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 * Buttons:: Adding clickable buttons to Emacs buffers.
31 * Abstract Display:: Emacs's Widget for Object Collections.
32 * Blinking:: How Emacs shows the matching open parenthesis.
33 * Character Display:: How Emacs displays individual characters.
34 * Beeping:: Audible signal to the user.
35 * Window Systems:: Which window system is being used.
36 * Bidirectional Display:: Display of bidirectional scripts, such as
41 @section Refreshing the Screen
42 @cindex refresh the screen
43 @cindex screen refresh
45 The function @code{redraw-frame} clears and redisplays the entire
46 contents of a given frame (@pxref{Frames}). This is useful if the
49 @defun redraw-frame frame
50 This function clears and redisplays frame @var{frame}.
53 Even more powerful is @code{redraw-display}:
55 @deffn Command redraw-display
56 This function clears and redisplays all visible frames.
59 In Emacs, processing user input takes priority over redisplay. If
60 you call these functions when input is available, they don't redisplay
61 immediately, but the requested redisplay does happen
62 eventually---after all the input has been processed.
64 On text terminals, suspending and resuming Emacs normally also
65 refreshes the screen. Some terminal emulators record separate
66 contents for display-oriented programs such as Emacs and for ordinary
67 sequential display. If you are using such a terminal, you might want
68 to inhibit the redisplay on resumption.
70 @defopt no-redraw-on-reenter
71 @cindex suspend (cf. @code{no-redraw-on-reenter})
72 @cindex resume (cf. @code{no-redraw-on-reenter})
73 This variable controls whether Emacs redraws the entire screen after it
74 has been suspended and resumed. Non-@code{nil} means there is no need
75 to redraw, @code{nil} means redrawing is needed. The default is @code{nil}.
78 @node Forcing Redisplay
79 @section Forcing Redisplay
80 @cindex forcing redisplay
82 Emacs normally tries to redisplay the screen whenever it waits for
83 input. With the following function, you can request an immediate
84 attempt to redisplay, in the middle of Lisp code, without actually
87 @defun redisplay &optional force
88 This function tries immediately to redisplay. The optional argument
89 @var{force}, if non-@code{nil}, forces the redisplay to be performed,
90 instead of being preempted if input is pending.
92 The function returns @code{t} if it actually tried to redisplay, and
93 @code{nil} otherwise. A value of @code{t} does not mean that
94 redisplay proceeded to completion; it could have been preempted by
98 @defvar pre-redisplay-function
99 A function run just before redisplay. It is called with one argument,
100 the set of windows to redisplay.
103 Although @code{redisplay} tries immediately to redisplay, it does
104 not change how Emacs decides which parts of its frame(s) to redisplay.
105 By contrast, the following function adds certain windows to the
106 pending redisplay work (as if their contents had completely changed),
107 but does not immediately try to perform redisplay.
109 @defun force-window-update &optional object
110 This function forces some or all windows to be updated the next time
111 Emacs does a redisplay. If @var{object} is a window, that window is
112 to be updated. If @var{object} is a buffer or buffer name, all
113 windows displaying that buffer are to be updated. If @var{object} is
114 @code{nil} (or omitted), all windows are to be updated.
116 This function does not do a redisplay immediately; Emacs does that as
117 it waits for input, or when the function @code{redisplay} is called.
122 @cindex line wrapping
123 @cindex line truncation
124 @cindex continuation lines
125 @cindex @samp{$} in display
126 @cindex @samp{\} in display
128 When a line of text extends beyond the right edge of a window, Emacs
129 can @dfn{continue} the line (make it wrap to the next screen
130 line), or @dfn{truncate} the line (limit it to one screen line). The
131 additional screen lines used to display a long text line are called
132 @dfn{continuation} lines. Continuation is not the same as filling;
133 continuation happens on the screen only, not in the buffer contents,
134 and it breaks a line precisely at the right margin, not at a word
135 boundary. @xref{Filling}.
137 On a graphical display, tiny arrow images in the window fringes
138 indicate truncated and continued lines (@pxref{Fringes}). On a text
139 terminal, a @samp{$} in the rightmost column of the window indicates
140 truncation; a @samp{\} on the rightmost column indicates a line that
141 wraps. (The display table can specify alternate characters to use
142 for this; @pxref{Display Tables}).
144 @defopt truncate-lines
145 If this buffer-local variable is non-@code{nil}, lines that extend
146 beyond the right edge of the window are truncated; otherwise, they are
147 continued. As a special exception, the variable
148 @code{truncate-partial-width-windows} takes precedence in
149 @dfn{partial-width} windows (i.e., windows that do not occupy the
153 @defopt truncate-partial-width-windows
154 @cindex partial-width windows
155 This variable controls line truncation in @dfn{partial-width} windows.
156 A partial-width window is one that does not occupy the entire frame
157 width (@pxref{Splitting Windows}). If the value is @code{nil}, line
158 truncation is determined by the variable @code{truncate-lines} (see
159 above). If the value is an integer @var{n}, lines are truncated if
160 the partial-width window has fewer than @var{n} columns, regardless of
161 the value of @code{truncate-lines}; if the partial-width window has
162 @var{n} or more columns, line truncation is determined by
163 @code{truncate-lines}. For any other non-@code{nil} value, lines are
164 truncated in every partial-width window, regardless of the value of
165 @code{truncate-lines}.
168 When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in
169 a window, that forces truncation.
172 If this buffer-local variable is non-@code{nil}, it defines a
173 @dfn{wrap prefix} which Emacs displays at the start of every
174 continuation line. (If lines are truncated, @code{wrap-prefix} is
175 never used.) Its value may be a string or an image (@pxref{Other
176 Display Specs}), or a stretch of whitespace such as specified by the
177 @code{:width} or @code{:align-to} display properties (@pxref{Specified
178 Space}). The value is interpreted in the same way as a @code{display}
179 text property. @xref{Display Property}.
181 A wrap prefix may also be specified for regions of text, using the
182 @code{wrap-prefix} text or overlay property. This takes precedence
183 over the @code{wrap-prefix} variable. @xref{Special Properties}.
187 If this buffer-local variable is non-@code{nil}, it defines a
188 @dfn{line prefix} which Emacs displays at the start of every
189 non-continuation line. Its value may be a string or an image
190 (@pxref{Other Display Specs}), or a stretch of whitespace such as
191 specified by the @code{:width} or @code{:align-to} display properties
192 (@pxref{Specified Space}). The value is interpreted in the same way
193 as a @code{display} text property. @xref{Display Property}.
195 A line prefix may also be specified for regions of text using the
196 @code{line-prefix} text or overlay property. This takes precedence
197 over the @code{line-prefix} variable. @xref{Special Properties}.
201 If your buffer contains only very short lines, you might find it
202 advisable to set @code{cache-long-scans} to @code{nil}.
204 @defvar cache-long-scans
205 If this variable is non-@code{nil} (the default), various indentation
206 and motion functions, and Emacs redisplay, cache the results of
207 scanning the buffer, and consult the cache to avoid rescanning regions
208 of the buffer unless they are modified.
210 Turning off the cache speeds up processing of short lines somewhat.
212 This variable is automatically buffer-local in every buffer.
217 @section The Echo Area
218 @cindex error display
221 @c FIXME: Why not use @xref{Minibuffers} directly? --xfq
222 The @dfn{echo area} is used for displaying error messages
223 (@pxref{Errors}), for messages made with the @code{message} primitive,
224 and for echoing keystrokes. It is not the same as the minibuffer,
225 despite the fact that the minibuffer appears (when active) in the same
226 place on the screen as the echo area. @xref{Minibuffer,, The
227 Minibuffer, emacs, The GNU Emacs Manual}.
229 Apart from the functions documented in this section, you can print
230 Lisp objects to the echo area by specifying @code{t} as the output
231 stream. @xref{Output Streams}.
234 * Displaying Messages:: Explicitly displaying text in the echo area.
235 * Progress:: Informing user about progress of a long operation.
236 * Logging Messages:: Echo area messages are logged for the user.
237 * Echo Area Customization:: Controlling the echo area.
240 @node Displaying Messages
241 @subsection Displaying Messages in the Echo Area
242 @cindex display message in echo area
244 This section describes the standard functions for displaying
245 messages in the echo area.
247 @defun message format-string &rest arguments
248 This function displays a message in the echo area.
249 @var{format-string} is a format string, and @var{arguments} are the
250 objects for its format specifications, like in the @code{format-message}
251 function (@pxref{Formatting Strings}). The resulting formatted string
252 is displayed in the echo area; if it contains @code{face} text
253 properties, it is displayed with the specified faces (@pxref{Faces}).
254 The string is also added to the @file{*Messages*} buffer, but without
255 text properties (@pxref{Logging Messages}).
257 In a format string containing single quotes, curved quotes @t{‘like
258 this’} and grave quotes @t{`like this'} work better than straight
259 quotes @t{'like this'}, as @code{message} typically formats every
260 straight quote as a curved closing quote.
262 In batch mode, the message is printed to the standard error stream,
263 followed by a newline.
265 When @code{inhibit-message} is non-@code{nil}, no message will be displayed
266 in the echo area, it will only be logged to @samp{*Messages*}.
268 If @var{format-string} is @code{nil} or the empty string,
269 @code{message} clears the echo area; if the echo area has been
270 expanded automatically, this brings it back to its normal size. If
271 the minibuffer is active, this brings the minibuffer contents back
272 onto the screen immediately.
276 (message "Reverting `%s'..." (buffer-name))
277 @print{} Reverting ‘subr.el’...
278 @result{} "Reverting ‘subr.el’..."
282 ---------- Echo Area ----------
283 Reverting ‘subr.el’...
284 ---------- Echo Area ----------
288 To automatically display a message in the echo area or in a pop-buffer,
289 depending on its size, use @code{display-message-or-buffer} (see below).
291 @strong{Warning:} If you want to use your own string as a message
292 verbatim, don't just write @code{(message @var{string})}. If
293 @var{string} contains @samp{%}, @samp{`}, or @samp{'} it may be
294 reformatted, with undesirable results. Instead, use @code{(message
298 @defvar inhibit-message
299 When this variable is non-@code{nil}, @code{message} and related functions
300 will not use the Echo Area to display messages.
303 @defmac with-temp-message message &rest body
304 This construct displays a message in the echo area temporarily, during
305 the execution of @var{body}. It displays @var{message}, executes
306 @var{body}, then returns the value of the last body form while restoring
307 the previous echo area contents.
310 @defun message-or-box format-string &rest arguments
311 This function displays a message like @code{message}, but may display it
312 in a dialog box instead of the echo area. If this function is called in
313 a command that was invoked using the mouse---more precisely, if
314 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
315 @code{nil} or a list---then it uses a dialog box or pop-up menu to
316 display the message. Otherwise, it uses the echo area. (This is the
317 same criterion that @code{y-or-n-p} uses to make a similar decision; see
318 @ref{Yes-or-No Queries}.)
320 You can force use of the mouse or of the echo area by binding
321 @code{last-nonmenu-event} to a suitable value around the call.
324 @defun message-box format-string &rest arguments
326 This function displays a message like @code{message}, but uses a dialog
327 box (or a pop-up menu) whenever that is possible. If it is impossible
328 to use a dialog box or pop-up menu, because the terminal does not
329 support them, then @code{message-box} uses the echo area, like
333 @defun display-message-or-buffer message &optional buffer-name action frame
334 This function displays the message @var{message}, which may be either a
335 string or a buffer. If it is shorter than the maximum height of the
336 echo area, as defined by @code{max-mini-window-height}, it is displayed
337 in the echo area, using @code{message}. Otherwise,
338 @code{display-buffer} is used to show it in a pop-up buffer.
340 Returns either the string shown in the echo area, or when a pop-up
341 buffer is used, the window used to display it.
343 If @var{message} is a string, then the optional argument
344 @var{buffer-name} is the name of the buffer used to display it when a
345 pop-up buffer is used, defaulting to @file{*Message*}. In the case
346 where @var{message} is a string and displayed in the echo area, it is
347 not specified whether the contents are inserted into the buffer anyway.
349 The optional arguments @var{action} and @var{frame} are as for
350 @code{display-buffer}, and only used if a buffer is displayed.
353 @defun current-message
354 This function returns the message currently being displayed in the
355 echo area, or @code{nil} if there is none.
359 @subsection Reporting Operation Progress
360 @cindex progress reporting
362 When an operation can take a while to finish, you should inform the
363 user about the progress it makes. This way the user can estimate
364 remaining time and clearly see that Emacs is busy working, not hung.
365 A convenient way to do this is to use a @dfn{progress reporter}.
367 Here is a working example that does nothing useful:
370 (let ((progress-reporter
371 (make-progress-reporter "Collecting mana for Emacs..."
375 (progress-reporter-update progress-reporter k))
376 (progress-reporter-done progress-reporter))
379 @defun make-progress-reporter message &optional min-value max-value current-value min-change min-time
380 This function creates and returns a progress reporter object, which
381 you will use as an argument for the other functions listed below. The
382 idea is to precompute as much data as possible to make progress
385 When this progress reporter is subsequently used, it will display
386 @var{message} in the echo area, followed by progress percentage.
387 @var{message} is treated as a simple string. If you need it to depend
388 on a filename, for instance, use @code{format-message} before calling this
391 The arguments @var{min-value} and @var{max-value} should be numbers
392 standing for the starting and final states of the operation. For
393 instance, an operation that scans a buffer should set these to the
394 results of @code{point-min} and @code{point-max} correspondingly.
395 @var{max-value} should be greater than @var{min-value}.
397 Alternatively, you can set @var{min-value} and @var{max-value} to
398 @code{nil}. In that case, the progress reporter does not report
399 process percentages; it instead displays a ``spinner'' that rotates a
400 notch each time you update the progress reporter.
402 If @var{min-value} and @var{max-value} are numbers, you can give the
403 argument @var{current-value} a numerical value specifying the initial
404 progress; if omitted, this defaults to @var{min-value}.
406 The remaining arguments control the rate of echo area updates. The
407 progress reporter will wait for at least @var{min-change} more
408 percents of the operation to be completed before printing next
409 message; the default is one percent. @var{min-time} specifies the
410 minimum time in seconds to pass between successive prints; the default
411 is 0.2 seconds. (On some operating systems, the progress reporter may
412 handle fractions of seconds with varying precision).
414 This function calls @code{progress-reporter-update}, so the first
415 message is printed immediately.
418 @defun progress-reporter-update reporter &optional value
419 This function does the main work of reporting progress of your
420 operation. It displays the message of @var{reporter}, followed by
421 progress percentage determined by @var{value}. If percentage is zero,
422 or close enough according to the @var{min-change} and @var{min-time}
423 arguments, then it is omitted from the output.
425 @var{reporter} must be the result of a call to
426 @code{make-progress-reporter}. @var{value} specifies the current
427 state of your operation and must be between @var{min-value} and
428 @var{max-value} (inclusive) as passed to
429 @code{make-progress-reporter}. For instance, if you scan a buffer,
430 then @var{value} should be the result of a call to @code{point}.
