read
1023 in the file, it looks OK, with nothing hidden. The selective display
1024 effect is seen only within Emacs.
1026 @defvar selective-display
1027 This buffer-local variable enables selective display. This means that
1028 lines, or portions of lines, may be made hidden.
1032 If the value of @code{selective-display} is @code{t}, then the character
1033 control-m marks the start of hidden text; the control-m, and the rest
1034 of the line following it, are not displayed. This is explicit selective
1038 If the value of @code{selective-display} is a positive integer, then
1039 lines that start with more than that many columns of indentation are not
1043 When some portion of a buffer is hidden, the vertical movement
1044 commands operate as if that portion did not exist, allowing a single
1045 @code{next-line} command to skip any number of hidden lines.
1046 However, character movement commands (such as @code{forward-char}) do
1047 not skip the hidden portion, and it is possible (if tricky) to insert
1048 or delete text in an hidden portion.
1050 In the examples below, we show the @emph{display appearance} of the
1051 buffer @code{foo}, which changes with the value of
1052 @code{selective-display}. The @emph{contents} of the buffer do not
1057 (setq selective-display nil)
1060 ---------- Buffer: foo ----------
1067 ---------- Buffer: foo ----------
1071 (setq selective-display 2)
1074 ---------- Buffer: foo ----------
1079 ---------- Buffer: foo ----------
1084 @defopt selective-display-ellipses
1085 If this buffer-local variable is non-@code{nil}, then Emacs displays
1086 @samp{@dots{}} at the end of a line that is followed by hidden text.
1087 This example is a continuation of the previous one.
1091 (setq selective-display-ellipses t)
1094 ---------- Buffer: foo ----------
1099 ---------- Buffer: foo ----------
1103 You can use a display table to substitute other text for the ellipsis
1104 (@samp{@dots{}}). @xref{Display Tables}.
1107 @node Temporary Displays
1108 @section Temporary Displays
1109 @cindex temporary display
1110 @cindex temporary buffer display
1112 Temporary displays are used by Lisp programs to put output into a
1113 buffer and then present it to the user for perusal rather than for
1114 editing. Many help commands use this feature.
1116 @defmac with-output-to-temp-buffer buffer-name body@dots{}
1117 This function executes the forms in @var{body} while arranging to insert
1118 any output they print into the buffer named @var{buffer-name}, which is
1119 first created if necessary, and put into Help mode. (See the similar
1120 form @code{with-temp-buffer-window} below.) Finally, the buffer is
1121 displayed in some window, but that window is not selected.
1123 If the forms in @var{body} do not change the major mode in the output
1124 buffer, so that it is still Help mode at the end of their execution,
1125 then @code{with-output-to-temp-buffer} makes this buffer read-only at
1126 the end, and also scans it for function and variable names to make them
1127 into clickable cross-references. @xref{Docstring hyperlinks, , Tips for
1128 Documentation Strings}, in particular the item on hyperlinks in
1129 documentation strings, for more details.
1131 The string @var{buffer-name} specifies the temporary buffer, which need
1132 not already exist. The argument must be a string, not a buffer. The
1133 buffer is erased initially (with no questions asked), and it is marked
1134 as unmodified after @code{with-output-to-temp-buffer} exits.
1136 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
1137 temporary buffer, then it evaluates the forms in @var{body}. Output
1138 using the Lisp output functions within @var{body} goes by default to
1139 that buffer (but screen display and messages in the echo area, although
1140 they are ``output'' in the general sense of the word, are not affected).
1141 @xref{Output Functions}.
1143 Several hooks are available for customizing the behavior
1144 of this construct; they are listed below.
1146 The value of the last form in @var{body} is returned.
1150 ---------- Buffer: foo ----------
1151 This is the contents of foo.
1152 ---------- Buffer: foo ----------
1156 (with-output-to-temp-buffer "foo"
1158 (print standard-output))
1159 @result{} #<buffer foo>
1161 ---------- Buffer: foo ----------
1167 ---------- Buffer: foo ----------
1172 @defopt temp-buffer-show-function
1173 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
1174 calls it as a function to do the job of displaying a help buffer. The
1175 function gets one argument, which is the buffer it should display.
1177 It is a good idea for this function to run @code{temp-buffer-show-hook}
1178 just as @code{with-output-to-temp-buffer} normally would, inside of
1179 @code{save-selected-window} and with the chosen window and buffer
1183 @defvar temp-buffer-setup-hook
1184 This normal hook is run by @code{with-output-to-temp-buffer} before
1185 evaluating @var{body}. When the hook runs, the temporary buffer is
1186 current. This hook is normally set up with a function to put the
1187 buffer in Help mode.
1190 @defvar temp-buffer-show-hook
1191 This normal hook is run by @code{with-output-to-temp-buffer} after
1192 displaying the temporary buffer. When the hook runs, the temporary buffer
1193 is current, and the window it was displayed in is selected.
1196 @defmac with-temp-buffer-window buffer-or-name action quit-function body@dots{}
1197 This macro is similar to @code{with-output-to-temp-buffer}. Like that
1198 construct, it executes @var{body} while arranging to insert any output
1199 it prints into the buffer named @var{buffer-or-name} and displays that
1200 buffer in some window. Unlike @code{with-output-to-temp-buffer},
1201 however, it does not automatically switch that buffer to Help mode.
1203 The argument @var{buffer-or-name} specifies the temporary buffer. It
1204 can be either a buffer, which must already exist, or a string, in which
1205 case a buffer of that name is created, if necessary. The buffer is
1206 marked as unmodified and read-only when @code{with-temp-buffer-window}
1209 This macro does not call @code{temp-buffer-show-function}. Rather, it
1210 passes the @var{action} argument to @code{display-buffer}
1211 (@pxref{Choosing Window}) in order to display the buffer.
1213 The value of the last form in @var{body} is returned, unless the
1214 argument @var{quit-function} is specified. In that case, it is called
1215 with two arguments: the window showing the buffer and the result of
1216 @var{body}. The final return value is then whatever @var{quit-function}
1219 @vindex temp-buffer-window-setup-hook
1220 @vindex temp-buffer-window-show-hook
1221 This macro uses the normal hooks @code{temp-buffer-window-setup-hook}
1222 and @code{temp-buffer-window-show-hook} in place of the analogous hooks
1223 run by @code{with-output-to-temp-buffer}.
1226 The two constructs described next are mostly identical to
1227 @code{with-temp-buffer-window} but differ from it as specified:
1229 @defmac with-current-buffer-window buffer-or-name action quit-function &rest body
1230 This macro is like @code{with-temp-buffer-window} but unlike that makes
1231 the buffer specified by @var{buffer-or-name} current for running
1235 @defmac with-displayed-buffer-window buffer-or-name action quit-function &rest body
1236 This macro is like @code{with-current-buffer-window} but unlike that
1237 displays the buffer specified by @var{buffer-or-name} @emph{before}
1241 A window showing a temporary buffer can be fit to the size of that
1242 buffer using the following mode:
1244 @defopt temp-buffer-resize-mode
1245 When this minor mode is enabled, windows showing a temporary buffer are
1246 automatically resized to fit their buffer's contents.
1248 A window is resized if and only if it has been specially created for the
1249 buffer. In particular, windows that have shown another buffer before
1250 are not resized. By default, this mode uses @code{fit-window-to-buffer}
1251 (@pxref{Resizing Windows}) for resizing. You can specify a different
1252 function by customizing the options @code{temp-buffer-max-height} and
1253 @code{temp-buffer-max-width} below.
1256 @defopt temp-buffer-max-height
1257 This option specifies the maximum height (in lines) of a window
1258 displaying a temporary buffer when @code{temp-buffer-resize-mode} is
1259 enabled. It can also be a function to be called to choose the height
1260 for such a buffer. It gets one argument, the buffer, and should return
1261 a positive integer. At the time the function is called, the window to
1262 be resized is selected.
1265 @defopt temp-buffer-max-width
1266 This option specifies the maximum width of a window (in columns)
1267 displaying a temporary buffer when @code{temp-buffer-resize-mode} is
1268 enabled. It can also be a function to be called to choose the width for
1269 such a buffer. It gets one argument, the buffer, and should return a
1270 positive integer. At the time the function is called, the window to be
1271 resized is selected.
1274 The following function uses the current buffer for temporal display:
1276 @defun momentary-string-display string position &optional char message
1277 This function momentarily displays @var{string} in the current buffer at
1278 @var{position}. It has no effect on the undo list or on the buffer's
1279 modification status.
1281 The momentary display remains until the next input event. If the next
1282 input event is @var{char}, @code{momentary-string-display} ignores it
1283 and returns. Otherwise, that event remains buffered for subsequent use
1284 as input. Thus, typing @var{char} will simply remove the string from
1285 the display, while typing (say) @kbd{C-f} will remove the string from
1286 the display and later (presumably) move point forward. The argument
1287 @var{char} is a space by default.
1289 The return value of @code{momentary-string-display} is not meaningful.
1291 If the string @var{string} does not contain control characters, you can
1292 do the same job in a more general way by creating (and then subsequently
1293 deleting) an overlay with a @code{before-string} property.
1294 @xref{Overlay Properties}.
1296 If @var{message} is non-@code{nil}, it is displayed in the echo area
1297 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1298 default message says to type @var{char} to continue.
1300 In this example, point is initially located at the beginning of the
1305 ---------- Buffer: foo ----------
1306 This is the contents of foo.
1307 @point{}Second line.
1308 ---------- Buffer: foo ----------
1312 (momentary-string-display
1313 "**** Important Message! ****"
1315 "Type RET when done reading")
1320 ---------- Buffer: foo ----------
1321 This is the contents of foo.
1322 **** Important Message! ****Second line.
1323 ---------- Buffer: foo ----------
1325 ---------- Echo Area ----------
1326 Type RET when done reading
1327 ---------- Echo Area ----------
1335 @c FIXME: mention intervals in this section?
1337 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1338 the screen, for the sake of presentation features. An overlay is an
1339 object that belongs to a particular buffer, and has a specified
1340 beginning and end. It also has properties that you can examine and set;
1341 these affect the display of the text within the overlay.
1343 @cindex scalability of overlays
1344 @cindex overlays, scalability
1345 The visual effect of an overlay is the same as of the corresponding
1346 text property (@pxref{Text Properties}). However, due to a different
1347 implementation, overlays generally don't scale well (many operations
1348 take a time that is proportional to the number of overlays in the
1349 buffer). If you need to affect the visual appearance of many portions
1350 in the buffer, we recommend using text properties.
1352 An overlay uses markers to record its beginning and end; thus,
1353 editing the text of the buffer adjusts the beginning and end of each
1354 overlay so that it stays with the text. When you create the overlay,
1355 you can specify whether text inserted at the beginning should be
1356 inside the overlay or outside, and likewise for the end of the overlay.
1359 * Managing Overlays:: Creating and moving overlays.
1360 * Overlay Properties:: How to read and set properties.
1361 What properties do to the screen display.
1362 * Finding Overlays:: Searching for overlays.
1365 @node Managing Overlays
1366 @subsection Managing Overlays
1367 @cindex managing overlays
1368 @cindex overlays, managing
1370 This section describes the functions to create, delete and move
1371 overlays, and to examine their contents. Overlay changes are not
1372 recorded in the buffer's undo list, since the overlays are not
1373 part of the buffer's contents.
1375 @defun overlayp object
1376 This function returns @code{t} if @var{object} is an overlay.
1379 @defun make-overlay start end &optional buffer front-advance rear-advance
1380 This function creates and returns an overlay that belongs to
1381 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1382 and @var{end} must specify buffer positions; they may be integers or
1383 markers. If @var{buffer} is omitted, the overlay is created in the
1386 @cindex empty overlay
1387 @cindex overlay, empty
1388 An overlay whose @var{start} and @var{end} specify the same buffer
1389 position is known as @dfn{empty}. A non-empty overlay can become
1390 empty if the text between its @var{start} and @var{end} is deleted.
1391 When that happens, the overlay is by default not deleted, but you can
1392 cause it to be deleted by giving it the @samp{evaporate} property
1393 (@pxref{Overlay Properties, evaporate property}).
1395 The arguments @var{front-advance} and @var{rear-advance} specify the
1396 marker insertion type for the start of the overlay and for the end of
1397 the overlay, respectively. @xref{Marker Insertion Types}. If they
1398 are both @code{nil}, the default, then the overlay extends to include
1399 any text inserted at the beginning, but not text inserted at the end.
1400 If @var{front-advance} is non-@code{nil}, text inserted at the
1401 beginning of the overlay is excluded from the overlay. If
1402 @var{rear-advance} is non-@code{nil}, text inserted at the end of the
1403 overlay is included in the overlay.
1406 @defun overlay-start overlay
1407 This function returns the position at which @var{overlay} starts,
1411 @defun overlay-end overlay
1412 This function returns the position at which @var{overlay} ends,
1416 @defun overlay-buffer overlay
1417 This function returns the buffer that @var{overlay} belongs to. It
1418 returns @code{nil} if @var{overlay} has been deleted.
1421 @defun delete-overlay overlay
1422 This function deletes @var{overlay}. The overlay continues to exist as
1423 a Lisp object, and its property list is unchanged, but it ceases to be
1424 attached to the buffer it belonged to, and ceases to have any effect on
1427 A deleted overlay is not permanently disconnected. You can give it a
1428 position in a buffer again by calling @code{move-overlay}.
1431 @defun move-overlay overlay start end &optional buffer
1432 This function moves @var{overlay} to @var{buffer}, and places its bounds
1433 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1434 must specify buffer positions; they may be integers or markers.
1436 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1437 was already associated with; if @var{overlay} was deleted, it goes into
1440 The return value is @var{overlay}.
1442 This is the only valid way to change the endpoints of an overlay. Do
1443 not try modifying the markers in the overlay by hand, as that fails to
1444 update other vital data structures and can cause some overlays to be
1448 @defun remove-overlays &optional start end name value
1449 This function removes all the overlays between @var{start} and
1450 @var{end} whose property @var{name} has the value @var{value}. It can
1451 move the endpoints of the overlays in the region, or split them.
1453 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1454 the specified region. If @var{start} and/or @var{end} are omitted or
1455 @code{nil}, that means the beginning and end of the buffer respectively.
1456 Therefore, @code{(remove-overlays)} removes all the overlays in the
1460 @defun copy-overlay overlay
1461 This function returns a copy of @var{overlay}. The copy has the same
1462 endpoints and properties as @var{overlay}. However, the marker
1463 insertion type for the start of the overlay and for the end of the
1464 overlay are set to their default values (@pxref{Marker Insertion
1468 Here are some examples:
1471 ;; @r{Create an overlay.}
1472 (setq foo (make-overlay 1 10))
1473 @result{} #<overlay from 1 to 10 in display.texi>
1478 (overlay-buffer foo)
1479 @result{} #<buffer display.texi>
1480 ;; @r{Give it a property we can check later.}
1481 (overlay-put foo 'happy t)
1483 ;; @r{Verify the property is present.}
1484 (overlay-get foo 'happy)
1486 ;; @r{Move the overlay.}
1487 (move-overlay foo 5 20)
1488 @result{} #<overlay from 5 to 20 in display.texi>
1493 ;; @r{Delete the overlay.}
1494 (delete-overlay foo)
1496 ;; @r{Verify it is deleted.}
1498 @result{} #<overlay in no buffer>
1499 ;; @r{A deleted overlay has no position.}
1504 (overlay-buffer foo)
1506 ;; @r{Undelete the overlay.}
1507 (move-overlay foo 1 20)
1508 @result{} #<overlay from 1 to 20 in display.texi>
1509 ;; @r{Verify the results.}
1514 (overlay-buffer foo)
1515 @result{} #<buffer display.texi>
1516 ;; @r{Moving and deleting the overlay does not change its properties.}
1517 (overlay-get foo 'happy)
1521 Emacs stores the overlays of each buffer in two lists, divided
1522 around an arbitrary center position. One list extends backwards
1523 through the buffer from that center position, and the other extends
1524 forwards from that center position. The center position can be anywhere
1527 @defun overlay-recenter pos
1528 This function recenters the overlays of the current buffer around
1529 position @var{pos}. That makes overlay lookup faster for positions
1530 near @var{pos}, but slower for positions far away from @var{pos}.
1533 A loop that scans the buffer forwards, creating overlays, can run
1534 faster if you do @code{(overlay-recenter (point-max))} first.
1536 @node Overlay Properties
1537 @subsection Overlay Properties
1538 @cindex overlay properties
1540 Overlay properties are like text properties in that the properties that
1541 alter how a character is displayed can come from either source. But in
1542 most respects they are different. @xref{Text Properties}, for comparison.
1544 Text properties are considered a part of the text; overlays and
1545 their properties are specifically considered not to be part of the
1546 text. Thus, copying text between various buffers and strings
1547 preserves text properties, but does not try to preserve overlays.
1548 Changing a buffer's text properties marks the buffer as modified,
1549 while moving an overlay or changing its properties does not. Unlike
1550 text property changes, overlay property changes are not recorded in
1551 the buffer's undo list.
1553 Since more than one overlay can specify a property value for the
1554 same character, Emacs lets you specify a priority value of each
1555 overlay. In case two overlays have the same priority value, and one
1556 is nested in the other, then the inner one will have priority over the
1557 outer one. If neither is nested in the other then you should not make
1558 assumptions about which overlay will prevail.
1560 These functions read and set the properties of an overlay:
1562 @defun overlay-get overlay prop
1563 This function returns the value of property @var{prop} recorded in
1564 @var{overlay}, if any. If @var{overlay} does not record any value for
1565 that property, but it does have a @code{category} property which is a
1566 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1570 @defun overlay-put overlay prop value
1571 This function sets the value of property @var{prop} recorded in
1572 @var{overlay} to @var{value}. It returns @var{value}.
1575 @defun overlay-properties overlay
1576 This returns a copy of the property list of @var{overlay}.
1579 See also the function @code{get-char-property} which checks both
1580 overlay properties and text properties for a given character.
1581 @xref{Examining Properties}.
1583 Many overlay properties have special meanings; here is a table
1588 @kindex priority @r{(overlay property)}
1589 This property's value determines the priority of the overlay.
1590 If you want to specify a priority value, use either @code{nil}
1591 (or zero), or a positive integer. Any other value has undefined behavior.
1593 The priority matters when two or more overlays cover the same
1594 character and both specify the same property; the one whose
1595 @code{priority} value is larger overrides the other. For the
1596 @code{face} property, the higher priority overlay's value does not
1597 completely override the other value; instead, its face attributes
1598 override the face attributes of the lower priority @code{face}
1601 Currently, all overlays take priority over text properties.
1603 Note that Emacs sometimes uses non-numeric priority values for some of
1604 its internal overlays, so do not try to do arithmetic on the
1605 priority of an overlay (unless it is one that you created). If you
1606 need to put overlays in priority order, use the @var{sorted} argument
1607 of @code{overlays-at}. @xref{Finding Overlays}.
1610 @kindex window @r{(overlay property)}
1611 If the @code{window} property is non-@code{nil}, then the overlay
1612 applies only on that window.
1615 @kindex category @r{(overlay property)}
1616 If an overlay has a @code{category} property, we call it the
1617 @dfn{category} of the overlay. It should be a symbol. The properties
1618 of the symbol serve as defaults for the properties of the overlay.
1621 @kindex face @r{(overlay property)}
1622 This property controls the appearance of the text (@pxref{Faces}).
1623 The value of the property can be the following:
1627 A face name (a symbol or string).
1630 An anonymous face: a property list of the form @code{(@var{keyword}
1631 @var{value} @dots{})}, where each @var{keyword} is a face attribute
1632 name and @var{value} is a value for that attribute.
1635 A list of faces. Each list element should be either a face name or an
1636 anonymous face. This specifies a face which is an aggregate of the
1637 attributes of each of the listed faces. Faces occurring earlier in
1638 the list have higher priority.
1641 A cons cell of the form @code{(foreground-color . @var{color-name})}
1642 or @code{(background-color . @var{color-name})}. This specifies the
1643 foreground or background color, similar to @code{(:foreground
1644 @var{color-name})} or @code{(:background @var{color-name})}. This
1645 form is supported for backward compatibility only, and should be
1650 @kindex mouse-face @r{(overlay property)}
1651 This property is used instead of @code{face} when the mouse is within
1652 the range of the overlay. However, Emacs ignores all face attributes
1653 from this property that alter the text size (e.g., @code{:height},
1654 @code{:weight}, and @code{:slant}). Those attributes are always the
1655 same as in the unhighlighted text.
1658 @kindex display @r{(overlay property)}
1659 This property activates various features that change the
1660 way text is displayed. For example, it can make text appear taller
1661 or shorter, higher or lower, wider or narrower, or replaced with an image.
1662 @xref{Display Property}.
1665 @kindex help-echo @r{(overlay property)}
1666 If an overlay has a @code{help-echo} property, then when you move the
1667 mouse onto the text in the overlay, Emacs displays a help string in the
1668 echo area, or in the tooltip window. For details see @ref{Text
1672 @kindex field @r{(overlay property)}
1673 @c Copied from Special Properties.
1674 Consecutive characters with the same @code{field} property constitute a
1675 @emph{field}. Some motion functions including @code{forward-word} and
1676 @code{beginning-of-line} stop moving at a field boundary.
1679 @item modification-hooks
1680 @kindex modification-hooks @r{(overlay property)}
1681 This property's value is a list of functions to be called if any
1682 character within the overlay is changed or if text is inserted strictly
1685 The hook functions are called both before and after each change.
1686 If the functions save the information they receive, and compare notes
1687 between calls, they can determine exactly what change has been made
1690 When called before a change, each function receives four arguments: the
1691 overlay, @code{nil}, and the beginning and end of the text range to be
1694 When called after a change, each function receives five arguments: the
1695 overlay, @code{t}, the beginning and end of the text range just
1696 modified, and the length of the pre-change text replaced by that range.
1697 (For an insertion, the pre-change length is zero; for a deletion, that
1698 length is the number of characters deleted, and the post-change
1699 beginning and end are equal.)
1701 If these functions modify the buffer, they should bind
1702 @code{inhibit-modification-hooks} to @code{t} around doing so, to
1703 avoid confusing the internal mechanism that calls these hooks.
1705 Text properties also support the @code{modification-hooks} property,
1706 but the details are somewhat different (@pxref{Special Properties}).
1708 @item insert-in-front-hooks
1709 @kindex insert-in-front-hooks @r{(overlay property)}
1710 This property's value is a list of functions to be called before and
1711 after inserting text right at the beginning of the overlay. The calling
1712 conventions are the same as for the @code{modification-hooks} functions.
1714 @item insert-behind-hooks
1715 @kindex insert-behind-hooks @r{(overlay property)}
1716 This property's value is a list of functions to be called before and
1717 after inserting text right at the end of the overlay. The calling
1718 conventions are the same as for the @code{modification-hooks} functions.
1721 @kindex invisible @r{(overlay property)}
1722 The @code{invisible} property can make the text in the overlay
1723 invisible, which means that it does not appear on the screen.
1724 @xref{Invisible Text}, for details.
1727 @kindex intangible @r{(overlay property)}
1728 The @code{intangible} property on an overlay works just like the
1729 @code{intangible} text property. It is obsolete. @xref{Special
1730 Properties}, for details.
1732 @item isearch-open-invisible
1733 This property tells incremental search how to make an invisible overlay
1734 visible, permanently, if the final match overlaps it. @xref{Invisible
1737 @item isearch-open-invisible-temporary
1738 This property tells incremental search how to make an invisible overlay
1739 visible, temporarily, during the search. @xref{Invisible Text}.
1742 @kindex before-string @r{(overlay property)}
1743 This property's value is a string to add to the display at the beginning
1744 of the overlay. The string does not appear in the buffer in any
1745 sense---only on the screen.
1748 @kindex after-string @r{(overlay property)}
1749 This property's value is a string to add to the display at the end of
1750 the overlay. The string does not appear in the buffer in any
1751 sense---only on the screen.
1754 This property specifies a display spec to prepend to each
1755 non-continuation line at display-time. @xref{Truncation}.
1758 This property specifies a display spec to prepend to each continuation
1759 line at display-time. @xref{Truncation}.
1762 @kindex evaporate @r{(overlay property)}
1763 If this property is non-@code{nil}, the overlay is deleted automatically
1764 if it becomes empty (i.e., if its length becomes zero). If you give
1765 an empty overlay (@pxref{Managing Overlays, empty overlay}) a
1766 non-@code{nil} @code{evaporate} property, that deletes it immediately.
1767 Note that, unless an overlay has this property, it will not be deleted
1768 when the text between its starting and ending positions is deleted
1772 @cindex keymap of character (and overlays)
1773 @kindex keymap @r{(overlay property)}
1774 If this property is non-@code{nil}, it specifies a keymap for a portion of the
1775 text. This keymap is used when the character after point is within the
1776 overlay, and takes precedence over most other keymaps. @xref{Active Keymaps}.
1779 @kindex local-map @r{(overlay property)}
1780 The @code{local-map} property is similar to @code{keymap} but replaces the
1781 buffer's local map rather than augmenting existing keymaps. This also means it
1782 has lower precedence than minor mode keymaps.
1785 The @code{keymap} and @code{local-map} properties do not affect a
1786 string displayed by the @code{before-string}, @code{after-string}, or
1787 @code{display} properties. This is only relevant for mouse clicks and
1788 other mouse events that fall on the string, since point is never on
1789 the string. To bind special mouse events for the string, assign it a
1790 @code{keymap} or @code{local-map} text property. @xref{Special
1793 @node Finding Overlays
1794 @subsection Searching for Overlays
1795 @cindex searching for overlays
1796 @cindex overlays, searching for
1798 @defun overlays-at pos &optional sorted
1799 This function returns a list of all the overlays that cover the character at
1800 position @var{pos} in the current buffer. If @var{sorted} is non-@code{nil},
1801 the list is in decreasing order of priority, otherwise it is in no particular
1802 order. An overlay contains position @var{pos} if it begins at or before
1803 @var{pos}, and ends after @var{pos}.
1805 To illustrate usage, here is a Lisp function that returns a list of the
1806 overlays that specify property @var{prop} for the character at point:
1809 (defun find-overlays-specifying (prop)
1810 (let ((overlays (overlays-at (point)))
1813 (let ((overlay (car overlays)))
1814 (if (overlay-get overlay prop)
1815 (setq found (cons overlay found))))
1816 (setq overlays (cdr overlays)))
1821 @defun overlays-in beg end
1822 This function returns a list of the overlays that overlap the region
1823 @var{beg} through @var{end}. An overlay overlaps with a region if it
1824 contains one or more characters in the region; empty overlays
1825 (@pxref{Managing Overlays, empty overlay}) overlap if they are at
1826 @var{beg}, strictly between @var{beg} and @var{end}, or at @var{end}
1827 when @var{end} denotes the position at the end of the buffer.
1830 @defun next-overlay-change pos
1831 This function returns the buffer position of the next beginning or end
1832 of an overlay, after @var{pos}. If there is none, it returns
1836 @defun previous-overlay-change pos
1837 This function returns the buffer position of the previous beginning or
1838 end of an overlay, before @var{pos}. If there is none, it returns
1842 As an example, here's a simplified (and inefficient) version of the
1843 primitive function @code{next-single-char-property-change}
1844 (@pxref{Property Search}). It searches forward from position
1845 @var{pos} for the next position where the value of a given property
1846 @code{prop}, as obtained from either overlays or text properties,
1850 (defun next-single-char-property-change (position prop)
1852 (goto-char position)
1853 (let ((propval (get-char-property (point) prop)))
1854 (while (and (not (eobp))
1855 (eq (get-char-property (point) prop) propval))
1856 (goto-char (min (next-overlay-change (point))
1857 (next-single-property-change (point) prop)))))
1861 @node Size of Displayed Text
1862 @section Size of Displayed Text
1863 @cindex size of text on display
1864 @cindex character width on display
1866 Since not all characters have the same width, these functions let you
1867 check the width of a character. @xref{Primitive Indent}, and
1868 @ref{Screen Lines}, for related functions.