432 This function respects @var{min-change} and @var{min-time} as passed
433 to @code{make-progress-reporter} and so does not output new messages
434 on every invocation. It is thus very fast and normally you should not
435 try to reduce the number of calls to it: resulting overhead will most
436 likely negate your effort.
439 @defun progress-reporter-force-update reporter &optional value new-message
440 This function is similar to @code{progress-reporter-update} except
441 that it prints a message in the echo area unconditionally.
443 The first two arguments have the same meaning as for
444 @code{progress-reporter-update}. Optional @var{new-message} allows
445 you to change the message of the @var{reporter}. Since this function
446 always updates the echo area, such a change will be immediately
447 presented to the user.
450 @defun progress-reporter-done reporter
451 This function should be called when the operation is finished. It
452 prints the message of @var{reporter} followed by word @samp{done} in the
455 You should always call this function and not hope for
456 @code{progress-reporter-update} to print @samp{100%}. Firstly, it may
457 never print it, there are many good reasons for this not to happen.
458 Secondly, @samp{done} is more explicit.
461 @defmac dotimes-with-progress-reporter (var count [result]) message body@dots{}
462 This is a convenience macro that works the same way as @code{dotimes}
463 does, but also reports loop progress using the functions described
464 above. It allows you to save some typing.
466 You can rewrite the example in the beginning of this node using
470 (dotimes-with-progress-reporter
472 "Collecting some mana for Emacs..."
477 @node Logging Messages
478 @subsection Logging Messages in @file{*Messages*}
479 @cindex logging echo-area messages
481 Almost all the messages displayed in the echo area are also recorded
482 in the @file{*Messages*} buffer so that the user can refer back to
483 them. This includes all the messages that are output with
484 @code{message}. By default, this buffer is read-only and uses the major
485 mode @code{messages-buffer-mode}. Nothing prevents the user from
486 killing the @file{*Messages*} buffer, but the next display of a message
487 recreates it. Any Lisp code that needs to access the
488 @file{*Messages*} buffer directly and wants to ensure that it exists
489 should use the function @code{messages-buffer}.
491 @defun messages-buffer
492 This function returns the @file{*Messages*} buffer. If it does not
493 exist, it creates it, and switches it to @code{messages-buffer-mode}.
496 @defopt message-log-max
497 This variable specifies how many lines to keep in the @file{*Messages*}
498 buffer. The value @code{t} means there is no limit on how many lines to
499 keep. The value @code{nil} disables message logging entirely. Here's
500 how to display a message and prevent it from being logged:
503 (let (message-log-max)
508 To make @file{*Messages*} more convenient for the user, the logging
509 facility combines successive identical messages. It also combines
510 successive related messages for the sake of two cases: question
511 followed by answer, and a series of progress messages.
513 A question followed by an answer has two messages like the
514 ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
515 and the second is @samp{@var{question}...@var{answer}}. The first
516 message conveys no additional information beyond what's in the second,
517 so logging the second message discards the first from the log.
519 A series of progress messages has successive messages like
520 those produced by @code{make-progress-reporter}. They have the form
521 @samp{@var{base}...@var{how-far}}, where @var{base} is the same each
522 time, while @var{how-far} varies. Logging each message in the series
523 discards the previous one, provided they are consecutive.
525 The functions @code{make-progress-reporter} and @code{y-or-n-p}
526 don't have to do anything special to activate the message log
527 combination feature. It operates whenever two consecutive messages
528 are logged that share a common prefix ending in @samp{...}.
530 @node Echo Area Customization
531 @subsection Echo Area Customization
532 @cindex echo area customization
534 These variables control details of how the echo area works.
536 @defvar cursor-in-echo-area
537 This variable controls where the cursor appears when a message is
538 displayed in the echo area. If it is non-@code{nil}, then the cursor
539 appears at the end of the message. Otherwise, the cursor appears at
540 point---not in the echo area at all.
542 The value is normally @code{nil}; Lisp programs bind it to @code{t}
543 for brief periods of time.
546 @defvar echo-area-clear-hook
547 This normal hook is run whenever the echo area is cleared---either by
548 @code{(message nil)} or for any other reason.
551 @defopt echo-keystrokes
552 This variable determines how much time should elapse before command
553 characters echo. Its value must be a number, and specifies the
554 number of seconds to wait before echoing. If the user types a prefix
555 key (such as @kbd{C-x}) and then delays this many seconds before
556 continuing, the prefix key is echoed in the echo area. (Once echoing
557 begins in a key sequence, all subsequent characters in the same key
558 sequence are echoed immediately.)
560 If the value is zero, then command input is not echoed.
563 @defvar message-truncate-lines
564 Normally, displaying a long message resizes the echo area to display
565 the entire message. But if the variable @code{message-truncate-lines}
566 is non-@code{nil}, the echo area does not resize, and the message is
570 The variable @code{max-mini-window-height}, which specifies the
571 maximum height for resizing minibuffer windows, also applies to the
572 echo area (which is really a special use of the minibuffer window;
573 @pxref{Minibuffer Misc}).
576 @section Reporting Warnings
579 @dfn{Warnings} are a facility for a program to inform the user of a
580 possible problem, but continue running.
583 * Warning Basics:: Warnings concepts and functions to report them.
584 * Warning Variables:: Variables programs bind to customize their warnings.
585 * Warning Options:: Variables users set to control display of warnings.
586 * Delayed Warnings:: Deferring a warning until the end of a command.
590 @subsection Warning Basics
591 @cindex severity level
593 Every warning has a textual message, which explains the problem for
594 the user, and a @dfn{severity level} which is a symbol. Here are the
595 possible severity levels, in order of decreasing severity, and their
600 A problem that will seriously impair Emacs operation soon
601 if you do not attend to it promptly.
603 A report of data or circumstances that are inherently wrong.
605 A report of data or circumstances that are not inherently wrong, but
606 raise suspicion of a possible problem.
608 A report of information that may be useful if you are debugging.
611 When your program encounters invalid input data, it can either
612 signal a Lisp error by calling @code{error} or @code{signal} or report
613 a warning with severity @code{:error}. Signaling a Lisp error is the
614 easiest thing to do, but it means the program cannot continue
615 processing. If you want to take the trouble to implement a way to
616 continue processing despite the bad data, then reporting a warning of
617 severity @code{:error} is the right way to inform the user of the
618 problem. For instance, the Emacs Lisp byte compiler can report an
619 error that way and continue compiling other functions. (If the
620 program signals a Lisp error and then handles it with
621 @code{condition-case}, the user won't see the error message; it could
622 show the message to the user by reporting it as a warning.)
624 @c FIXME: Why use "(bytecomp)" instead of "'bytecomp" or simply
625 @c "bytecomp" here? The parens are part of warning-type-format but
626 @c not part of the warning type. --xfq
628 Each warning has a @dfn{warning type} to classify it. The type is a
629 list of symbols. The first symbol should be the custom group that you
630 use for the program's user options. For example, byte compiler
631 warnings use the warning type @code{(bytecomp)}. You can also
632 subcategorize the warnings, if you wish, by using more symbols in the
635 @defun display-warning type message &optional level buffer-name
636 This function reports a warning, using @var{message} as the message
637 and @var{type} as the warning type. @var{level} should be the
638 severity level, with @code{:warning} being the default.
640 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
641 for logging the warning. By default, it is @file{*Warnings*}.
644 @defun lwarn type level message &rest args
645 This function reports a warning using the value of @code{(format-message
646 @var{message} @var{args}...)} as the message in the @file{*Warnings*}
647 buffer. In other respects it is equivalent to @code{display-warning}.
650 @defun warn message &rest args
651 This function reports a warning using the value of @code{(format-message
652 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
653 type, and @code{:warning} as the severity level. It exists for
654 compatibility only; we recommend not using it, because you should
655 specify a specific warning type.
658 @node Warning Variables
659 @subsection Warning Variables
660 @cindex warning variables
662 Programs can customize how their warnings appear by binding
663 the variables described in this section.
665 @defvar warning-levels
666 This list defines the meaning and severity order of the warning
667 severity levels. Each element defines one severity level,
668 and they are arranged in order of decreasing severity.
670 Each element has the form @code{(@var{level} @var{string}
671 @var{function})}, where @var{level} is the severity level it defines.
672 @var{string} specifies the textual description of this level.
673 @var{string} should use @samp{%s} to specify where to put the warning
674 type information, or it can omit the @samp{%s} so as not to include
677 The optional @var{function}, if non-@code{nil}, is a function to call
678 with no arguments, to get the user's attention.
680 Normally you should not change the value of this variable.
683 @defvar warning-prefix-function
684 If non-@code{nil}, the value is a function to generate prefix text for
685 warnings. Programs can bind the variable to a suitable function.
686 @code{display-warning} calls this function with the warnings buffer
687 current, and the function can insert text in it. That text becomes
688 the beginning of the warning message.
690 The function is called with two arguments, the severity level and its
691 entry in @code{warning-levels}. It should return a list to use as the
692 entry (this value need not be an actual member of
693 @code{warning-levels}). By constructing this value, the function can
694 change the severity of the warning, or specify different handling for
695 a given severity level.
697 If the variable's value is @code{nil} then there is no function
701 @defvar warning-series
702 Programs can bind this variable to @code{t} to say that the next
703 warning should begin a series. When several warnings form a series,
704 that means to leave point on the first warning of the series, rather
705 than keep moving it for each warning so that it appears on the last one.
706 The series ends when the local binding is unbound and
707 @code{warning-series} becomes @code{nil} again.
709 The value can also be a symbol with a function definition. That is
710 equivalent to @code{t}, except that the next warning will also call
711 the function with no arguments with the warnings buffer current. The
712 function can insert text which will serve as a header for the series
715 Once a series has begun, the value is a marker which points to the
716 buffer position in the warnings buffer of the start of the series.
718 The variable's normal value is @code{nil}, which means to handle
719 each warning separately.
722 @defvar warning-fill-prefix
723 When this variable is non-@code{nil}, it specifies a fill prefix to
724 use for filling each warning's text.
727 @defvar warning-type-format
728 This variable specifies the format for displaying the warning type
729 in the warning message. The result of formatting the type this way
730 gets included in the message under the control of the string in the
731 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
732 If you bind it to @code{""} then the warning type won't appear at
736 @node Warning Options
737 @subsection Warning Options
738 @cindex warning options
740 These variables are used by users to control what happens
741 when a Lisp program reports a warning.
743 @defopt warning-minimum-level
744 This user option specifies the minimum severity level that should be
745 shown immediately to the user. The default is @code{:warning}, which
746 means to immediately display all warnings except @code{:debug}
750 @defopt warning-minimum-log-level
751 This user option specifies the minimum severity level that should be
752 logged in the warnings buffer. The default is @code{:warning}, which
753 means to log all warnings except @code{:debug} warnings.
756 @defopt warning-suppress-types
757 This list specifies which warning types should not be displayed
758 immediately for the user. Each element of the list should be a list
759 of symbols. If its elements match the first elements in a warning
760 type, then that warning is not displayed immediately.
763 @defopt warning-suppress-log-types
764 This list specifies which warning types should not be logged in the
765 warnings buffer. Each element of the list should be a list of
766 symbols. If it matches the first few elements in a warning type, then
767 that warning is not logged.
770 @node Delayed Warnings
771 @subsection Delayed Warnings
772 @cindex delayed warnings
774 Sometimes, you may wish to avoid showing a warning while a command is
775 running, and only show it only after the end of the command. You can
776 use the variable @code{delayed-warnings-list} for this.
778 @defvar delayed-warnings-list
779 The value of this variable is a list of warnings to be displayed after
780 the current command has finished. Each element must be a list
783 (@var{type} @var{message} [@var{level} [@var{buffer-name}]])
787 with the same form, and the same meanings, as the argument list of
788 @code{display-warning} (@pxref{Warning Basics}). Immediately after
789 running @code{post-command-hook} (@pxref{Command Overview}), the Emacs
790 command loop displays all the warnings specified by this variable,
791 then resets it to @code{nil}.
794 Programs which need to further customize the delayed warnings
795 mechanism can change the variable @code{delayed-warnings-hook}:
797 @defvar delayed-warnings-hook
798 This is a normal hook which is run by the Emacs command loop, after
799 @code{post-command-hook}, in order to to process and display delayed
802 Its default value is a list of two functions:
805 (collapse-delayed-warnings display-delayed-warnings)
808 @findex collapse-delayed-warnings
809 @findex display-delayed-warnings
811 The function @code{collapse-delayed-warnings} removes repeated entries
812 from @code{delayed-warnings-list}. The function
813 @code{display-delayed-warnings} calls @code{display-warning} on each
814 of the entries in @code{delayed-warnings-list}, in turn, and then sets
815 @code{delayed-warnings-list} to @code{nil}.
819 @section Invisible Text
821 @cindex invisible text
822 You can make characters @dfn{invisible}, so that they do not appear on
823 the screen, with the @code{invisible} property. This can be either a
824 text property (@pxref{Text Properties}) or an overlay property
825 (@pxref{Overlays}). Cursor motion also partly ignores these
826 characters; if the command loop finds that point is inside a range of
827 invisible text after a command, it relocates point to the other side
830 In the simplest case, any non-@code{nil} @code{invisible} property makes
831 a character invisible. This is the default case---if you don't alter
832 the default value of @code{buffer-invisibility-spec}, this is how the
833 @code{invisible} property works. You should normally use @code{t}
834 as the value of the @code{invisible} property if you don't plan
835 to set @code{buffer-invisibility-spec} yourself.
837 More generally, you can use the variable @code{buffer-invisibility-spec}
838 to control which values of the @code{invisible} property make text
839 invisible. This permits you to classify the text into different subsets
840 in advance, by giving them different @code{invisible} values, and
841 subsequently make various subsets visible or invisible by changing the
842 value of @code{buffer-invisibility-spec}.
844 Controlling visibility with @code{buffer-invisibility-spec} is
845 especially useful in a program to display the list of entries in a
846 database. It permits the implementation of convenient filtering
847 commands to view just a part of the entries in the database. Setting
848 this variable is very fast, much faster than scanning all the text in
849 the buffer looking for properties to change.
851 @defvar buffer-invisibility-spec
852 This variable specifies which kinds of @code{invisible} properties
853 actually make a character invisible. Setting this variable makes it
858 A character is invisible if its @code{invisible} property is
859 non-@code{nil}. This is the default.
862 Each element of the list specifies a criterion for invisibility; if a
863 character's @code{invisible} property fits any one of these criteria,
864 the character is invisible. The list can have two kinds of elements:
868 A character is invisible if its @code{invisible} property value is
869 @var{atom} or if it is a list with @var{atom} as a member; comparison
870 is done with @code{eq}.
872 @item (@var{atom} . t)
873 A character is invisible if its @code{invisible} property value is
874 @var{atom} or if it is a list with @var{atom} as a member; comparison
875 is done with @code{eq}. Moreover, a sequence of such characters
876 displays as an ellipsis.