1870 @defun char-width char
1871 This function returns the width in columns of the character
1872 @var{char}, if it were displayed in the current buffer (i.e., taking
1873 into account the buffer's display table, if any; @pxref{Display
1874 Tables}). The width of a tab character is usually @code{tab-width}
1875 (@pxref{Usual Display}).
1878 @defun string-width string
1879 This function returns the width in columns of the string @var{string},
1880 if it were displayed in the current buffer and the selected window.
1883 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1884 This function returns the part of @var{string} that fits within
1885 @var{width} columns, as a new string.
1887 If @var{string} does not reach @var{width}, then the result ends where
1888 @var{string} ends. If one multi-column character in @var{string}
1889 extends across the column @var{width}, that character is not included in
1890 the result. Thus, the result can fall short of @var{width} but cannot
1893 The optional argument @var{start-column} specifies the starting column.
1894 If this is non-@code{nil}, then the first @var{start-column} columns of
1895 the string are omitted from the value. If one multi-column character in
1896 @var{string} extends across the column @var{start-column}, that
1897 character is not included.
1899 The optional argument @var{padding}, if non-@code{nil}, is a padding
1900 character added at the beginning and end of the result string, to extend
1901 it to exactly @var{width} columns. The padding character is used at the
1902 end of the result if it falls short of @var{width}. It is also used at
1903 the beginning of the result if one multi-column character in
1904 @var{string} extends across the column @var{start-column}.
1906 @vindex truncate-string-ellipsis
1907 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1908 replace the end of @var{string} (including any padding) if it extends
1909 beyond @var{width}, unless the display width of @var{string} is equal
1910 to or less than the display width of @var{ellipsis}. If
1911 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1912 the value of the variable @code{truncate-string-ellipsis}.
1915 (truncate-string-to-width "\tab\t" 12 4)
1917 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1922 The following function returns the size in pixels of text as if it were
1923 displayed in a given window. This function is used by
1924 @code{fit-window-to-buffer} and @code{fit-frame-to-buffer}
1925 (@pxref{Resizing Windows}) to make a window exactly as large as the text
1928 @defun window-text-pixel-size &optional window from to x-limit y-limit mode-and-header-line
1929 This function returns the size of the text of @var{window}'s buffer in
1930 pixels. @var{window} must be a live window and defaults to the selected
1931 one. The return value is a cons of the maximum pixel-width of any text
1932 line and the maximum pixel-height of all text lines.
1934 The optional argument @var{from}, if non-@code{nil}, specifies the first
1935 text position to consider and defaults to the minimum accessible
1936 position of the buffer. If @var{from} is @code{t}, it uses the minimum
1937 accessible position that is not a newline character. The optional
1938 argument @var{to}, if non-@code{nil}, specifies the last text position
1939 to consider and defaults to the maximum accessible position of the
1940 buffer. If @var{to} is @code{t}, it uses the maximum accessible
1941 position that is not a newline character.
1943 The optional argument @var{x-limit}, if non-@code{nil}, specifies the
1944 maximum pixel-width that can be returned. @var{x-limit} @code{nil} or
1945 omitted, means to use the pixel-width of @var{window}'s body
1946 (@pxref{Window Sizes}); this is useful when the caller does not intend
1947 to change the width of @var{window}. Otherwise, the caller should
1948 specify here the maximum width @var{window}'s body may assume. Text
1949 whose x-coordinate is beyond @var{x-limit} is ignored. Since
1950 calculating the width of long lines can take some time, it's always a
1951 good idea to make this argument as small as needed; in particular, if
1952 the buffer might contain long lines that will be truncated anyway.
1954 The optional argument @var{y-limit}, if non-@code{nil}, specifies the
1955 maximum pixel-height that can be returned. Text lines whose
1956 y-coordinate is beyond @var{y-limit} are ignored. Since calculating the
1957 pixel-height of a large buffer can take some time, it makes sense to
1958 specify this argument; in particular, if the caller does not know the
1961 The optional argument @var{mode-and-header-line} @code{nil} or omitted
1962 means to not include the height of the mode- or header-line of
1963 @var{window} in the return value. If it is either the symbol
1964 @code{mode-line} or @code{header-line}, include only the height of that
1965 line, if present, in the return value. If it is @code{t}, include the
1966 height of both, if present, in the return value.
1971 @section Line Height
1973 @cindex height of a line
1975 The total height of each display line consists of the height of the
1976 contents of the line, plus optional additional vertical line spacing
1977 above or below the display line.
1979 The height of the line contents is the maximum height of any character
1980 or image on that display line, including the final newline if there is
1981 one. (A display line that is continued doesn't include a final
1982 newline.) That is the default line height, if you do nothing to specify
1983 a greater height. (In the most common case, this equals the height of
1984 the corresponding frame's default font, see @ref{Frame Font}.)
1986 There are several ways to explicitly specify a larger line height,
1987 either by specifying an absolute height for the display line, or by
1988 specifying vertical space. However, no matter what you specify, the
1989 actual line height can never be less than the default.
1991 @kindex line-height @r{(text property)}
1992 A newline can have a @code{line-height} text or overlay property
1993 that controls the total height of the display line ending in that
1996 If the property value is @code{t}, the newline character has no
1997 effect on the displayed height of the line---the visible contents
1998 alone determine the height. This is useful for tiling small images
1999 (or image slices) without adding blank areas between the images.
2001 If the property value is a list of the form @code{(@var{height}
2002 @var{total})}, that adds extra space @emph{below} the display line.
2003 First Emacs uses @var{height} as a height spec to control extra space
2004 @emph{above} the line; then it adds enough space @emph{below} the line
2005 to bring the total line height up to @var{total}. In this case, the
2006 other ways to specify the line spacing are ignored.
2009 Any other kind of property value is a height spec, which translates
2010 into a number---the specified line height. There are several ways to
2011 write a height spec; here's how each of them translates into a number:
2015 If the height spec is a positive integer, the height value is that integer.
2017 If the height spec is a float, @var{float}, the numeric height value
2018 is @var{float} times the frame's default line height.
2019 @item (@var{face} . @var{ratio})
2020 If the height spec is a cons of the format shown, the numeric height
2021 is @var{ratio} times the height of face @var{face}. @var{ratio} can
2022 be any type of number, or @code{nil} which means a ratio of 1.
2023 If @var{face} is @code{t}, it refers to the current face.
2024 @item (nil . @var{ratio})
2025 If the height spec is a cons of the format shown, the numeric height
2026 is @var{ratio} times the height of the contents of the line.
2029 Thus, any valid height spec determines the height in pixels, one way
2030 or another. If the line contents' height is less than that, Emacs
2031 adds extra vertical space above the line to achieve the specified
2034 If you don't specify the @code{line-height} property, the line's
2035 height consists of the contents' height plus the line spacing.
2036 There are several ways to specify the line spacing for different
2037 parts of Emacs text.
2039 On graphical terminals, you can specify the line spacing for all
2040 lines in a frame, using the @code{line-spacing} frame parameter
2041 (@pxref{Layout Parameters}). However, if the default value of
2042 @code{line-spacing} is non-@code{nil}, it overrides the
2043 frame's @code{line-spacing} parameter. An integer specifies the
2044 number of pixels put below lines. A floating-point number specifies
2045 the spacing relative to the frame's default line height.
2047 @vindex line-spacing
2048 You can specify the line spacing for all lines in a buffer via the
2049 buffer-local @code{line-spacing} variable. An integer specifies
2050 the number of pixels put below lines. A floating-point number
2051 specifies the spacing relative to the default frame line height. This
2052 overrides line spacings specified for the frame.
2054 @kindex line-spacing @r{(text property)}
2055 Finally, a newline can have a @code{line-spacing} text or overlay
2056 property that overrides the default frame line spacing and the buffer
2057 local @code{line-spacing} variable, for the display line ending in
2060 One way or another, these mechanisms specify a Lisp value for the
2061 spacing of each line. The value is a height spec, and it translates
2062 into a Lisp value as described above. However, in this case the
2063 numeric height value specifies the line spacing, rather than the line
2066 On text terminals, the line spacing cannot be altered.
2072 A @dfn{face} is a collection of graphical attributes for displaying
2073 text: font, foreground color, background color, optional underlining,
2074 etc. Faces control how Emacs displays text in buffers, as well as
2075 other parts of the frame such as the mode line.
2077 @cindex anonymous face
2078 One way to represent a face is as a property list of attributes,
2079 like @code{(:foreground "red" :weight bold)}. Such a list is called
2080 an @dfn{anonymous face}. For example, you can assign an anonymous
2081 face as the value of the @code{face} text property, and Emacs will
2082 display the underlying text with the specified attributes.
2083 @xref{Special Properties}.
2086 More commonly, a face is referred to via a @dfn{face name}: a Lisp
2087 symbol associated with a set of face attributes@footnote{For backward
2088 compatibility, you can also use a string to specify a face name; that
2089 is equivalent to a Lisp symbol with the same name.}. Named faces are
2090 defined using the @code{defface} macro (@pxref{Defining Faces}).
2091 Emacs comes with several standard named faces (@pxref{Basic Faces}).
2093 Many parts of Emacs required named faces, and do not accept
2094 anonymous faces. These include the functions documented in
2095 @ref{Attribute Functions}, and the variable @code{font-lock-keywords}
2096 (@pxref{Search-based Fontification}). Unless otherwise stated, we
2097 will use the term @dfn{face} to refer only to named faces.
2100 This function returns a non-@code{nil} value if @var{object} is a
2101 named face: a Lisp symbol or string which serves as a face name.
2102 Otherwise, it returns @code{nil}.
2106 * Face Attributes:: What is in a face?
2107 * Defining Faces:: How to define a face.
2108 * Attribute Functions:: Functions to examine and set face attributes.
2109 * Displaying Faces:: How Emacs combines the faces specified for a character.
2110 * Face Remapping:: Remapping faces to alternative definitions.
2111 * Face Functions:: How to define and examine faces.
2112 * Auto Faces:: Hook for automatic face assignment.
2113 * Basic Faces:: Faces that are defined by default.
2114 * Font Selection:: Finding the best available font for a face.
2115 * Font Lookup:: Looking up the names of available fonts
2116 and information about them.
2117 * Fontsets:: A fontset is a collection of fonts
2118 that handle a range of character sets.
2119 * Low-Level Font:: Lisp representation for character display fonts.
2122 @node Face Attributes
2123 @subsection Face Attributes
2124 @cindex face attributes
2126 @dfn{Face attributes} determine the visual appearance of a face.
2127 The following table lists all the face attributes, their possible
2128 values, and their effects.
2130 Apart from the values given below, each face attribute can have the
2131 value @code{unspecified}. This special value means that the face
2132 doesn't specify that attribute directly. An @code{unspecified}
2133 attribute tells Emacs to refer instead to a parent face (see the
2134 description @code{:inherit} attribute below); or, failing that, to an
2135 underlying face (@pxref{Displaying Faces}). The @code{default} face
2136 must specify all attributes.
2138 Some of these attributes are meaningful only on certain kinds of
2139 displays. If your display cannot handle a certain attribute, the
2140 attribute is ignored.
2144 Font family or fontset (a string). @xref{Fonts,,, emacs, The GNU
2145 Emacs Manual}, for more information about font families. The function
2146 @code{font-family-list} (see below) returns a list of available family
2147 names. @xref{Fontsets}, for information about fontsets.
2150 The name of the @dfn{font foundry} for the font family specified by
2151 the @code{:family} attribute (a string). @xref{Fonts,,, emacs, The
2155 Relative character width. This should be one of the symbols
2156 @code{ultra-condensed}, @code{extra-condensed}, @code{condensed},
2157 @code{semi-condensed}, @code{normal}, @code{semi-expanded},
2158 @code{expanded}, @code{extra-expanded}, or @code{ultra-expanded}.
2161 The height of the font. In the simplest case, this is an integer in
2162 units of 1/10 point.
2164 The value can also be floating point or a function, which
2165 specifies the height relative to an @dfn{underlying face}
2166 (@pxref{Displaying Faces}). A floating-point value
2167 specifies the amount by which to scale the height of the
2168 underlying face. A function value is called
2169 with one argument, the height of the underlying face, and returns the
2170 height of the new face. If the function is passed an integer
2171 argument, it must return an integer.
2173 The height of the default face must be specified using an integer;
2174 floating point and function values are not allowed.
2177 Font weight---one of the symbols (from densest to faintest)
2178 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
2179 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or
2180 @code{ultra-light}. On text terminals which support
2181 variable-brightness text, any weight greater than normal is displayed
2182 as extra bright, and any weight less than normal is displayed as
2187 Font slant---one of the symbols @code{italic}, @code{oblique},
2188 @code{normal}, @code{reverse-italic}, or @code{reverse-oblique}. On
2189 text terminals that support variable-brightness text, slanted text is
2190 displayed as half-bright.
2193 Foreground color, a string. The value can be a system-defined color
2194 name, or a hexadecimal color specification. @xref{Color Names}. On
2195 black-and-white displays, certain shades of gray are implemented by
2198 @item :distant-foreground
2199 Alternative foreground color, a string. This is like @code{:foreground}
2200 but the color is only used as a foreground when the background color is
2201 near to the foreground that would have been used. This is useful for
2202 example when marking text (i.e., the region face). If the text has a foreground
2203 that is visible with the region face, that foreground is used.
2204 If the foreground is near the region face background,
2205 @code{:distant-foreground} is used instead so the text is readable.
2208 Background color, a string. The value can be a system-defined color
2209 name, or a hexadecimal color specification. @xref{Color Names}.
2211 @cindex underlined text
2213 Whether or not characters should be underlined, and in what
2214 way. The possible values of the @code{:underline} attribute are:
2221 Underline with the foreground color of the face.
2224 Underline in color @var{color}, a string specifying a color.
2226 @item @code{(:color @var{color} :style @var{style})}
2227 @var{color} is either a string, or the symbol @code{foreground-color},
2228 meaning the foreground color of the face. Omitting the attribute
2229 @code{:color} means to use the foreground color of the face.
2230 @var{style} should be a symbol @code{line} or @code{wave}, meaning to
2231 use a straight or wavy line. Omitting the attribute @code{:style}
2232 means to use a straight line.
2235 @cindex overlined text
2237 Whether or not characters should be overlined, and in what color.
2238 If the value is @code{t}, overlining uses the foreground color of the
2239 face. If the value is a string, overlining uses that color. The
2240 value @code{nil} means do not overline.
2242 @cindex strike-through text
2243 @item :strike-through
2244 Whether or not characters should be strike-through, and in what
2245 color. The value is used like that of @code{:overline}.
2250 Whether or not a box should be drawn around characters, its color, the
2251 width of the box lines, and 3D appearance. Here are the possible
2252 values of the @code{:box} attribute, and what they mean:
2259 Draw a box with lines of width 1, in the foreground color.
2262 Draw a box with lines of width 1, in color @var{color}.
2264 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2265 This way you can explicitly specify all aspects of the box. The value
2266 @var{width} specifies the width of the lines to draw; it defaults to
2267 1. A negative width @var{-n} means to draw a line of width @var{n}
2268 that occupies the space of the underlying text, thus avoiding any
2269 increase in the character height or width.
2271 The value @var{color} specifies the color to draw with. The default is
2272 the foreground color of the face for simple boxes, and the background
2273 color of the face for 3D boxes.
2275 The value @var{style} specifies whether to draw a 3D box. If it is
2276 @code{released-button}, the box looks like a 3D button that is not being
2277 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2278 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2282 @item :inverse-video
2283 Whether or not characters should be displayed in inverse video. The
2284 value should be @code{t} (yes) or @code{nil} (no).
2287 The background stipple, a bitmap.
2289 The value can be a string; that should be the name of a file containing
2290 external-format X bitmap data. The file is found in the directories
2291 listed in the variable @code{x-bitmap-file-path}.
2293 Alternatively, the value can specify the bitmap directly, with a list
2294 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2295 @var{width} and @var{height} specify the size in pixels, and
2296 @var{data} is a string containing the raw bits of the bitmap, row by
2297 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2298 in the string (which should be a unibyte string for best results).
2299 This means that each row always occupies at least one whole byte.
2301 If the value is @code{nil}, that means use no stipple pattern.
2303 Normally you do not need to set the stipple attribute, because it is
2304 used automatically to handle certain shades of gray.
2307 The font used to display the face. Its value should be a font object.
2308 @xref{Low-Level Font}, for information about font objects, font specs,
2311 When specifying this attribute using @code{set-face-attribute}
2312 (@pxref{Attribute Functions}), you may also supply a font spec, a font
2313 entity, or a string. Emacs converts such values to an appropriate
2314 font object, and stores that font object as the actual attribute
2315 value. If you specify a string, the contents of the string should be
2316 a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the
2317 font name is an XLFD containing wildcards, Emacs chooses the first
2318 font matching those wildcards. Specifying this attribute also changes
2319 the values of the @code{:family}, @code{:foundry}, @code{:width},
2320 @code{:height}, @code{:weight}, and @code{:slant} attributes.
2322 @cindex inheritance, for faces
2324 The name of a face from which to inherit attributes, or a list of face
2325 names. Attributes from inherited faces are merged into the face like
2326 an underlying face would be, with higher priority than underlying
2327 faces (@pxref{Displaying Faces}). If a list of faces is used,
2328 attributes from faces earlier in the list override those from later
2332 @defun font-family-list &optional frame
2333 This function returns a list of available font family names. The
2334 optional argument @var{frame} specifies the frame on which the text is
2335 to be displayed; if it is @code{nil}, the selected frame is used.
2338 @defopt underline-minimum-offset
2339 This variable specifies the minimum distance between the baseline and
2340 the underline, in pixels, when displaying underlined text.
2343 @defopt x-bitmap-file-path
2344 This variable specifies a list of directories for searching
2345 for bitmap files, for the @code{:stipple} attribute.
2348 @defun bitmap-spec-p object
2349 This returns @code{t} if @var{object} is a valid bitmap specification,
2350 suitable for use with @code{:stipple} (see above). It returns
2351 @code{nil} otherwise.
2354 @node Defining Faces
2355 @subsection Defining Faces
2356 @cindex defining faces
2359 The usual way to define a face is through the @code{defface} macro.
2360 This macro associates a face name (a symbol) with a default @dfn{face
2361 spec}. A face spec is a construct which specifies what attributes a
2362 face should have on any given terminal; for example, a face spec might
2363 specify one foreground color on high-color terminals, and a different
2364 foreground color on low-color terminals.
2366 People are sometimes tempted to create a variable whose value is a
2367 face name. In the vast majority of cases, this is not necessary; the
2368 usual procedure is to define a face with @code{defface}, and then use
2371 @defmac defface face spec doc [keyword value]@dots{}
2372 This macro declares @var{face} as a named face whose default face spec
2373 is given by @var{spec}. You should not quote the symbol @var{face},
2374 and it should not end in @samp{-face} (that would be redundant). The
2375 argument @var{doc} is a documentation string for the face. The
2376 additional @var{keyword} arguments have the same meanings as in
2377 @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}).
2379 If @var{face} already has a default face spec, this macro does
2382 The default face spec determines @var{face}'s appearance when no
2383 customizations are in effect (@pxref{Customization}). If @var{face}
2384 has already been customized (via Custom themes or via customizations
2385 read from the init file), its appearance is determined by the custom
2386 face spec(s), which override the default face spec @var{spec}.
2387 However, if the customizations are subsequently removed, the
2388 appearance of @var{face} will again be determined by its default face
2391 As an exception, if you evaluate a @code{defface} form with
2392 @kbd{C-M-x} in Emacs Lisp mode (@code{eval-defun}), a special feature
2393 of @code{eval-defun} overrides any custom face specs on the face,
2394 causing the face to reflect exactly what the @code{defface} says.
2396 The @var{spec} argument is a @dfn{face spec}, which states how the
2397 face should appear on different kinds of terminals. It should be an
2398 alist whose elements each have the form
2401 (@var{display} . @var{plist})
2405 @var{display} specifies a class of terminals (see below). @var{plist}
2406 is a property list of face attributes and their values, specifying how
2407 the face appears on such terminals. For backward compatibility, you
2408 can also write an element as @code{(@var{display} @var{plist})}.
2410 The @var{display} part of an element of @var{spec} determines which
2411 terminals the element matches. If more than one element of @var{spec}
2412 matches a given terminal, the first element that matches is the one
2413 used for that terminal. There are three possibilities for
2417 @item @code{default}
2418 This element of @var{spec} doesn't match any terminal; instead, it
2419 specifies defaults that apply to all terminals. This element, if
2420 used, must be the first element of @var{spec}. Each of the following
2421 elements can override any or all of these defaults.
2424 This element of @var{spec} matches all terminals. Therefore, any
2425 subsequent elements of @var{spec} are never used. Normally @code{t}
2426 is used in the last (or only) element of @var{spec}.
2429 If @var{display} is a list, each element should have the form
2430 @code{(@var{characteristic} @var{value}@dots{})}. Here
2431 @var{characteristic} specifies a way of classifying terminals, and the
2432 @var{value}s are possible classifications which @var{display} should
2433 apply to. Here are the possible values of @var{characteristic}:
2437 The kind of window system the terminal uses---either @code{graphic}
2438 (any graphics-capable display), @code{x}, @code{pc} (for the MS-DOS
2439 console), @code{w32} (for MS Windows 9X/NT/2K/XP), or @code{tty} (a
2440 non-graphics-capable display). @xref{Window Systems, window-system}.
2443 What kinds of colors the terminal supports---either @code{color},
2444 @code{grayscale}, or @code{mono}.
2447 The kind of background---either @code{light} or @code{dark}.
2450 An integer that represents the minimum number of colors the terminal
2451 should support. This matches a terminal if its
2452 @code{display-color-cells} value is at least the specified integer.
2455 Whether or not the terminal can display the face attributes given in
2456 @var{value}@dots{} (@pxref{Face Attributes}). @xref{Display Face
2457 Attribute Testing}, for more information on exactly how this testing
2461 If an element of @var{display} specifies more than one @var{value} for
2462 a given @var{characteristic}, any of those values is acceptable. If
2463 @var{display} has more than one element, each element should specify a
2464 different @var{characteristic}; then @emph{each} characteristic of the
2465 terminal must match one of the @var{value}s specified for it in
2470 For example, here's the definition of the standard face
2475 '((((class color) (min-colors 88) (background light))
2476 :background "darkseagreen2")
2477 (((class color) (min-colors 88) (background dark))
2478 :background "darkolivegreen")
2479 (((class color) (min-colors 16) (background light))
2480 :background "darkseagreen2")
2481 (((class color) (min-colors 16) (background dark))
2482 :background "darkolivegreen")
2483 (((class color) (min-colors 8))
2484 :background "green" :foreground "black")
2485 (t :inverse-video t))
2486 "Basic face for highlighting."
2487 :group 'basic-faces)
2490 Internally, Emacs stores each face's default spec in its
2491 @code{face-defface-spec} symbol property (@pxref{Symbol Properties}).
2492 The @code{saved-face} property stores any face spec saved by the user
2493 using the customization buffer; the @code{customized-face} property
2494 stores the face spec customized for the current session, but not
2495 saved; and the @code{theme-face} property stores an alist associating
2496 the active customization settings and Custom themes with the face
2497 specs for that face. The face's documentation string is stored in the
2498 @code{face-documentation} property.
2500 Normally, a face is declared just once, using @code{defface}, and
2501 any further changes to its appearance are applied using the Customize
2502 framework (e.g., via the Customize user interface or via the
2503 @code{custom-set-faces} function; @pxref{Applying Customizations}), or
2504 by face remapping (@pxref{Face Remapping}). In the rare event that
2505 you need to change a face spec directly from Lisp, you can use the
2506 @code{face-spec-set} function.
2508 @defun face-spec-set face spec &optional spec-type
2509 This function applies @var{spec} as a face spec for @code{face}.
2510 @var{spec} should be a face spec, as described in the above
2511 documentation for @code{defface}.
2513 This function also defines @var{face} as a valid face name if it is
2514 not already one, and (re)calculates its attributes on existing frames.
2516 @cindex override spec @r{(for a face)}
2517 The argument @var{spec-type} determines which spec to set. If it is
2518 @code{nil} or @code{face-override-spec}, this function sets the
2519 @dfn{override spec}, which overrides over all other face specs on
2520 @var{face}. If it is @code{customized-face} or @code{saved-face},
2521 this function sets the customized spec or the saved custom spec. If
2522 it is @code{face-defface-spec}, this function sets the default face
2523 spec (the same one set by @code{defface}). If it is @code{reset},
2524 this function clears out all customization specs and override specs
2525 from @var{face} (in this case, the value of @var{spec} is ignored).
2526 Any other value of @var{spec-type} is reserved for internal use.
2529 @node Attribute Functions
2530 @subsection Face Attribute Functions
2531 @cindex face attributes, access and modification
2533 This section describes functions for directly accessing and
2534 modifying the attributes of a named face.
2536 @defun face-attribute face attribute &optional frame inherit
2537 This function returns the value of the @var{attribute} attribute for
2538 @var{face} on @var{frame}.
2540 If @var{frame} is @code{nil}, that means the selected frame
2541 (@pxref{Input Focus}). If @var{frame} is @code{t}, this function
2542 returns the value of the specified attribute for newly-created frames
2543 (this is normally @code{unspecified}, unless you have specified some
2544 value using @code{set-face-attribute}; see below).
2546 If @var{inherit} is @code{nil}, only attributes directly defined by
2547 @var{face} are considered, so the return value may be
2548 @code{unspecified}, or a relative value. If @var{inherit} is
2549 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2550 with the faces specified by its @code{:inherit} attribute; however the
2551 return value may still be @code{unspecified} or relative. If
2552 @var{inherit} is a face or a list of faces, then the result is further
2553 merged with that face (or faces), until it becomes specified and
2556 To ensure that the return value is always specified and absolute, use
2557 a value of @code{default} for @var{inherit}; this will resolve any
2558 unspecified or relative values by merging with the @code{default} face
2559 (which is always completely specified).
2564 (face-attribute 'bold :weight)
2569 @c FIXME: Add an index for "relative face attribute", maybe here? --xfq
2570 @defun face-attribute-relative-p attribute value
2571 This function returns non-@code{nil} if @var{value}, when used as the
2572 value of the face attribute @var{attribute}, is relative. This means
2573 it would modify, rather than completely override, any value that comes
2574 from a subsequent face in the face list or that is inherited from
2577 @code{unspecified} is a relative value for all attributes. For
2578 @code{:height}, floating point and function values are also relative.
2583 (face-attribute-relative-p :height 2.0)
2588 @defun face-all-attributes face &optional frame
2589 This function returns an alist of attributes of @var{face}. The
2590 elements of the result are name-value pairs of the form
2591 @w{@code{(@var{attr-name} . @var{attr-value})}}. Optional argument
2592 @var{frame} specifies the frame whose definition of @var{face} to
2593 return; if omitted or @code{nil}, the returned value describes the
2594 default attributes of @var{face} for newly created frames.
2597 @defun merge-face-attribute attribute value1 value2
2598 If @var{value1} is a relative value for the face attribute
2599 @var{attribute}, returns it merged with the underlying value
2600 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2601 face attribute @var{attribute}, returns @var{value1} unchanged.
2604 Normally, Emacs uses the face specs of each face to automatically
2605 calculate its attributes on each frame (@pxref{Defining Faces}). The
2606 function @code{set-face-attribute} can override this calculation by
2607 directly assigning attributes to a face, either on a specific frame or
2608 for all frames. This function is mostly intended for internal usage.
2610 @defun set-face-attribute face frame &rest arguments
2611 This function sets one or more attributes of @var{face} for
2612 @var{frame}. The attributes specifies in this way override the face
2613 spec(s) belonging to @var{face}.
2615 The extra arguments @var{arguments} specify the attributes to set, and
2616 the values for them. They should consist of alternating attribute
2617 names (such as @code{:family} or @code{:underline}) and values. Thus,
2620 (set-face-attribute 'foo nil :weight 'bold :slant 'italic)
2624 sets the attribute @code{:weight} to @code{bold} and the attribute
2625 @code{:slant} to @code{italic}.
2628 If @var{frame} is @code{t}, this function sets the default attributes
2629 for newly created frames. If @var{frame} is @code{nil}, this function
2630 sets the attributes for all existing frames, as well as for newly
2634 The following commands and functions mostly provide compatibility
2635 with old versions of Emacs. They work by calling
2636 @code{set-face-attribute}. Values of @code{t} and @code{nil} for
2637 their @var{frame} argument are handled just like
2638 @code{set-face-attribute} and @code{face-attribute}. The commands
2639 read their arguments using the minibuffer, if called interactively.
2641 @deffn Command set-face-foreground face color &optional frame
2642 @deffnx Command set-face-background face color &optional frame
2643 These set the @code{:foreground} attribute (or @code{:background}
2644 attribute, respectively) of @var{face} to @var{color}.
2647 @deffn Command set-face-stipple face pattern &optional frame
2648 This sets the @code{:stipple} attribute of @var{face} to
2652 @deffn Command set-face-font face font &optional frame
2653 This sets the @code{:font} attribute of @var{face} to @var{font}.
2656 @defun set-face-bold face bold-p &optional frame
2657 This sets the @code{:weight} attribute of @var{face} to @var{normal}
2658 if @var{bold-p} is @code{nil}, and to @var{bold} otherwise.
2661 @defun set-face-italic face italic-p &optional frame
2662 This sets the @code{:slant} attribute of @var{face} to @var{normal} if
2663 @var{italic-p} is @code{nil}, and to @var{italic} otherwise.
2666 @defun set-face-underline face underline &optional frame
2667 This sets the @code{:underline} attribute of @var{face} to
2671 @defun set-face-inverse-video face inverse-video-p &optional frame
2672 This sets the @code{:inverse-video} attribute of @var{face} to
2673 @var{inverse-video-p}.
2676 @deffn Command invert-face face &optional frame
2677 This swaps the foreground and background colors of face @var{face}.
2680 The following functions examine the attributes of a face. They
2681 mostly provide compatibility with old versions of Emacs. If you don't
2682 specify @var{frame}, they refer to the selected frame; @code{t} refers
2683 to the default data for new frames. They return @code{unspecified} if
2684 the face doesn't define any value for that attribute. If
2685 @var{inherit} is @code{nil}, only an attribute directly defined by the
2686 face is returned. If @var{inherit} is non-@code{nil}, any faces
2687 specified by its @code{:inherit} attribute are considered as well, and
2688 if @var{inherit} is a face or a list of faces, then they are also
2689 considered, until a specified attribute is found. To ensure that the
2690 return value is always specified, use a value of @code{default} for
2693 @defun face-font face &optional frame character
2694 This function returns the name of the font of face @var{face}.
2696 If the optional argument @var{frame} is specified, it returns the name
2697 of the font of @var{face} for that frame. If @var{frame} is omitted or
2698 @code{nil}, the selected frame is used. And, in this case, if the
2699 optional third argument @var{character} is supplied, it returns the font
2700 name used for @var{character}.
2703 @defun face-foreground face &optional frame inherit
2704 @defunx face-background face &optional frame inherit
2705 These functions return the foreground color (or background color,
2706 respectively) of face @var{face}, as a string.
2709 @defun face-stipple face &optional frame inherit
2710 This function returns the name of the background stipple pattern of face
2711 @var{face}, or @code{nil} if it doesn't have one.
2714 @defun face-bold-p face &optional frame inherit
2715 This function returns a non-@code{nil} value if the @code{:weight}
2716 attribute of @var{face} is bolder than normal (i.e., one of
2717 @code{semi-bold}, @code{bold}, @code{extra-bold}, or
2718 @code{ultra-bold}). Otherwise, it returns @code{nil}.
2721 @defun face-italic-p face &optional frame inherit
2722 This function returns a non-@code{nil} value if the @code{:slant}
2723 attribute of @var{face} is @code{italic} or @code{oblique}, and
2724 @code{nil} otherwise.
2727 @defun face-underline-p face &optional frame inherit
2728 This function returns non-@code{nil} if face @var{face} specifies
2729 a non-@code{nil} @code{:underline} attribute.
2732 @defun face-inverse-video-p face &optional frame inherit
2733 This function returns non-@code{nil} if face @var{face} specifies
2734 a non-@code{nil} @code{:inverse-video} attribute.
2737 @node Displaying Faces
2738 @subsection Displaying Faces
2739 @cindex displaying faces
2740 @cindex face merging
2742 When Emacs displays a given piece of text, the visual appearance of
2743 the text may be determined by faces drawn from different sources. If
2744 these various sources together specify more than one face for a
2745 particular character, Emacs merges the attributes of the various
2746 faces. Here is the order in which Emacs merges the faces, from
2747 highest to lowest priority:
2751 If the text consists of a special glyph, the glyph can specify a
2752 particular face. @xref{Glyphs}.
2755 If the text lies within an active region, Emacs highlights it using
2756 the @code{region} face. @xref{Standard Faces,,, emacs, The GNU Emacs
2760 If the text lies within an overlay with a non-@code{nil} @code{face}
2761 property, Emacs applies the face(s) specified by that property. If
2762 the overlay has a @code{mouse-face} property and the mouse is near
2763 enough to the overlay, Emacs applies the face or face attributes
2764 specified by the @code{mouse-face} property instead. @xref{Overlay
2767 When multiple overlays cover one character, an overlay with higher
2768 priority overrides those with lower priority. @xref{Overlays}.
2771 If the text contains a @code{face} or @code{mouse-face} property,
2772 Emacs applies the specified faces and face attributes. @xref{Special
2773 Properties}. (This is how Font Lock mode faces are applied.
2774 @xref{Font Lock Mode}.)
2777 If the text lies within the mode line of the selected window, Emacs
2778 applies the @code{mode-line} face. For the mode line of a
2779 non-selected window, Emacs applies the @code{mode-line-inactive} face.
2780 For a header line, Emacs applies the @code{header-line} face.
2783 If any given attribute has not been specified during the preceding
2784 steps, Emacs applies the attribute of the @code{default} face.
2787 At each stage, if a face has a valid @code{:inherit} attribute,
2788 Emacs treats any attribute with an @code{unspecified} value as having
2789 the corresponding value drawn from the parent face(s). @pxref{Face
2790 Attributes}. Note that the parent face(s) may also leave the
2791 attribute unspecified; in that case, the attribute remains unspecified
2792 at the next level of face merging.
2794 @node Face Remapping
2795 @subsection Face Remapping
2796 @cindex face remapping
2798 The variable @code{face-remapping-alist} is used for buffer-local or
2799 global changes in the appearance of a face. For instance, it is used
2800 to implement the @code{text-scale-adjust} command (@pxref{Text
2801 Scale,,, emacs, The GNU Emacs Manual}).
2803 @defvar face-remapping-alist
2804 The value of this variable is an alist whose elements have the form
2805 @code{(@var{face} . @var{remapping})}. This causes Emacs to display
2806 any text having the face @var{face} with @var{remapping}, rather than
2807 the ordinary definition of @var{face}.
2809 @var{remapping} may be any face spec suitable for a @code{face} text
2810 property: either a face (i.e., a face name or a property list of
2811 attribute/value pairs), or a list of faces. For details, see the
2812 description of the @code{face} text property in @ref{Special
2813 Properties}. @var{remapping} serves as the complete specification for
2814 the remapped face---it replaces the normal definition of @var{face},
2815 instead of modifying it.
2817 If @code{face-remapping-alist} is buffer-local, its local value takes
2818 effect only within that buffer.
2820 Note: face remapping is non-recursive. If @var{remapping} references
2821 the same face name @var{face}, either directly or via the
2822 @code{:inherit} attribute of some other face in @var{remapping}, that
2823 reference uses the normal definition of @var{face}. For instance, if
2824 the @code{mode-line} face is remapped using this entry in
2825 @code{face-remapping-alist}:
2828 (mode-line italic mode-line)
2832 then the new definition of the @code{mode-line} face inherits from the
2833 @code{italic} face, and the @emph{normal} (non-remapped) definition of
2834 @code{mode-line} face.
2837 @cindex relative remapping, faces
2838 @cindex base remapping, faces
2839 The following functions implement a higher-level interface to
2840 @code{face-remapping-alist}. Most Lisp code should use these
2841 functions instead of setting @code{face-remapping-alist} directly, to
2842 avoid trampling on remappings applied elsewhere. These functions are
2843 intended for buffer-local remappings, so they all make
2844 @code{face-remapping-alist} buffer-local as a side-effect. They manage
2845 @code{face-remapping-alist} entries of the form
2848 (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec})
2852 where, as explained above, each of the @var{relative-spec-N} and
2853 @var{base-spec} is either a face name, or a property list of
2854 attribute/value pairs. Each of the @dfn{relative remapping} entries,
2855 @var{relative-spec-N}, is managed by the
2856 @code{face-remap-add-relative} and @code{face-remap-remove-relative}
2857 functions; these are intended for simple modifications like changing
2858 the text size. The @dfn{base remapping} entry, @var{base-spec}, has
2859 the lowest priority and is managed by the @code{face-remap-set-base}
2860 and @code{face-remap-reset-base} functions; it is intended for major
2861 modes to remap faces in the buffers they control.
2863 @defun face-remap-add-relative face &rest specs
2864 This function adds the face spec in @var{specs} as relative
2865 remappings for face @var{face} in the current buffer. The remaining
2866 arguments, @var{specs}, should form either a list of face names, or a
2867 property list of attribute/value pairs.
2869 The return value is a Lisp object that serves as a cookie; you can
2870 pass this object as an argument to @code{face-remap-remove-relative}
2871 if you need to remove the remapping later.
2874 ;; Remap the 'escape-glyph' face into a combination
2875 ;; of the 'highlight' and 'italic' faces:
2876 (face-remap-add-relative 'escape-glyph 'highlight 'italic)
2878 ;; Increase the size of the 'default' face by 50%:
2879 (face-remap-add-relative 'default :height 1.5)
2883 @defun face-remap-remove-relative cookie
2884 This function removes a relative remapping previously added by
2885 @code{face-remap-add-relative}. @var{cookie} should be the Lisp
2886 object returned by @code{face-remap-add-relative} when the remapping
2890 @defun face-remap-set-base face &rest specs
2891 This function sets the base remapping of @var{face} in the current
2892 buffer to @var{specs}. If @var{specs} is empty, the default base
2893 remapping is restored, similar to calling @code{face-remap-reset-base}
2894 (see below); note that this is different from @var{specs} containing a
2895 single value @code{nil}, which has the opposite result (the global
2896 definition of @var{face} is ignored).
2898 This overwrites the default @var{base-spec}, which inherits the global
2899 face definition, so it is up to the caller to add such inheritance if
2903 @defun face-remap-reset-base face
2904 This function sets the base remapping of @var{face} to its default
2905 value, which inherits from @var{face}'s global definition.
2908 @node Face Functions
2909 @subsection Functions for Working with Faces
2911 Here are additional functions for creating and working with faces.
2914 This function returns a list of all defined face names.
2918 This function returns the @dfn{face number} of face @var{face}. This
2919 is a number that uniquely identifies a face at low levels within
2920 Emacs. It is seldom necessary to refer to a face by its face number.
2923 @defun face-documentation face
2924 This function returns the documentation string of face @var{face}, or
2925 @code{nil} if none was specified for it.
2928 @defun face-equal face1 face2 &optional frame
2929 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2930 same attributes for display.
2933 @defun face-differs-from-default-p face &optional frame
2934 This returns non-@code{nil} if the face @var{face} displays
2935 differently from the default face.
2939 @cindex alias, for faces
2940 A @dfn{face alias} provides an equivalent name for a face. You can
2941 define a face alias by giving the alias symbol the @code{face-alias}
2942 property, with a value of the target face name. The following example
2943 makes @code{modeline} an alias for the @code{mode-line} face.
2946 (put 'modeline 'face-alias 'mode-line)
2949 @defmac define-obsolete-face-alias obsolete-face current-face when
2950 This macro defines @code{obsolete-face} as an alias for
2951 @var{current-face}, and also marks it as obsolete, indicating that it
2952 may be removed in future. @var{when} should be a string indicating
2953 when @code{obsolete-face} was made obsolete (usually a version number
2958 @subsection Automatic Face Assignment
2959 @cindex automatic face assignment
2960 @cindex faces, automatic choice
2962 This hook is used for automatically assigning faces to text in the
2963 buffer. It is part of the implementation of Jit-Lock mode, used by
2966 @defvar fontification-functions
2967 This variable holds a list of functions that are called by Emacs
2968 redisplay as needed, just before doing redisplay. They are called even
2969 when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this
2970 variable usually holds just one function, @code{jit-lock-function}.
2972 The functions are called in the order listed, with one argument, a
2973 buffer position @var{pos}. Collectively they should attempt to assign
2974 faces to the text in the current buffer starting at @var{pos}.
2976 The functions should record the faces they assign by setting the
2977 @code{face} property. They should also add a non-@code{nil}
2978 @code{fontified} property to all the text they have assigned faces to.
2979 That property tells redisplay that faces have been assigned to that text
2982 It is probably a good idea for the functions to do nothing if the
2983 character after @var{pos} already has a non-@code{nil} @code{fontified}
2984 property, but this is not required. If one function overrides the
2985 assignments made by a previous one, the properties after the last
2986 function finishes are the ones that really matter.
2988 For efficiency, we recommend writing these functions so that they
2989 usually assign faces to around 400 to 600 characters at each call.
2993 @subsection Basic Faces
2996 If your Emacs Lisp program needs to assign some faces to text, it is
2997 often a good idea to use certain existing faces or inherit from them,
2998 rather than defining entirely new faces. This way, if other users
2999 have customized the basic faces to give Emacs a certain look, your
3000 program will fit in without additional customization.
3002 Some of the basic faces defined in Emacs are listed below. In
3003 addition to these, you might want to make use of the Font Lock faces
3004 for syntactic highlighting, if highlighting is not already handled by
3005 Font Lock mode, or if some Font Lock faces are not in use.
3006 @xref{Faces for Font Lock}.
3010 The default face, whose attributes are all specified. All other faces
3011 implicitly inherit from it: any unspecified attribute defaults to the
3012 attribute on this face (@pxref{Face Attributes}).
3019 @itemx variable-pitch
3020 These have the attributes indicated by their names (e.g., @code{bold}
3021 has a bold @code{:weight} attribute), with all other attributes
3022 unspecified (and so given by @code{default}).
3025 For dimmed-out text. For example, it is used for the ignored
3026 part of a filename in the minibuffer (@pxref{Minibuffer File,,
3027 Minibuffers for File Names, emacs, The GNU Emacs Manual}).
3031 For clickable text buttons that send the user to a different
3035 For stretches of text that should temporarily stand out. For example,
3036 it is commonly assigned to the @code{mouse-face} property for cursor
3037 highlighting (@pxref{Special Properties}).
3041 @itemx lazy-highlight
3042 For text matching (respectively) permanent search matches, interactive
3043 search matches, and lazy highlighting other matches than the current
3049 For text concerning errors, warnings, or successes. For example,
3050 these are used for messages in @file{*Compilation*} buffers.
3053 @node Font Selection
3054 @subsection Font Selection
3055 @cindex font selection
3056 @cindex selecting a font
3058 Before Emacs can draw a character on a graphical display, it must
3059 select a @dfn{font} for that character@footnote{In this context, the
3060 term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock
3061 Mode}).}. @xref{Fonts,,, emacs, The GNU Emacs Manual}. Normally,
3062 Emacs automatically chooses a font based on the faces assigned to that
3063 character---specifically, the face attributes @code{:family},
3064 @code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face
3065 Attributes}). The choice of font also depends on the character to be
3066 displayed; some fonts can only display a limited set of characters.
3067 If no available font exactly fits the requirements, Emacs looks for
3068 the @dfn{closest matching font}. The variables in this section
3069 control how Emacs makes this selection.
3071 @defopt face-font-family-alternatives
3072 If a given family is specified but does not exist, this variable
3073 specifies alternative font families to try. Each element should have
3077 (@var{family} @var{alternate-families}@dots{})
3080 If @var{family} is specified but not available, Emacs will try the other
3081 families given in @var{alternate-families}, one by one, until it finds a
3082 family that does exist.
3085 @defopt face-font-selection-order
3086 If there is no font that exactly matches all desired face attributes
3087 (@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}),
3088 this variable specifies the order in which these attributes should be
3089 considered when selecting the closest matching font. The value should
3090 be a list containing those four attribute symbols, in order of
3091 decreasing importance. The default is @code{(:width :height :weight
3094 Font selection first finds the best available matches for the first
3095 attribute in the list; then, among the fonts which are best in that
3096 way, it searches for the best matches in the second attribute, and so
3099 The attributes @code{:weight} and @code{:width} have symbolic values in
3100 a range centered around @code{normal}. Matches that are more extreme
3101 (farther from @code{normal}) are somewhat preferred to matches that are
3102 less extreme (closer to @code{normal}); this is designed to ensure that
3103 non-normal faces contrast with normal ones, whenever possible.
3105 One example of a case where this variable makes a difference is when the
3106 default font has no italic equivalent. With the default ordering, the
3107 @code{italic} face will use a non-italic font that is similar to the
3108 default one. But if you put @code{:slant} before @code{:height}, the
3109 @code{italic} face will use an italic font, even if its height is not
3113 @defopt face-font-registry-alternatives
3114 This variable lets you specify alternative font registries to try, if a
3115 given registry is specified and doesn't exist. Each element should have
3119 (@var{registry} @var{alternate-registries}@dots{})
3122 If @var{registry} is specified but not available, Emacs will try the
3123 other registries given in @var{alternate-registries}, one by one,
3124 until it finds a registry that does exist.
3127 @cindex scalable fonts
3128 Emacs can make use of scalable fonts, but by default it does not use
3131 @defopt scalable-fonts-allowed
3132 This variable controls which scalable fonts to use. A value of
3133 @code{nil}, the default, means do not use scalable fonts. @code{t}
3134 means to use any scalable font that seems appropriate for the text.
3136 Otherwise, the value must be a list of regular expressions. Then a
3137 scalable font is enabled for use if its name matches any regular
3138 expression in the list. For example,
3141 (setq scalable-fonts-allowed '("iso10646-1$"))
3145 allows the use of scalable fonts with registry @code{iso10646-1}.
3148 @defvar face-font-rescale-alist
3149 This variable specifies scaling for certain faces. Its value should
3150 be a list of elements of the form
3153 (@var{fontname-regexp} . @var{scale-factor})
3156 If @var{fontname-regexp} matches the font name that is about to be
3157 used, this says to choose a larger similar font according to the
3158 factor @var{scale-factor}. You would use this feature to normalize
3159 the font size if certain fonts are bigger or smaller than their
3160 nominal heights and widths would suggest.
3164 @subsection Looking Up Fonts
3166 @cindex looking up fonts
3168 @defun x-list-fonts name &optional reference-face frame maximum width
3169 This function returns a list of available font names that match
3170 @var{name}. @var{name} should be a string containing a font name in
3171 either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The
3172 GNU Emacs Manual}). Within an XLFD string, wildcard characters may be
3173 used: the @samp{*} character matches any substring, and the @samp{?}
3174 character matches any single character. Case is ignored when matching
3177 If the optional arguments @var{reference-face} and @var{frame} are
3178 specified, the returned list includes only fonts that are the same
3179 size as @var{reference-face} (a face name) currently is on the frame
3182 The optional argument @var{maximum} sets a limit on how many fonts to
3183 return. If it is non-@code{nil}, then the return value is truncated
3184 after the first @var{maximum} matching fonts. Specifying a small
3185 value for @var{maximum} can make this function much faster, in cases
3186 where many fonts match the pattern.
3188 The optional argument @var{width} specifies a desired font width. If
3189 it is non-@code{nil}, the function only returns those fonts whose
3190 characters are (on average) @var{width} times as wide as
3191 @var{reference-face}.
3194 @defun x-family-fonts &optional family frame
3195 This function returns a list describing the available fonts for family
3196 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
3197 this list applies to all families, and therefore, it contains all
3198 available fonts. Otherwise, @var{family} must be a string; it may
3199 contain the wildcards @samp{?} and @samp{*}.
3201 The list describes the display that @var{frame} is on; if @var{frame} is
3202 omitted or @code{nil}, it applies to the selected frame's display
3203 (@pxref{Input Focus}).
3205 Each element in the list is a vector of the following form:
3208 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
3209 @var{fixed-p} @var{full} @var{registry-and-encoding}]
3212 The first five elements correspond to face attributes; if you
3213 specify these attributes for a face, it will use this font.
3215 The last three elements give additional information about the font.
3216 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
3217 @var{full} is the full name of the font, and
3218 @var{registry-and-encoding} is a string giving the registry and
3219 encoding of the font.
3223 @subsection Fontsets
3226 A @dfn{fontset} is a list of fonts, each assigned to a range of
3227 character codes. An individual font cannot display the whole range of
3228 characters that Emacs supports, but a fontset can. Fontsets have names,
3229 just as fonts do, and you can use a fontset name in place of a font name
3230 when you specify the font for a frame or a face. Here is
3231 information about defining a fontset under Lisp program control.
3233 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
3234 This function defines a new fontset according to the specification
3235 string @var{fontset-spec}. The string should have this format:
3238 @var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}}
3242 Whitespace characters before and after the commas are ignored.
3244 The first part of the string, @var{fontpattern}, should have the form of
3245 a standard X font name, except that the last two fields should be
3246 @samp{fontset-@var{alias}}.
3248 The new fontset has two names, one long and one short. The long name is
3249 @var{fontpattern} in its entirety. The short name is
3250 @samp{fontset-@var{alias}}. You can refer to the fontset by either
3251 name. If a fontset with the same name already exists, an error is
3252 signaled, unless @var{noerror} is non-@code{nil}, in which case this
3253 function does nothing.
3255 If optional argument @var{style-variant-p} is non-@code{nil}, that says
3256 to create bold, italic and bold-italic variants of the fontset as well.
3257 These variant fontsets do not have a short name, only a long one, which
3258 is made by altering @var{fontpattern} to indicate the bold and/or italic
3261 The specification string also says which fonts to use in the fontset.
3262 See below for the details.
3265 The construct @samp{@var{charset}:@var{font}} specifies which font to
3266 use (in this fontset) for one particular character set. Here,
3267 @var{charset} is the name of a character set, and @var{font} is the font
3268 to use for that character set. You can use this construct any number of
3269 times in the specification string.
3271 For the remaining character sets, those that you don't specify
3272 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
3273 @samp{fontset-@var{alias}} with a value that names one character set.
3274 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
3275 with @samp{ISO8859-1}.
3277 In addition, when several consecutive fields are wildcards, Emacs
3278 collapses them into a single wildcard. This is to prevent use of
3279 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
3280 for editing, and scaling a smaller font is not useful because it is
3281 better to use the smaller font in its own size, which Emacs does.
3283 Thus if @var{fontpattern} is this,
3286 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
3290 the font specification for @acronym{ASCII} characters would be this:
3293 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
3297 and the font specification for Chinese GB2312 characters would be this:
3300 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
3303 You may not have any Chinese font matching the above font
3304 specification. Most X distributions include only Chinese fonts that
3305 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
3306 such a case, @samp{Fontset-@var{n}} can be specified as below:
3309 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
3310 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
3314 Then, the font specifications for all but Chinese GB2312 characters have
3315 @samp{fixed} in the @var{family} field, and the font specification for
3316 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
3319 @defun set-fontset-font name character font-spec &optional frame add
3320 This function modifies the existing fontset @var{name} to use the font
3321 matching with @var{font-spec} for the specified @var{character}.
3323 If @var{name} is @code{nil}, this function modifies the fontset of the
3324 selected frame or that of @var{frame} if @var{frame} is not
3327 If @var{name} is @code{t}, this function modifies the default
3328 fontset, whose short name is @samp{fontset-default}.
3330 In addition to specifying a single codepoint, @var{character} may be a
3331 cons @code{(@var{from} . @var{to})}, where @var{from} and @var{to} are
3332 character codepoints. In that case, use @var{font-spec} for all the
3333 characters in the range @var{from} and @var{to} (inclusive).
3335 @var{character} may be a charset. In that case, use
3336 @var{font-spec} for all character in the charsets.
3338 @var{character} may be a script name. In that case, use
3339 @var{font-spec} for all character in the charsets.
3341 @var{font-spec} may be a font-spec object created by the function
3342 @code{font-spec} (@pxref{Low-Level Font}).
3344 @var{font-spec} may be a cons; @code{(@var{family} . @var{registry})},
3345 where @var{family} is a family name of a font (possibly including a
3346 foundry name at the head), @var{registry} is a registry name of a font
3347 (possibly including an encoding name at the tail).
3349 @var{font-spec} may be a font name string.
3351 @var{font-spec} may be @code{nil}, which explicitly specifies that
3352 there's no font for the specified @var{character}. This is useful,
3353 for example, to avoid expensive system-wide search for fonts for
3354 characters that have no glyphs, like those from the Unicode Private
3357 The optional argument @var{add}, if non-@code{nil}, specifies how to
3358 add @var{font-spec} to the font specifications previously set. If it
3359 is @code{prepend}, @var{font-spec} is prepended. If it is
3360 @code{append}, @var{font-spec} is appended. By default,
3361 @var{font-spec} overrides the previous settings.
3363 For instance, this changes the default fontset to use a font of which
3364 family name is @samp{Kochi Gothic} for all characters belonging to
3365 the charset @code{japanese-jisx0208}.
3368 (set-fontset-font t 'japanese-jisx0208
3369 (font-spec :family "Kochi Gothic"))
3373 @defun char-displayable-p char
3374 This function returns @code{t} if Emacs ought to be able to display
3375 @var{char}. More precisely, if the selected frame's fontset has a
3376 font to display the character set that @var{char} belongs to.
3378 Fontsets can specify a font on a per-character basis; when the fontset
3379 does that, this function's value may not be accurate.
3382 @node Low-Level Font
3383 @subsection Low-Level Font Representation
3384 @cindex font property
3386 Normally, it is not necessary to manipulate fonts directly. In case
3387 you need to do so, this section explains how.
3389 In Emacs Lisp, fonts are represented using three different Lisp
3390 object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font
3393 @defun fontp object &optional type
3394 Return @code{t} if @var{object} is a font object, font spec, or font
3395 entity. Otherwise, return @code{nil}.
3397 The optional argument @var{type}, if non-@code{nil}, determines the
3398 exact type of Lisp object to check for. In that case, @var{type}
3399 should be one of @code{font-object}, @code{font-spec}, or
3404 A font object is a Lisp object that represents a font that Emacs has
3405 @dfn{opened}. Font objects cannot be modified in Lisp, but they can
3408 @defun font-at position &optional window string
3409 Return the font object that is being used to display the character at
3410 position @var{position} in the window @var{window}. If @var{window}
3411 is @code{nil}, it defaults to the selected window. If @var{string} is
3412 @code{nil}, @var{position} specifies a position in the current buffer;
3413 otherwise, @var{string} should be a string, and @var{position}
3414 specifies a position in that string.
3418 A font spec is a Lisp object that contains a set of specifications
3419 that can be used to find a font. More than one font may match the
3420 specifications in a font spec.
3422 @defun font-spec &rest arguments
3423 Return a new font spec using the specifications in @var{arguments},
3424 which should come in @code{property}-@code{value} pairs. The possible
3425 specifications are as follows:
3429 The font name (a string), in either XLFD, Fontconfig, or GTK format.
3430 @xref{Fonts,,, emacs, The GNU Emacs Manual}.
3437 These have the same meanings as the face attributes of the same name.
3438 @xref{Face Attributes}.
3441 The font size---either a non-negative integer that specifies the pixel
3442 size, or a floating-point number that specifies the point size.
3445 Additional typographic style information for the font, such as
3446 @samp{sans}. The value should be a string or a symbol.
3448 @cindex font registry
3450 The charset registry and encoding of the font, such as
3451 @samp{iso8859-1}. The value should be a string or a symbol.
3454 The script that the font must support (a symbol).
3457 The language that the font should support. The value should be a
3458 symbol whose name is a two-letter ISO-639 language name. On X, the
3459 value is matched against the ``Additional Style'' field of the XLFD
3460 name of a font, if it is non-empty. On MS-Windows, fonts matching the
3461 spec are required to support codepages needed for the language.