881 Two functions are specifically provided for adding elements to
882 @code{buffer-invisibility-spec} and removing elements from it.
884 @defun add-to-invisibility-spec element
885 This function adds the element @var{element} to
886 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
887 was @code{t}, it changes to a list, @code{(t)}, so that text whose
888 @code{invisible} property is @code{t} remains invisible.
891 @defun remove-from-invisibility-spec element
892 This removes the element @var{element} from
893 @code{buffer-invisibility-spec}. This does nothing if @var{element}
897 A convention for use of @code{buffer-invisibility-spec} is that a
898 major mode should use the mode's own name as an element of
899 @code{buffer-invisibility-spec} and as the value of the
900 @code{invisible} property:
903 ;; @r{If you want to display an ellipsis:}
904 (add-to-invisibility-spec '(my-symbol . t))
905 ;; @r{If you don't want ellipsis:}
906 (add-to-invisibility-spec 'my-symbol)
908 (overlay-put (make-overlay beginning end)
909 'invisible 'my-symbol)
911 ;; @r{When done with the invisibility:}
912 (remove-from-invisibility-spec '(my-symbol . t))
913 ;; @r{Or respectively:}
914 (remove-from-invisibility-spec 'my-symbol)
917 You can check for invisibility using the following function:
919 @defun invisible-p pos-or-prop
920 If @var{pos-or-prop} is a marker or number, this function returns a
921 non-@code{nil} value if the text at that position is invisible.
923 If @var{pos-or-prop} is any other kind of Lisp object, that is taken
924 to mean a possible value of the @code{invisible} text or overlay
925 property. In that case, this function returns a non-@code{nil} value
926 if that value would cause text to become invisible, based on the
927 current value of @code{buffer-invisibility-spec}.
930 @vindex line-move-ignore-invisible
931 Ordinarily, functions that operate on text or move point do not care
932 whether the text is invisible, they process invisible characters and
933 visible characters alike. The user-level line motion commands,
934 such as @code{next-line}, @code{previous-line}, ignore invisible
935 newlines if @code{line-move-ignore-invisible} is non-@code{nil} (the
936 default), i.e., behave like these invisible newlines didn't exist in
937 the buffer, but only because they are explicitly programmed to do so.
939 If a command ends with point inside or at the boundary of
940 invisible text, the main editing loop relocates point to one of the
941 two ends of the invisible text. Emacs chooses the direction of
942 relocation so that it is the same as the overall movement direction of
943 the command; if in doubt, it prefers a position where an inserted char
944 would not inherit the @code{invisible} property. Additionally, if the
945 text is not replaced by an ellipsis and the command only moved within
946 the invisible text, then point is moved one extra character so as to
947 try and reflect the command's movement by a visible movement of the
950 Thus, if the command moved point back to an invisible range (with the usual
951 stickiness), Emacs moves point back to the beginning of that range. If the
952 command moved point forward into an invisible range, Emacs moves point forward
953 to the first visible character that follows the invisible text and then forward
956 These @dfn{adjustments} of point that ended up in the middle of
957 invisible text can be disabled by setting @code{disable-point-adjustment}
958 to a non-@code{nil} value. @xref{Adjusting Point}.
960 Incremental search can make invisible overlays visible temporarily
961 and/or permanently when a match includes invisible text. To enable
962 this, the overlay should have a non-@code{nil}
963 @code{isearch-open-invisible} property. The property value should be a
964 function to be called with the overlay as an argument. This function
965 should make the overlay visible permanently; it is used when the match
966 overlaps the overlay on exit from the search.
968 During the search, such overlays are made temporarily visible by
969 temporarily modifying their invisible and intangible properties. If you
970 want this to be done differently for a certain overlay, give it an
971 @code{isearch-open-invisible-temporary} property which is a function.
972 The function is called with two arguments: the first is the overlay, and
973 the second is @code{nil} to make the overlay visible, or @code{t} to
974 make it invisible again.
976 @node Selective Display
977 @section Selective Display
978 @c @cindex selective display Duplicates selective-display
980 @dfn{Selective display} refers to a pair of related features for
981 hiding certain lines on the screen.
983 @cindex explicit selective display
984 The first variant, explicit selective display, was designed for use in a Lisp
985 program: it controls which lines are hidden by altering the text. This kind of
986 hiding is now obsolete; instead you can get the same effect with the
987 @code{invisible} property (@pxref{Invisible Text}).
989 In the second variant, the choice of lines to hide is made
990 automatically based on indentation. This variant is designed to be a
993 The way you control explicit selective display is by replacing a
994 newline (control-j) with a carriage return (control-m). The text that
995 was formerly a line following that newline is now hidden. Strictly
996 speaking, it is temporarily no longer a line at all, since only
997 newlines can separate lines; it is now part of the previous line.
999 Selective display does not directly affect editing commands. For
1000 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
1001 into hidden text. However, the replacement of newline characters with
1002 carriage return characters affects some editing commands. For
1003 example, @code{next-line} skips hidden lines, since it searches only
1004 for newlines. Modes that use selective display can also define
1005 commands that take account of the newlines, or that control which
1006 parts of the text are hidden.
1008 When you write a selectively displayed buffer into a file, all the
1009 control-m's are output as newlines. This means that when you next read
1010 in the file, it looks OK, with nothing hidden. The selective display
1011 effect is seen only within Emacs.
1013 @defvar selective-display
1014 This buffer-local variable enables selective display. This means that
1015 lines, or portions of lines, may be made hidden.
1019 If the value of @code{selective-display} is @code{t}, then the character
1020 control-m marks the start of hidden text; the control-m, and the rest
1021 of the line following it, are not displayed. This is explicit selective
1025 If the value of @code{selective-display} is a positive integer, then
1026 lines that start with more than that many columns of indentation are not
1030 When some portion of a buffer is hidden, the vertical movement
1031 commands operate as if that portion did not exist, allowing a single
1032 @code{next-line} command to skip any number of hidden lines.
1033 However, character movement commands (such as @code{forward-char}) do
1034 not skip the hidden portion, and it is possible (if tricky) to insert
1035 or delete text in an hidden portion.
1037 In the examples below, we show the @emph{display appearance} of the
1038 buffer @code{foo}, which changes with the value of
1039 @code{selective-display}. The @emph{contents} of the buffer do not
1044 (setq selective-display nil)
1047 ---------- Buffer: foo ----------
1054 ---------- Buffer: foo ----------
1058 (setq selective-display 2)
1061 ---------- Buffer: foo ----------
1066 ---------- Buffer: foo ----------
1071 @defopt selective-display-ellipses
1072 If this buffer-local variable is non-@code{nil}, then Emacs displays
1073 @samp{@dots{}} at the end of a line that is followed by hidden text.
1074 This example is a continuation of the previous one.
1078 (setq selective-display-ellipses t)
1081 ---------- Buffer: foo ----------
1086 ---------- Buffer: foo ----------
1090 You can use a display table to substitute other text for the ellipsis
1091 (@samp{@dots{}}). @xref{Display Tables}.
1094 @node Temporary Displays
1095 @section Temporary Displays
1096 @cindex temporary display
1097 @cindex temporary buffer display
1099 Temporary displays are used by Lisp programs to put output into a
1100 buffer and then present it to the user for perusal rather than for
1101 editing. Many help commands use this feature.
1103 @defmac with-output-to-temp-buffer buffer-name body@dots{}
1104 This function executes the forms in @var{body} while arranging to insert
1105 any output they print into the buffer named @var{buffer-name}, which is
1106 first created if necessary, and put into Help mode. (See the similar
1107 form @code{with-temp-buffer-window} below.) Finally, the buffer is
1108 displayed in some window, but that window is not selected.
1110 If the forms in @var{body} do not change the major mode in the output
1111 buffer, so that it is still Help mode at the end of their execution,
1112 then @code{with-output-to-temp-buffer} makes this buffer read-only at
1113 the end, and also scans it for function and variable names to make them
1114 into clickable cross-references. @xref{Docstring hyperlinks, , Tips for
1115 Documentation Strings}, in particular the item on hyperlinks in
1116 documentation strings, for more details.
1118 The string @var{buffer-name} specifies the temporary buffer, which need
1119 not already exist. The argument must be a string, not a buffer. The
1120 buffer is erased initially (with no questions asked), and it is marked
1121 as unmodified after @code{with-output-to-temp-buffer} exits.
1123 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
1124 temporary buffer, then it evaluates the forms in @var{body}. Output
1125 using the Lisp output functions within @var{body} goes by default to
1126 that buffer (but screen display and messages in the echo area, although
1127 they are ``output'' in the general sense of the word, are not affected).
1128 @xref{Output Functions}.
1130 Several hooks are available for customizing the behavior
1131 of this construct; they are listed below.
1133 The value of the last form in @var{body} is returned.
1137 ---------- Buffer: foo ----------
1138 This is the contents of foo.
1139 ---------- Buffer: foo ----------
1143 (with-output-to-temp-buffer "foo"
1145 (print standard-output))
1146 @result{} #<buffer foo>
1148 ---------- Buffer: foo ----------
1154 ---------- Buffer: foo ----------
1159 @defopt temp-buffer-show-function
1160 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
1161 calls it as a function to do the job of displaying a help buffer. The
1162 function gets one argument, which is the buffer it should display.
1164 It is a good idea for this function to run @code{temp-buffer-show-hook}
1165 just as @code{with-output-to-temp-buffer} normally would, inside of
1166 @code{save-selected-window} and with the chosen window and buffer
1170 @defvar temp-buffer-setup-hook
1171 This normal hook is run by @code{with-output-to-temp-buffer} before
1172 evaluating @var{body}. When the hook runs, the temporary buffer is
1173 current. This hook is normally set up with a function to put the
1174 buffer in Help mode.
1177 @defvar temp-buffer-show-hook
1178 This normal hook is run by @code{with-output-to-temp-buffer} after
1179 displaying the temporary buffer. When the hook runs, the temporary buffer
1180 is current, and the window it was displayed in is selected.
1183 @defmac with-temp-buffer-window buffer-or-name action quit-function body@dots{}
1184 This macro is similar to @code{with-output-to-temp-buffer}. Like that
1185 construct, it executes @var{body} while arranging to insert any output
1186 it prints into the buffer named @var{buffer-or-name} and displays that
1187 buffer in some window. Unlike @code{with-output-to-temp-buffer},
1188 however, it does not automatically switch that buffer to Help mode.
1190 The argument @var{buffer-or-name} specifies the temporary buffer. It
1191 can be either a buffer, which must already exist, or a string, in which
1192 case a buffer of that name is created, if necessary. The buffer is
1193 marked as unmodified and read-only when @code{with-temp-buffer-window}
1196 This macro does not call @code{temp-buffer-show-function}. Rather, it
1197 passes the @var{action} argument to @code{display-buffer}
1198 (@pxref{Choosing Window}) in order to display the buffer.
1200 The value of the last form in @var{body} is returned, unless the
1201 argument @var{quit-function} is specified. In that case, it is called
1202 with two arguments: the window showing the buffer and the result of
1203 @var{body}. The final return value is then whatever @var{quit-function}
1206 @vindex temp-buffer-window-setup-hook
1207 @vindex temp-buffer-window-show-hook
1208 This macro uses the normal hooks @code{temp-buffer-window-setup-hook}
1209 and @code{temp-buffer-window-show-hook} in place of the analogous hooks
1210 run by @code{with-output-to-temp-buffer}.
1213 The two constructs described next are mostly identical to
1214 @code{with-temp-buffer-window} but differ from it as specified:
1216 @defmac with-current-buffer-window buffer-or-name action quit-function &rest body
1217 This macro is like @code{with-temp-buffer-window} but unlike that makes
1218 the buffer specified by @var{buffer-or-name} current for running
1222 @defmac with-displayed-buffer-window buffer-or-name action quit-function &rest body
1223 This macro is like @code{with-current-buffer-window} but unlike that
1224 displays the buffer specified by @var{buffer-or-name} @emph{before}
1228 A window showing a temporary buffer can be fit to the size of that
1229 buffer using the following mode:
1231 @defopt temp-buffer-resize-mode
1232 When this minor mode is enabled, windows showing a temporary buffer are
1233 automatically resized to fit their buffer's contents.
1235 A window is resized if and only if it has been specially created for the
1236 buffer. In particular, windows that have shown another buffer before
1237 are not resized. By default, this mode uses @code{fit-window-to-buffer}
1238 (@pxref{Resizing Windows}) for resizing. You can specify a different
1239 function by customizing the options @code{temp-buffer-max-height} and
1240 @code{temp-buffer-max-width} below.
1243 @defopt temp-buffer-max-height
1244 This option specifies the maximum height (in lines) of a window
1245 displaying a temporary buffer when @code{temp-buffer-resize-mode} is
1246 enabled. It can also be a function to be called to choose the height
1247 for such a buffer. It gets one argument, the buffer, and should return
1248 a positive integer. At the time the function is called, the window to
1249 be resized is selected.
1252 @defopt temp-buffer-max-width
1253 This option specifies the maximum width of a window (in columns)
1254 displaying a temporary buffer when @code{temp-buffer-resize-mode} is
1255 enabled. It can also be a function to be called to choose the width for
1256 such a buffer. It gets one argument, the buffer, and should return a
1257 positive integer. At the time the function is called, the window to be
1258 resized is selected.
1261 The following function uses the current buffer for temporal display:
1263 @defun momentary-string-display string position &optional char message
1264 This function momentarily displays @var{string} in the current buffer at
1265 @var{position}. It has no effect on the undo list or on the buffer's
1266 modification status.
1268 The momentary display remains until the next input event. If the next
1269 input event is @var{char}, @code{momentary-string-display} ignores it
1270 and returns. Otherwise, that event remains buffered for subsequent use
1271 as input. Thus, typing @var{char} will simply remove the string from
1272 the display, while typing (say) @kbd{C-f} will remove the string from
1273 the display and later (presumably) move point forward. The argument
1274 @var{char} is a space by default.
1276 The return value of @code{momentary-string-display} is not meaningful.
1278 If the string @var{string} does not contain control characters, you can
1279 do the same job in a more general way by creating (and then subsequently
1280 deleting) an overlay with a @code{before-string} property.
1281 @xref{Overlay Properties}.
1283 If @var{message} is non-@code{nil}, it is displayed in the echo area
1284 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1285 default message says to type @var{char} to continue.
1287 In this example, point is initially located at the beginning of the
1292 ---------- Buffer: foo ----------
1293 This is the contents of foo.
1294 @point{}Second line.
1295 ---------- Buffer: foo ----------
1299 (momentary-string-display
1300 "**** Important Message! ****"
1302 "Type RET when done reading")
1307 ---------- Buffer: foo ----------
1308 This is the contents of foo.
1309 **** Important Message! ****Second line.
1310 ---------- Buffer: foo ----------
1312 ---------- Echo Area ----------
1313 Type RET when done reading
1314 ---------- Echo Area ----------
1322 @c FIXME: mention intervals in this section?