3462 Currently, only a small set of CJK languages is supported with this
3463 property: @samp{ja}, @samp{ko}, and @samp{zh}.
3466 @cindex OpenType font
3467 The font must be an OpenType font that supports these OpenType
3468 features, provided Emacs is compiled with a library, such as
3469 @samp{libotf} on GNU/Linux, that supports complex text layout for
3470 scripts which need that. The value must be a list of the form
3473 @code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
3476 where @var{script-tag} is the OpenType script tag symbol;
3477 @var{langsys-tag} is the OpenType language system tag symbol, or
3478 @code{nil} to use the default language system; @code{gsub} is a list
3479 of OpenType GSUB feature tag symbols, or @code{nil} if none is
3480 required; and @code{gpos} is a list of OpenType GPOS feature tag
3481 symbols, or @code{nil} if none is required. If @code{gsub} or
3482 @code{gpos} is a list, a @code{nil} element in that list means that
3483 the font must not match any of the remaining tag symbols. The
3484 @code{gpos} element may be omitted.
3488 @defun font-put font-spec property value
3489 Set the font property @var{property} in the font-spec @var{font-spec}
3494 A font entity is a reference to a font that need not be open. Its
3495 properties are intermediate between a font object and a font spec:
3496 like a font object, and unlike a font spec, it refers to a single,
3497 specific font. Unlike a font object, creating a font entity does not
3498 load the contents of that font into computer memory. Emacs may open
3499 multiple font objects of different sizes from a single font entity
3500 referring to a scalable font.
3502 @defun find-font font-spec &optional frame
3503 This function returns a font entity that best matches the font spec
3504 @var{font-spec} on frame @var{frame}. If @var{frame} is @code{nil},
3505 it defaults to the selected frame.
3508 @defun list-fonts font-spec &optional frame num prefer
3509 This function returns a list of all font entities that match the font
3510 spec @var{font-spec}.
3512 The optional argument @var{frame}, if non-@code{nil}, specifies the
3513 frame on which the fonts are to be displayed. The optional argument
3514 @var{num}, if non-@code{nil}, should be an integer that specifies the
3515 maximum length of the returned list. The optional argument
3516 @var{prefer}, if non-@code{nil}, should be another font spec, which is
3517 used to control the order of the returned list; the returned font
3518 entities are sorted in order of decreasing closeness to that font
3522 If you call @code{set-face-attribute} and pass a font spec, font
3523 entity, or font name string as the value of the @code{:font}
3524 attribute, Emacs opens the best matching font that is available
3525 for display. It then stores the corresponding font object as the
3526 actual value of the @code{:font} attribute for that face.
3528 The following functions can be used to obtain information about a
3529 font. For these functions, the @var{font} argument can be a font
3530 object, a font entity, or a font spec.
3532 @defun font-get font property
3533 This function returns the value of the font property @var{property}
3536 If @var{font} is a font spec and the font spec does not specify
3537 @var{property}, the return value is @code{nil}. If @var{font} is a
3538 font object or font entity, the value for the @var{:script} property
3539 may be a list of scripts supported by the font.
3542 @defun font-face-attributes font &optional frame
3543 This function returns a list of face attributes corresponding to
3544 @var{font}. The optional argument @var{frame} specifies the frame on
3545 which the font is to be displayed. If it is @code{nil}, the selected
3546 frame is used. The return value has the form
3549 (:family @var{family} :height @var{height} :weight @var{weight}
3550 :slant @var{slant} :width @var{width})
3553 where the values of @var{family}, @var{height}, @var{weight},
3554 @var{slant}, and @var{width} are face attribute values. Some of these
3555 key-attribute pairs may be omitted from the list if they are not
3556 specified by @var{font}.
3559 @defun font-xlfd-name font &optional fold-wildcards
3560 This function returns the XLFD (X Logical Font Descriptor), a string,
3561 matching @var{font}. @xref{Fonts,,, emacs, The GNU Emacs Manual}, for
3562 information about XLFDs. If the name is too long for an XLFD (which
3563 can contain at most 255 characters), the function returns @code{nil}.
3565 If the optional argument @var{fold-wildcards} is non-@code{nil},
3566 consecutive wildcards in the XLFD are folded into one.
3569 The following two functions return important information about a font.
3571 @defun font-info name &optional frame
3572 This function returns information about a font specified by its
3573 @var{name}, a string, as it is used on @var{frame}. If @var{frame} is
3574 omitted or @code{nil}, it defaults to the selected frame.
3576 The value returned by the function is a vector of the form
3577 @code{[@var{opened-name} @var{full-name} @var{size} @var{height}
3578 @var{baseline-offset} @var{relative-compose} @var{default-ascent}
3579 @var{max-width} @var{ascent} @var{descent} @var{space-width}
3580 @var{average-width} @var{filename} @var{capability}]}. Here's the
3581 description of each components of this vector:
3585 The name used to open the font, a string.
3588 The full name of the font, a string.
3591 The pixel size of the font.
3594 The height of the font in pixels.
3596 @item baseline-offset
3597 The offset in pixels from the @acronym{ASCII} baseline, positive
3600 @item relative-compose
3601 @itemx default-ascent
3602 Numbers controlling how to compose characters.
3606 The ascent and descent of this font. The sum of these two numbers
3607 should be equal to the value of @var{height} above.
3610 The width, in pixels, of the font's space character.
3613 The average width of the font characters. If this is zero, Emacs uses
3614 the value of @var{space-width} instead, when it calculates text layout
3618 The file name of the font as a string. This can be @code{nil} if the
3619 font back-end does not provide a way to find out the font's file name.
3622 A list whose first element is a symbol representing the font type, one
3623 of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
3624 @code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
3625 additional elements describing the @sc{gsub} and @sc{gpos} features
3626 supported by the font. Each of these elements is a list of the form
3627 @code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
3628 @dots{})}, where @var{script} is a symbol representing an OpenType
3629 script tag, @var{langsys} is a symbol representing an OpenType langsys
3630 tag (or @code{nil}, which stands for the default langsys), and each
3631 @var{feature} is a symbol representing an OpenType feature tag.
3635 @defun query-font font-object
3636 This function returns information about a @var{font-object}. (This is
3637 in contrast to @code{font-info}, which takes the font name, a string,
3640 The value returned by the function is a vector of the form
3641 @code{[@var{name} @var{filename} @var{pixel-size} @var{max-width}
3642 @var{ascent} @var{descent} @var{space-width} @var{average-width}
3643 @var{capability}]}. Here's the description of each components of this
3648 The font name, a string.
3651 The file name of the font as a string. This can be @code{nil} if the
3652 font back-end does not provide a way to find out the font's file name.
3655 The pixel size of the font used to open the font.
3658 The maximum advance width of the font.
3662 The ascent and descent of this font. The sum of these two numbers
3663 gives the font height.
3666 The width, in pixels, of the font's space character.
3669 The average width of the font characters. If this is zero, Emacs uses
3670 the value of @var{space-width} instead, when it calculates text layout
3674 A list whose first element is a symbol representing the font type, one
3675 of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
3676 @code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
3677 additional elements describing the @sc{gsub} and @sc{gpos} features
3678 supported by the font. Each of these elements is a list of the form
3679 @code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
3680 @dots{})}, where @var{script} is a symbol representing an OpenType
3681 script tag, @var{langsys} is a symbol representing an OpenType langsys
3682 tag (or @code{nil}, which stands for the default langsys), and each
3683 @var{feature} is a symbol representing an OpenType feature tag.
3687 @cindex font information for layout
3688 The following four functions return size information about fonts used
3689 by various faces, allowing various layout considerations in Lisp
3690 programs. These functions take face remapping into consideration,
3691 returning information about the remapped face, if the face in question
3692 was remapped. @xref{Face Remapping}.
3694 @defun default-font-width
3695 This function returns the average width in pixels of the font used by
3696 the current buffer's default face.
3699 @defun default-font-height
3700 This function returns the height in pixels of the font used by the
3701 current buffer's default face.
3704 @defun window-font-width &optional window face
3705 This function returns the average width in pixels for the font used by
3706 @var{face} in @var{window}. The specified @var{window} must be a live
3707 window. If @code{nil} or omitted, @var{window} defaults to the
3708 selected window, and @var{face} defaults to the default face in
3712 @defun window-font-height &optional window face
3713 This function returns the height in pixels for the font used by
3714 @var{face} in @var{window}. The specified @var{window} must be a live
3715 window. If @code{nil} or omitted, @var{window} defaults to the
3716 selected window, and @var{face} defaults to the default face in
3724 On graphical displays, Emacs draws @dfn{fringes} next to each
3725 window: thin vertical strips down the sides which can display bitmaps
3726 indicating truncation, continuation, horizontal scrolling, and so on.
3729 * Fringe Size/Pos:: Specifying where to put the window fringes.
3730 * Fringe Indicators:: Displaying indicator icons in the window fringes.
3731 * Fringe Cursors:: Displaying cursors in the right fringe.
3732 * Fringe Bitmaps:: Specifying bitmaps for fringe indicators.
3733 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
3734 * Overlay Arrow:: Display of an arrow to indicate position.
3737 @node Fringe Size/Pos
3738 @subsection Fringe Size and Position
3740 The following buffer-local variables control the position and width
3741 of fringes in windows showing that buffer.
3743 @defvar fringes-outside-margins
3744 The fringes normally appear between the display margins and the window
3745 text. If the value is non-@code{nil}, they appear outside the display
3746 margins. @xref{Display Margins}.
3749 @defvar left-fringe-width
3750 This variable, if non-@code{nil}, specifies the width of the left
3751 fringe in pixels. A value of @code{nil} means to use the left fringe
3752 width from the window's frame.
3755 @defvar right-fringe-width
3756 This variable, if non-@code{nil}, specifies the width of the right
3757 fringe in pixels. A value of @code{nil} means to use the right fringe
3758 width from the window's frame.
3761 Any buffer which does not specify values for these variables uses
3762 the values specified by the @code{left-fringe} and @code{right-fringe}
3763 frame parameters (@pxref{Layout Parameters}).
3765 The above variables actually take effect via the function
3766 @code{set-window-buffer} (@pxref{Buffers and Windows}), which calls
3767 @code{set-window-fringes} as a subroutine. If you change one of these
3768 variables, the fringe display is not updated in existing windows
3769 showing the buffer, unless you call @code{set-window-buffer} again in
3770 each affected window. You can also use @code{set-window-fringes} to
3771 control the fringe display in individual windows.
3773 @defun set-window-fringes window left &optional right outside-margins
3774 This function sets the fringe widths of window @var{window}.
3775 If @var{window} is @code{nil}, the selected window is used.
3777 The argument @var{left} specifies the width in pixels of the left
3778 fringe, and likewise @var{right} for the right fringe. A value of
3779 @code{nil} for either one stands for the default width. If
3780 @var{outside-margins} is non-@code{nil}, that specifies that fringes
3781 should appear outside of the display margins.
3784 @defun window-fringes &optional window
3785 This function returns information about the fringes of a window
3786 @var{window}. If @var{window} is omitted or @code{nil}, the selected
3787 window is used. The value has the form @code{(@var{left-width}
3788 @var{right-width} @var{outside-margins})}.
3792 @node Fringe Indicators
3793 @subsection Fringe Indicators
3794 @cindex fringe indicators
3795 @cindex indicators, fringe
3797 @dfn{Fringe indicators} are tiny icons displayed in the window
3798 fringe to indicate truncated or continued lines, buffer boundaries,
3801 @defopt indicate-empty-lines
3802 @cindex fringes, and empty line indication
3803 @cindex empty lines, indicating
3804 When this is non-@code{nil}, Emacs displays a special glyph in the
3805 fringe of each empty line at the end of the buffer, on graphical
3806 displays. @xref{Fringes}. This variable is automatically
3807 buffer-local in every buffer.
3810 @defopt indicate-buffer-boundaries
3811 @cindex buffer boundaries, indicating
3812 This buffer-local variable controls how the buffer boundaries and
3813 window scrolling are indicated in the window fringes.
3815 Emacs can indicate the buffer boundaries---that is, the first and last
3816 line in the buffer---with angle icons when they appear on the screen.
3817 In addition, Emacs can display an up-arrow in the fringe to show
3818 that there is text above the screen, and a down-arrow to show
3819 there is text below the screen.
3821 There are three kinds of basic values:
3825 Don't display any of these fringe icons.
3827 Display the angle icons and arrows in the left fringe.
3829 Display the angle icons and arrows in the right fringe.
3831 Display the angle icons in the left fringe
3832 and don't display the arrows.
3835 Otherwise the value should be an alist that specifies which fringe
3836 indicators to display and where. Each element of the alist should
3837 have the form @code{(@var{indicator} . @var{position})}. Here,
3838 @var{indicator} is one of @code{top}, @code{bottom}, @code{up},
3839 @code{down}, and @code{t} (which covers all the icons not yet
3840 specified), while @var{position} is one of @code{left}, @code{right}
3843 For example, @code{((top . left) (t . right))} places the top angle
3844 bitmap in left fringe, and the bottom angle bitmap as well as both
3845 arrow bitmaps in right fringe. To show the angle bitmaps in the left
3846 fringe, and no arrow bitmaps, use @code{((top . left) (bottom . left))}.
3849 @defvar fringe-indicator-alist
3850 This buffer-local variable specifies the mapping from logical fringe
3851 indicators to the actual bitmaps displayed in the window fringes. The
3852 value is an alist of elements @code{(@var{indicator}
3853 . @var{bitmaps})}, where @var{indicator} specifies a logical indicator
3854 type and @var{bitmaps} specifies the fringe bitmaps to use for that
3857 Each @var{indicator} should be one of the following symbols:
3860 @item @code{truncation}, @code{continuation}.
3861 Used for truncation and continuation lines.
3863 @item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom}
3864 Used when @code{indicate-buffer-boundaries} is non-@code{nil}:
3865 @code{up} and @code{down} indicate a buffer boundary lying above or
3866 below the window edge; @code{top} and @code{bottom} indicate the
3867 topmost and bottommost buffer text line; and @code{top-bottom}
3868 indicates where there is just one line of text in the buffer.
3870 @item @code{empty-line}
3871 Used to indicate empty lines when @code{indicate-empty-lines} is
3874 @item @code{overlay-arrow}
3875 Used for overlay arrows (@pxref{Overlay Arrow}).
3876 @c Is this used anywhere?
3877 @c @item Unknown bitmap indicator:
3881 Each @var{bitmaps} value may be a list of symbols @code{(@var{left}
3882 @var{right} [@var{left1} @var{right1}])}. The @var{left} and
3883 @var{right} symbols specify the bitmaps shown in the left and/or right
3884 fringe, for the specific indicator. @var{left1} and @var{right1} are
3885 specific to the @code{bottom} and @code{top-bottom} indicators, and
3886 are used to indicate that the last text line has no final newline.
3887 Alternatively, @var{bitmaps} may be a single symbol which is used in
3888 both left and right fringes.
3890 @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how
3891 to define your own. In addition, @code{nil} represents the empty
3892 bitmap (i.e., an indicator that is not shown).
3894 When @code{fringe-indicator-alist} has a buffer-local value, and
3895 there is no bitmap defined for a logical indicator, or the bitmap is
3896 @code{t}, the corresponding value from the default value of
3897 @code{fringe-indicator-alist} is used.
3900 @node Fringe Cursors
3901 @subsection Fringe Cursors
3902 @cindex fringe cursors
3903 @cindex cursor, fringe
3905 When a line is exactly as wide as the window, Emacs displays the
3906 cursor in the right fringe instead of using two lines. Different
3907 bitmaps are used to represent the cursor in the fringe depending on
3908 the current buffer's cursor type.
3910 @defopt overflow-newline-into-fringe
3911 If this is non-@code{nil}, lines exactly as wide as the window (not
3912 counting the final newline character) are not continued. Instead,
3913 when point is at the end of the line, the cursor appears in the right
3917 @defvar fringe-cursor-alist
3918 This variable specifies the mapping from logical cursor type to the
3919 actual fringe bitmaps displayed in the right fringe. The value is an
3920 alist where each element has the form @code{(@var{cursor-type}
3921 . @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to
3922 display cursors of type @var{cursor-type}.
3924 Each @var{cursor-type} should be one of @code{box}, @code{hollow},
3925 @code{bar}, @code{hbar}, or @code{hollow-small}. The first four have
3926 the same meanings as in the @code{cursor-type} frame parameter
3927 (@pxref{Cursor Parameters}). The @code{hollow-small} type is used
3928 instead of @code{hollow} when the normal @code{hollow-rectangle}
3929 bitmap is too tall to fit on a specific display line.
3931 Each @var{bitmap} should be a symbol specifying the fringe bitmap to
3932 be displayed for that logical cursor type.
3934 See the next subsection for details.
3937 @xref{Fringe Bitmaps}.
3940 @c FIXME: I can't find the fringes-indicator-alist variable. Maybe
3941 @c it should be fringe-indicator-alist or fringe-cursor-alist? --xfq
3942 When @code{fringe-cursor-alist} has a buffer-local value, and there is
3943 no bitmap defined for a cursor type, the corresponding value from the
3944 default value of @code{fringes-indicator-alist} is used.
3947 @node Fringe Bitmaps
3948 @subsection Fringe Bitmaps
3949 @cindex fringe bitmaps
3950 @cindex bitmaps, fringe
3952 The @dfn{fringe bitmaps} are the actual bitmaps which represent the
3953 logical fringe indicators for truncated or continued lines, buffer
3954 boundaries, overlay arrows, etc. Each bitmap is represented by a
3957 These symbols are referred to by the variables
3958 @code{fringe-indicator-alist} and @code{fringe-cursor-alist},
3959 described in the previous subsections.
3962 These symbols are referred to by the variable
3963 @code{fringe-indicator-alist}, which maps fringe indicators to bitmaps
3964 (@pxref{Fringe Indicators}), and the variable
3965 @code{fringe-cursor-alist}, which maps fringe cursors to bitmaps
3966 (@pxref{Fringe Cursors}).
3969 Lisp programs can also directly display a bitmap in the left or
3970 right fringe, by using a @code{display} property for one of the
3971 characters appearing in the line (@pxref{Other Display Specs}). Such
3972 a display specification has the form
3975 (@var{fringe} @var{bitmap} [@var{face}])
3979 @var{fringe} is either the symbol @code{left-fringe} or
3980 @code{right-fringe}. @var{bitmap} is a symbol identifying the bitmap
3981 to display. The optional @var{face} names a face whose foreground
3982 color is used to display the bitmap; this face is automatically merged
3983 with the @code{fringe} face.
3985 Here is a list of the standard fringe bitmaps defined in Emacs, and
3986 how they are currently used in Emacs (via
3987 @code{fringe-indicator-alist} and @code{fringe-cursor-alist}):
3990 @item @code{left-arrow}, @code{right-arrow}
3991 Used to indicate truncated lines.
3993 @item @code{left-curly-arrow}, @code{right-curly-arrow}
3994 Used to indicate continued lines.
3996 @item @code{right-triangle}, @code{left-triangle}
3997 The former is used by overlay arrows. The latter is unused.
3999 @item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle}
4000 @itemx @code{bottom-left-angle}, @code{bottom-right-angle}
4001 @itemx @code{top-right-angle}, @code{top-left-angle}
4002 @itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle}
4003 Used to indicate buffer boundaries.
4005 @item @code{filled-rectangle}, @code{hollow-rectangle}
4006 @itemx @code{filled-square}, @code{hollow-square}
4007 @itemx @code{vertical-bar}, @code{horizontal-bar}
4008 Used for different types of fringe cursors.
4010 @item @code{empty-line}, @code{exclamation-mark}, @code{question-mark}, @code{exclamation-mark}
4011 Not used by core Emacs features.
4015 The next subsection describes how to define your own fringe bitmaps.
4017 @defun fringe-bitmaps-at-pos &optional pos window
4018 This function returns the fringe bitmaps of the display line
4019 containing position @var{pos} in window @var{window}. The return
4020 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
4021 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
4022 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
4023 is non-@code{nil} if there is an overlay arrow in the left fringe.
4025 The value is @code{nil} if @var{pos} is not visible in @var{window}.
4026 If @var{window} is @code{nil}, that stands for the selected window.
4027 If @var{pos} is @code{nil}, that stands for the value of point in
4031 @node Customizing Bitmaps
4032 @subsection Customizing Fringe Bitmaps
4033 @cindex fringe bitmaps, customizing
4035 @defun define-fringe-bitmap bitmap bits &optional height width align
4036 This function defines the symbol @var{bitmap} as a new fringe bitmap,
4037 or replaces an existing bitmap with that name.
4039 The argument @var{bits} specifies the image to use. It should be
4040 either a string or a vector of integers, where each element (an
4041 integer) corresponds to one row of the bitmap. Each bit of an integer
4042 corresponds to one pixel of the bitmap, where the low bit corresponds
4043 to the rightmost pixel of the bitmap.
4045 The height is normally the length of @var{bits}. However, you
4046 can specify a different height with non-@code{nil} @var{height}. The width
4047 is normally 8, but you can specify a different width with non-@code{nil}
4048 @var{width}. The width must be an integer between 1 and 16.
4050 The argument @var{align} specifies the positioning of the bitmap
4051 relative to the range of rows where it is used; the default is to
4052 center the bitmap. The allowed values are @code{top}, @code{center},
4055 The @var{align} argument may also be a list @code{(@var{align}
4056 @var{periodic})} where @var{align} is interpreted as described above.
4057 If @var{periodic} is non-@code{nil}, it specifies that the rows in
4058 @code{bits} should be repeated enough times to reach the specified
4062 @defun destroy-fringe-bitmap bitmap
4063 This function destroy the fringe bitmap identified by @var{bitmap}.
4064 If @var{bitmap} identifies a standard fringe bitmap, it actually
4065 restores the standard definition of that bitmap, instead of
4066 eliminating it entirely.
4069 @defun set-fringe-bitmap-face bitmap &optional face
4070 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
4071 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
4072 bitmap's face controls the color to draw it in.
4074 @var{face} is merged with the @code{fringe} face, so normally
4075 @var{face} should specify only the foreground color.
4079 @subsection The Overlay Arrow
4080 @c @cindex overlay arrow Duplicates variable names
4082 The @dfn{overlay arrow} is useful for directing the user's attention
4083 to a particular line in a buffer. For example, in the modes used for
4084 interface to debuggers, the overlay arrow indicates the line of code
4085 about to be executed. This feature has nothing to do with
4086 @dfn{overlays} (@pxref{Overlays}).
4088 @defvar overlay-arrow-string
4089 This variable holds the string to display to call attention to a
4090 particular line, or @code{nil} if the arrow feature is not in use.
4091 On a graphical display the contents of the string are ignored; instead a
4092 glyph is displayed in the fringe area to the left of the display area.
4095 @defvar overlay-arrow-position
4096 This variable holds a marker that indicates where to display the overlay
4097 arrow. It should point at the beginning of a line. On a non-graphical
4098 display the arrow text
4099 appears at the beginning of that line, overlaying any text that would
4100 otherwise appear. Since the arrow is usually short, and the line
4101 usually begins with indentation, normally nothing significant is
4104 The overlay-arrow string is displayed in any given buffer if the value
4105 of @code{overlay-arrow-position} in that buffer points into that
4106 buffer. Thus, it is possible to display multiple overlay arrow strings
4107 by creating buffer-local bindings of @code{overlay-arrow-position}.
4108 However, it is usually cleaner to use
4109 @code{overlay-arrow-variable-list} to achieve this result.
4110 @c !!! overlay-arrow-position: but the overlay string may remain in the display
4111 @c of some other buffer until an update is required. This should be fixed
4115 You can do a similar job by creating an overlay with a
4116 @code{before-string} property. @xref{Overlay Properties}.
4118 You can define multiple overlay arrows via the variable
4119 @code{overlay-arrow-variable-list}.
4121 @defvar overlay-arrow-variable-list
4122 This variable's value is a list of variables, each of which specifies
4123 the position of an overlay arrow. The variable
4124 @code{overlay-arrow-position} has its normal meaning because it is on
4128 Each variable on this list can have properties
4129 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
4130 specify an overlay arrow string (for text terminals) or fringe bitmap
4131 (for graphical terminals) to display at the corresponding overlay
4132 arrow position. If either property is not set, the default
4133 @code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator
4138 @section Scroll Bars
4141 Normally the frame parameter @code{vertical-scroll-bars} controls
4142 whether the windows in the frame have vertical scroll bars, and whether
4143 they are on the left or right. The frame parameter
4144 @code{scroll-bar-width} specifies how wide they are (@code{nil} meaning
4147 The frame parameter @code{horizontal-scroll-bars} controls whether
4148 the windows in the frame have horizontal scroll bars. The frame
4149 parameter @code{scroll-bar-height} specifies how high they are
4150 (@code{nil} meaning the default). @xref{Layout Parameters}.
4152 @vindex horizontal-scroll-bars-available-p
4153 Horizontal scroll bars are not available on all platforms. The
4154 function @code{horizontal-scroll-bars-available-p} which takes no
4155 argument returns non-@code{nil} if they are available on your system.
4157 The following three functions take as argument a live frame which
4158 defaults to the selected one.
4160 @defun frame-current-scroll-bars &optional frame
4161 This function reports the scroll bar types for frame @var{frame}. The
4162 value is a cons cell @code{(@var{vertical-type} .@:
4163 @var{horizontal-type})}, where @var{vertical-type} is either
4164 @code{left}, @code{right}, or @code{nil} (which means no vertical scroll
4165 bar.) @var{horizontal-type} is either @code{bottom} or @code{nil}
4166 (which means no horizontal scroll bar).
4169 @defun frame-scroll-bar-width &optional Lisp_Object &optional frame
4170 This function returns the width of vertical scroll bars of @var{frame}
4174 @defun frame-scroll-bar-height &optional Lisp_Object &optional frame
4175 This function returns the height of horizontal scroll bars of
4176 @var{frame} in pixels.
4179 You can override the frame specific settings for individual windows by
4180 using the following function:
4182 @defun set-window-scroll-bars window &optional width vertical-type height horizontal-type
4183 This function sets the width and/or height and the types of scroll bars
4184 for window @var{window}.
4186 @var{width} specifies the width of the vertical scroll bar in pixels
4187 (@code{nil} means use the width specified for the frame).
4188 @var{vertical-type} specifies whether to have a vertical scroll bar and,
4189 if so, where. The possible values are @code{left}, @code{right},
4190 @code{t}, which means to use the frame's default, and @code{nil} for no
4191 vertical scroll bar.
4193 @var{height} specifies the height of the horizontal scroll bar in pixels
4194 (@code{nil} means use the height specified for the frame).
4195 @var{horizontal-type} specifies whether to have a horizontal scroll bar.
4196 The possible values are @code{bottom}, @code{t}, which means to use the
4197 frame's default, and @code{nil} for no horizontal scroll bar.
4199 If @var{window} is @code{nil}, the selected window is used.
4202 The following four functions take as argument a live window which
4203 defaults to the selected one.
4205 @defun window-scroll-bars &optional window
4206 This function returns a list of the form @code{(@var{width}
4207 @var{columns} @var{vertical-type} @var{height} @var{lines}
4208 @var{horizontal-type})}.
4210 The value @var{width} is the value that was specified for the width of
4211 the vertical scroll bar (which may be @code{nil}); @var{columns} is the
4212 (possibly rounded) number of columns that the vertical scroll bar
4215 The value @var{height} is the value that was specified for the height of
4216 the horizontal scroll bar (which may be @code{nil}); @var{lines} is the
4217 (possibly rounded) number of lines that the horizontally scroll bar
4221 @defun window-current-scroll-bars &optional window
4222 This function reports the scroll bar type for window @var{window}. The
4223 value is a cons cell @code{(@var{vertical-type} .@:
4224 @var{horizontal-type})}. Unlike @code{window-scroll-bars}, this reports
4225 the scroll bar type actually used, once frame defaults and
4226 @code{scroll-bar-mode} are taken into account.