1324 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1325 the screen, for the sake of presentation features. An overlay is an
1326 object that belongs to a particular buffer, and has a specified
1327 beginning and end. It also has properties that you can examine and set;
1328 these affect the display of the text within the overlay.
1330 @cindex scalability of overlays
1331 @cindex overlays, scalability
1332 The visual effect of an overlay is the same as of the corresponding
1333 text property (@pxref{Text Properties}). However, due to a different
1334 implementation, overlays generally don't scale well (many operations
1335 take a time that is proportional to the number of overlays in the
1336 buffer). If you need to affect the visual appearance of many portions
1337 in the buffer, we recommend using text properties.
1339 An overlay uses markers to record its beginning and end; thus,
1340 editing the text of the buffer adjusts the beginning and end of each
1341 overlay so that it stays with the text. When you create the overlay,
1342 you can specify whether text inserted at the beginning should be
1343 inside the overlay or outside, and likewise for the end of the overlay.
1346 * Managing Overlays:: Creating and moving overlays.
1347 * Overlay Properties:: How to read and set properties.
1348 What properties do to the screen display.
1349 * Finding Overlays:: Searching for overlays.
1352 @node Managing Overlays
1353 @subsection Managing Overlays
1354 @cindex managing overlays
1355 @cindex overlays, managing
1357 This section describes the functions to create, delete and move
1358 overlays, and to examine their contents. Overlay changes are not
1359 recorded in the buffer's undo list, since the overlays are not
1360 part of the buffer's contents.
1362 @defun overlayp object
1363 This function returns @code{t} if @var{object} is an overlay.
1366 @defun make-overlay start end &optional buffer front-advance rear-advance
1367 This function creates and returns an overlay that belongs to
1368 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1369 and @var{end} must specify buffer positions; they may be integers or
1370 markers. If @var{buffer} is omitted, the overlay is created in the
1373 @cindex empty overlay
1374 @cindex overlay, empty
1375 An overlay whose @var{start} and @var{end} specify the same buffer
1376 position is known as @dfn{empty}. A non-empty overlay can become
1377 empty if the text between its @var{start} and @var{end} is deleted.
1378 When that happens, the overlay is by default not deleted, but you can
1379 cause it to be deleted by giving it the @samp{evaporate} property
1380 (@pxref{Overlay Properties, evaporate property}).
1382 The arguments @var{front-advance} and @var{rear-advance} specify the
1383 marker insertion type for the start of the overlay and for the end of
1384 the overlay, respectively. @xref{Marker Insertion Types}. If they
1385 are both @code{nil}, the default, then the overlay extends to include
1386 any text inserted at the beginning, but not text inserted at the end.
1387 If @var{front-advance} is non-@code{nil}, text inserted at the
1388 beginning of the overlay is excluded from the overlay. If
1389 @var{rear-advance} is non-@code{nil}, text inserted at the end of the
1390 overlay is included in the overlay.
1393 @defun overlay-start overlay
1394 This function returns the position at which @var{overlay} starts,
1398 @defun overlay-end overlay
1399 This function returns the position at which @var{overlay} ends,
1403 @defun overlay-buffer overlay
1404 This function returns the buffer that @var{overlay} belongs to. It
1405 returns @code{nil} if @var{overlay} has been deleted.
1408 @defun delete-overlay overlay
1409 This function deletes @var{overlay}. The overlay continues to exist as
1410 a Lisp object, and its property list is unchanged, but it ceases to be
1411 attached to the buffer it belonged to, and ceases to have any effect on
1414 A deleted overlay is not permanently disconnected. You can give it a
1415 position in a buffer again by calling @code{move-overlay}.
1418 @defun move-overlay overlay start end &optional buffer
1419 This function moves @var{overlay} to @var{buffer}, and places its bounds
1420 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1421 must specify buffer positions; they may be integers or markers.
1423 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1424 was already associated with; if @var{overlay} was deleted, it goes into
1427 The return value is @var{overlay}.
1429 This is the only valid way to change the endpoints of an overlay. Do
1430 not try modifying the markers in the overlay by hand, as that fails to
1431 update other vital data structures and can cause some overlays to be
1435 @defun remove-overlays &optional start end name value
1436 This function removes all the overlays between @var{start} and
1437 @var{end} whose property @var{name} has the value @var{value}. It can
1438 move the endpoints of the overlays in the region, or split them.
1440 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1441 the specified region. If @var{start} and/or @var{end} are omitted or
1442 @code{nil}, that means the beginning and end of the buffer respectively.
1443 Therefore, @code{(remove-overlays)} removes all the overlays in the
1447 @defun copy-overlay overlay
1448 This function returns a copy of @var{overlay}. The copy has the same
1449 endpoints and properties as @var{overlay}. However, the marker
1450 insertion type for the start of the overlay and for the end of the
1451 overlay are set to their default values (@pxref{Marker Insertion
1455 Here are some examples:
1458 ;; @r{Create an overlay.}
1459 (setq foo (make-overlay 1 10))
1460 @result{} #<overlay from 1 to 10 in display.texi>
1465 (overlay-buffer foo)
1466 @result{} #<buffer display.texi>
1467 ;; @r{Give it a property we can check later.}
1468 (overlay-put foo 'happy t)
1470 ;; @r{Verify the property is present.}
1471 (overlay-get foo 'happy)
1473 ;; @r{Move the overlay.}
1474 (move-overlay foo 5 20)
1475 @result{} #<overlay from 5 to 20 in display.texi>
1480 ;; @r{Delete the overlay.}
1481 (delete-overlay foo)
1483 ;; @r{Verify it is deleted.}
1485 @result{} #<overlay in no buffer>
1486 ;; @r{A deleted overlay has no position.}
1491 (overlay-buffer foo)
1493 ;; @r{Undelete the overlay.}
1494 (move-overlay foo 1 20)
1495 @result{} #<overlay from 1 to 20 in display.texi>
1496 ;; @r{Verify the results.}
1501 (overlay-buffer foo)
1502 @result{} #<buffer display.texi>
1503 ;; @r{Moving and deleting the overlay does not change its properties.}
1504 (overlay-get foo 'happy)
1508 Emacs stores the overlays of each buffer in two lists, divided
1509 around an arbitrary center position. One list extends backwards
1510 through the buffer from that center position, and the other extends
1511 forwards from that center position. The center position can be anywhere
1514 @defun overlay-recenter pos
1515 This function recenters the overlays of the current buffer around
1516 position @var{pos}. That makes overlay lookup faster for positions
1517 near @var{pos}, but slower for positions far away from @var{pos}.
1520 A loop that scans the buffer forwards, creating overlays, can run
1521 faster if you do @code{(overlay-recenter (point-max))} first.
1523 @node Overlay Properties
1524 @subsection Overlay Properties
1525 @cindex overlay properties
1527 Overlay properties are like text properties in that the properties that
1528 alter how a character is displayed can come from either source. But in
1529 most respects they are different. @xref{Text Properties}, for comparison.
1531 Text properties are considered a part of the text; overlays and
1532 their properties are specifically considered not to be part of the
1533 text. Thus, copying text between various buffers and strings
1534 preserves text properties, but does not try to preserve overlays.
1535 Changing a buffer's text properties marks the buffer as modified,
1536 while moving an overlay or changing its properties does not. Unlike
1537 text property changes, overlay property changes are not recorded in
1538 the buffer's undo list.
1540 Since more than one overlay can specify a property value for the
1541 same character, Emacs lets you specify a priority value of each
1542 overlay. In case two overlays have the same priority value, and one
1543 is nested in the other, then the inner one will have priority over the
1544 outer one. If neither is nested in the other then you should not make
1545 assumptions about which overlay will prevail.
1547 These functions read and set the properties of an overlay:
1549 @defun overlay-get overlay prop
1550 This function returns the value of property @var{prop} recorded in
1551 @var{overlay}, if any. If @var{overlay} does not record any value for
1552 that property, but it does have a @code{category} property which is a
1553 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1557 @defun overlay-put overlay prop value
1558 This function sets the value of property @var{prop} recorded in
1559 @var{overlay} to @var{value}. It returns @var{value}.
1562 @defun overlay-properties overlay
1563 This returns a copy of the property list of @var{overlay}.
1566 See also the function @code{get-char-property} which checks both
1567 overlay properties and text properties for a given character.
1568 @xref{Examining Properties}.
1570 Many overlay properties have special meanings; here is a table
1575 @kindex priority @r{(overlay property)}
1576 This property's value determines the priority of the overlay.
1577 If you want to specify a priority value, use either @code{nil}
1578 (or zero), or a positive integer. Any other value has undefined behavior.
1580 The priority matters when two or more overlays cover the same
1581 character and both specify the same property; the one whose
1582 @code{priority} value is larger overrides the other. For the
1583 @code{face} property, the higher priority overlay's value does not
1584 completely override the other value; instead, its face attributes
1585 override the face attributes of the lower priority @code{face}
1588 Currently, all overlays take priority over text properties.
1590 Note that Emacs sometimes uses non-numeric priority values for some of
1591 its internal overlays, so do not try to do arithmetic on the
1592 priority of an overlay (unless it is one that you created). If you
1593 need to put overlays in priority order, use the @var{sorted} argument
1594 of @code{overlays-at}. @xref{Finding Overlays}.
1597 @kindex window @r{(overlay property)}
1598 If the @code{window} property is non-@code{nil}, then the overlay
1599 applies only on that window.
1602 @kindex category @r{(overlay property)}
1603 If an overlay has a @code{category} property, we call it the
1604 @dfn{category} of the overlay. It should be a symbol. The properties
1605 of the symbol serve as defaults for the properties of the overlay.
1608 @kindex face @r{(overlay property)}
1609 This property controls the appearance of the text (@pxref{Faces}).
1610 The value of the property can be the following:
1614 A face name (a symbol or string).
1617 An anonymous face: a property list of the form @code{(@var{keyword}
1618 @var{value} @dots{})}, where each @var{keyword} is a face attribute
1619 name and @var{value} is a value for that attribute.
1622 A list of faces. Each list element should be either a face name or an
1623 anonymous face. This specifies a face which is an aggregate of the
1624 attributes of each of the listed faces. Faces occurring earlier in
1625 the list have higher priority.
1628 A cons cell of the form @code{(foreground-color . @var{color-name})}
1629 or @code{(background-color . @var{color-name})}. This specifies the
1630 foreground or background color, similar to @code{(:foreground
1631 @var{color-name})} or @code{(:background @var{color-name})}. This
1632 form is supported for backward compatibility only, and should be
1637 @kindex mouse-face @r{(overlay property)}
1638 This property is used instead of @code{face} when the mouse is within
1639 the range of the overlay. However, Emacs ignores all face attributes
1640 from this property that alter the text size (e.g., @code{:height},
1641 @code{:weight}, and @code{:slant}). Those attributes are always the
1642 same as in the unhighlighted text.
1645 @kindex display @r{(overlay property)}
1646 This property activates various features that change the
1647 way text is displayed. For example, it can make text appear taller
1648 or shorter, higher or lower, wider or narrower, or replaced with an image.
1649 @xref{Display Property}.
1652 @kindex help-echo @r{(overlay property)}
1653 If an overlay has a @code{help-echo} property, then when you move the
1654 mouse onto the text in the overlay, Emacs displays a help string in the
1655 echo area, or in the tooltip window. For details see @ref{Text
1659 @kindex field @r{(overlay property)}
1660 @c Copied from Special Properties.
1661 Consecutive characters with the same @code{field} property constitute a
1662 @emph{field}. Some motion functions including @code{forward-word} and
1663 @code{beginning-of-line} stop moving at a field boundary.
1666 @item modification-hooks
1667 @kindex modification-hooks @r{(overlay property)}
1668 This property's value is a list of functions to be called if any
1669 character within the overlay is changed or if text is inserted strictly
1672 The hook functions are called both before and after each change.
1673 If the functions save the information they receive, and compare notes
1674 between calls, they can determine exactly what change has been made
1677 When called before a change, each function receives four arguments: the
1678 overlay, @code{nil}, and the beginning and end of the text range to be
1681 When called after a change, each function receives five arguments: the
1682 overlay, @code{t}, the beginning and end of the text range just
1683 modified, and the length of the pre-change text replaced by that range.
1684 (For an insertion, the pre-change length is zero; for a deletion, that
1685 length is the number of characters deleted, and the post-change
1686 beginning and end are equal.)
1688 If these functions modify the buffer, they should bind
1689 @code{inhibit-modification-hooks} to @code{t} around doing so, to
1690 avoid confusing the internal mechanism that calls these hooks.
1692 Text properties also support the @code{modification-hooks} property,
1693 but the details are somewhat different (@pxref{Special Properties}).
1695 @item insert-in-front-hooks
1696 @kindex insert-in-front-hooks @r{(overlay property)}
1697 This property's value is a list of functions to be called before and
1698 after inserting text right at the beginning of the overlay. The calling
1699 conventions are the same as for the @code{modification-hooks} functions.
1701 @item insert-behind-hooks
1702 @kindex insert-behind-hooks @r{(overlay property)}
1703 This property's value is a list of functions to be called before and
1704 after inserting text right at the end of the overlay. The calling
1705 conventions are the same as for the @code{modification-hooks} functions.
1708 @kindex invisible @r{(overlay property)}
1709 The @code{invisible} property can make the text in the overlay
1710 invisible, which means that it does not appear on the screen.
1711 @xref{Invisible Text}, for details.
1714 @kindex intangible @r{(overlay property)}
1715 The @code{intangible} property on an overlay works just like the
1716 @code{intangible} text property. @xref{Special Properties}, for details.
1718 @item isearch-open-invisible
1719 This property tells incremental search how to make an invisible overlay
1720 visible, permanently, if the final match overlaps it. @xref{Invisible
1723 @item isearch-open-invisible-temporary
1724 This property tells incremental search how to make an invisible overlay
1725 visible, temporarily, during the search. @xref{Invisible Text}.
1728 @kindex before-string @r{(overlay property)}
1729 This property's value is a string to add to the display at the beginning
1730 of the overlay. The string does not appear in the buffer in any
1731 sense---only on the screen.
1734 @kindex after-string @r{(overlay property)}
1735 This property's value is a string to add to the display at the end of
1736 the overlay. The string does not appear in the buffer in any
1737 sense---only on the screen.
1740 This property specifies a display spec to prepend to each
1741 non-continuation line at display-time. @xref{Truncation}.
1744 This property specifies a display spec to prepend to each continuation
1745 line at display-time. @xref{Truncation}.
1748 @kindex evaporate @r{(overlay property)}
1749 If this property is non-@code{nil}, the overlay is deleted automatically
1750 if it becomes empty (i.e., if its length becomes zero). If you give
1751 an empty overlay (@pxref{Managing Overlays, empty overlay}) a
1752 non-@code{nil} @code{evaporate} property, that deletes it immediately.