4229 @defun window-scroll-bar-width &optional window
4230 This function returns the width in pixels of @var{window}'s vertical
4234 @defun window-scroll-bar-height &optional window
4235 This function returns the height in pixels of @var{window}'s horizontal
4239 If you don't specify these values for a window with
4240 @code{set-window-scroll-bars}, the buffer-local variables
4241 @code{vertical-scroll-bar}, @code{horizontal-scroll-bar},
4242 @code{scroll-bar-width} and @code{scroll-bar-height} in the buffer being
4243 displayed control the window's scroll bars. The function
4244 @code{set-window-buffer} examines these variables. If you change them
4245 in a buffer that is already visible in a window, you can make the window
4246 take note of the new values by calling @code{set-window-buffer}
4247 specifying the same buffer that is already displayed.
4249 You can control the appearance of scroll bars for a particular buffer by
4250 setting the following variables which automatically become buffer-local
4253 @defvar vertical-scroll-bar
4254 This variable specifies the location of the vertical scroll bar. The
4255 possible values are @code{left}, @code{right}, @code{t}, which means to
4256 use the frame's default, and @code{nil} for no scroll bar.
4259 @defvar horizontal-scroll-bar
4260 This variable specifies the location of the horizontal scroll bar. The
4261 possible values are @code{bottom}, @code{t}, which means to use the
4262 frame's default, and @code{nil} for no scroll bar.
4265 @defvar scroll-bar-width
4266 This variable specifies the width of the buffer's vertical scroll bars,
4267 measured in pixels. A value of @code{nil} means to use the value
4268 specified by the frame.
4271 @defvar scroll-bar-height
4272 This variable specifies the height of the buffer's horizontal scroll
4273 bar, measured in pixels. A value of @code{nil} means to use the value
4274 specified by the frame.
4277 Finally you can toggle the display of scroll bars on all frames by
4278 customizing the variables @code{scroll-bar-mode} and
4279 @code{horizontal-scroll-bar-mode}.
4281 @defopt scroll-bar-mode
4282 This variable controls whether and where to put vertical scroll bars in
4283 all frames. The possible values are @code{nil} for no scroll bars,
4284 @code{left} to put scroll bars on the left and @code{right} to put
4285 scroll bars on the right.
4288 @defopt horizontal-scroll-bar-mode
4289 This variable controls whether to display horizontal scroll bars on all
4294 @node Window Dividers
4295 @section Window Dividers
4296 @cindex window dividers
4297 @cindex right dividers
4298 @cindex bottom dividers
4300 Window dividers are bars drawn between a frame's windows. A right
4301 divider is drawn between a window and any adjacent windows on the right.
4302 Its width (thickness) is specified by the frame parameter
4303 @code{right-divider-width}. A bottom divider is drawn between a
4304 window and adjacent windows on the bottom or the echo area. Its width
4305 is specified by the frame parameter @code{bottom-divider-width}. In
4306 either case, specifying a width of zero means to not draw such dividers.
4307 @xref{Layout Parameters}.
4309 Technically, a right divider belongs to the window on its left,
4310 which means that its width contributes to the total width of that
4311 window. A bottom divider belongs to the window above it, which
4312 means that its width contributes to the total height of that window.
4313 @xref{Window Sizes}. When a window has both, a right and a bottom
4314 divider, the bottom divider prevails. This means that a bottom
4315 divider is drawn over the full total width of its window while the right
4316 divider ends above the bottom divider.
4318 Dividers can be dragged with the mouse and are therefore useful for
4319 adjusting the sizes of adjacent windows with the mouse. They also serve
4320 to visually set apart adjacent windows when no scroll bars or mode lines
4321 are present. The following three faces allow the customization of the
4322 appearance of dividers:
4325 @item window-divider
4326 When a divider is less than three pixels wide, it is drawn solidly with
4327 the foreground of this face. For larger dividers this face is used for
4328 the inner part only, excluding the first and last pixel.
4330 @item window-divider-first-pixel
4331 This is the face used for drawing the first pixel of a divider that is
4332 at least three pixels wide. To obtain a solid appearance, set this to
4333 the same value used for the @code{window-divider} face.
4335 @item window-divider-last-pixel
4336 This is the face used for drawing the last pixel of a divider that is at
4337 least three pixels wide. To obtain a solid appearance, set this to the
4338 same value used for the @code{window-divider} face.
4341 You can get the sizes of the dividers of a specific window with the
4342 following two functions.
4344 @defun window-right-divider-width &optional window
4345 Return the width (thickness) in pixels of @var{window}'s right divider.
4346 @var{window} must be a live window and defaults to the selected one.
4347 The return value is always zero for a rightmost window.
4350 @defun window-bottom-divider-width &optional window
4351 Return the width (thickness) in pixels of @var{window}'s bottom divider.
4352 @var{window} must be a live window and defaults to the selected one.
4353 The return value is zero for the minibuffer window or a bottommost
4354 window on a minibuffer-less frame.
4358 @node Display Property
4359 @section The @code{display} Property
4360 @cindex display specification
4361 @kindex display @r{(text property)}
4363 The @code{display} text property (or overlay property) is used to
4364 insert images into text, and to control other aspects of how text
4365 displays. The value of the @code{display} property should be a
4366 display specification, or a list or vector containing several display
4367 specifications. Display specifications in the same @code{display}
4368 property value generally apply in parallel to the text they cover.
4370 If several sources (overlays and/or a text property) specify values
4371 for the @code{display} property, only one of the values takes effect,
4372 following the rules of @code{get-char-property}. @xref{Examining
4375 The rest of this section describes several kinds of
4376 display specifications and what they mean.
4379 * Replacing Specs:: Display specs that replace the text.
4380 * Specified Space:: Displaying one space with a specified width.
4381 * Pixel Specification:: Specifying space width or height in pixels.
4382 * Other Display Specs:: Displaying an image; adjusting the height,
4383 spacing, and other properties of text.
4384 * Display Margins:: Displaying text or images to the side of the main text.
4387 @node Replacing Specs
4388 @subsection Display Specs That Replace The Text
4389 @cindex replacing display specs
4391 Some kinds of display specifications specify something to display
4392 instead of the text that has the property. These are called
4393 @dfn{replacing} display specifications. Emacs does not allow the user
4394 to interactively move point into the middle of buffer text that is
4395 replaced in this way.
4397 If a list of display specifications includes more than one replacing
4398 display specification, the first overrides the rest. Replacing
4399 display specifications make most other display specifications
4400 irrelevant, since those don't apply to the replacement.
4402 For replacing display specifications, @dfn{the text that has the
4403 property} means all the consecutive characters that have the same
4404 Lisp object as their @code{display} property; these characters are
4405 replaced as a single unit. If two characters have different Lisp
4406 objects as their @code{display} properties (i.e., objects which are
4407 not @code{eq}), they are handled separately.
4409 Here is an example which illustrates this point. A string serves as
4410 a replacing display specification, which replaces the text that has
4411 the property with the specified string (@pxref{Other Display Specs}).
4412 Consider the following function:
4417 (let ((string (concat "A"))
4418 (start (+ i i (point-min))))
4419 (put-text-property start (1+ start) 'display string)
4420 (put-text-property start (+ 2 start) 'display string))))
4424 This function gives each of the first ten characters in the buffer a
4425 @code{display} property which is a string @code{"A"}, but they don't
4426 all get the same string object. The first two characters get the same
4427 string object, so they are replaced with one @samp{A}; the fact that
4428 the display property was assigned in two separate calls to
4429 @code{put-text-property} is irrelevant. Similarly, the next two
4430 characters get a second string (@code{concat} creates a new string
4431 object), so they are replaced with one @samp{A}; and so on. Thus, the
4432 ten characters appear as five A's.
4434 @node Specified Space
4435 @subsection Specified Spaces
4436 @cindex spaces, specified height or width
4437 @cindex variable-width spaces
4439 To display a space of specified width and/or height, use a display
4440 specification of the form @code{(space . @var{props})}, where
4441 @var{props} is a property list (a list of alternating properties and
4442 values). You can put this property on one or more consecutive
4443 characters; a space of the specified height and width is displayed in
4444 place of @emph{all} of those characters. These are the properties you
4445 can use in @var{props} to specify the weight of the space:
4448 @item :width @var{width}
4449 If @var{width} is a number, it specifies
4450 that the space width should be @var{width} times the normal character
4451 width. @var{width} can also be a @dfn{pixel width} specification
4452 (@pxref{Pixel Specification}).
4454 @item :relative-width @var{factor}
4455 Specifies that the width of the stretch should be computed from the
4456 first character in the group of consecutive characters that have the
4457 same @code{display} property. The space width is the pixel width of
4458 that character, multiplied by @var{factor}. (On text-mode terminals,
4459 the ``pixel width'' of a character is usually 1, but it could be more
4460 for TABs and double-width CJK characters.)
4462 @item :align-to @var{hpos}
4463 Specifies that the space should be wide enough to reach @var{hpos}.
4464 If @var{hpos} is a number, it is measured in units of the normal
4465 character width. @var{hpos} can also be a @dfn{pixel width}
4466 specification (@pxref{Pixel Specification}).
4469 You should use one and only one of the above properties. You can
4470 also specify the height of the space, with these properties:
4473 @item :height @var{height}
4474 Specifies the height of the space.
4475 If @var{height} is a number, it specifies
4476 that the space height should be @var{height} times the normal character
4477 height. The @var{height} may also be a @dfn{pixel height} specification
4478 (@pxref{Pixel Specification}).
4480 @item :relative-height @var{factor}
4481 Specifies the height of the space, multiplying the ordinary height
4482 of the text having this display specification by @var{factor}.
4484 @item :ascent @var{ascent}
4485 If the value of @var{ascent} is a non-negative number no greater than
4486 100, it specifies that @var{ascent} percent of the height of the space
4487 should be considered as the ascent of the space---that is, the part
4488 above the baseline. The ascent may also be specified in pixel units
4489 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
4493 Don't use both @code{:height} and @code{:relative-height} together.
4495 The @code{:width} and @code{:align-to} properties are supported on
4496 non-graphic terminals, but the other space properties in this section
4499 Note that space properties are treated as paragraph separators for
4500 the purposes of reordering bidirectional text for display.
4501 @xref{Bidirectional Display}, for the details.
4503 @node Pixel Specification
4504 @subsection Pixel Specification for Spaces
4505 @cindex spaces, pixel specification
4507 The value of the @code{:width}, @code{:align-to}, @code{:height},
4508 and @code{:ascent} properties can be a special kind of expression that
4509 is evaluated during redisplay. The result of the evaluation is used
4510 as an absolute number of pixels.
4512 The following expressions are supported:
4516 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
4517 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
4518 @var{unit} ::= in | mm | cm | width | height
4521 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
4523 @var{pos} ::= left | center | right
4524 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
4529 The form @var{num} specifies a fraction of the default frame font
4530 height or width. The form @code{(@var{num})} specifies an absolute
4531 number of pixels. If @var{num} is a symbol, @var{symbol}, its
4532 buffer-local variable binding is used.
4534 The @code{in}, @code{mm}, and @code{cm} units specify the number of
4535 pixels per inch, millimeter, and centimeter, respectively. The
4536 @code{width} and @code{height} units correspond to the default width
4537 and height of the current face. An image specification @code{image}
4538 corresponds to the width or height of the image.
4540 The elements @code{left-fringe}, @code{right-fringe},
4541 @code{left-margin}, @code{right-margin}, @code{scroll-bar}, and
4542 @code{text} specify to the width of the corresponding area of the
4545 The @code{left}, @code{center}, and @code{right} positions can be
4546 used with @code{:align-to} to specify a position relative to the left
4547 edge, center, or right edge of the text area.
4549 Any of the above window elements (except @code{text}) can also be
4550 used with @code{:align-to} to specify that the position is relative to
4551 the left edge of the given area. Once the base offset for a relative
4552 position has been set (by the first occurrence of one of these
4553 symbols), further occurrences of these symbols are interpreted as the
4554 width of the specified area. For example, to align to the center of
4555 the left-margin, use
4558 :align-to (+ left-margin (0.5 . left-margin))
4561 If no specific base offset is set for alignment, it is always relative
4562 to the left edge of the text area. For example, @samp{:align-to 0} in a
4563 header-line aligns with the first text column in the text area.
4565 A value of the form @code{(@var{num} . @var{expr})} stands for the
4566 product of the values of @var{num} and @var{expr}. For example,
4567 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
4568 @var{image})} specifies half the width (or height) of the specified
4571 The form @code{(+ @var{expr} ...)} adds up the value of the
4572 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
4573 the value of the expressions.
4575 @node Other Display Specs
4576 @subsection Other Display Specifications
4578 Here are the other sorts of display specifications that you can use
4579 in the @code{display} text property.
4583 Display @var{string} instead of the text that has this property.
4585 Recursive display specifications are not supported---@var{string}'s
4586 @code{display} properties, if any, are not used.
4588 @item (image . @var{image-props})
4589 This kind of display specification is an image descriptor (@pxref{Images}).
4590 When used as a display specification, it means to display the image
4591 instead of the text that has the display specification.
4593 @item (slice @var{x} @var{y} @var{width} @var{height})
4594 This specification together with @code{image} specifies a @dfn{slice}
4595 (a partial area) of the image to display. The elements @var{y} and
4596 @var{x} specify the top left corner of the slice, within the image;
4597 @var{width} and @var{height} specify the width and height of the
4598 slice. Integers are numbers of pixels. A floating-point number
4599 in the range 0.0--1.0 stands for that fraction of the width or height
4600 of the entire image.
4602 @item ((margin nil) @var{string})
4603 A display specification of this form means to display @var{string}
4604 instead of the text that has the display specification, at the same
4605 position as that text. It is equivalent to using just @var{string},
4606 but it is done as a special case of marginal display (@pxref{Display
4609 @item (left-fringe @var{bitmap} @r{[}@var{face}@r{]})
4610 @itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]})
4611 This display specification on any character of a line of text causes
4612 the specified @var{bitmap} be displayed in the left or right fringes
4613 for that line, instead of the characters that have the display
4614 specification. The optional @var{face} specifies the colors to be
4615 used for the bitmap. @xref{Fringe Bitmaps}, for the details.
4617 @item (space-width @var{factor})
4618 This display specification affects all the space characters within the
4619 text that has the specification. It displays all of these spaces
4620 @var{factor} times as wide as normal. The element @var{factor} should
4621 be an integer or float. Characters other than spaces are not affected
4622 at all; in particular, this has no effect on tab characters.
4624 @item (height @var{height})
4625 This display specification makes the text taller or shorter.
4626 Here are the possibilities for @var{height}:
4629 @item @code{(+ @var{n})}
4630 @c FIXME: Add an index for "step"? --xfq
4631 This means to use a font that is @var{n} steps larger. A @dfn{step} is
4632 defined by the set of available fonts---specifically, those that match
4633 what was otherwise specified for this text, in all attributes except
4634 height. Each size for which a suitable font is available counts as
4635 another step. @var{n} should be an integer.
4637 @item @code{(- @var{n})}
4638 This means to use a font that is @var{n} steps smaller.
4640 @item a number, @var{factor}
4641 A number, @var{factor}, means to use a font that is @var{factor} times
4642 as tall as the default font.
4644 @item a symbol, @var{function}
4645 A symbol is a function to compute the height. It is called with the
4646 current height as argument, and should return the new height to use.
4648 @item anything else, @var{form}
4649 If the @var{height} value doesn't fit the previous possibilities, it is
4650 a form. Emacs evaluates it to get the new height, with the symbol
4651 @code{height} bound to the current specified font height.
4654 @item (raise @var{factor})
4655 This kind of display specification raises or lowers the text
4656 it applies to, relative to the baseline of the line.
4658 @var{factor} must be a number, which is interpreted as a multiple of the
4659 height of the affected text. If it is positive, that means to display
4660 the characters raised. If it is negative, that means to display them
4663 If the text also has a @code{height} display specification, that does
4664 not affect the amount of raising or lowering, which is based on the
4665 faces used for the text.
4668 @c We put all the '@code{(when ...)}' on one line to encourage
4669 @c makeinfo's end-of-sentence heuristics to DTRT. Previously, the dot
4670 @c was at eol; the info file ended up w/ two spaces rendered after it.
4671 You can make any display specification conditional. To do that,
4672 package it in another list of the form
4673 @code{(when @var{condition} . @var{spec})}.
4674 Then the specification @var{spec} applies only when
4675 @var{condition} evaluates to a non-@code{nil} value. During the
4676 evaluation, @code{object} is bound to the string or buffer having the
4677 conditional @code{display} property. @code{position} and
4678 @code{buffer-position} are bound to the position within @code{object}
4679 and the buffer position where the @code{display} property was found,
4680 respectively. Both positions can be different when @code{object} is a
4683 @node Display Margins
4684 @subsection Displaying in the Margins
4685 @cindex display margins
4686 @cindex margins, display
4688 A buffer can have blank areas called @dfn{display margins} on the
4689 left and on the right. Ordinary text never appears in these areas,
4690 but you can put things into the display margins using the
4691 @code{display} property. There is currently no way to make text or
4692 images in the margin mouse-sensitive.
4694 The way to display something in the margins is to specify it in a
4695 margin display specification in the @code{display} property of some
4696 text. This is a replacing display specification, meaning that the
4697 text you put it on does not get displayed; the margin display appears,
4698 but that text does not.
4700 A margin display specification looks like @code{((margin
4701 right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}.
4702 Here, @var{spec} is another display specification that says what to
4703 display in the margin. Typically it is a string of text to display,
4704 or an image descriptor.
4706 To display something in the margin @emph{in association with}
4707 certain buffer text, without altering or preventing the display of
4708 that text, put a @code{before-string} property on the text and put the
4709 margin display specification on the contents of the before-string.
4711 Before the display margins can display anything, you must give
4712 them a nonzero width. The usual way to do that is to set these
4715 @defvar left-margin-width
4716 This variable specifies the width of the left margin, in character
4717 cell (a.k.a.@: ``column'') units. It is buffer-local in all buffers.
4718 A value of @code{nil} means no left marginal area.
4721 @defvar right-margin-width
4722 This variable specifies the width of the right margin, in character
4723 cell units. It is buffer-local in all buffers. A value of @code{nil}
4724 means no right marginal area.
4727 Setting these variables does not immediately affect the window. These
4728 variables are checked when a new buffer is displayed in the window.
4729 Thus, you can make changes take effect by calling
4730 @code{set-window-buffer}.
4732 You can also set the margin widths immediately.
4734 @defun set-window-margins window left &optional right
4735 This function specifies the margin widths for window @var{window}, in
4736 character cell units. The argument @var{left} controls the left
4737 margin, and @var{right} controls the right margin (default @code{0}).
4740 @defun window-margins &optional window
4741 This function returns the width of the left and right margins of
4742 @var{window} as a cons cell of the form @w{@code{(@var{left}
4743 . @var{right})}}. If one of the two marginal areas does not exist,
4744 its width is returned as @code{nil}; if neither of the two margins exist,
4745 the function returns @code{(nil)}. If @var{window} is @code{nil}, the
4746 selected window is used.
4751 @cindex images in buffers
4753 To display an image in an Emacs buffer, you must first create an image
4754 descriptor, then use it as a display specifier in the @code{display}
4755 property of text that is displayed (@pxref{Display Property}).
4757 Emacs is usually able to display images when it is run on a
4758 graphical terminal. Images cannot be displayed in a text terminal, on
4759 certain graphical terminals that lack the support for this, or if
4760 Emacs is compiled without image support. You can use the function
4761 @code{display-images-p} to determine if images can in principle be
4762 displayed (@pxref{Display Feature Testing}).
4765 * Image Formats:: Supported image formats.
4766 * Image Descriptors:: How to specify an image for use in @code{:display}.
4767 * XBM Images:: Special features for XBM format.
4768 * XPM Images:: Special features for XPM format.
4769 * PostScript Images:: Special features for PostScript format.
4770 * ImageMagick Images:: Special features available through ImageMagick.
4771 * Other Image Types:: Various other formats are supported.
4772 * Defining Images:: Convenient ways to define an image for later use.
4773 * Showing Images:: Convenient ways to display an image once it is defined.
4774 * Multi-Frame Images:: Some images contain more than one frame.
4775 * Image Cache:: Internal mechanisms of image display.
4779 @subsection Image Formats
4780 @cindex image formats
4783 Emacs can display a number of different image formats. Some of
4784 these image formats are supported only if particular support libraries
4785 are installed. On some platforms, Emacs can load support libraries on
4786 demand; if so, the variable @code{dynamic-library-alist} can be used
4787 to modify the set of known names for these dynamic libraries.
4788 @xref{Dynamic Libraries}.
4790 Supported image formats (and the required support libraries) include
4791 PBM and XBM (which do not depend on support libraries and are always
4792 available), XPM (@code{libXpm}), GIF (@code{libgif} or
4793 @code{libungif}), PostScript (@code{gs}), JPEG (@code{libjpeg}), TIFF
4794 (@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}).
4796 Each of these image formats is associated with an @dfn{image type
4797 symbol}. The symbols for the above formats are, respectively,
4798 @code{pbm}, @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
4799 @code{jpeg}, @code{tiff}, @code{png}, and @code{svg}.
4801 Furthermore, if you build Emacs with ImageMagick
4802 (@code{libMagickWand}) support, Emacs can display any image format
4803 that ImageMagick can. @xref{ImageMagick Images}. All images
4804 displayed via ImageMagick have type symbol @code{imagemagick}.
4807 This variable contains a list of type symbols for image formats which
4808 are potentially supported in the current configuration.
4810 ``Potentially'' means that Emacs knows about the image types, not
4811 necessarily that they can be used (for example, they could depend on
4812 unavailable dynamic libraries). To know which image types are really
4813 available, use @code{image-type-available-p}.
4816 @defun image-type-available-p type
4817 This function returns non-@code{nil} if images of type @var{type} can
4818 be loaded and displayed. @var{type} must be an image type symbol.
4820 For image types whose support libraries are statically linked, this
4821 function always returns @code{t}. For image types whose support
4822 libraries are dynamically loaded, it returns @code{t} if the library
4823 could be loaded and @code{nil} otherwise.
4826 @node Image Descriptors
4827 @subsection Image Descriptors
4828 @cindex image descriptor
4830 An @dfn{image descriptor} is a list which specifies the underlying
4831 data for an image, and how to display it. It is typically used as the
4832 value of a @code{display} overlay or text property (@pxref{Other
4833 Display Specs}); but @xref{Showing Images}, for convenient helper
4834 functions to insert images into buffers.
4836 Each image descriptor has the form @code{(image . @var{props})},
4837 where @var{props} is a property list of alternating keyword symbols
4838 and values, including at least the pair @code{:type @var{type}} that
4839 specifies the image type.
4841 The following is a list of properties that are meaningful for all
4842 image types (there are also properties which are meaningful only for
4843 certain image types, as documented in the following subsections):
4846 @item :type @var{type}
4849 @xref{Image Formats}.
4851 Every image descriptor must include this property.
4853 @item :file @var{file}
4854 This says to load the image from file @var{file}. If @var{file} is
4855 not an absolute file name, it is expanded in @code{data-directory}.
4857 @item :data @var{data}
4858 This specifies the raw image data. Each image descriptor must have
4859 either @code{:data} or @code{:file}, but not both.
4861 For most image types, the value of a @code{:data} property should be a
4862 string containing the image data. Some image types do not support
4863 @code{:data}; for some others, @code{:data} alone is not enough, so
4864 you need to use other image properties along with @code{:data}. See
4865 the following subsections for details.
4867 @item :margin @var{margin}
4868 This specifies how many pixels to add as an extra margin around the
4869 image. The value, @var{margin}, must be a non-negative number, or a
4870 pair @code{(@var{x} . @var{y})} of such numbers. If it is a pair,
4871 @var{x} specifies how many pixels to add horizontally, and @var{y}
4872 specifies how many pixels to add vertically. If @code{:margin} is not
4873 specified, the default is zero.
4875 @item :ascent @var{ascent}
4876 This specifies the amount of the image's height to use for its
4877 ascent---that is, the part above the baseline. The value,
4878 @var{ascent}, must be a number in the range 0 to 100, or the symbol
4881 If @var{ascent} is a number, that percentage of the image's height is
4882 used for its ascent.
4884 If @var{ascent} is @code{center}, the image is vertically centered
4885 around a centerline which would be the vertical centerline of text drawn
4886 at the position of the image, in the manner specified by the text
4887 properties and overlays that apply to the image.
4889 If this property is omitted, it defaults to 50.
4891 @item :relief @var{relief}
4892 This adds a shadow rectangle around the image. The value,
4893 @var{relief}, specifies the width of the shadow lines, in pixels. If
4894 @var{relief} is negative, shadows are drawn so that the image appears
4895 as a pressed button; otherwise, it appears as an unpressed button.
4897 @item :conversion @var{algorithm}
4898 This specifies a conversion algorithm that should be applied to the
4899 image before it is displayed; the value, @var{algorithm}, specifies
4905 Specifies the Laplace edge detection algorithm, which blurs out small
4906 differences in color while highlighting larger differences. People
4907 sometimes consider this useful for displaying the image for a
4910 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
4911 @cindex edge detection, images
4912 Specifies a general edge-detection algorithm. @var{matrix} must be
4913 either a nine-element list or a nine-element vector of numbers. A pixel
4914 at position @math{x/y} in the transformed image is computed from
4915 original pixels around that position. @var{matrix} specifies, for each
4916 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
4917 will influence the transformed pixel; element @math{0} specifies the
4918 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
4919 the pixel at @math{x/y-1} etc., as shown below:
4922 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
4923 x-1/y & x/y & x+1/y \cr
4924 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
4929 (x-1/y-1 x/y-1 x+1/y-1
4931 x-1/y+1 x/y+1 x+1/y+1)
4935 The resulting pixel is computed from the color intensity of the color
4936 resulting from summing up the RGB values of surrounding pixels,
4937 multiplied by the specified factors, and dividing that sum by the sum
4938 of the factors' absolute values.
4940 Laplace edge-detection currently uses a matrix of
4943 $$\pmatrix{1 & 0 & 0 \cr
4956 Emboss edge-detection uses a matrix of
4959 $$\pmatrix{ 2 & -1 & 0 \cr
4973 Specifies transforming the image so that it looks disabled.
4976 @item :mask @var{mask}
4977 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
4978 a clipping mask for the image, so that the background of a frame is
4979 visible behind the image. If @var{bg} is not specified, or if @var{bg}
4980 is @code{t}, determine the background color of the image by looking at
4981 the four corners of the image, assuming the most frequently occurring
4982 color from the corners is the background color of the image. Otherwise,
4983 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
4984 specifying the color to assume for the background of the image.
4986 If @var{mask} is @code{nil}, remove a mask from the image, if it has
4987 one. Images in some formats include a mask which can be removed by
4988 specifying @code{:mask nil}.
4990 @item :pointer @var{shape}
4991 This specifies the pointer shape when the mouse pointer is over this
4992 image. @xref{Pointer Shape}, for available pointer shapes.
4994 @item :map @var{map}
4996 This associates an image map of @dfn{hot spots} with this image.
4998 An image map is an alist where each element has the format
4999 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
5000 as either a rectangle, a circle, or a polygon.
5002 A rectangle is a cons
5003 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
5004 which specifies the pixel coordinates of the upper left and bottom right
5005 corners of the rectangle area.
5008 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
5009 which specifies the center and the radius of the circle; @var{r} may
5010 be a float or integer.
5013 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
5014 where each pair in the vector describes one corner in the polygon.
5016 When the mouse pointer lies on a hot-spot area of an image, the
5017 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
5018 property, that defines a tool-tip for the hot-spot, and if it contains
5019 a @code{pointer} property, that defines the shape of the mouse cursor when
5020 it is on the hot-spot.
5021 @xref{Pointer Shape}, for available pointer shapes.
5023 When you click the mouse when the mouse pointer is over a hot-spot, an
5024 event is composed by combining the @var{id} of the hot-spot with the
5025 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
5026 @var{id} is @code{area4}.
5029 @defun image-mask-p spec &optional frame
5030 This function returns @code{t} if image @var{spec} has a mask bitmap.
5031 @var{frame} is the frame on which the image will be displayed.