1753 Note that, unless an overlay has this property, it will not be deleted
1754 when the text between its starting and ending positions is deleted
1758 @cindex keymap of character (and overlays)
1759 @kindex keymap @r{(overlay property)}
1760 If this property is non-@code{nil}, it specifies a keymap for a portion of the
1761 text. This keymap is used when the character after point is within the
1762 overlay, and takes precedence over most other keymaps. @xref{Active Keymaps}.
1765 @kindex local-map @r{(overlay property)}
1766 The @code{local-map} property is similar to @code{keymap} but replaces the
1767 buffer's local map rather than augmenting existing keymaps. This also means it
1768 has lower precedence than minor mode keymaps.
1771 The @code{keymap} and @code{local-map} properties do not affect a
1772 string displayed by the @code{before-string}, @code{after-string}, or
1773 @code{display} properties. This is only relevant for mouse clicks and
1774 other mouse events that fall on the string, since point is never on
1775 the string. To bind special mouse events for the string, assign it a
1776 @code{keymap} or @code{local-map} text property. @xref{Special
1779 @node Finding Overlays
1780 @subsection Searching for Overlays
1781 @cindex searching for overlays
1782 @cindex overlays, searching for
1784 @defun overlays-at pos &optional sorted
1785 This function returns a list of all the overlays that cover the character at
1786 position @var{pos} in the current buffer. If @var{sorted} is non-@code{nil},
1787 the list is in decreasing order of priority, otherwise it is in no particular
1788 order. An overlay contains position @var{pos} if it begins at or before
1789 @var{pos}, and ends after @var{pos}.
1791 To illustrate usage, here is a Lisp function that returns a list of the
1792 overlays that specify property @var{prop} for the character at point:
1795 (defun find-overlays-specifying (prop)
1796 (let ((overlays (overlays-at (point)))
1799 (let ((overlay (car overlays)))
1800 (if (overlay-get overlay prop)
1801 (setq found (cons overlay found))))
1802 (setq overlays (cdr overlays)))
1807 @defun overlays-in beg end
1808 This function returns a list of the overlays that overlap the region
1809 @var{beg} through @var{end}. An overlay overlaps with a region if it
1810 contains one or more characters in the region; empty overlays
1811 (@pxref{Managing Overlays, empty overlay}) overlap if they are at
1812 @var{beg}, strictly between @var{beg} and @var{end}, or at @var{end}
1813 when @var{end} denotes the position at the end of the buffer.
1816 @defun next-overlay-change pos
1817 This function returns the buffer position of the next beginning or end
1818 of an overlay, after @var{pos}. If there is none, it returns
1822 @defun previous-overlay-change pos
1823 This function returns the buffer position of the previous beginning or
1824 end of an overlay, before @var{pos}. If there is none, it returns
1828 As an example, here's a simplified (and inefficient) version of the
1829 primitive function @code{next-single-char-property-change}
1830 (@pxref{Property Search}). It searches forward from position
1831 @var{pos} for the next position where the value of a given property
1832 @code{prop}, as obtained from either overlays or text properties,
1836 (defun next-single-char-property-change (position prop)
1838 (goto-char position)
1839 (let ((propval (get-char-property (point) prop)))
1840 (while (and (not (eobp))
1841 (eq (get-char-property (point) prop) propval))
1842 (goto-char (min (next-overlay-change (point))
1843 (next-single-property-change (point) prop)))))
1847 @node Size of Displayed Text
1848 @section Size of Displayed Text
1849 @cindex size of text on display
1850 @cindex character width on display
1852 Since not all characters have the same width, these functions let you
1853 check the width of a character. @xref{Primitive Indent}, and
1854 @ref{Screen Lines}, for related functions.
1856 @defun char-width char
1857 This function returns the width in columns of the character
1858 @var{char}, if it were displayed in the current buffer (i.e., taking
1859 into account the buffer's display table, if any; @pxref{Display
1860 Tables}). The width of a tab character is usually @code{tab-width}
1861 (@pxref{Usual Display}).
1864 @defun string-width string
1865 This function returns the width in columns of the string @var{string},
1866 if it were displayed in the current buffer and the selected window.
1869 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1870 This function returns the part of @var{string} that fits within
1871 @var{width} columns, as a new string.
1873 If @var{string} does not reach @var{width}, then the result ends where
1874 @var{string} ends. If one multi-column character in @var{string}
1875 extends across the column @var{width}, that character is not included in
1876 the result. Thus, the result can fall short of @var{width} but cannot
1879 The optional argument @var{start-column} specifies the starting column.
1880 If this is non-@code{nil}, then the first @var{start-column} columns of
1881 the string are omitted from the value. If one multi-column character in
1882 @var{string} extends across the column @var{start-column}, that
1883 character is not included.
1885 The optional argument @var{padding}, if non-@code{nil}, is a padding
1886 character added at the beginning and end of the result string, to extend
1887 it to exactly @var{width} columns. The padding character is used at the
1888 end of the result if it falls short of @var{width}. It is also used at
1889 the beginning of the result if one multi-column character in
1890 @var{string} extends across the column @var{start-column}.
1892 @vindex truncate-string-ellipsis
1893 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1894 replace the end of @var{string} (including any padding) if it extends
1895 beyond @var{width}, unless the display width of @var{string} is equal
1896 to or less than the display width of @var{ellipsis}. If
1897 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1898 the value of the variable @code{truncate-string-ellipsis}.
1901 (truncate-string-to-width "\tab\t" 12 4)
1903 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1908 The following function returns the size in pixels of text as if it were
1909 displayed in a given window. This function is used by
1910 @code{fit-window-to-buffer} and @code{fit-frame-to-buffer}
1911 (@pxref{Resizing Windows}) to make a window exactly as large as the text
1914 @defun window-text-pixel-size &optional window from to x-limit y-limit mode-and-header-line
1915 This function returns the size of the text of @var{window}'s buffer in
1916 pixels. @var{window} must be a live window and defaults to the selected
1917 one. The return value is a cons of the maximum pixel-width of any text
1918 line and the maximum pixel-height of all text lines.
1920 The optional argument @var{from}, if non-@code{nil}, specifies the first
1921 text position to consider and defaults to the minimum accessible
1922 position of the buffer. If @var{from} is @code{t}, it uses the minimum
1923 accessible position that is not a newline character. The optional
1924 argument @var{to}, if non-@code{nil}, specifies the last text position
1925 to consider and defaults to the maximum accessible position of the
1926 buffer. If @var{to} is @code{t}, it uses the maximum accessible
1927 position that is not a newline character.
1929 The optional argument @var{x-limit}, if non-@code{nil}, specifies the
1930 maximum pixel-width that can be returned. @var{x-limit} @code{nil} or
1931 omitted, means to use the pixel-width of @var{window}'s body
1932 (@pxref{Window Sizes}); this is useful when the caller does not intend
1933 to change the width of @var{window}. Otherwise, the caller should
1934 specify here the maximum width @var{window}'s body may assume. Text
1935 whose x-coordinate is beyond @var{x-limit} is ignored. Since
1936 calculating the width of long lines can take some time, it's always a
1937 good idea to make this argument as small as needed; in particular, if
1938 the buffer might contain long lines that will be truncated anyway.
1940 The optional argument @var{y-limit}, if non-@code{nil}, specifies the
1941 maximum pixel-height that can be returned. Text lines whose
1942 y-coordinate is beyond @var{y-limit} are ignored. Since calculating the
1943 pixel-height of a large buffer can take some time, it makes sense to
1944 specify this argument; in particular, if the caller does not know the
1947 The optional argument @var{mode-and-header-line} @code{nil} or omitted
1948 means to not include the height of the mode- or header-line of
1949 @var{window} in the return value. If it is either the symbol
1950 @code{mode-line} or @code{header-line}, include only the height of that
1951 line, if present, in the return value. If it is @code{t}, include the
1952 height of both, if present, in the return value.
1957 @section Line Height
1959 @cindex height of a line
1961 The total height of each display line consists of the height of the
1962 contents of the line, plus optional additional vertical line spacing
1963 above or below the display line.
1965 The height of the line contents is the maximum height of any character
1966 or image on that display line, including the final newline if there is
1967 one. (A display line that is continued doesn't include a final
1968 newline.) That is the default line height, if you do nothing to specify
1969 a greater height. (In the most common case, this equals the height of
1970 the corresponding frame's default font, see @ref{Frame Font}.)
1972 There are several ways to explicitly specify a larger line height,
1973 either by specifying an absolute height for the display line, or by
1974 specifying vertical space. However, no matter what you specify, the
1975 actual line height can never be less than the default.
1977 @kindex line-height @r{(text property)}
1978 A newline can have a @code{line-height} text or overlay property
1979 that controls the total height of the display line ending in that
1982 If the property value is @code{t}, the newline character has no
1983 effect on the displayed height of the line---the visible contents
1984 alone determine the height. This is useful for tiling small images
1985 (or image slices) without adding blank areas between the images.
1987 If the property value is a list of the form @code{(@var{height}
1988 @var{total})}, that adds extra space @emph{below} the display line.
1989 First Emacs uses @var{height} as a height spec to control extra space
1990 @emph{above} the line; then it adds enough space @emph{below} the line
1991 to bring the total line height up to @var{total}. In this case, the
1992 other ways to specify the line spacing are ignored.
1995 Any other kind of property value is a height spec, which translates
1996 into a number---the specified line height. There are several ways to
1997 write a height spec; here's how each of them translates into a number:
2001 If the height spec is a positive integer, the height value is that integer.
2003 If the height spec is a float, @var{float}, the numeric height value
2004 is @var{float} times the frame's default line height.
2005 @item (@var{face} . @var{ratio})
2006 If the height spec is a cons of the format shown, the numeric height
2007 is @var{ratio} times the height of face @var{face}. @var{ratio} can
2008 be any type of number, or @code{nil} which means a ratio of 1.
2009 If @var{face} is @code{t}, it refers to the current face.
2010 @item (nil . @var{ratio})
2011 If the height spec is a cons of the format shown, the numeric height
2012 is @var{ratio} times the height of the contents of the line.
2015 Thus, any valid height spec determines the height in pixels, one way
2016 or another. If the line contents' height is less than that, Emacs
2017 adds extra vertical space above the line to achieve the specified
2020 If you don't specify the @code{line-height} property, the line's
2021 height consists of the contents' height plus the line spacing.
2022 There are several ways to specify the line spacing for different
2023 parts of Emacs text.
2025 On graphical terminals, you can specify the line spacing for all
2026 lines in a frame, using the @code{line-spacing} frame parameter
2027 (@pxref{Layout Parameters}). However, if the default value of
2028 @code{line-spacing} is non-@code{nil}, it overrides the
2029 frame's @code{line-spacing} parameter. An integer specifies the
2030 number of pixels put below lines. A floating-point number specifies
2031 the spacing relative to the frame's default line height.
2033 @vindex line-spacing
2034 You can specify the line spacing for all lines in a buffer via the
2035 buffer-local @code{line-spacing} variable. An integer specifies
2036 the number of pixels put below lines. A floating-point number
2037 specifies the spacing relative to the default frame line height. This
2038 overrides line spacings specified for the frame.
2040 @kindex line-spacing @r{(text property)}
2041 Finally, a newline can have a @code{line-spacing} text or overlay
2042 property that overrides the default frame line spacing and the buffer
2043 local @code{line-spacing} variable, for the display line ending in
2046 One way or another, these mechanisms specify a Lisp value for the
2047 spacing of each line. The value is a height spec, and it translates
2048 into a Lisp value as described above. However, in this case the
2049 numeric height value specifies the line spacing, rather than the line
2052 On text terminals, the line spacing cannot be altered.
2058 A @dfn{face} is a collection of graphical attributes for displaying
2059 text: font, foreground color, background color, optional underlining,
2060 etc. Faces control how Emacs displays text in buffers, as well as
2061 other parts of the frame such as the mode line.
2063 @cindex anonymous face
2064 One way to represent a face is as a property list of attributes,
2065 like @code{(:foreground "red" :weight bold)}. Such a list is called
2066 an @dfn{anonymous face}. For example, you can assign an anonymous
2067 face as the value of the @code{face} text property, and Emacs will
2068 display the underlying text with the specified attributes.
2069 @xref{Special Properties}.
2072 More commonly, a face is referred to via a @dfn{face name}: a Lisp
2073 symbol associated with a set of face attributes@footnote{For backward
2074 compatibility, you can also use a string to specify a face name; that
2075 is equivalent to a Lisp symbol with the same name.}. Named faces are
2076 defined using the @code{defface} macro (@pxref{Defining Faces}).
2077 Emacs comes with several standard named faces (@pxref{Basic Faces}).
2079 Many parts of Emacs required named faces, and do not accept
2080 anonymous faces. These include the functions documented in
2081 @ref{Attribute Functions}, and the variable @code{font-lock-keywords}
2082 (@pxref{Search-based Fontification}). Unless otherwise stated, we
2083 will use the term @dfn{face} to refer only to named faces.
2086 This function returns a non-@code{nil} value if @var{object} is a
2087 named face: a Lisp symbol or string which serves as a face name.
2088 Otherwise, it returns @code{nil}.
2092 * Face Attributes:: What is in a face?
2093 * Defining Faces:: How to define a face.
2094 * Attribute Functions:: Functions to examine and set face attributes.
2095 * Displaying Faces:: How Emacs combines the faces specified for a character.
2096 * Face Remapping:: Remapping faces to alternative definitions.
2097 * Face Functions:: How to define and examine faces.
2098 * Auto Faces:: Hook for automatic face assignment.
2099 * Basic Faces:: Faces that are defined by default.
2100 * Font Selection:: Finding the best available font for a face.
2101 * Font Lookup:: Looking up the names of available fonts
2102 and information about them.
2103 * Fontsets:: A fontset is a collection of fonts
2104 that handle a range of character sets.
2105 * Low-Level Font:: Lisp representation for character display fonts.
2108 @node Face Attributes
2109 @subsection Face Attributes
2110 @cindex face attributes
2112 @dfn{Face attributes} determine the visual appearance of a face.
2113 The following table lists all the face attributes, their possible
2114 values, and their effects.
2116 Apart from the values given below, each face attribute can have the
2117 value @code{unspecified}. This special value means that the face
2118 doesn't specify that attribute directly. An @code{unspecified}
2119 attribute tells Emacs to refer instead to a parent face (see the
2120 description @code{:inherit} attribute below); or, failing that, to an
2121 underlying face (@pxref{Displaying Faces}). The @code{default} face
2122 must specify all attributes.
2124 Some of these attributes are meaningful only on certain kinds of
2125 displays. If your display cannot handle a certain attribute, the
2126 attribute is ignored.
2130 Font family or fontset (a string). @xref{Fonts,,, emacs, The GNU
2131 Emacs Manual}, for more information about font families. The function
2132 @code{font-family-list} (see below) returns a list of available family
2133 names. @xref{Fontsets}, for information about fontsets.