5032 @var{frame} @code{nil} or omitted means to use the selected frame
5033 (@pxref{Input Focus}).
5037 @subsection XBM Images
5040 To use XBM format, specify @code{xbm} as the image type. This image
5041 format doesn't require an external library, so images of this type are
5044 Additional image properties supported for the @code{xbm} image type are:
5047 @item :foreground @var{foreground}
5048 The value, @var{foreground}, should be a string specifying the image
5049 foreground color, or @code{nil} for the default color. This color is
5050 used for each pixel in the XBM that is 1. The default is the frame's
5053 @item :background @var{background}
5054 The value, @var{background}, should be a string specifying the image
5055 background color, or @code{nil} for the default color. This color is
5056 used for each pixel in the XBM that is 0. The default is the frame's
5060 If you specify an XBM image using data within Emacs instead of an
5061 external file, use the following three properties:
5064 @item :data @var{data}
5065 The value, @var{data}, specifies the contents of the image.
5066 There are three formats you can use for @var{data}:
5070 A vector of strings or bool-vectors, each specifying one line of the
5071 image. Do specify @code{:height} and @code{:width}.
5074 A string containing the same byte sequence as an XBM file would contain.
5075 You must not specify @code{:height} and @code{:width} in this case,
5076 because omitting them is what indicates the data has the format of an
5077 XBM file. The file contents specify the height and width of the image.
5080 A string or a bool-vector containing the bits of the image (plus perhaps
5081 some extra bits at the end that will not be used). It should contain at
5082 least @var{width} * @code{height} bits. In this case, you must specify
5083 @code{:height} and @code{:width}, both to indicate that the string
5084 contains just the bits rather than a whole XBM file, and to specify the
5088 @item :width @var{width}
5089 The value, @var{width}, specifies the width of the image, in pixels.
5091 @item :height @var{height}
5092 The value, @var{height}, specifies the height of the image, in pixels.
5096 @subsection XPM Images
5099 To use XPM format, specify @code{xpm} as the image type. The
5100 additional image property @code{:color-symbols} is also meaningful with
5101 the @code{xpm} image type:
5104 @item :color-symbols @var{symbols}
5105 The value, @var{symbols}, should be an alist whose elements have the
5106 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
5107 the name of a color as it appears in the image file, and @var{color}
5108 specifies the actual color to use for displaying that name.
5111 @node PostScript Images
5112 @subsection PostScript Images
5113 @cindex postscript images
5115 To use PostScript for an image, specify image type @code{postscript}.
5116 This works only if you have Ghostscript installed. You must always use
5117 these three properties:
5120 @item :pt-width @var{width}
5121 The value, @var{width}, specifies the width of the image measured in
5122 points (1/72 inch). @var{width} must be an integer.
5124 @item :pt-height @var{height}
5125 The value, @var{height}, specifies the height of the image in points
5126 (1/72 inch). @var{height} must be an integer.
5128 @item :bounding-box @var{box}
5129 The value, @var{box}, must be a list or vector of four integers, which
5130 specifying the bounding box of the PostScript image, analogous to the
5131 @samp{BoundingBox} comment found in PostScript files.
5134 %%BoundingBox: 22 171 567 738
5138 @node ImageMagick Images
5139 @subsection ImageMagick Images
5140 @cindex ImageMagick images
5141 @cindex images, support for more formats
5143 If you build Emacs with ImageMagick support, you can use the
5144 ImageMagick library to load many image formats (@pxref{File
5145 Conveniences,,, emacs, The GNU Emacs Manual}). The image type symbol
5146 for images loaded via ImageMagick is @code{imagemagick}, regardless of
5147 the actual underlying image format.
5149 @defun imagemagick-types
5150 This function returns a list of image file extensions supported by the
5151 current ImageMagick installation. Each list element is a symbol
5152 representing an internal ImageMagick name for an image type, such as
5153 @code{BMP} for @file{.bmp} images.
5156 @defopt imagemagick-enabled-types
5157 The value of this variable is a list of ImageMagick image types which
5158 Emacs may attempt to render using ImageMagick. Each list element
5159 should be one of the symbols in the list returned by
5160 @code{imagemagick-types}, or an equivalent string. Alternatively, a
5161 value of @code{t} enables ImageMagick for all possible image types.
5162 Regardless of the value of this variable,
5163 @code{imagemagick-types-inhibit} (see below) takes precedence.
5166 @defopt imagemagick-types-inhibit
5167 The value of this variable lists the ImageMagick image types which
5168 should never be rendered using ImageMagick, regardless of the value of
5169 @code{imagemagick-enabled-types}. A value of @code{t} disables
5170 ImageMagick entirely.
5173 @defvar image-format-suffixes
5174 This variable is an alist mapping image types to file name extensions.
5175 Emacs uses this in conjunction with the @code{:format} image property
5176 (see below) to give a hint to the ImageMagick library as to the type
5177 of an image. Each element has the form @code{(@var{type}
5178 @var{extension})}, where @var{type} is a symbol specifying an image
5179 content-type, and @var{extension} is a string that specifies the
5180 associated file name extension.
5183 Images loaded with ImageMagick support the following additional
5184 image descriptor properties:
5187 @item :background @var{background}
5188 @var{background}, if non-@code{nil}, should be a string specifying a
5189 color, which is used as the image's background color if the image
5190 supports transparency. If the value is @code{nil}, it defaults to the
5191 frame's background color.
5193 @item :width @var{width}, :height @var{height}
5194 The @code{:width} and @code{:height} keywords are used for scaling the
5195 image. If only one of them is specified, the other one will be
5196 calculated so as to preserve the aspect ratio. If both are specified,
5197 aspect ratio may not be preserved.
5199 @item :max-width @var{max-width}, :max-height @var{max-height}
5200 The @code{:max-width} and @code{:max-height} keywords are used for
5201 scaling if the size of the image of the image exceeds these values.
5202 If @code{:width} is set it will have precedence over @code{max-width},
5203 and if @code{:height} is set it will have precedence over
5204 @code{max-height}, but you can otherwise mix these keywords as you
5205 wish. @code{:max-width} and @code{:max-height} will always preserve
5208 @item :format @var{type}
5209 The value, @var{type}, should be a symbol specifying the type of the
5210 image data, as found in @code{image-format-suffixes}. This is used
5211 when the image does not have an associated file name, to provide a
5212 hint to ImageMagick to help it detect the image type.
5214 @item :rotation @var{angle}
5215 Specifies a rotation angle in degrees.
5217 @item :index @var{frame}
5218 @c Doesn't work: http://debbugs.gnu.org/7978
5219 @xref{Multi-Frame Images}.
5222 @node Other Image Types
5223 @subsection Other Image Types
5226 For PBM images, specify image type @code{pbm}. Color, gray-scale and
5227 monochromatic images are supported. For mono PBM images, two additional
5228 image properties are supported.
5231 @item :foreground @var{foreground}
5232 The value, @var{foreground}, should be a string specifying the image
5233 foreground color, or @code{nil} for the default color. This color is
5234 used for each pixel in the PBM that is 1. The default is the frame's
5237 @item :background @var{background}
5238 The value, @var{background}, should be a string specifying the image
5239 background color, or @code{nil} for the default color. This color is
5240 used for each pixel in the PBM that is 0. The default is the frame's
5245 The remaining image types that Emacs can support are:
5249 Image type @code{gif}.
5250 Supports the @code{:index} property. @xref{Multi-Frame Images}.
5253 Image type @code{jpeg}.
5256 Image type @code{png}.
5259 Image type @code{svg}.
5262 Image type @code{tiff}.
5263 Supports the @code{:index} property. @xref{Multi-Frame Images}.
5266 @node Defining Images
5267 @subsection Defining Images
5268 @cindex define image
5270 The functions @code{create-image}, @code{defimage} and
5271 @code{find-image} provide convenient ways to create image descriptors.
5273 @defun create-image file-or-data &optional type data-p &rest props
5274 This function creates and returns an image descriptor which uses the
5275 data in @var{file-or-data}. @var{file-or-data} can be a file name or
5276 a string containing the image data; @var{data-p} should be @code{nil}
5277 for the former case, non-@code{nil} for the latter case.
5279 The optional argument @var{type} is a symbol specifying the image type.
5280 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
5281 determine the image type from the file's first few bytes, or else
5282 from the file's name.
5284 The remaining arguments, @var{props}, specify additional image
5285 properties---for example,
5287 @c ':heuristic-mask' is not documented?
5289 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
5292 The function returns @code{nil} if images of this type are not
5293 supported. Otherwise it returns an image descriptor.
5296 @defmac defimage symbol specs &optional doc
5297 This macro defines @var{symbol} as an image name. The arguments
5298 @var{specs} is a list which specifies how to display the image.
5299 The third argument, @var{doc}, is an optional documentation string.
5301 Each argument in @var{specs} has the form of a property list, and each
5302 one should specify at least the @code{:type} property and either the
5303 @code{:file} or the @code{:data} property. The value of @code{:type}
5304 should be a symbol specifying the image type, the value of
5305 @code{:file} is the file to load the image from, and the value of
5306 @code{:data} is a string containing the actual image data. Here is an
5310 (defimage test-image
5311 ((:type xpm :file "~/test1.xpm")
5312 (:type xbm :file "~/test1.xbm")))
5315 @code{defimage} tests each argument, one by one, to see if it is
5316 usable---that is, if the type is supported and the file exists. The
5317 first usable argument is used to make an image descriptor which is
5318 stored in @var{symbol}.
5320 If none of the alternatives will work, then @var{symbol} is defined
5324 @defun find-image specs
5325 This function provides a convenient way to find an image satisfying one
5326 of a list of image specifications @var{specs}.
5328 Each specification in @var{specs} is a property list with contents
5329 depending on image type. All specifications must at least contain the
5330 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
5331 or @w{@code{:data @var{data}}}, where @var{type} is a symbol specifying
5332 the image type, e.g., @code{xbm}, @var{file} is the file to load the
5333 image from, and @var{data} is a string containing the actual image data.
5334 The first specification in the list whose @var{type} is supported, and
5335 @var{file} exists, is used to construct the image specification to be
5336 returned. If no specification is satisfied, @code{nil} is returned.
5338 The image is looked for in @code{image-load-path}.
5341 @defopt image-load-path
5342 This variable's value is a list of locations in which to search for
5343 image files. If an element is a string or a variable symbol whose
5344 value is a string, the string is taken to be the name of a directory
5345 to search. If an element is a variable symbol whose value is a list,
5346 that is taken to be a list of directory names to search.
5348 The default is to search in the @file{images} subdirectory of the
5349 directory specified by @code{data-directory}, then the directory
5350 specified by @code{data-directory}, and finally in the directories in
5351 @code{load-path}. Subdirectories are not automatically included in
5352 the search, so if you put an image file in a subdirectory, you have to
5353 supply the subdirectory name explicitly. For example, to find the
5354 image @file{images/foo/bar.xpm} within @code{data-directory}, you
5355 should specify the image as follows:
5358 (defimage foo-image '((:type xpm :file "foo/bar.xpm")))
5362 @defun image-load-path-for-library library image &optional path no-error
5363 This function returns a suitable search path for images used by the
5364 Lisp package @var{library}.
5366 The function searches for @var{image} first using @code{image-load-path},
5367 excluding @file{@code{data-directory}/images}, and then in
5368 @code{load-path}, followed by a path suitable for @var{library}, which
5369 includes @file{../../etc/images} and @file{../etc/images} relative to
5370 the library file itself, and finally in
5371 @file{@code{data-directory}/images}.
5373 Then this function returns a list of directories which contains first
5374 the directory in which @var{image} was found, followed by the value of
5375 @code{load-path}. If @var{path} is given, it is used instead of
5378 If @var{no-error} is non-@code{nil} and a suitable path can't be
5379 found, don't signal an error. Instead, return a list of directories as
5380 before, except that @code{nil} appears in place of the image directory.
5382 Here is an example of using @code{image-load-path-for-library}:
5385 (defvar image-load-path) ; shush compiler
5386 (let* ((load-path (image-load-path-for-library
5387 "mh-e" "mh-logo.xpm"))
5388 (image-load-path (cons (car load-path)
5390 (mh-tool-bar-folder-buttons-init))
5394 @node Showing Images
5395 @subsection Showing Images
5398 You can use an image descriptor by setting up the @code{display}
5399 property yourself, but it is easier to use the functions in this
5402 @defun insert-image image &optional string area slice
5403 This function inserts @var{image} in the current buffer at point. The
5404 value @var{image} should be an image descriptor; it could be a value
5405 returned by @code{create-image}, or the value of a symbol defined with
5406 @code{defimage}. The argument @var{string} specifies the text to put
5407 in the buffer to hold the image. If it is omitted or @code{nil},
5408 @code{insert-image} uses @code{" "} by default.
5410 The argument @var{area} specifies whether to put the image in a margin.
5411 If it is @code{left-margin}, the image appears in the left margin;
5412 @code{right-margin} specifies the right margin. If @var{area} is
5413 @code{nil} or omitted, the image is displayed at point within the
5416 The argument @var{slice} specifies a slice of the image to insert. If
5417 @var{slice} is @code{nil} or omitted the whole image is inserted.
5418 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
5419 @var{height})} which specifies the @var{x} and @var{y} positions and
5420 @var{width} and @var{height} of the image area to insert. Integer
5421 values are in units of pixels. A floating-point number in the range
5422 0.0--1.0 stands for that fraction of the width or height of the entire
5425 Internally, this function inserts @var{string} in the buffer, and gives
5426 it a @code{display} property which specifies @var{image}. @xref{Display
5430 @cindex slice, image
5432 @defun insert-sliced-image image &optional string area rows cols
5433 This function inserts @var{image} in the current buffer at point, like
5434 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
5435 equally sized slices.
5437 Emacs displays each slice as a
5438 separate image, and allows more intuitive scrolling up/down, instead of
5439 jumping up/down the entire image when paging through a buffer that
5440 displays (large) images.
5443 @defun put-image image pos &optional string area
5444 This function puts image @var{image} in front of @var{pos} in the
5445 current buffer. The argument @var{pos} should be an integer or a
5446 marker. It specifies the buffer position where the image should appear.
5447 The argument @var{string} specifies the text that should hold the image
5448 as an alternative to the default.
5450 The argument @var{image} must be an image descriptor, perhaps returned
5451 by @code{create-image} or stored by @code{defimage}.
5453 The argument @var{area} specifies whether to put the image in a margin.
5454 If it is @code{left-margin}, the image appears in the left margin;
5455 @code{right-margin} specifies the right margin. If @var{area} is
5456 @code{nil} or omitted, the image is displayed at point within the
5459 Internally, this function creates an overlay, and gives it a
5460 @code{before-string} property containing text that has a @code{display}
5461 property whose value is the image. (Whew!)
5464 @defun remove-images start end &optional buffer
5465 This function removes images in @var{buffer} between positions
5466 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
5467 images are removed from the current buffer.
5469 This removes only images that were put into @var{buffer} the way
5470 @code{put-image} does it, not images that were inserted with
5471 @code{insert-image} or in other ways.
5474 @defun image-size spec &optional pixels frame
5475 @cindex size of image
5476 This function returns the size of an image as a pair
5477 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
5478 specification. @var{pixels} non-@code{nil} means return sizes measured
5479 in pixels, otherwise return sizes measured in the default character size
5480 of @var{frame} (@pxref{Frame Font}). @var{frame} is the frame on which
5481 the image will be displayed. @var{frame} null or omitted means use the
5482 selected frame (@pxref{Input Focus}).
5485 @defvar max-image-size
5486 This variable is used to define the maximum size of image that Emacs
5487 will load. Emacs will refuse to load (and display) any image that is
5488 larger than this limit.
5490 If the value is an integer, it directly specifies the maximum
5491 image height and width, measured in pixels. If it is floating
5492 point, it specifies the maximum image height and width
5493 as a ratio to the frame height and width. If the value is
5494 non-numeric, there is no explicit limit on the size of images.
5496 The purpose of this variable is to prevent unreasonably large images
5497 from accidentally being loaded into Emacs. It only takes effect the
5498 first time an image is loaded. Once an image is placed in the image
5499 cache, it can always be displayed, even if the value of
5500 @code{max-image-size} is subsequently changed (@pxref{Image Cache}).
5503 @node Multi-Frame Images
5504 @subsection Multi-Frame Images
5505 @cindex multi-frame images
5508 @cindex image animation
5509 @cindex image frames
5510 Some image files can contain more than one image. We say that there
5511 are multiple ``frames'' in the image. At present, Emacs supports
5512 multiple frames for GIF, TIFF, and certain ImageMagick formats such as
5515 The frames can be used either to represent multiple pages (this is
5516 usually the case with multi-frame TIFF files, for example), or to
5517 create animation (usually the case with multi-frame GIF files).
5519 A multi-frame image has a property @code{:index}, whose value is an
5520 integer (counting from 0) that specifies which frame is being displayed.
5522 @defun image-multi-frame-p image
5523 This function returns non-@code{nil} if @var{image} contains more than
5524 one frame. The actual return value is a cons @code{(@var{nimages}
5525 . @var{delay})}, where @var{nimages} is the number of frames and
5526 @var{delay} is the delay in seconds between them, or @code{nil}
5527 if the image does not specify a delay. Images that are intended to be
5528 animated usually specify a frame delay, whereas ones that are intended
5529 to be treated as multiple pages do not.
5532 @defun image-current-frame image
5533 This function returns the index of the current frame number for
5534 @var{image}, counting from 0.
5537 @defun image-show-frame image n &optional nocheck
5538 This function switches @var{image} to frame number @var{n}. It
5539 replaces a frame number outside the valid range with that of the end
5540 of the range, unless @var{nocheck} is non-@code{nil}. If @var{image}
5541 does not contain a frame with the specified number, the image displays
5545 @defun image-animate image &optional index limit
5546 This function animates @var{image}. The optional integer @var{index}
5547 specifies the frame from which to start (default 0). The optional
5548 argument @var{limit} controls the length of the animation. If omitted
5549 or @code{nil}, the image animates once only; if @code{t} it loops
5550 forever; if a number animation stops after that many seconds.
5553 @vindex image-minimum-frame-delay
5554 @vindex image-default-frame-delay
5555 @noindent Animation operates by means of a timer. Note that Emacs imposes a
5556 minimum frame delay of 0.01 (@code{image-minimum-frame-delay}) seconds.
5557 If the image itself does not specify a delay, Emacs uses
5558 @code{image-default-frame-delay}.
5560 @defun image-animate-timer image
5561 This function returns the timer responsible for animating @var{image},
5567 @subsection Image Cache
5570 Emacs caches images so that it can display them again more
5571 efficiently. When Emacs displays an image, it searches the image
5572 cache for an existing image specification @code{equal} to the desired
5573 specification. If a match is found, the image is displayed from the
5574 cache. Otherwise, Emacs loads the image normally.
5576 @defun image-flush spec &optional frame
5577 This function removes the image with specification @var{spec} from the
5578 image cache of frame @var{frame}. Image specifications are compared
5579 using @code{equal}. If @var{frame} is @code{nil}, it defaults to the
5580 selected frame. If @var{frame} is @code{t}, the image is flushed on
5581 all existing frames.
5583 In Emacs's current implementation, each graphical terminal possesses an
5584 image cache, which is shared by all the frames on that terminal
5585 (@pxref{Multiple Terminals}). Thus, refreshing an image in one frame
5586 also refreshes it in all other frames on the same terminal.
5589 One use for @code{image-flush} is to tell Emacs about a change in an
5590 image file. If an image specification contains a @code{:file}
5591 property, the image is cached based on the file's contents when the
5592 image is first displayed. Even if the file subsequently changes,
5593 Emacs continues displaying the old version of the image. Calling
5594 @code{image-flush} flushes the image from the cache, forcing Emacs to
5595 re-read the file the next time it needs to display that image.
5597 Another use for @code{image-flush} is for memory conservation. If
5598 your Lisp program creates a large number of temporary images over a
5599 period much shorter than @code{image-cache-eviction-delay} (see
5600 below), you can opt to flush unused images yourself, instead of
5601 waiting for Emacs to do it automatically.
5603 @defun clear-image-cache &optional filter
5604 This function clears an image cache, removing all the images stored in
5605 it. If @var{filter} is omitted or @code{nil}, it clears the cache for
5606 the selected frame. If @var{filter} is a frame, it clears the cache
5607 for that frame. If @var{filter} is @code{t}, all image caches are
5608 cleared. Otherwise, @var{filter} is taken to be a file name, and all
5609 images associated with that file name are removed from all image
5613 If an image in the image cache has not been displayed for a specified
5614 period of time, Emacs removes it from the cache and frees the
5617 @defvar image-cache-eviction-delay
5618 This variable specifies the number of seconds an image can remain in
5619 the cache without being displayed. When an image is not displayed for
5620 this length of time, Emacs removes it from the image cache.
5622 Under some circumstances, if the number of images in the cache grows
5623 too large, the actual eviction delay may be shorter than this.
5625 If the value is @code{nil}, Emacs does not remove images from the cache
5626 except when you explicitly clear it. This mode can be useful for
5631 @section Embedded Native Widgets
5633 @cindex embedded widgets
5634 @cindex webkit browser widget
5636 Emacs is able to display native widgets, such as GTK WebKit widgets,
5637 in Emacs buffers when it was built with the necessary support
5638 libraries and is running on a graphical terminal. To test whether
5639 Emacs supports display of embedded widgets, check that the
5640 @code{xwidget-internal} feature is available (@pxref{Named Features}).
5642 To display an embedded widget in a buffer, you must first create an
5643 xwidget object, and then use that object as the display specifier
5644 in a @code{display} text or overlay property (@pxref{Display
5647 @defun make-xwidget type title width height arguments &optional buffer
5648 This creates and returns an xwidget object. If
5649 @var{buffer} is omitted or @code{nil}, it defaults to the current
5650 buffer. If @var{buffer} names a buffer that doesn't exist, it will be
5651 created. The @var{type} identifies the type of the xwidget component,
5652 it can be one of the following:
5656 The WebKit component.
5659 The @var{width} and @var{height} arguments specify the widget size in
5660 pixels, and @var{title}, a string, specifies its title.
5663 @defun xwidgetp object
5664 This function returns @code{t} if @var{object} is an xwidget,
5665 @code{nil} otherwise.
5668 @defun xwidget-plist xwidget
5669 This function returns the property list of @var{xwidget}.
5672 @defun set-xwidget-plist xwidget plist
5673 This function replaces the property list of @var{xwidget} with a new
5674 property list given by @var{plist}.
5677 @defun xwidget-buffer xwidget
5678 This function returns the buffer of @var{xwidget}.
5681 @defun get-buffer-xwidgets buffer
5682 This function returns a list of xwidget objects associated with the
5683 @var{buffer}, which can be specified as a buffer object or a name of
5684 an existing buffer, a string. The value is @code{nil} if @var{buffer}
5685 contains no xwidgets.
5688 @defun xwidget-webkit-goto-uri xwidget uri
5689 This function browses the specified @var{uri} in the given
5690 @var{xwidget}. The @var{uri} is a string that specifies the name of a
5691 file or a URL. @c FIXME: What else can a URI specify in this context?
5694 @defun xwidget-webkit-execute-script xwidget script
5695 This function causes the browser widget specified by @var{xwidget} to
5696 execute the specified JavaScript @code{script}.
5699 @defun xwidget-webkit-execute-script-rv xwidget script &optional default
5700 This function executes the specified @var{script} like
5701 @code{xwidget-webkit-execute-script} does, but it also returns the
5702 script's return value as a string. If @var{script} doesn't return a
5703 value, this function returns @var{default}, or @code{nil} if
5704 @var{default} was omitted.
5707 @defun xwidget-webkit-get-title xwidget
5708 This function returns the title of @var{xwidget} as a string.
5711 @defun xwidget-resize xwidget width height
5712 This function resizes the specified @var{xwidget} to the size
5713 @var{width}x@var{height} pixels.
5716 @defun xwidget-size-request xwidget
5717 This function returns the desired size of @var{xwidget} as a list of
5718 the form @code{(@var{width} @var{height})}. The dimensions are in
5722 @defun xwidget-info xwidget
5723 This function returns the attributes of @var{xwidget} as a vector of
5724 the form @code{[@var{type} @var{title} @var{width} @var{height}]}.
5725 The attributes are usually determined by @code{make-xwidget} when the
5729 @defun set-xwidget-query-on-exit-flag xwidget flag
5730 This function allows you to arrange that Emacs will ask the user for
5731 confirmation before exiting or before killing a buffer that has
5732 @var{xwidget} associated with it. If @var{flag} is non-@code{nil},
5733 Emacs will query the user, otherwise it will not.
5736 @defun xwidget-query-on-exit-flag xwidget
5737 This function returns the current setting of @var{xwidget}s
5738 query-on-exit flag, either @code{t} or @code{nil}.
5743 @cindex buttons in buffers
5744 @cindex clickable buttons in buffers
5746 The Button package defines functions for inserting and manipulating
5747 @dfn{buttons} that can be activated with the mouse or via keyboard
5748 commands. These buttons are typically used for various kinds of
5751 A button is essentially a set of text or overlay properties,
5752 attached to a stretch of text in a buffer. These properties are
5753 called @dfn{button properties}. One of these properties, the
5754 @dfn{action property}, specifies a function which is called when the
5755 user invokes the button using the keyboard or the mouse. The action
5756 function may examine the button and use its other properties as
5759 In some ways, the Button package duplicates the functionality in the
5760 Widget package. @xref{Top, , Introduction, widget, The Emacs Widget
5761 Library}. The advantage of the Button package is that it is faster,
5762 smaller, and simpler to program. From the point of view of the user,
5763 the interfaces produced by the two packages are very similar.
5766 * Button Properties:: Button properties with special meanings.
5767 * Button Types:: Defining common properties for classes of buttons.
5768 * Making Buttons:: Adding buttons to Emacs buffers.
5769 * Manipulating Buttons:: Getting and setting properties of buttons.
5770 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
5773 @node Button Properties
5774 @subsection Button Properties
5775 @cindex button properties
5777 Each button has an associated list of properties defining its
5778 appearance and behavior, and other arbitrary properties may be used
5779 for application specific purposes. The following properties have
5780 special meaning to the Button package:
5784 @kindex action @r{(button property)}
5785 The function to call when the user invokes the button, which is passed
5786 the single argument @var{button}. By default this is @code{ignore},
5790 @kindex mouse-action @r{(button property)}
5791 This is similar to @code{action}, and when present, will be used
5792 instead of @code{action} for button invocations resulting from
5793 mouse-clicks (instead of the user hitting @key{RET}). If not
5794 present, mouse-clicks use @code{action} instead.
5797 @kindex face @r{(button property)}
5798 This is an Emacs face controlling how buttons of this type are
5799 displayed; by default this is the @code{button} face.
5802 @kindex mouse-face @r{(button property)}
5803 This is an additional face which controls appearance during
5804 mouse-overs (merged with the usual button face); by default this is
5805 the usual Emacs @code{highlight} face.
5808 @kindex keymap @r{(button property)}
5809 The button's keymap, defining bindings active within the button
5810 region. By default this is the usual button region keymap, stored
5811 in the variable @code{button-map}, which defines @key{RET} and
5812 @key{mouse-2} to invoke the button.
5815 @kindex type @r{(button property)}
5816 The button type. @xref{Button Types}.
5819 @kindex help-index @r{(button property)}
5820 A string displayed by the Emacs tool-tip help system; by default,
5821 @code{"mouse-2, RET: Push this button"}.
5824 @kindex follow-link @r{(button property)}
5825 The follow-link property, defining how a @key{mouse-1} click behaves
5826 on this button, @xref{Clickable Text}.
5829 @kindex button @r{(button property)}
5830 All buttons have a non-@code{nil} @code{button} property, which may be useful
5831 in finding regions of text that comprise buttons (which is what the
5832 standard button functions do).
5835 There are other properties defined for the regions of text in a
5836 button, but these are not generally interesting for typical uses.
5839 @subsection Button Types
5840 @cindex button types
5842 Every button has a @dfn{button type}, which defines default values
5843 for the button's properties. Button types are arranged in a
5844 hierarchy, with specialized types inheriting from more general types,
5845 so that it's easy to define special-purpose types of buttons for
5848 @defun define-button-type name &rest properties
5849 Define a button type called @var{name} (a symbol).
5850 The remaining arguments
5851 form a sequence of @var{property value} pairs, specifying default
5852 property values for buttons with this type (a button's type may be set
5853 by giving it a @code{type} property when creating the button, using
5854 the @code{:type} keyword argument).
5856 In addition, the keyword argument @code{:supertype} may be used to
5857 specify a button-type from which @var{name} inherits its default
5858 property values. Note that this inheritance happens only when
5859 @var{name} is defined; subsequent changes to a supertype are not
5860 reflected in its subtypes.
5863 Using @code{define-button-type} to define default properties for
5864 buttons is not necessary---buttons without any specified type use the
5865 built-in button-type @code{button}---but it is encouraged, since
5866 doing so usually makes the resulting code clearer and more efficient.
5868 @node Making Buttons
5869 @subsection Making Buttons
5870 @cindex making buttons
5872 Buttons are associated with a region of text, using an overlay or
5873 text properties to hold button-specific information, all of which are
5874 initialized from the button's type (which defaults to the built-in
5875 button type @code{button}). Like all Emacs text, the appearance of
5876 the button is governed by the @code{face} property; by default (via
5877 the @code{face} property inherited from the @code{button} button-type)
5878 this is a simple underline, like a typical web-page link.
5880 For convenience, there are two sorts of button-creation functions,
5881 those that add button properties to an existing region of a buffer,
5882 called @code{make-...button}, and those that also insert the button
5883 text, called @code{insert-...button}.
5885 The button-creation functions all take the @code{&rest} argument
5886 @var{properties}, which should be a sequence of @var{property value}
5887 pairs, specifying properties to add to the button; see @ref{Button
5888 Properties}. In addition, the keyword argument @code{:type} may be
5889 used to specify a button-type from which to inherit other properties;
5890 see @ref{Button Types}. Any properties not explicitly specified
5891 during creation will be inherited from the button's type (if the type
5892 defines such a property).
5894 The following functions add a button using an overlay
5895 (@pxref{Overlays}) to hold the button properties:
5897 @defun make-button beg end &rest properties
5898 This makes a button from @var{beg} to @var{end} in the
5899 current buffer, and returns it.
5902 @defun insert-button label &rest properties
5903 This insert a button with the label @var{label} at point,
5907 The following functions are similar, but using text properties
5908 (@pxref{Text Properties}) to hold the button properties. Such buttons
5909 do not add markers to the buffer, so editing in the buffer does not
5910 slow down if there is an extremely large numbers of buttons. However,
5911 if there is an existing face text property on the text (e.g., a face
5912 assigned by Font Lock mode), the button face may not be visible. Both
5913 of these functions return the starting position of the new button.
5915 @defun make-text-button beg end &rest properties
5916 This makes a button from @var{beg} to @var{end} in the current buffer,
5917 using text properties.
5920 @defun insert-text-button label &rest properties
5921 This inserts a button with the label @var{label} at point, using text
5925 @node Manipulating Buttons
5926 @subsection Manipulating Buttons
5927 @cindex manipulating buttons
5929 These are functions for getting and setting properties of buttons.
5930 Often these are used by a button's invocation function to determine
5933 Where a @var{button} parameter is specified, it means an object
5934 referring to a specific button, either an overlay (for overlay
5935 buttons), or a buffer-position or marker (for text property buttons).
5936 Such an object is passed as the first argument to a button's
5937 invocation function when it is invoked.
5939 @defun button-start button
5940 Return the position at which @var{button} starts.
5943 @defun button-end button
5944 Return the position at which @var{button} ends.
5947 @defun button-get button prop
5948 Get the property of button @var{button} named @var{prop}.
5951 @defun button-put button prop val
5952 Set @var{button}'s @var{prop} property to @var{val}.
5955 @defun button-activate button &optional use-mouse-action
5956 Call @var{button}'s @code{action} property (i.e., invoke the function
5957 that is the value of that property, passing it the single argument
5958 @var{button}). If @var{use-mouse-action} is non-@code{nil}, try to
5959 invoke the button's @code{mouse-action} property instead of
5960 @code{action}; if the button has no @code{mouse-action} property, use
5961 @code{action} as normal.
5964 @defun button-label button
5965 Return @var{button}'s text label.
5968 @defun button-type button
5969 Return @var{button}'s button-type.
5972 @defun button-has-type-p button type
5973 Return @code{t} if @var{button} has button-type @var{type}, or one of
5974 @var{type}'s subtypes.
5977 @defun button-at pos
5978 Return the button at position @var{pos} in the current buffer, or
5979 @code{nil}. If the button at @var{pos} is a text property button, the
5980 return value is a marker pointing to @var{pos}.
5983 @defun button-type-put type prop val
5984 Set the button-type @var{type}'s @var{prop} property to @var{val}.
5987 @defun button-type-get type prop
5988 Get the property of button-type @var{type} named @var{prop}.
5991 @defun button-type-subtype-p type supertype
5992 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
5995 @node Button Buffer Commands
5996 @subsection Button Buffer Commands
5997 @cindex button buffer commands
5999 These are commands and functions for locating and operating on
6000 buttons in an Emacs buffer.
6002 @code{push-button} is the command that a user uses to actually push
6003 a button, and is bound by default in the button itself to @key{RET}
6004 and to @key{mouse-2} using a local keymap in the button's overlay or
6005 text properties. Commands that are useful outside the buttons itself,
6006 such as @code{forward-button} and @code{backward-button} are
6007 additionally available in the keymap stored in
6008 @code{button-buffer-map}; a mode which uses buttons may want to use
6009 @code{button-buffer-map} as a parent keymap for its keymap.
6011 If the button has a non-@code{nil} @code{follow-link} property, and
6012 @code{mouse-1-click-follows-link} is set, a quick @key{mouse-1} click
6013 will also activate the @code{push-button} command.
6014 @xref{Clickable Text}.
6016 @deffn Command push-button &optional pos use-mouse-action
6017 Perform the action specified by a button at location @var{pos}.
6018 @var{pos} may be either a buffer position or a mouse-event. If
6019 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
6020 mouse-event (@pxref{Mouse Events}), try to invoke the button's
6021 @code{mouse-action} property instead of @code{action}; if the button
6022 has no @code{mouse-action} property, use @code{action} as normal.
6023 @var{pos} defaults to point, except when @code{push-button} is invoked
6024 interactively as the result of a mouse-event, in which case, the mouse
6025 event's position is used. If there's no button at @var{pos}, do
6026 nothing and return @code{nil}, otherwise return @code{t}.
6029 @deffn Command forward-button n &optional wrap display-message
6030 Move to the @var{n}th next button, or @var{n}th previous button if
6031 @var{n} is negative. If @var{n} is zero, move to the start of any
6032 button at point. If @var{wrap} is non-@code{nil}, moving past either
6033 end of the buffer continues from the other end. If
6034 @var{display-message} is non-@code{nil}, the button's help-echo string
6035 is displayed. Any button with a non-@code{nil} @code{skip} property
6036 is skipped over. Returns the button found.
6039 @deffn Command backward-button n &optional wrap display-message
6040 Move to the @var{n}th previous button, or @var{n}th next button if
6041 @var{n} is negative. If @var{n} is zero, move to the start of any
6042 button at point. If @var{wrap} is non-@code{nil}, moving past either
6043 end of the buffer continues from the other end. If
6044 @var{display-message} is non-@code{nil}, the button's help-echo string
6045 is displayed. Any button with a non-@code{nil} @code{skip} property
6046 is skipped over. Returns the button found.
6049 @defun next-button pos &optional count-current
6050 @defunx previous-button pos &optional count-current
6051 Return the next button after (for @code{next-button}) or before (for
6052 @code{previous-button}) position @var{pos} in the current buffer. If
6053 @var{count-current} is non-@code{nil}, count any button at @var{pos}
6054 in the search, instead of starting at the next button.
6057 @node Abstract Display
6058 @section Abstract Display
6060 @cindex display, abstract
6061 @cindex display, arbitrary objects
6062 @cindex model/view/controller
6063 @cindex view part, model/view/controller
6065 The Ewoc package constructs buffer text that represents a structure
6066 of Lisp objects, and updates the text to follow changes in that
6067 structure. This is like the ``view'' component in the
6068 ``model--view--controller'' design paradigm. Ewoc means ``Emacs's
6069 Widget for Object Collections''.
6071 An @dfn{ewoc} is a structure that organizes information required to
6072 construct buffer text that represents certain Lisp data. The buffer
6073 text of the ewoc has three parts, in order: first, fixed @dfn{header}
6074 text; next, textual descriptions of a series of data elements (Lisp
6075 objects that you specify); and last, fixed @dfn{footer} text.
6076 Specifically, an ewoc contains information on:
6080 The buffer which its text is generated in.
6083 The text's start position in the buffer.
6086 The header and footer strings.
6090 @c or "@cindex node, abstract display"?
6091 A doubly-linked chain of @dfn{nodes}, each of which contains:
6095 A @dfn{data element}, a single Lisp object.
6098 Links to the preceding and following nodes in the chain.
6102 A @dfn{pretty-printer} function which is responsible for
6103 inserting the textual representation of a data
6104 element value into the current buffer.
6107 Typically, you define an ewoc with @code{ewoc-create}, and then pass
6108 the resulting ewoc structure to other functions in the Ewoc package to
6109 build nodes within it, and display it in the buffer. Once it is
6110 displayed in the buffer, other functions determine the correspondence
6111 between buffer positions and nodes, move point from one node's textual
6112 representation to another, and so forth. @xref{Abstract Display
6115 @cindex encapsulation, ewoc
6116 @c or "@cindex encapsulation, abstract display"?
6117 A node @dfn{encapsulates} a data element much the way a variable
6118 holds a value. Normally, encapsulation occurs as a part of adding a
6119 node to the ewoc. You can retrieve the data element value and place a
6120 new value in its place, like so:
6123 (ewoc-data @var{node})
6126 (ewoc-set-data @var{node} @var{new-value})
6127 @result{} @var{new-value}
6131 You can also use, as the data element value, a Lisp object (list or
6132 vector) that is a container for the real value, or an index into
6133 some other structure. The example (@pxref{Abstract Display Example})
6134 uses the latter approach.
6136 When the data changes, you will want to update the text in the
6137 buffer. You can update all nodes by calling @code{ewoc-refresh}, or
6138 just specific nodes using @code{ewoc-invalidate}, or all nodes
6139 satisfying a predicate using @code{ewoc-map}. Alternatively, you can
6140 delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter},
6141 and add new nodes in their place. Deleting a node from an ewoc deletes
6142 its associated textual description from buffer, as well.
6145 * Abstract Display Functions:: Functions in the Ewoc package.
6146 * Abstract Display Example:: Example of using Ewoc.
6149 @node Abstract Display Functions
6150 @subsection Abstract Display Functions
6152 In this subsection, @var{ewoc} and @var{node} stand for the
6153 structures described above (@pxref{Abstract Display}), while
6154 @var{data} stands for an arbitrary Lisp object used as a data element.
6156 @defun ewoc-create pretty-printer &optional header footer nosep
6157 This constructs and returns a new ewoc, with no nodes (and thus no data
6158 elements). @var{pretty-printer} should be a function that takes one
6159 argument, a data element of the sort you plan to use in this ewoc, and
6160 inserts its textual description at point using @code{insert} (and never
6161 @code{insert-before-markers}, because that would interfere with the
6162 Ewoc package's internal mechanisms).
6164 Normally, a newline is automatically inserted after the header,
6165 the footer and every node's textual description. If @var{nosep}
6166 is non-@code{nil}, no newline is inserted. This may be useful for
6167 displaying an entire ewoc on a single line, for example, or for
6168 making nodes invisible by arranging for @var{pretty-printer}
6169 to do nothing for those nodes.
6171 An ewoc maintains its text in the buffer that is current when
6172 you create it, so switch to the intended buffer before calling
6176 @defun ewoc-buffer ewoc
6177 This returns the buffer where @var{ewoc} maintains its text.
6180 @defun ewoc-get-hf ewoc
6181 This returns a cons cell @code{(@var{header} . @var{footer})}
6182 made from @var{ewoc}'s header and footer.
6185 @defun ewoc-set-hf ewoc header footer
6186 This sets the header and footer of @var{ewoc} to the strings
6187 @var{header} and @var{footer}, respectively.
6190 @defun ewoc-enter-first ewoc data
6191 @defunx ewoc-enter-last ewoc data
6192 These add a new node encapsulating @var{data}, putting it, respectively,
6193 at the beginning or end of @var{ewoc}'s chain of nodes.
6196 @defun ewoc-enter-before ewoc node data
6197 @defunx ewoc-enter-after ewoc node data
6198 These add a new node encapsulating @var{data}, adding it to
6199 @var{ewoc} before or after @var{node}, respectively.
6202 @defun ewoc-prev ewoc node
6203 @defunx ewoc-next ewoc node
6204 These return, respectively, the previous node and the next node of @var{node}
6208 @defun ewoc-nth ewoc n
6209 This returns the node in @var{ewoc} found at zero-based index @var{n}.
6210 A negative @var{n} means count from the end. @code{ewoc-nth} returns
6211 @code{nil} if @var{n} is out of range.
6214 @defun ewoc-data node
6215 This extracts the data encapsulated by @var{node} and returns it.
6218 @defun ewoc-set-data node data
6219 This sets the data encapsulated by @var{node} to @var{data}.
6222 @defun ewoc-locate ewoc &optional pos guess
6223 This determines the node in @var{ewoc} which contains point (or
6224 @var{pos} if specified), and returns that node. If @var{ewoc} has no
6225 nodes, it returns @code{nil}. If @var{pos} is before the first node,
6226 it returns the first node; if @var{pos} is after the last node, it returns
6227 the last node. The optional third arg @var{guess}
6228 should be a node that is likely to be near @var{pos}; this doesn't
6229 alter the result, but makes the function run faster.
6232 @defun ewoc-location node
6233 This returns the start position of @var{node}.
6236 @defun ewoc-goto-prev ewoc arg
6237 @defunx ewoc-goto-next ewoc arg
6238 These move point to the previous or next, respectively, @var{arg}th node
6239 in @var{ewoc}. @code{ewoc-goto-prev} does not move if it is already at
6240 the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next}
6241 moves past the last node, returning @code{nil}. Excepting this special
6242 case, these functions return the node moved to.
6245 @defun ewoc-goto-node ewoc node
6246 This moves point to the start of @var{node} in @var{ewoc}.
6249 @defun ewoc-refresh ewoc
6250 This function regenerates the text of @var{ewoc}. It works by
6251 deleting the text between the header and the footer, i.e., all the
6252 data elements' representations, and then calling the pretty-printer
6253 function for each node, one by one, in order.
6256 @defun ewoc-invalidate ewoc &rest nodes
6257 This is similar to @code{ewoc-refresh}, except that only @var{nodes} in
6258 @var{ewoc} are updated instead of the entire set.
6261 @defun ewoc-delete ewoc &rest nodes
6262 This deletes each node in @var{nodes} from @var{ewoc}.
6265 @defun ewoc-filter ewoc predicate &rest args
6266 This calls @var{predicate} for each data element in @var{ewoc} and
6267 deletes those nodes for which @var{predicate} returns @code{nil}.
6268 Any @var{args} are passed to @var{predicate}.
6271 @defun ewoc-collect ewoc predicate &rest args
6272 This calls @var{predicate} for each data element in @var{ewoc}
6273 and returns a list of those elements for which @var{predicate}
6274 returns non-@code{nil}. The elements in the list are ordered
6275 as in the buffer. Any @var{args} are passed to @var{predicate}.
6278 @defun ewoc-map map-function ewoc &rest args
6279 This calls @var{map-function} for each data element in @var{ewoc} and
6280 updates those nodes for which @var{map-function} returns non-@code{nil}.
6281 Any @var{args} are passed to @var{map-function}.
6284 @node Abstract Display Example
6285 @subsection Abstract Display Example
6287 Here is a simple example using functions of the ewoc package to
6288 implement a @dfn{color components} display, an area in a buffer that
6289 represents a vector of three integers (itself representing a 24-bit RGB
6290 value) in various ways.
6293 (setq colorcomp-ewoc nil
6295 colorcomp-mode-map nil
6296 colorcomp-labels ["Red" "Green" "Blue"])
6298 (defun colorcomp-pp (data)
6300 (let ((comp (aref colorcomp-data data)))
6301 (insert (aref colorcomp-labels data) "\t: #x"
6302 (format "%02X" comp) " "
6303 (make-string (ash comp -2) ?#) "\n"))
6304 (let ((cstr (format "#%02X%02X%02X"
6305 (aref colorcomp-data 0)
6306 (aref colorcomp-data 1)
6307 (aref colorcomp-data 2)))
6308 (samp " (sample text) "))
6310 (propertize samp 'face
6311 `(foreground-color . ,cstr))
6312 (propertize samp 'face
6313 `(background-color . ,cstr))
6316 (defun colorcomp (color)
6317 "Allow fiddling with COLOR in a new buffer.
6318 The buffer is in Color Components mode."
6319 (interactive "sColor (name or #RGB or #RRGGBB): ")
6320 (when (string= "" color)
6321 (setq color "green"))
6322 (unless (color-values color)
6323 (error "No such color: %S" color))
6325 (generate-new-buffer (format "originally: %s" color)))
6326 (kill-all-local-variables)
6327 (setq major-mode 'colorcomp-mode
6328 mode-name "Color Components")
6329 (use-local-map colorcomp-mode-map)
6331 (buffer-disable-undo)
6332 (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
6333 (color-values color))))
6334 (ewoc (ewoc-create 'colorcomp-pp
6335 "\nColor Components\n\n"
6336 (substitute-command-keys
6337 "\n\\@{colorcomp-mode-map@}"))))
6338 (set (make-local-variable 'colorcomp-data) data)
6339 (set (make-local-variable 'colorcomp-ewoc) ewoc)
6340 (ewoc-enter-last ewoc 0)
6341 (ewoc-enter-last ewoc 1)
6342 (ewoc-enter-last ewoc 2)
6343 (ewoc-enter-last ewoc nil)))
6346 @cindex controller part, model/view/controller
6347 This example can be extended to be a color selection widget (in
6348 other words, the ``controller'' part of the ``model--view--controller''
6349 design paradigm) by defining commands to modify @code{colorcomp-data}
6350 and to finish the selection process, and a keymap to tie it all
6351 together conveniently.
6354 (defun colorcomp-mod (index limit delta)
6355 (let ((cur (aref colorcomp-data index)))
6356 (unless (= limit cur)
6357 (aset colorcomp-data index (+ cur delta)))
6360 (ewoc-nth colorcomp-ewoc index)
6361 (ewoc-nth colorcomp-ewoc -1))))
6363 (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
6364 (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
6365 (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
6366 (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
6367 (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
6368 (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
6370 (defun colorcomp-copy-as-kill-and-exit ()
6371 "Copy the color components into the kill ring and kill the buffer.
6372 The string is formatted #RRGGBB (hash followed by six hex digits)."
6374 (kill-new (format "#%02X%02X%02X"
6375 (aref colorcomp-data 0)
6376 (aref colorcomp-data 1)
6377 (aref colorcomp-data 2)))
6380 (setq colorcomp-mode-map
6381 (let ((m (make-sparse-keymap)))
6383 (define-key m "i" 'colorcomp-R-less)
6384 (define-key m "o" 'colorcomp-R-more)
6385 (define-key m "k" 'colorcomp-G-less)
6386 (define-key m "l" 'colorcomp-G-more)
6387 (define-key m "," 'colorcomp-B-less)
6388 (define-key m "." 'colorcomp-B-more)
6389 (define-key m " " 'colorcomp-copy-as-kill-and-exit)
6393 Note that we never modify the data in each node, which is fixed when the
6394 ewoc is created to be either @code{nil} or an index into the vector
6395 @code{colorcomp-data}, the actual color components.
6398 @section Blinking Parentheses
6399 @cindex parenthesis matching
6400 @cindex blinking parentheses
6401 @cindex balancing parentheses
6403 This section describes the mechanism by which Emacs shows a matching
6404 open parenthesis when the user inserts a close parenthesis.
6406 @defvar blink-paren-function
6407 The value of this variable should be a function (of no arguments) to
6408 be called whenever a character with close parenthesis syntax is inserted.
6409 The value of @code{blink-paren-function} may be @code{nil}, in which
6410 case nothing is done.
6413 @defopt blink-matching-paren
6414 If this variable is @code{nil}, then @code{blink-matching-open} does
6418 @defopt blink-matching-paren-distance
6419 This variable specifies the maximum distance to scan for a matching
6420 parenthesis before giving up.
6423 @defopt blink-matching-delay
6424 This variable specifies the number of seconds to keep indicating the
6425 matching parenthesis. A fraction of a second often gives good
6426 results, but the default is 1, which works on all systems.
6429 @deffn Command blink-matching-open
6430 This function is the default value of @code{blink-paren-function}. It
6431 assumes that point follows a character with close parenthesis syntax
6432 and applies the appropriate effect momentarily to the matching opening
6433 character. If that character is not already on the screen, it
6434 displays the character's context in the echo area. To avoid long
6435 delays, this function does not search farther than
6436 @code{blink-matching-paren-distance} characters.
6438 Here is an example of calling this function explicitly.
6442 (defun interactive-blink-matching-open ()
6443 "Indicate momentarily the start of parenthesized sexp before point."
6447 (let ((blink-matching-paren-distance
6449 (blink-matching-paren t))
6450 (blink-matching-open)))
6455 @node Character Display
6456 @section Character Display
6458 This section describes how characters are actually displayed by
6459 Emacs. Typically, a character is displayed as a @dfn{glyph} (a
6460 graphical symbol which occupies one character position on the screen),
6461 whose appearance corresponds to the character itself. For example,
6462 the character @samp{a} (character code 97) is displayed as @samp{a}.
6463 Some characters, however, are displayed specially. For example, the
6464 formfeed character (character code 12) is usually displayed as a
6465 sequence of two glyphs, @samp{^L}, while the newline character
6466 (character code 10) starts a new screen line.
6468 You can modify how each character is displayed by defining a
6469 @dfn{display table}, which maps each character code into a sequence of
6470 glyphs. @xref{Display Tables}.
6473 * Usual Display:: The usual conventions for displaying characters.
6474 * Display Tables:: What a display table consists of.
6475 * Active Display Table:: How Emacs selects a display table to use.
6476 * Glyphs:: How to define a glyph, and what glyphs mean.
6477 * Glyphless Chars:: How glyphless characters are drawn.
6481 @subsection Usual Display Conventions
6483 Here are the conventions for displaying each character code (in the
6484 absence of a display table, which can override these
6489 conventions; @pxref{Display Tables}).
6492 @cindex printable ASCII characters
6495 The @dfn{printable @acronym{ASCII} characters}, character codes 32
6496 through 126 (consisting of numerals, English letters, and symbols like
6497 @samp{#}) are displayed literally.
6500 The tab character (character code 9) displays as whitespace stretching
6501 up to the next tab stop column. @xref{Text Display,,, emacs, The GNU
6502 Emacs Manual}. The variable @code{tab-width} controls the number of
6503 spaces per tab stop (see below).
6506 The newline character (character code 10) has a special effect: it
6507 ends the preceding line and starts a new line.
6509 @cindex ASCII control characters
6511 The non-printable @dfn{@acronym{ASCII} control characters}---character
6512 codes 0 through 31, as well as the @key{DEL} character (character code
6513 127)---display in one of two ways according to the variable
6514 @code{ctl-arrow}. If this variable is non-@code{nil} (the default),
6515 these characters are displayed as sequences of two glyphs, where the
6516 first glyph is @samp{^} (a display table can specify a glyph to use
6517 instead of @samp{^}); e.g., the @key{DEL} character is displayed as
6520 If @code{ctl-arrow} is @code{nil}, these characters are displayed as
6521 octal escapes (see below).
6523 This rule also applies to carriage return (character code 13), if that
6524 character appears in the buffer. But carriage returns usually do not
6525 appear in buffer text; they are eliminated as part of end-of-line
6526 conversion (@pxref{Coding System Basics}).
6528 @cindex octal escapes
6530 @dfn{Raw bytes} are non-@acronym{ASCII} characters with codes 128
6531 through 255 (@pxref{Text Representations}). These characters display
6532 as @dfn{octal escapes}: sequences of four glyphs, where the first
6533 glyph is the @acronym{ASCII} code for @samp{\}, and the others are
6534 digit characters representing the character code in octal. (A display
6535 table can specify a glyph to use instead of @samp{\}.)
6538 Each non-@acronym{ASCII} character with code above 255 is displayed
6539 literally, if the terminal supports it. If the terminal does not
6540 support it, the character is said to be @dfn{glyphless}, and it is
6541 usually displayed using a placeholder glyph. For example, if a
6542 graphical terminal has no font for a character, Emacs usually displays
6543 a box containing the character code in hexadecimal. @xref{Glyphless
6547 The above display conventions apply even when there is a display
6548 table, for any character whose entry in the active display table is
6549 @code{nil}. Thus, when you set up a display table, you need only
6550 specify the characters for which you want special behavior.
6552 The following variables affect how certain characters are displayed
6553 on the screen. Since they change the number of columns the characters
6554 occupy, they also affect the indentation functions. They also affect
6555 how the mode line is displayed; if you want to force redisplay of the
6556 mode line using the new values, call the function
6557 @code{force-mode-line-update} (@pxref{Mode Line Format}).
6560 @cindex control characters in display
6561 This buffer-local variable controls how control characters are
6562 displayed. If it is non-@code{nil}, they are displayed as a caret
6563 followed by the character: @samp{^A}. If it is @code{nil}, they are
6564 displayed as octal escapes: a backslash followed by three octal
6565 digits, as in @samp{\001}.
6569 The value of this buffer-local variable is the spacing between tab
6570 stops used for displaying tab characters in Emacs buffers. The value
6571 is in units of columns, and the default is 8. Note that this feature
6572 is completely independent of the user-settable tab stops used by the
6573 command @code{tab-to-tab-stop}. @xref{Indent Tabs}.
6576 @node Display Tables
6577 @subsection Display Tables
6579 @cindex display table
6580 A display table is a special-purpose char-table
6581 (@pxref{Char-Tables}), with @code{display-table} as its subtype, which
6582 is used to override the usual character display conventions. This
6583 section describes how to make, inspect, and assign elements to a
6584 display table object.
6586 @defun make-display-table
6587 This creates and returns a display table. The table initially has
6588 @code{nil} in all elements.
6591 The ordinary elements of the display table are indexed by character
6592 codes; the element at index @var{c} says how to display the character
6593 code @var{c}. The value should be @code{nil} (which means to display
6594 the character @var{c} according to the usual display conventions;
6595 @pxref{Usual Display}), or a vector of glyph codes (which means to
6596 display the character @var{c} as those glyphs; @pxref{Glyphs}).
6598 @strong{Warning:} if you use the display table to change the display
6599 of newline characters, the whole buffer will be displayed as one long
6602 The display table also has six @dfn{extra slots} which serve special
6603 purposes. Here is a table of their meanings; @code{nil} in any slot
6604 means to use the default for that slot, as stated below.
6608 The glyph for the end of a truncated screen line (the default for this
6609 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
6610 arrows in the fringes to indicate truncation, so the display table has
6614 The glyph for the end of a continued line (the default is @samp{\}).
6615 On graphical terminals, Emacs uses curved arrows in the fringes to
6616 indicate continuation, so the display table has no effect.
6619 The glyph for indicating a character displayed as an octal character
6620 code (the default is @samp{\}).
6623 The glyph for indicating a control character (the default is @samp{^}).
6626 A vector of glyphs for indicating the presence of invisible lines (the
6627 default is @samp{...}). @xref{Selective Display}.
6630 The glyph used to draw the border between side-by-side windows (the
6631 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
6632 when there are no scroll bars; if scroll bars are supported and in use,
6633 a scroll bar separates the two windows.