2136 The name of the @dfn{font foundry} for the font family specified by
2137 the @code{:family} attribute (a string). @xref{Fonts,,, emacs, The
2141 Relative character width. This should be one of the symbols
2142 @code{ultra-condensed}, @code{extra-condensed}, @code{condensed},
2143 @code{semi-condensed}, @code{normal}, @code{semi-expanded},
2144 @code{expanded}, @code{extra-expanded}, or @code{ultra-expanded}.
2147 The height of the font. In the simplest case, this is an integer in
2148 units of 1/10 point.
2150 The value can also be floating point or a function, which
2151 specifies the height relative to an @dfn{underlying face}
2152 (@pxref{Displaying Faces}). A floating-point value
2153 specifies the amount by which to scale the height of the
2154 underlying face. A function value is called
2155 with one argument, the height of the underlying face, and returns the
2156 height of the new face. If the function is passed an integer
2157 argument, it must return an integer.
2159 The height of the default face must be specified using an integer;
2160 floating point and function values are not allowed.
2163 Font weight---one of the symbols (from densest to faintest)
2164 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
2165 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or
2166 @code{ultra-light}. On text terminals which support
2167 variable-brightness text, any weight greater than normal is displayed
2168 as extra bright, and any weight less than normal is displayed as
2173 Font slant---one of the symbols @code{italic}, @code{oblique},
2174 @code{normal}, @code{reverse-italic}, or @code{reverse-oblique}. On
2175 text terminals that support variable-brightness text, slanted text is
2176 displayed as half-bright.
2179 Foreground color, a string. The value can be a system-defined color
2180 name, or a hexadecimal color specification. @xref{Color Names}. On
2181 black-and-white displays, certain shades of gray are implemented by
2184 @item :distant-foreground
2185 Alternative foreground color, a string. This is like @code{:foreground}
2186 but the color is only used as a foreground when the background color is
2187 near to the foreground that would have been used. This is useful for
2188 example when marking text (i.e., the region face). If the text has a foreground
2189 that is visible with the region face, that foreground is used.
2190 If the foreground is near the region face background,
2191 @code{:distant-foreground} is used instead so the text is readable.
2194 Background color, a string. The value can be a system-defined color
2195 name, or a hexadecimal color specification. @xref{Color Names}.
2197 @cindex underlined text
2199 Whether or not characters should be underlined, and in what
2200 way. The possible values of the @code{:underline} attribute are:
2207 Underline with the foreground color of the face.
2210 Underline in color @var{color}, a string specifying a color.
2212 @item @code{(:color @var{color} :style @var{style})}
2213 @var{color} is either a string, or the symbol @code{foreground-color},
2214 meaning the foreground color of the face. Omitting the attribute
2215 @code{:color} means to use the foreground color of the face.
2216 @var{style} should be a symbol @code{line} or @code{wave}, meaning to
2217 use a straight or wavy line. Omitting the attribute @code{:style}
2218 means to use a straight line.
2221 @cindex overlined text
2223 Whether or not characters should be overlined, and in what color.
2224 If the value is @code{t}, overlining uses the foreground color of the
2225 face. If the value is a string, overlining uses that color. The
2226 value @code{nil} means do not overline.
2228 @cindex strike-through text
2229 @item :strike-through
2230 Whether or not characters should be strike-through, and in what
2231 color. The value is used like that of @code{:overline}.
2236 Whether or not a box should be drawn around characters, its color, the
2237 width of the box lines, and 3D appearance. Here are the possible
2238 values of the @code{:box} attribute, and what they mean:
2245 Draw a box with lines of width 1, in the foreground color.
2248 Draw a box with lines of width 1, in color @var{color}.
2250 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2251 This way you can explicitly specify all aspects of the box. The value
2252 @var{width} specifies the width of the lines to draw; it defaults to
2253 1. A negative width @var{-n} means to draw a line of width @var{n}
2254 that occupies the space of the underlying text, thus avoiding any
2255 increase in the character height or width.
2257 The value @var{color} specifies the color to draw with. The default is
2258 the foreground color of the face for simple boxes, and the background
2259 color of the face for 3D boxes.
2261 The value @var{style} specifies whether to draw a 3D box. If it is
2262 @code{released-button}, the box looks like a 3D button that is not being
2263 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2264 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2268 @item :inverse-video
2269 Whether or not characters should be displayed in inverse video. The
2270 value should be @code{t} (yes) or @code{nil} (no).
2273 The background stipple, a bitmap.
2275 The value can be a string; that should be the name of a file containing
2276 external-format X bitmap data. The file is found in the directories
2277 listed in the variable @code{x-bitmap-file-path}.
2279 Alternatively, the value can specify the bitmap directly, with a list
2280 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2281 @var{width} and @var{height} specify the size in pixels, and
2282 @var{data} is a string containing the raw bits of the bitmap, row by
2283 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2284 in the string (which should be a unibyte string for best results).
2285 This means that each row always occupies at least one whole byte.
2287 If the value is @code{nil}, that means use no stipple pattern.
2289 Normally you do not need to set the stipple attribute, because it is
2290 used automatically to handle certain shades of gray.
2293 The font used to display the face. Its value should be a font object.
2294 @xref{Low-Level Font}, for information about font objects, font specs,
2297 When specifying this attribute using @code{set-face-attribute}
2298 (@pxref{Attribute Functions}), you may also supply a font spec, a font
2299 entity, or a string. Emacs converts such values to an appropriate
2300 font object, and stores that font object as the actual attribute
2301 value. If you specify a string, the contents of the string should be
2302 a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the
2303 font name is an XLFD containing wildcards, Emacs chooses the first
2304 font matching those wildcards. Specifying this attribute also changes
2305 the values of the @code{:family}, @code{:foundry}, @code{:width},
2306 @code{:height}, @code{:weight}, and @code{:slant} attributes.
2308 @cindex inheritance, for faces
2310 The name of a face from which to inherit attributes, or a list of face
2311 names. Attributes from inherited faces are merged into the face like
2312 an underlying face would be, with higher priority than underlying
2313 faces (@pxref{Displaying Faces}). If a list of faces is used,
2314 attributes from faces earlier in the list override those from later
2318 @defun font-family-list &optional frame
2319 This function returns a list of available font family names. The
2320 optional argument @var{frame} specifies the frame on which the text is
2321 to be displayed; if it is @code{nil}, the selected frame is used.
2324 @defopt underline-minimum-offset
2325 This variable specifies the minimum distance between the baseline and
2326 the underline, in pixels, when displaying underlined text.
2329 @defopt x-bitmap-file-path
2330 This variable specifies a list of directories for searching
2331 for bitmap files, for the @code{:stipple} attribute.
2334 @defun bitmap-spec-p object
2335 This returns @code{t} if @var{object} is a valid bitmap specification,
2336 suitable for use with @code{:stipple} (see above). It returns
2337 @code{nil} otherwise.
2340 @node Defining Faces
2341 @subsection Defining Faces
2342 @cindex defining faces
2345 The usual way to define a face is through the @code{defface} macro.
2346 This macro associates a face name (a symbol) with a default @dfn{face
2347 spec}. A face spec is a construct which specifies what attributes a
2348 face should have on any given terminal; for example, a face spec might
2349 specify one foreground color on high-color terminals, and a different
2350 foreground color on low-color terminals.
2352 People are sometimes tempted to create a variable whose value is a
2353 face name. In the vast majority of cases, this is not necessary; the
2354 usual procedure is to define a face with @code{defface}, and then use
2357 @defmac defface face spec doc [keyword value]@dots{}
2358 This macro declares @var{face} as a named face whose default face spec
2359 is given by @var{spec}. You should not quote the symbol @var{face},
2360 and it should not end in @samp{-face} (that would be redundant). The
2361 argument @var{doc} is a documentation string for the face. The
2362 additional @var{keyword} arguments have the same meanings as in
2363 @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}).
2365 If @var{face} already has a default face spec, this macro does
2368 The default face spec determines @var{face}'s appearance when no
2369 customizations are in effect (@pxref{Customization}). If @var{face}
2370 has already been customized (via Custom themes or via customizations
2371 read from the init file), its appearance is determined by the custom
2372 face spec(s), which override the default face spec @var{spec}.
2373 However, if the customizations are subsequently removed, the
2374 appearance of @var{face} will again be determined by its default face
2377 As an exception, if you evaluate a @code{defface} form with
2378 @kbd{C-M-x} in Emacs Lisp mode (@code{eval-defun}), a special feature
2379 of @code{eval-defun} overrides any custom face specs on the face,
2380 causing the face to reflect exactly what the @code{defface} says.
2382 The @var{spec} argument is a @dfn{face spec}, which states how the
2383 face should appear on different kinds of terminals. It should be an
2384 alist whose elements each have the form
2387 (@var{display} . @var{plist})
2391 @var{display} specifies a class of terminals (see below). @var{plist}
2392 is a property list of face attributes and their values, specifying how
2393 the face appears on such terminals. For backward compatibility, you
2394 can also write an element as @code{(@var{display} @var{plist})}.
2396 The @var{display} part of an element of @var{spec} determines which
2397 terminals the element matches. If more than one element of @var{spec}
2398 matches a given terminal, the first element that matches is the one
2399 used for that terminal. There are three possibilities for
2403 @item @code{default}
2404 This element of @var{spec} doesn't match any terminal; instead, it
2405 specifies defaults that apply to all terminals. This element, if
2406 used, must be the first element of @var{spec}. Each of the following
2407 elements can override any or all of these defaults.
2410 This element of @var{spec} matches all terminals. Therefore, any
2411 subsequent elements of @var{spec} are never used. Normally @code{t}
2412 is used in the last (or only) element of @var{spec}.
2415 If @var{display} is a list, each element should have the form
2416 @code{(@var{characteristic} @var{value}@dots{})}. Here
2417 @var{characteristic} specifies a way of classifying terminals, and the
2418 @var{value}s are possible classifications which @var{display} should
2419 apply to. Here are the possible values of @var{characteristic}:
2423 The kind of window system the terminal uses---either @code{graphic}
2424 (any graphics-capable display), @code{x}, @code{pc} (for the MS-DOS
2425 console), @code{w32} (for MS Windows 9X/NT/2K/XP), or @code{tty} (a
2426 non-graphics-capable display). @xref{Window Systems, window-system}.
2429 What kinds of colors the terminal supports---either @code{color},
2430 @code{grayscale}, or @code{mono}.
2433 The kind of background---either @code{light} or @code{dark}.
2436 An integer that represents the minimum number of colors the terminal
2437 should support. This matches a terminal if its
2438 @code{display-color-cells} value is at least the specified integer.
2441 Whether or not the terminal can display the face attributes given in
2442 @var{value}@dots{} (@pxref{Face Attributes}). @xref{Display Face
2443 Attribute Testing}, for more information on exactly how this testing
2447 If an element of @var{display} specifies more than one @var{value} for
2448 a given @var{characteristic}, any of those values is acceptable. If
2449 @var{display} has more than one element, each element should specify a
2450 different @var{characteristic}; then @emph{each} characteristic of the
2451 terminal must match one of the @var{value}s specified for it in
2456 For example, here's the definition of the standard face
2461 '((((class color) (min-colors 88) (background light))
2462 :background "darkseagreen2")
2463 (((class color) (min-colors 88) (background dark))
2464 :background "darkolivegreen")
2465 (((class color) (min-colors 16) (background light))
2466 :background "darkseagreen2")
2467 (((class color) (min-colors 16) (background dark))
2468 :background "darkolivegreen")
2469 (((class color) (min-colors 8))
2470 :background "green" :foreground "black")
2471 (t :inverse-video t))
2472 "Basic face for highlighting."
2473 :group 'basic-faces)
2476 Internally, Emacs stores each face's default spec in its
2477 @code{face-defface-spec} symbol property (@pxref{Symbol Properties}).
2478 The @code{saved-face} property stores any face spec saved by the user
2479 using the customization buffer; the @code{customized-face} property
2480 stores the face spec customized for the current session, but not
2481 saved; and the @code{theme-face} property stores an alist associating
2482 the active customization settings and Custom themes with the face
2483 specs for that face. The face's documentation string is stored in the
2484 @code{face-documentation} property.
2486 Normally, a face is declared just once, using @code{defface}, and
2487 any further changes to its appearance are applied using the Customize
2488 framework (e.g., via the Customize user interface or via the
2489 @code{custom-set-faces} function; @pxref{Applying Customizations}), or
2490 by face remapping (@pxref{Face Remapping}). In the rare event that
2491 you need to change a face spec directly from Lisp, you can use the
2492 @code{face-spec-set} function.
2494 @defun face-spec-set face spec &optional spec-type
2495 This function applies @var{spec} as a face spec for @code{face}.
2496 @var{spec} should be a face spec, as described in the above
2497 documentation for @code{defface}.
2499 This function also defines @var{face} as a valid face name if it is
2500 not already one, and (re)calculates its attributes on existing frames.
2502 @cindex override spec @r{(for a face)}
2503 The argument @var{spec-type} determines which spec to set. If it is
2504 @code{nil} or @code{face-override-spec}, this function sets the
2505 @dfn{override spec}, which overrides over all other face specs on
2506 @var{face}. If it is @code{customized-face} or @code{saved-face},
2507 this function sets the customized spec or the saved custom spec. If
2508 it is @code{face-defface-spec}, this function sets the default face
2509 spec (the same one set by @code{defface}). If it is @code{reset},
2510 this function clears out all customization specs and override specs
2511 from @var{face} (in this case, the value of @var{spec} is ignored).
2512 Any other value of @var{spec-type} is reserved for internal use.
2515 @node Attribute Functions
2516 @subsection Face Attribute Functions
2517 @cindex face attributes, access and modification
2519 This section describes functions for directly accessing and
2520 modifying the attributes of a named face.
2522 @defun face-attribute face attribute &optional frame inherit
2523 This function returns the value of the @var{attribute} attribute for
2524 @var{face} on @var{frame}.
2526 If @var{frame} is @code{nil}, that means the selected frame
2527 (@pxref{Input Focus}). If @var{frame} is @code{t}, this function
2528 returns the value of the specified attribute for newly-created frames
2529 (this is normally @code{unspecified}, unless you have specified some
2530 value using @code{set-face-attribute}; see below).
2532 If @var{inherit} is @code{nil}, only attributes directly defined by
2533 @var{face} are considered, so the return value may be
2534 @code{unspecified}, or a relative value. If @var{inherit} is
2535 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2536 with the faces specified by its @code{:inherit} attribute; however the
2537 return value may still be @code{unspecified} or relative. If
2538 @var{inherit} is a face or a list of faces, then the result is further
2539 merged with that face (or faces), until it becomes specified and
2542 To ensure that the return value is always specified and absolute, use
2543 a value of @code{default} for @var{inherit}; this will resolve any
2544 unspecified or relative values by merging with the @code{default} face
2545 (which is always completely specified).