6636 For example, here is how to construct a display table that mimics
6637 the effect of setting @code{ctl-arrow} to a non-@code{nil} value
6638 (@pxref{Glyphs}, for the function @code{make-glyph-code}):
6641 (setq disptab (make-display-table))
6646 (vector (make-glyph-code ?^ 'escape-glyph)
6647 (make-glyph-code (+ i 64) 'escape-glyph)))))
6649 (vector (make-glyph-code ?^ 'escape-glyph)
6650 (make-glyph-code ?? 'escape-glyph)))))
6653 @defun display-table-slot display-table slot
6654 This function returns the value of the extra slot @var{slot} of
6655 @var{display-table}. The argument @var{slot} may be a number from 0 to
6656 5 inclusive, or a slot name (symbol). Valid symbols are
6657 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6658 @code{selective-display}, and @code{vertical-border}.
6661 @defun set-display-table-slot display-table slot value
6662 This function stores @var{value} in the extra slot @var{slot} of
6663 @var{display-table}. The argument @var{slot} may be a number from 0 to
6664 5 inclusive, or a slot name (symbol). Valid symbols are
6665 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6666 @code{selective-display}, and @code{vertical-border}.
6669 @defun describe-display-table display-table
6670 This function displays a description of the display table
6671 @var{display-table} in a help buffer.
6674 @deffn Command describe-current-display-table
6675 This command displays a description of the current display table in a
6679 @node Active Display Table
6680 @subsection Active Display Table
6681 @cindex active display table
6683 Each window can specify a display table, and so can each buffer.
6684 The window's display table, if there is one, takes precedence over the
6685 buffer's display table. If neither exists, Emacs tries to use the
6686 standard display table; if that is @code{nil}, Emacs uses the usual
6687 character display conventions (@pxref{Usual Display}).
6689 Note that display tables affect how the mode line is displayed, so
6690 if you want to force redisplay of the mode line using a new display
6691 table, call @code{force-mode-line-update} (@pxref{Mode Line Format}).
6693 @defun window-display-table &optional window
6694 This function returns @var{window}'s display table, or @code{nil} if
6695 there is none. The default for @var{window} is the selected window.
6698 @defun set-window-display-table window table
6699 This function sets the display table of @var{window} to @var{table}.
6700 The argument @var{table} should be either a display table or
6704 @defvar buffer-display-table
6705 This variable is automatically buffer-local in all buffers; its value
6706 specifies the buffer's display table. If it is @code{nil}, there is
6707 no buffer display table.
6710 @defvar standard-display-table
6711 The value of this variable is the standard display table, which is
6712 used when Emacs is displaying a buffer in a window with neither a
6713 window display table nor a buffer display table defined, or when Emacs
6714 is outputting text to the standard output or error streams. Although its
6715 default is typically @code{nil}, in an interactive session if the
6716 terminal cannot display curved quotes, its default maps curved quotes
6717 to ASCII approximations. @xref{Keys in Documentation}.
6720 The @file{disp-table} library defines several functions for changing
6721 the standard display table.
6728 A @dfn{glyph} is a graphical symbol which occupies a single
6729 character position on the screen. Each glyph is represented in Lisp
6730 as a @dfn{glyph code}, which specifies a character and optionally a
6731 face to display it in (@pxref{Faces}). The main use of glyph codes is
6732 as the entries of display tables (@pxref{Display Tables}). The
6733 following functions are used to manipulate glyph codes:
6735 @defun make-glyph-code char &optional face
6736 This function returns a glyph code representing char @var{char} with
6737 face @var{face}. If @var{face} is omitted or @code{nil}, the glyph
6738 uses the default face; in that case, the glyph code is an integer. If
6739 @var{face} is non-@code{nil}, the glyph code is not necessarily an
6743 @defun glyph-char glyph
6744 This function returns the character of glyph code @var{glyph}.
6747 @defun glyph-face glyph
6748 This function returns face of glyph code @var{glyph}, or @code{nil} if
6749 @var{glyph} uses the default face.
6753 You can set up a @dfn{glyph table} to change how glyph codes are
6754 actually displayed on text terminals. This feature is semi-obsolete;
6755 use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}).
6758 The value of this variable, if non-@code{nil}, is the current glyph
6759 table. It takes effect only on character terminals; on graphical
6760 displays, all glyphs are displayed literally. The glyph table should
6761 be a vector whose @var{g}th element specifies how to display glyph
6762 code @var{g}, where @var{g} is the glyph code for a glyph whose face
6763 is unspecified. Each element should be one of the following:
6767 Display this glyph literally.
6770 Display this glyph by sending the specified string to the terminal.
6773 Display the specified glyph code instead.
6776 Any integer glyph code greater than or equal to the length of the
6777 glyph table is displayed literally.
6781 @node Glyphless Chars
6782 @subsection Glyphless Character Display
6783 @cindex glyphless characters
6785 @dfn{Glyphless characters} are characters which are displayed in a
6786 special way, e.g., as a box containing a hexadecimal code, instead of
6787 being displayed literally. These include characters which are
6788 explicitly defined to be glyphless, as well as characters for which
6789 there is no available font (on a graphical display), and characters
6790 which cannot be encoded by the terminal's coding system (on a text
6793 @defvar glyphless-char-display
6794 The value of this variable is a char-table which defines glyphless
6795 characters and how they are displayed. Each entry must be one of the
6796 following display methods:
6800 Display the character in the usual way.
6802 @item @code{zero-width}
6803 Don't display the character.
6805 @item @code{thin-space}
6806 Display a thin space, 1-pixel wide on graphical displays, or
6807 1-character wide on text terminals.
6809 @item @code{empty-box}
6810 Display an empty box.
6812 @item @code{hex-code}
6813 Display a box containing the Unicode codepoint of the character, in
6814 hexadecimal notation.
6816 @item an @acronym{ASCII} string
6817 Display a box containing that string. The string should contain at
6818 most 6 @acronym{ASCII} characters.
6820 @item a cons cell @code{(@var{graphical} . @var{text})}
6821 Display with @var{graphical} on graphical displays, and with
6822 @var{text} on text terminals. Both @var{graphical} and @var{text}
6823 must be one of the display methods described above.
6827 The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
6828 @acronym{ASCII} string display methods are drawn with the
6829 @code{glyphless-char} face. On text terminals, a box is emulated by
6830 square brackets, @samp{[]}.
6832 The char-table has one extra slot, which determines how to display any
6833 character that cannot be displayed with any available font, or cannot
6834 be encoded by the terminal's coding system. Its value should be one
6835 of the above display methods, except @code{zero-width} or a cons cell.
6837 If a character has a non-@code{nil} entry in an active display table,
6838 the display table takes effect; in this case, Emacs does not consult
6839 @code{glyphless-char-display} at all.
6842 @defopt glyphless-char-display-control
6843 This user option provides a convenient way to set
6844 @code{glyphless-char-display} for groups of similar characters. Do
6845 not set its value directly from Lisp code; the value takes effect only
6846 via a custom @code{:set} function (@pxref{Variable Definitions}),
6847 which updates @code{glyphless-char-display}.
6849 Its value should be an alist of elements @code{(@var{group}
6850 . @var{method})}, where @var{group} is a symbol specifying a group of
6851 characters, and @var{method} is a symbol specifying how to display
6854 @var{group} should be one of the following:
6858 @acronym{ASCII} control characters @code{U+0000} to @code{U+001F},
6859 excluding the newline and tab characters (normally displayed as escape
6860 sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed,
6861 emacs, The GNU Emacs Manual}).
6864 Non-@acronym{ASCII}, non-printing characters @code{U+0080} to
6865 @code{U+009F} (normally displayed as octal escape sequences like
6868 @item format-control
6869 Characters of Unicode General Category [Cf], such as @samp{U+200E}
6870 (Left-to-Right Mark), but excluding characters that have graphic
6871 images, such as @samp{U+00AD} (Soft Hyphen).
6874 Characters for there is no suitable font, or which cannot be encoded
6875 by the terminal's coding system.
6878 @c FIXME: this can also be 'acronym', but that's not currently
6879 @c completely implemented; it applies only to the format-control
6880 @c group, and only works if the acronym is in 'char-acronym-table'.
6881 The @var{method} symbol should be one of @code{zero-width},
6882 @code{thin-space}, @code{empty-box}, or @code{hex-code}. These have
6883 the same meanings as in @code{glyphless-char-display}, above.
6890 This section describes how to make Emacs ring the bell (or blink the
6891 screen) to attract the user's attention. Be conservative about how
6892 often you do this; frequent bells can become irritating. Also be
6893 careful not to use just beeping when signaling an error is more
6894 appropriate (@pxref{Errors}).
6896 @defun ding &optional do-not-terminate
6897 @cindex keyboard macro termination
6898 This function beeps, or flashes the screen (see @code{visible-bell} below).
6899 It also terminates any keyboard macro currently executing unless
6900 @var{do-not-terminate} is non-@code{nil}.
6903 @defun beep &optional do-not-terminate
6904 This is a synonym for @code{ding}.
6907 @defopt visible-bell
6908 This variable determines whether Emacs should flash the screen to
6909 represent a bell. Non-@code{nil} means yes, @code{nil} means no.
6910 This is effective on graphical displays, and on text terminals
6911 provided the terminal's Termcap entry defines the visible bell
6912 capability (@samp{vb}).
6915 @defopt ring-bell-function
6916 If this is non-@code{nil}, it specifies how Emacs should ring the
6917 bell. Its value should be a function of no arguments. If this is
6918 non-@code{nil}, it takes precedence over the @code{visible-bell}
6922 @node Window Systems
6923 @section Window Systems
6925 Emacs works with several window systems, most notably the X Window
6926 System. Both Emacs and X use the term ``window'', but use it
6927 differently. An Emacs frame is a single window as far as X is
6928 concerned; the individual Emacs windows are not known to X at all.
6930 @defvar window-system
6931 This terminal-local variable tells Lisp programs what window system
6932 Emacs is using for displaying the frame. The possible values are
6936 @cindex X Window System
6937 Emacs is displaying the frame using X.
6939 Emacs is displaying the frame using native MS-Windows GUI.
6941 Emacs is displaying the frame using the Nextstep interface (used on
6942 GNUstep and Mac OS X).
6944 Emacs is displaying the frame using MS-DOS direct screen writes.
6946 Emacs is displaying the frame on a character-based terminal.
6950 @defvar initial-window-system
6951 This variable holds the value of @code{window-system} used for the
6952 first frame created by Emacs during startup. (When Emacs is invoked
6953 with the @option{--daemon} option, it does not create any initial
6954 frames, so @code{initial-window-system} is @code{nil}, except on
6955 MS-Windows, where it is still @code{w32}. @xref{Initial Options,
6956 daemon,, emacs, The GNU Emacs Manual}.)
6959 @defun window-system &optional frame
6960 This function returns a symbol whose name tells what window system is
6961 used for displaying @var{frame} (which defaults to the currently
6962 selected frame). The list of possible symbols it returns is the same
6963 one documented for the variable @code{window-system} above.
6966 Do @emph{not} use @code{window-system} and
6967 @code{initial-window-system} as predicates or boolean flag variables,
6968 if you want to write code that works differently on text terminals and
6969 graphic displays. That is because @code{window-system} is not a good
6970 indicator of Emacs capabilities on a given display type. Instead, use
6971 @code{display-graphic-p} or any of the other @code{display-*-p}
6972 predicates described in @ref{Display Feature Testing}.
6977 @dfn{Tooltips} are special frames (@pxref{Frames}) that are used to
6978 display helpful hints (a.k.a.@: ``tips'') related to the current
6979 position of the mouse pointer. Emacs uses tooltips to display help
6980 strings about active portions of text (@pxref{Special Properties}) and
6981 about various UI elements, such as menu items (@pxref{Extended Menu
6982 Items}) and tool-bar buttons (@pxref{Tool Bar}).
6985 Tooltip Mode is a minor mode that enables display of tooltips.
6986 Turning off this mode causes the tooltips be displayed in the echo
6987 area. On text-mode (a.k.a.@: ``TTY'') frames, tooltips are always
6988 displayed in the echo area.
6991 @vindex x-gtk-use-system-tooltips
6992 When Emacs is built with GTK+ support, it by default displays tooltips
6993 using GTK+ functions, and the appearance of the tooltips is then
6994 controlled by GTK+ settings. GTK+ tooltips can be disabled by
6995 changing the value of the variable @code{x-gtk-use-system-tooltips} to
6996 @code{nil}. The rest of this subsection describes how to control
6997 non-GTK+ tooltips, which are presented by Emacs itself.
6999 Since tooltips are special frames, they have their frame parameters
7000 (@pxref{Frame Parameters}). Unlike other frames, the frame parameters
7001 for tooltips are stored in a special variable.
7003 @defvar tooltip-frame-parameters
7004 This customizable option holds the frame parameters used for
7005 displaying tooltips. Any font and color parameters are ignored, and
7006 the corresponding attributes of the @code{tooltip} face are used
7007 instead. If @code{left} or @code{top} parameters are included, they
7008 are used as absolute frame-relative coordinates where the tooltip
7009 should be shown. (Mouse-relative position of the tooltip can be
7010 customized using the variables described in @ref{Tooltips,,, emacs,
7011 The GNU Emacs Manual}.) Note that the @code{left} and @code{top}
7012 parameters, if present, override the values of mouse-relative offsets.
7015 @vindex tooltip@r{ face}
7016 The @code{tooltip} face determines the appearance of text shown in
7017 tooltips. It should generally use a variable-pitch font of size that
7018 is preferably smaller than the default frame font.
7020 @findex tooltip-help-tips
7021 @defvar tooltip-functions
7022 This abnormal hook is a list of functions to call when Emacs needs to
7023 display a tooltip. Each function is called with a single argument
7024 @var{event} which is a copy of the last mouse movement event. If a
7025 function on this list actually displays the tooltip, it should return
7026 non-@code{nil}, and then the rest of the functions will not be
7027 called. The default value of this variable is a single function
7028 @code{tooltip-help-tips}.
7031 If you write your own function to be put on the
7032 @code{tooltip-functions} list, you may need to know the buffer of the
7033 mouse event that triggered the tooltip display. The following
7034 function provides that information.
7036 @defun tooltip-event-buffer event
7037 This function returns the buffer over which @var{event} occurred.
7038 Call it with the argument of the function from
7039 @code{tooltip-functions} to obtain the buffer whose text triggered the
7040 tooltip. Note that the event might occur not over a buffer (e.g.,
7041 over the tool bar), in which case this function will return
7045 Other aspects of tooltip display are controlled by several
7046 customizable settings; see @ref{Tooltips,,, emacs, The GNU Emacs
7049 @node Bidirectional Display
7050 @section Bidirectional Display
7051 @cindex bidirectional display
7052 @cindex right-to-left text
7054 Emacs can display text written in scripts, such as Arabic, Farsi,
7055 and Hebrew, whose natural ordering for horizontal text display runs
7056 from right to left. Furthermore, segments of Latin script and digits
7057 embedded in right-to-left text are displayed left-to-right, while
7058 segments of right-to-left script embedded in left-to-right text
7059 (e.g., Arabic or Hebrew text in comments or strings in a program
7060 source file) are appropriately displayed right-to-left. We call such
7061 mixtures of left-to-right and right-to-left text @dfn{bidirectional
7062 text}. This section describes the facilities and options for editing
7063 and displaying bidirectional text.
7065 @cindex logical order
7066 @cindex reading order
7067 @cindex visual order
7068 @cindex unicode bidirectional algorithm
7070 @cindex bidirectional reordering
7071 @cindex reordering, of bidirectional text
7072 Text is stored in Emacs buffers and strings in @dfn{logical} (or
7073 @dfn{reading}) order, i.e., the order in which a human would read
7074 each character. In right-to-left and bidirectional text, the order in
7075 which characters are displayed on the screen (called @dfn{visual
7076 order}) is not the same as logical order; the characters' screen
7077 positions do not increase monotonically with string or buffer
7078 position. In performing this @dfn{bidirectional reordering}, Emacs
7079 follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}),
7080 which is described in Annex #9 of the Unicode standard
7081 (@url{http://www.unicode.org/reports/tr9/}). Emacs provides a ``Full
7082 Bidirectionality'' class implementation of the @acronym{UBA},
7083 consistent with the requirements of the Unicode Standard v8.0.
7085 @defvar bidi-display-reordering
7086 If the value of this buffer-local variable is non-@code{nil} (the
7087 default), Emacs performs bidirectional reordering for display. The
7088 reordering affects buffer text, as well as display strings and overlay
7089 strings from text and overlay properties in the buffer (@pxref{Overlay
7090 Properties}, and @pxref{Display Property}). If the value is
7091 @code{nil}, Emacs does not perform bidirectional reordering in the
7094 The default value of @code{bidi-display-reordering} controls the
7095 reordering of strings which are not directly supplied by a buffer,
7096 including the text displayed in mode lines (@pxref{Mode Line Format})
7097 and header lines (@pxref{Header Lines}).
7100 @cindex unibyte buffers, and bidi reordering
7101 Emacs never reorders the text of a unibyte buffer, even if
7102 @code{bidi-display-reordering} is non-@code{nil} in the buffer. This
7103 is because unibyte buffers contain raw bytes, not characters, and thus
7104 lack the directionality properties required for reordering.
7105 Therefore, to test whether text in a buffer will be reordered for
7106 display, it is not enough to test the value of
7107 @code{bidi-display-reordering} alone. The correct test is this:
7110 (if (and enable-multibyte-characters
7111 bidi-display-reordering)
7112 ;; Buffer is being reordered for display
7116 However, unibyte display and overlay strings @emph{are} reordered if
7117 their parent buffer is reordered. This is because plain-@sc{ascii}
7118 strings are stored by Emacs as unibyte strings. If a unibyte display
7119 or overlay string includes non-@sc{ascii} characters, these characters
7120 are assumed to have left-to-right direction.
7122 @cindex display properties, and bidi reordering of text
7123 Text covered by @code{display} text properties, by overlays with
7124 @code{display} properties whose value is a string, and by any other
7125 properties that replace buffer text, is treated as a single unit when
7126 it is reordered for display. That is, the entire chunk of text
7127 covered by these properties is reordered together. Moreover, the
7128 bidirectional properties of the characters in such a chunk of text are
7129 ignored, and Emacs reorders them as if they were replaced with a
7130 single character @code{U+FFFC}, known as the @dfn{Object Replacement
7131 Character}. This means that placing a display property over a portion
7132 of text may change the way that the surrounding text is reordered for
7133 display. To prevent this unexpected effect, always place such
7134 properties on text whose directionality is identical with text that
7137 @cindex base direction of a paragraph
7138 Each paragraph of bidirectional text has a @dfn{base direction},
7139 either right-to-left or left-to-right. Left-to-right paragraphs are
7140 displayed beginning at the left margin of the window, and are
7141 truncated or continued when the text reaches the right margin.
7142 Right-to-left paragraphs are displayed beginning at the right margin,
7143 and are continued or truncated at the left margin.
7145 By default, Emacs determines the base direction of each paragraph by
7146 looking at the text at its beginning. The precise method of
7147 determining the base direction is specified by the @acronym{UBA}; in a
7148 nutshell, the first character in a paragraph that has an explicit
7149 directionality determines the base direction of the paragraph.
7150 However, sometimes a buffer may need to force a certain base direction
7151 for its paragraphs. For example, buffers containing program source
7152 code should force all paragraphs to be displayed left-to-right. You
7153 can use following variable to do this:
7155 @defvar bidi-paragraph-direction
7156 If the value of this buffer-local variable is the symbol
7157 @code{right-to-left} or @code{left-to-right}, all paragraphs in the
7158 buffer are assumed to have that specified direction. Any other value
7159 is equivalent to @code{nil} (the default), which means to determine
7160 the base direction of each paragraph from its contents.
7162 @cindex @code{prog-mode}, and @code{bidi-paragraph-direction}
7163 Modes for program source code should set this to @code{left-to-right}.
7164 Prog mode does this by default, so modes derived from Prog mode do not
7165 need to set this explicitly (@pxref{Basic Major Modes}).
7168 @defun current-bidi-paragraph-direction &optional buffer
7169 This function returns the paragraph direction at point in the named
7170 @var{buffer}. The returned value is a symbol, either
7171 @code{left-to-right} or @code{right-to-left}. If @var{buffer} is
7172 omitted or @code{nil}, it defaults to the current buffer. If the
7173 buffer-local value of the variable @code{bidi-paragraph-direction} is
7174 non-@code{nil}, the returned value will be identical to that value;
7175 otherwise, the returned value reflects the paragraph direction
7176 determined dynamically by Emacs. For buffers whose value of
7177 @code{bidi-display-reordering} is @code{nil} as well as unibyte
7178 buffers, this function always returns @code{left-to-right}.
7181 @cindex visual-order cursor motion
7182 Sometimes there's a need to move point in strict visual order,
7183 either to the left or to the right of its current screen position.
7184 Emacs provides a primitive to do that.
7186 @defun move-point-visually direction
7187 This function moves point of the currently selected window to the
7188 buffer position that appears immediately to the right or to the left
7189 of point on the screen. If @var{direction} is positive, point will
7190 move one screen position to the right, otherwise it will move one
7191 screen position to the left. Note that, depending on the surrounding
7192 bidirectional context, this could potentially move point many buffer
7193 positions away. If invoked at the end of a screen line, the function
7194 moves point to the rightmost or leftmost screen position of the next
7195 or previous screen line, as appropriate for the value of
7198 The function returns the new buffer position as its value.
7201 @cindex layout on display, and bidirectional text
7202 @cindex jumbled display of bidirectional text
7203 @cindex concatenating bidirectional strings
7204 Bidirectional reordering can have surprising and unpleasant effects
7205 when two strings with bidirectional content are juxtaposed in a
7206 buffer, or otherwise programmatically concatenated into a string of
7207 text. A typical problematic case is when a buffer consists of
7208 sequences of text fields separated by whitespace or punctuation
7209 characters, like Buffer Menu mode or Rmail Summary Mode. Because the
7210 punctuation characters used as separators have @dfn{weak
7211 directionality}, they take on the directionality of surrounding text.
7212 As result, a numeric field that follows a field with bidirectional
7213 content can be displayed @emph{to the left} of the preceding field,
7214 messing up the expected layout. There are several ways to avoid this
7219 Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or
7220 @acronym{LRM}, to the end of each field that may have bidirectional
7221 content, or prepend it to the beginning of the following field. The
7222 function @code{bidi-string-mark-left-to-right}, described below, comes
7223 in handy for this purpose. (In a right-to-left paragraph, use
7224 @code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.) This
7225 is one of the solutions recommended by the UBA.
7228 Include the tab character in the field separator. The tab character
7229 plays the role of @dfn{segment separator} in bidirectional reordering,
7230 causing the text on either side to be reordered separately.
7232 @cindex @code{space} display spec, and bidirectional text
7234 Separate fields with a @code{display} property or overlay with a
7235 property value of the form @code{(space . PROPS)} (@pxref{Specified
7236 Space}). Emacs treats this display specification as a @dfn{paragraph
7237 separator}, and reorders the text on either side separately.
7240 @defun bidi-string-mark-left-to-right string
7241 This function returns its argument @var{string}, possibly modified,
7242 such that the result can be safely concatenated with another string,
7243 or juxtaposed with another string in a buffer, without disrupting the
7244 relative layout of this string and the next one on display. If the
7245 string returned by this function is displayed as part of a
7246 left-to-right paragraph, it will always appear on display to the left
7247 of the text that follows it. The function works by examining the
7248 characters of its argument, and if any of those characters could cause
7249 reordering on display, the function appends the @acronym{LRM}
7250 character to the string. The appended @acronym{LRM} character is made
7251 invisible by giving it an @code{invisible} text property of @code{t}
7252 (@pxref{Invisible Text}).
7255 The reordering algorithm uses the bidirectional properties of the
7256 characters stored as their @code{bidi-class} property
7257 (@pxref{Character Properties}). Lisp programs can change these
7258 properties by calling the @code{put-char-code-property} function.
7259 However, doing this requires a thorough understanding of the
7260 @acronym{UBA}, and is therefore not recommended. Any changes to the
7261 bidirectional properties of a character have global effect: they
7262 affect all Emacs frames and windows.
7264 Similarly, the @code{mirroring} property is used to display the
7265 appropriate mirrored character in the reordered text. Lisp programs
7266 can affect the mirrored display by changing this property. Again, any
7267 such changes affect all of Emacs display.
7269 @cindex overriding bidirectional properties
7270 @cindex directional overrides
7273 The bidirectional properties of characters can be overridden by
7274 inserting into the text special directional control characters,
7275 LEFT-TO-RIGHT OVERRIDE (@acronym{LRO}) and RIGHT-TO-LEFT OVERRIDE
7276 (@acronym{RLO}). Any characters between a @acronym{RLO} and the
7277 following newline or POP DIRECTIONAL FORMATTING (@acronym{PDF})
7278 control character, whichever comes first, will be displayed as if they
7279 were strong right-to-left characters, i.e.@: they will be reversed on
7280 display. Similarly, any characters between @acronym{LRO} and
7281 @acronym{PDF} or newline will display as if they were strong
7282 left-to-right, and will @emph{not} be reversed even if they are strong
7283 right-to-left characters.
7285 @cindex phishing using directional overrides
7286 @cindex malicious use of directional overrides
7287 These overrides are useful when you want to make some text
7288 unaffected by the reordering algorithm, and instead directly control
7289 the display order. But they can also be used for malicious purposes,
7290 known as @dfn{phishing}. Specifically, a URL on a Web page or a link
7291 in an email message can be manipulated to make its visual appearance
7292 unrecognizable, or similar to some popular benign location, while the
7293 real location, interpreted by a browser in the logical order, is very
7296 Emacs provides a primitive that applications can use to detect
7297 instances of text whose bidirectional properties were overridden so as
7298 to make a left-to-right character display as if it were a
7299 right-to-left character, or vise versa.
7301 @defun bidi-find-overridden-directionality from to &optional object
7302 This function looks at the text of the specified @var{object} between
7303 positions @var{from} (inclusive) and @var{to} (exclusive), and returns
7304 the first position where it finds a strong left-to-right character
7305 whose directional properties were forced to display the character as
7306 right-to-left, or for a strong right-to-left character that was forced
7307 to display as left-to-right. If it finds no such characters in the
7308 specified region of text, it returns @code{nil}.
7310 The optional argument @var{object} specifies which text to search, and
7311 defaults to the current buffer. If @var{object} is non-@code{nil}, it
7312 can be some other buffer, or it can be a string or a window. If it is
7313 a string, the function searches that string. If it is a window, the
7314 function searches the buffer displayed in that window. If a buffer
7315 whose text you want to examine is displayed in some window, we
7316 recommend to specify it by that window, rather than pass the buffer to
7317 the function. This is because telling the function about the window
7318 allows it to correctly account for window-specific overlays, which
7319 might change the result of the function if some text in the buffer is
7320 covered by overlays.
7323 @cindex copying bidirectional text, preserve visual order
7324 @cindex visual order, preserve when copying bidirectional text
7325 When text that includes mixed right-to-left and left-to-right
7326 characters and bidirectional controls is copied into a different
7327 location, it can change its visual appearance, and also can affect the
7328 visual appearance of the surrounding text at destination. This is
7329 because reordering of bidirectional text specified by the
7330 @acronym{UBA} has non-trivial context-dependent effects both on the
7331 copied text and on the text at copy destination that will surround it.
7333 Sometimes, a Lisp program may need to preserve the exact visual
7334 appearance of the copied text at destination, and of the text that
7335 surrounds the copy. Lisp programs can use the following function to
7336 achieve that effect.
7338 @defun buffer-substring-with-bidi-context start end &optional no-properties
7339 This function works similar to @code{buffer-substring} (@pxref{Buffer
7340 Contents}), but it prepends and appends to the copied text bidi
7341 directional control characters necessary to preserve the visual
7342 appearance of the text when it is inserted at another place. Optional
7343 argument @var{no-properties}, if non-@code{nil}, means remove the text
7344 properties from the copy of the text.