2550 (face-attribute 'bold :weight)
2555 @c FIXME: Add an index for "relative face attribute", maybe here? --xfq
2556 @defun face-attribute-relative-p attribute value
2557 This function returns non-@code{nil} if @var{value}, when used as the
2558 value of the face attribute @var{attribute}, is relative. This means
2559 it would modify, rather than completely override, any value that comes
2560 from a subsequent face in the face list or that is inherited from
2563 @code{unspecified} is a relative value for all attributes. For
2564 @code{:height}, floating point and function values are also relative.
2569 (face-attribute-relative-p :height 2.0)
2574 @defun face-all-attributes face &optional frame
2575 This function returns an alist of attributes of @var{face}. The
2576 elements of the result are name-value pairs of the form
2577 @w{@code{(@var{attr-name} . @var{attr-value})}}. Optional argument
2578 @var{frame} specifies the frame whose definition of @var{face} to
2579 return; if omitted or @code{nil}, the returned value describes the
2580 default attributes of @var{face} for newly created frames.
2583 @defun merge-face-attribute attribute value1 value2
2584 If @var{value1} is a relative value for the face attribute
2585 @var{attribute}, returns it merged with the underlying value
2586 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2587 face attribute @var{attribute}, returns @var{value1} unchanged.
2590 Normally, Emacs uses the face specs of each face to automatically
2591 calculate its attributes on each frame (@pxref{Defining Faces}). The
2592 function @code{set-face-attribute} can override this calculation by
2593 directly assigning attributes to a face, either on a specific frame or
2594 for all frames. This function is mostly intended for internal usage.
2596 @defun set-face-attribute face frame &rest arguments
2597 This function sets one or more attributes of @var{face} for
2598 @var{frame}. The attributes specifies in this way override the face
2599 spec(s) belonging to @var{face}.
2601 The extra arguments @var{arguments} specify the attributes to set, and
2602 the values for them. They should consist of alternating attribute
2603 names (such as @code{:family} or @code{:underline}) and values. Thus,
2606 (set-face-attribute 'foo nil :weight 'bold :slant 'italic)
2610 sets the attribute @code{:weight} to @code{bold} and the attribute
2611 @code{:slant} to @code{italic}.
2614 If @var{frame} is @code{t}, this function sets the default attributes
2615 for newly created frames. If @var{frame} is @code{nil}, this function
2616 sets the attributes for all existing frames, as well as for newly
2620 The following commands and functions mostly provide compatibility
2621 with old versions of Emacs. They work by calling
2622 @code{set-face-attribute}. Values of @code{t} and @code{nil} for
2623 their @var{frame} argument are handled just like
2624 @code{set-face-attribute} and @code{face-attribute}. The commands
2625 read their arguments using the minibuffer, if called interactively.
2627 @deffn Command set-face-foreground face color &optional frame
2628 @deffnx Command set-face-background face color &optional frame
2629 These set the @code{:foreground} attribute (or @code{:background}
2630 attribute, respectively) of @var{face} to @var{color}.
2633 @deffn Command set-face-stipple face pattern &optional frame
2634 This sets the @code{:stipple} attribute of @var{face} to
2638 @deffn Command set-face-font face font &optional frame
2639 This sets the @code{:font} attribute of @var{face} to @var{font}.
2642 @defun set-face-bold face bold-p &optional frame
2643 This sets the @code{:weight} attribute of @var{face} to @var{normal}
2644 if @var{bold-p} is @code{nil}, and to @var{bold} otherwise.
2647 @defun set-face-italic face italic-p &optional frame
2648 This sets the @code{:slant} attribute of @var{face} to @var{normal} if
2649 @var{italic-p} is @code{nil}, and to @var{italic} otherwise.
2652 @defun set-face-underline face underline &optional frame
2653 This sets the @code{:underline} attribute of @var{face} to
2657 @defun set-face-inverse-video face inverse-video-p &optional frame
2658 This sets the @code{:inverse-video} attribute of @var{face} to
2659 @var{inverse-video-p}.
2662 @deffn Command invert-face face &optional frame
2663 This swaps the foreground and background colors of face @var{face}.
2666 The following functions examine the attributes of a face. They
2667 mostly provide compatibility with old versions of Emacs. If you don't
2668 specify @var{frame}, they refer to the selected frame; @code{t} refers
2669 to the default data for new frames. They return @code{unspecified} if
2670 the face doesn't define any value for that attribute. If
2671 @var{inherit} is @code{nil}, only an attribute directly defined by the
2672 face is returned. If @var{inherit} is non-@code{nil}, any faces
2673 specified by its @code{:inherit} attribute are considered as well, and
2674 if @var{inherit} is a face or a list of faces, then they are also
2675 considered, until a specified attribute is found. To ensure that the
2676 return value is always specified, use a value of @code{default} for
2679 @defun face-font face &optional frame
2680 This function returns the name of the font of face @var{face}.
2683 @defun face-foreground face &optional frame inherit
2684 @defunx face-background face &optional frame inherit
2685 These functions return the foreground color (or background color,
2686 respectively) of face @var{face}, as a string.
2689 @defun face-stipple face &optional frame inherit
2690 This function returns the name of the background stipple pattern of face
2691 @var{face}, or @code{nil} if it doesn't have one.
2694 @defun face-bold-p face &optional frame inherit
2695 This function returns a non-@code{nil} value if the @code{:weight}
2696 attribute of @var{face} is bolder than normal (i.e., one of
2697 @code{semi-bold}, @code{bold}, @code{extra-bold}, or
2698 @code{ultra-bold}). Otherwise, it returns @code{nil}.
2701 @defun face-italic-p face &optional frame inherit
2702 This function returns a non-@code{nil} value if the @code{:slant}
2703 attribute of @var{face} is @code{italic} or @code{oblique}, and
2704 @code{nil} otherwise.
2707 @defun face-underline-p face &optional frame inherit
2708 This function returns non-@code{nil} if face @var{face} specifies
2709 a non-@code{nil} @code{:underline} attribute.
2712 @defun face-inverse-video-p face &optional frame inherit
2713 This function returns non-@code{nil} if face @var{face} specifies
2714 a non-@code{nil} @code{:inverse-video} attribute.
2717 @node Displaying Faces
2718 @subsection Displaying Faces
2719 @cindex displaying faces
2720 @cindex face merging
2722 When Emacs displays a given piece of text, the visual appearance of
2723 the text may be determined by faces drawn from different sources. If
2724 these various sources together specify more than one face for a
2725 particular character, Emacs merges the attributes of the various
2726 faces. Here is the order in which Emacs merges the faces, from
2727 highest to lowest priority:
2731 If the text consists of a special glyph, the glyph can specify a
2732 particular face. @xref{Glyphs}.
2735 If the text lies within an active region, Emacs highlights it using
2736 the @code{region} face. @xref{Standard Faces,,, emacs, The GNU Emacs
2740 If the text lies within an overlay with a non-@code{nil} @code{face}
2741 property, Emacs applies the face(s) specified by that property. If
2742 the overlay has a @code{mouse-face} property and the mouse is near
2743 enough to the overlay, Emacs applies the face or face attributes
2744 specified by the @code{mouse-face} property instead. @xref{Overlay
2747 When multiple overlays cover one character, an overlay with higher
2748 priority overrides those with lower priority. @xref{Overlays}.
2751 If the text contains a @code{face} or @code{mouse-face} property,
2752 Emacs applies the specified faces and face attributes. @xref{Special
2753 Properties}. (This is how Font Lock mode faces are applied.
2754 @xref{Font Lock Mode}.)
2757 If the text lies within the mode line of the selected window, Emacs
2758 applies the @code{mode-line} face. For the mode line of a
2759 non-selected window, Emacs applies the @code{mode-line-inactive} face.
2760 For a header line, Emacs applies the @code{header-line} face.
2763 If any given attribute has not been specified during the preceding
2764 steps, Emacs applies the attribute of the @code{default} face.
2767 At each stage, if a face has a valid @code{:inherit} attribute,
2768 Emacs treats any attribute with an @code{unspecified} value as having
2769 the corresponding value drawn from the parent face(s). @pxref{Face
2770 Attributes}. Note that the parent face(s) may also leave the
2771 attribute unspecified; in that case, the attribute remains unspecified
2772 at the next level of face merging.
2774 @node Face Remapping
2775 @subsection Face Remapping
2776 @cindex face remapping
2778 The variable @code{face-remapping-alist} is used for buffer-local or
2779 global changes in the appearance of a face. For instance, it is used
2780 to implement the @code{text-scale-adjust} command (@pxref{Text
2781 Scale,,, emacs, The GNU Emacs Manual}).
2783 @defvar face-remapping-alist
2784 The value of this variable is an alist whose elements have the form
2785 @code{(@var{face} . @var{remapping})}. This causes Emacs to display
2786 any text having the face @var{face} with @var{remapping}, rather than
2787 the ordinary definition of @var{face}.
2789 @var{remapping} may be any face spec suitable for a @code{face} text
2790 property: either a face (i.e., a face name or a property list of
2791 attribute/value pairs), or a list of faces. For details, see the
2792 description of the @code{face} text property in @ref{Special
2793 Properties}. @var{remapping} serves as the complete specification for
2794 the remapped face---it replaces the normal definition of @var{face},
2795 instead of modifying it.
2797 If @code{face-remapping-alist} is buffer-local, its local value takes
2798 effect only within that buffer.
2800 Note: face remapping is non-recursive. If @var{remapping} references
2801 the same face name @var{face}, either directly or via the
2802 @code{:inherit} attribute of some other face in @var{remapping}, that
2803 reference uses the normal definition of @var{face}. For instance, if
2804 the @code{mode-line} face is remapped using this entry in
2805 @code{face-remapping-alist}:
2808 (mode-line italic mode-line)
2812 then the new definition of the @code{mode-line} face inherits from the
2813 @code{italic} face, and the @emph{normal} (non-remapped) definition of
2814 @code{mode-line} face.
2817 @cindex relative remapping, faces
2818 @cindex base remapping, faces
2819 The following functions implement a higher-level interface to
2820 @code{face-remapping-alist}. Most Lisp code should use these
2821 functions instead of setting @code{face-remapping-alist} directly, to
2822 avoid trampling on remappings applied elsewhere. These functions are
2823 intended for buffer-local remappings, so they all make
2824 @code{face-remapping-alist} buffer-local as a side-effect. They manage
2825 @code{face-remapping-alist} entries of the form
2828 (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec})
2832 where, as explained above, each of the @var{relative-spec-N} and
2833 @var{base-spec} is either a face name, or a property list of
2834 attribute/value pairs. Each of the @dfn{relative remapping} entries,
2835 @var{relative-spec-N}, is managed by the
2836 @code{face-remap-add-relative} and @code{face-remap-remove-relative}
2837 functions; these are intended for simple modifications like changing
2838 the text size. The @dfn{base remapping} entry, @var{base-spec}, has
2839 the lowest priority and is managed by the @code{face-remap-set-base}
2840 and @code{face-remap-reset-base} functions; it is intended for major
2841 modes to remap faces in the buffers they control.
2843 @defun face-remap-add-relative face &rest specs
2844 This function adds the face spec in @var{specs} as relative
2845 remappings for face @var{face} in the current buffer. The remaining
2846 arguments, @var{specs}, should form either a list of face names, or a
2847 property list of attribute/value pairs.
2849 The return value is a Lisp object that serves as a cookie; you can
2850 pass this object as an argument to @code{face-remap-remove-relative}
2851 if you need to remove the remapping later.
2854 ;; Remap the 'escape-glyph' face into a combination
2855 ;; of the 'highlight' and 'italic' faces:
2856 (face-remap-add-relative 'escape-glyph 'highlight 'italic)
2858 ;; Increase the size of the 'default' face by 50%:
2859 (face-remap-add-relative 'default :height 1.5)
2863 @defun face-remap-remove-relative cookie
2864 This function removes a relative remapping previously added by
2865 @code{face-remap-add-relative}. @var{cookie} should be the Lisp
2866 object returned by @code{face-remap-add-relative} when the remapping
2870 @defun face-remap-set-base face &rest specs
2871 This function sets the base remapping of @var{face} in the current
2872 buffer to @var{specs}. If @var{specs} is empty, the default base
2873 remapping is restored, similar to calling @code{face-remap-reset-base}
2874 (see below); note that this is different from @var{specs} containing a
2875 single value @code{nil}, which has the opposite result (the global
2876 definition of @var{face} is ignored).
2878 This overwrites the default @var{base-spec}, which inherits the global
2879 face definition, so it is up to the caller to add such inheritance if
2883 @defun face-remap-reset-base face
2884 This function sets the base remapping of @var{face} to its default
2885 value, which inherits from @var{face}'s global definition.
2888 @node Face Functions
2889 @subsection Functions for Working with Faces
2891 Here are additional functions for creating and working with faces.
2894 This function returns a list of all defined face names.
2898 This function returns the @dfn{face number} of face @var{face}. This
2899 is a number that uniquely identifies a face at low levels within
2900 Emacs. It is seldom necessary to refer to a face by its face number.
2903 @defun face-documentation face
2904 This function returns the documentation string of face @var{face}, or
2905 @code{nil} if none was specified for it.
2908 @defun face-equal face1 face2 &optional frame
2909 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2910 same attributes for display.
2913 @defun face-differs-from-default-p face &optional frame
2914 This returns non-@code{nil} if the face @var{face} displays
2915 differently from the default face.
2919 @cindex alias, for faces
2920 A @dfn{face alias} provides an equivalent name for a face. You can
2921 define a face alias by giving the alias symbol the @code{face-alias}
2922 property, with a value of the target face name. The following example
2923 makes @code{modeline} an alias for the @code{mode-line} face.
2926 (put 'modeline 'face-alias 'mode-line)
2929 @defmac define-obsolete-face-alias obsolete-face current-face when
2930 This macro defines @code{obsolete-face} as an alias for
2931 @var{current-face}, and also marks it as obsolete, indicating that it
2932 may be removed in future. @var{when} should be a string indicating
2933 when @code{obsolete-face} was made obsolete (usually a version number
2938 @subsection Automatic Face Assignment
2939 @cindex automatic face assignment
2940 @cindex faces, automatic choice
2942 This hook is used for automatically assigning faces to text in the
2943 buffer. It is part of the implementation of Jit-Lock mode, used by
2946 @defvar fontification-functions
2947 This variable holds a list of functions that are called by Emacs
2948 redisplay as needed, just before doing redisplay. They are called even
2949 when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this
2950 variable usually holds just one function, @code{jit-lock-function}.
2952 The functions are called in the order listed, with one argument, a
2953 buffer position @var{pos}. Collectively they should attempt to assign
2954 faces to the text in the current buffer starting at @var{pos}.
2956 The functions should record the faces they assign by setting the
2957 @code{face} property. They should also add a non-@code{nil}
2958 @code{fontified} property to all the text they have assigned faces to.
2959 That property tells redisplay that faces have been assigned to that text
2962 It is probably a good idea for the functions to do nothing if the
2963 character after @var{pos} already has a non-@code{nil} @code{fontified}
2964 property, but this is not required. If one function overrides the
2965 assignments made by a previous one, the properties after the last
2966 function finishes are the ones that really matter.
2968 For efficiency, we recommend writing these functions so that they
2969 usually assign faces to around 400 to 600 characters at each call.
2973 @subsection Basic Faces
2976 If your Emacs Lisp program needs to assign some faces to text, it is
2977 often a good idea to use certain existing faces or inherit from them,
2978 rather than defining entirely new faces. This way, if other users
2979 have customized the basic faces to give Emacs a certain look, your
2980 program will fit in without additional customization.
2982 Some of the basic faces defined in Emacs are listed below. In
2983 addition to these, you might want to make use of the Font Lock faces
2984 for syntactic highlighting, if highlighting is not already handled by
2985 Font Lock mode, or if some Font Lock faces are not in use.
2986 @xref{Faces for Font Lock}.
2990 The default face, whose attributes are all specified. All other faces
2991 implicitly inherit from it: any unspecified attribute defaults to the
2992 attribute on this face (@pxref{Face Attributes}).
2999 @itemx variable-pitch
3000 These have the attributes indicated by their names (e.g., @code{bold}
3001 has a bold @code{:weight} attribute), with all other attributes
3002 unspecified (and so given by @code{default}).
3005 For dimmed-out text. For example, it is used for the ignored
3006 part of a filename in the minibuffer (@pxref{Minibuffer File,,
3007 Minibuffers for File Names, emacs, The GNU Emacs Manual}).
3011 For clickable text buttons that send the user to a different
3015 For stretches of text that should temporarily stand out. For example,
3016 it is commonly assigned to the @code{mouse-face} property for cursor
3017 highlighting (@pxref{Special Properties}).
3020 For text matching a search command.
3025 For text concerning errors, warnings, or successes. For example,
3026 these are used for messages in @file{*Compilation*} buffers.
3029 @node Font Selection
3030 @subsection Font Selection
3031 @cindex font selection
3032 @cindex selecting a font
3034 Before Emacs can draw a character on a graphical display, it must
3035 select a @dfn{font} for that character@footnote{In this context, the
3036 term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock
3037 Mode}).}. @xref{Fonts,,, emacs, The GNU Emacs Manual}. Normally,
3038 Emacs automatically chooses a font based on the faces assigned to that
3039 character---specifically, the face attributes @code{:family},
3040 @code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face
3041 Attributes}). The choice of font also depends on the character to be
3042 displayed; some fonts can only display a limited set of characters.
3043 If no available font exactly fits the requirements, Emacs looks for
3044 the @dfn{closest matching font}. The variables in this section
3045 control how Emacs makes this selection.
3047 @defopt face-font-family-alternatives
3048 If a given family is specified but does not exist, this variable
3049 specifies alternative font families to try. Each element should have
3053 (@var{family} @var{alternate-families}@dots{})
3056 If @var{family} is specified but not available, Emacs will try the other
3057 families given in @var{alternate-families}, one by one, until it finds a
3058 family that does exist.
3061 @defopt face-font-selection-order
3062 If there is no font that exactly matches all desired face attributes
3063 (@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}),
3064 this variable specifies the order in which these attributes should be
3065 considered when selecting the closest matching font. The value should
3066 be a list containing those four attribute symbols, in order of
3067 decreasing importance. The default is @code{(:width :height :weight
3070 Font selection first finds the best available matches for the first
3071 attribute in the list; then, among the fonts which are best in that
3072 way, it searches for the best matches in the second attribute, and so
3075 The attributes @code{:weight} and @code{:width} have symbolic values in
3076 a range centered around @code{normal}. Matches that are more extreme
3077 (farther from @code{normal}) are somewhat preferred to matches that are
3078 less extreme (closer to @code{normal}); this is designed to ensure that
3079 non-normal faces contrast with normal ones, whenever possible.
3081 One example of a case where this variable makes a difference is when the
3082 default font has no italic equivalent. With the default ordering, the
3083 @code{italic} face will use a non-italic font that is similar to the
3084 default one. But if you put @code{:slant} before @code{:height}, the
3085 @code{italic} face will use an italic font, even if its height is not
3089 @defopt face-font-registry-alternatives
3090 This variable lets you specify alternative font registries to try, if a
3091 given registry is specified and doesn't exist. Each element should have
3095 (@var{registry} @var{alternate-registries}@dots{})
3098 If @var{registry} is specified but not available, Emacs will try the
3099 other registries given in @var{alternate-registries}, one by one,
3100 until it finds a registry that does exist.
3103 @cindex scalable fonts
3104 Emacs can make use of scalable fonts, but by default it does not use
3107 @defopt scalable-fonts-allowed
3108 This variable controls which scalable fonts to use. A value of
3109 @code{nil}, the default, means do not use scalable fonts. @code{t}
3110 means to use any scalable font that seems appropriate for the text.
3112 Otherwise, the value must be a list of regular expressions. Then a
3113 scalable font is enabled for use if its name matches any regular
3114 expression in the list. For example,
3117 (setq scalable-fonts-allowed '("iso10646-1$"))
3121 allows the use of scalable fonts with registry @code{iso10646-1}.
3124 @defvar face-font-rescale-alist
3125 This variable specifies scaling for certain faces. Its value should
3126 be a list of elements of the form
3129 (@var{fontname-regexp} . @var{scale-factor})
3132 If @var{fontname-regexp} matches the font name that is about to be
3133 used, this says to choose a larger similar font according to the
3134 factor @var{scale-factor}. You would use this feature to normalize
3135 the font size if certain fonts are bigger or smaller than their
3136 nominal heights and widths would suggest.
3140 @subsection Looking Up Fonts
3142 @cindex looking up fonts
3144 @defun x-list-fonts name &optional reference-face frame maximum width
3145 This function returns a list of available font names that match
3146 @var{name}. @var{name} should be a string containing a font name in
3147 either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The
3148 GNU Emacs Manual}). Within an XLFD string, wildcard characters may be
3149 used: the @samp{*} character matches any substring, and the @samp{?}
3150 character matches any single character. Case is ignored when matching
3153 If the optional arguments @var{reference-face} and @var{frame} are
3154 specified, the returned list includes only fonts that are the same
3155 size as @var{reference-face} (a face name) currently is on the frame
3158 The optional argument @var{maximum} sets a limit on how many fonts to
3159 return. If it is non-@code{nil}, then the return value is truncated
3160 after the first @var{maximum} matching fonts. Specifying a small
3161 value for @var{maximum} can make this function much faster, in cases
3162 where many fonts match the pattern.
3164 The optional argument @var{width} specifies a desired font width. If
3165 it is non-@code{nil}, the function only returns those fonts whose
3166 characters are (on average) @var{width} times as wide as
3167 @var{reference-face}.
3170 @defun x-family-fonts &optional family frame
3171 This function returns a list describing the available fonts for family
3172 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
3173 this list applies to all families, and therefore, it contains all
3174 available fonts. Otherwise, @var{family} must be a string; it may
3175 contain the wildcards @samp{?} and @samp{*}.
3177 The list describes the display that @var{frame} is on; if @var{frame} is
3178 omitted or @code{nil}, it applies to the selected frame's display
3179 (@pxref{Input Focus}).
3181 Each element in the list is a vector of the following form:
3184 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
3185 @var{fixed-p} @var{full} @var{registry-and-encoding}]
3188 The first five elements correspond to face attributes; if you
3189 specify these attributes for a face, it will use this font.
3191 The last three elements give additional information about the font.
3192 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
3193 @var{full} is the full name of the font, and
3194 @var{registry-and-encoding} is a string giving the registry and
3195 encoding of the font.
3199 @subsection Fontsets
3202 A @dfn{fontset} is a list of fonts, each assigned to a range of
3203 character codes. An individual font cannot display the whole range of
3204 characters that Emacs supports, but a fontset can. Fontsets have names,
3205 just as fonts do, and you can use a fontset name in place of a font name
3206 when you specify the font for a frame or a face. Here is
3207 information about defining a fontset under Lisp program control.
3209 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
3210 This function defines a new fontset according to the specification
3211 string @var{fontset-spec}. The string should have this format:
3214 @var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}}
3218 Whitespace characters before and after the commas are ignored.
3220 The first part of the string, @var{fontpattern}, should have the form of
3221 a standard X font name, except that the last two fields should be
3222 @samp{fontset-@var{alias}}.
3224 The new fontset has two names, one long and one short. The long name is
3225 @var{fontpattern} in its entirety. The short name is
3226 @samp{fontset-@var{alias}}. You can refer to the fontset by either
3227 name. If a fontset with the same name already exists, an error is
3228 signaled, unless @var{noerror} is non-@code{nil}, in which case this
3229 function does nothing.
3231 If optional argument @var{style-variant-p} is non-@code{nil}, that says
3232 to create bold, italic and bold-italic variants of the fontset as well.
3233 These variant fontsets do not have a short name, only a long one, which
3234 is made by altering @var{fontpattern} to indicate the bold and/or italic
3237 The specification string also says which fonts to use in the fontset.
3238 See below for the details.
3241 The construct @samp{@var{charset}:@var{font}} specifies which font to
3242 use (in this fontset) for one particular character set. Here,
3243 @var{charset} is the name of a character set, and @var{font} is the font
3244 to use for that character set. You can use this construct any number of
3245 times in the specification string.
3247 For the remaining character sets, those that you don't specify
3248 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
3249 @samp{fontset-@var{alias}} with a value that names one character set.
3250 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
3251 with @samp{ISO8859-1}.
3253 In addition, when several consecutive fields are wildcards, Emacs
3254 collapses them into a single wildcard. This is to prevent use of
3255 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
3256 for editing, and scaling a smaller font is not useful because it is
3257 better to use the smaller font in its own size, which Emacs does.
3259 Thus if @var{fontpattern} is this,
3262 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
3266 the font specification for @acronym{ASCII} characters would be this:
3269 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
3273 and the font specification for Chinese GB2312 characters would be this:
3276 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
3279 You may not have any Chinese font matching the above font
3280 specification. Most X distributions include only Chinese fonts that
3281 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
3282 such a case, @samp{Fontset-@var{n}} can be specified as below:
3285 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
3286 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
3290 Then, the font specifications for all but Chinese GB2312 characters have
3291 @samp{fixed} in the @var{family} field, and the font specification for
3292 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
3295 @defun set-fontset-font name character font-spec &optional frame add
3296 This function modifies the existing fontset @var{name} to use the font
3297 matching with @var{font-spec} for the specified @var{character}.
3299 If @var{name} is @code{nil}, this function modifies the fontset of the
3300 selected frame or that of @var{frame} if @var{frame} is not
3303 If @var{name} is @code{t}, this function modifies the default
3304 fontset, whose short name is @samp{fontset-default}.
3306 In addition to specifying a single codepoint, @var{character} may be a
3307 cons @code{(@var{from} . @var{to})}, where @var{from} and @var{to} are
3308 character codepoints. In that case, use @var{font-spec} for all the
3309 characters in the range @var{from} and @var{to} (inclusive).
3311 @var{character} may be a charset. In that case, use
3312 @var{font-spec} for all character in the charsets.
3314 @var{character} may be a script name. In that case, use
3315 @var{font-spec} for all character in the charsets.
3317 @var{font-spec} may be a font-spec object created by the function
3318 @code{font-spec} (@pxref{Low-Level Font}).
3320 @var{font-spec} may be a cons; @code{(@var{family} . @var{registry})},
3321 where @var{family} is a family name of a font (possibly including a
3322 foundry name at the head), @var{registry} is a registry name of a font
3323 (possibly including an encoding name at the tail).
3325 @var{font-spec} may be a font name string.
3327 @var{font-spec} may be @code{nil}, which explicitly specifies that
3328 there's no font for the specified @var{character}. This is useful,
3329 for example, to avoid expensive system-wide search for fonts for
3330 characters that have no glyphs, like those from the Unicode Private
3333 The optional argument @var{add}, if non-@code{nil}, specifies how to
3334 add @var{font-spec} to the font specifications previously set. If it
3335 is @code{prepend}, @var{font-spec} is prepended. If it is
3336 @code{append}, @var{font-spec} is appended. By default,
3337 @var{font-spec} overrides the previous settings.
3339 For instance, this changes the default fontset to use a font of which
3340 family name is @samp{Kochi Gothic} for all characters belonging to
3341 the charset @code{japanese-jisx0208}.
3344 (set-fontset-font t 'japanese-jisx0208
3345 (font-spec :family "Kochi Gothic"))
3349 @defun char-displayable-p char
3350 This function returns @code{t} if Emacs ought to be able to display
3351 @var{char}. More precisely, if the selected frame's fontset has a
3352 font to display the character set that @var{char} belongs to.
3354 Fontsets can specify a font on a per-character basis; when the fontset
3355 does that, this function's value may not be accurate.
3358 @node Low-Level Font
3359 @subsection Low-Level Font Representation
3360 @cindex font property
3362 Normally, it is not necessary to manipulate fonts directly. In case
3363 you need to do so, this section explains how.
3365 In Emacs Lisp, fonts are represented using three different Lisp
3366 object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font
3369 @defun fontp object &optional type
3370 Return @code{t} if @var{object} is a font object, font spec, or font
3371 entity. Otherwise, return @code{nil}.
3373 The optional argument @var{type}, if non-@code{nil}, determines the
3374 exact type of Lisp object to check for. In that case, @var{type}
3375 should be one of @code{font-object}, @code{font-spec}, or
3380 A font object is a Lisp object that represents a font that Emacs has
3381 @dfn{opened}. Font objects cannot be modified in Lisp, but they can
3384 @defun font-at position &optional window string
3385 Return the font object that is being used to display the character at
3386 position @var{position} in the window @var{window}. If @var{window}
3387 is @code{nil}, it defaults to the selected window. If @var{string} is
3388 @code{nil}, @var{position} specifies a position in the current buffer;
3389 otherwise, @var{string} should be a string, and @var{position}
3390 specifies a position in that string.
3394 A font spec is a Lisp object that contains a set of specifications
3395 that can be used to find a font. More than one font may match the
3396 specifications in a font spec.
3398 @defun font-spec &rest arguments
3399 Return a new font spec using the specifications in @var{arguments},
3400 which should come in @code{property}-@code{value} pairs. The possible
3401 specifications are as follows:
3405 The font name (a string), in either XLFD, Fontconfig, or GTK format.
3406 @xref{Fonts,,, emacs, The GNU Emacs Manual}.
3413 These have the same meanings as the face attributes of the same name.
3414 @xref{Face Attributes}.
3417 The font size---either a non-negative integer that specifies the pixel
3418 size, or a floating-point number that specifies the point size.
3421 Additional typographic style information for the font, such as
3422 @samp{sans}. The value should be a string or a symbol.
3424 @cindex font registry
3426 The charset registry and encoding of the font, such as
3427 @samp{iso8859-1}. The value should be a string or a symbol.
3430 The script that the font must support (a symbol).
3433 The language that the font should support. The value should be a
3434 symbol whose name is a two-letter ISO-639 language name. On X, the
3435 value is matched against the ``Additional Style'' field of the XLFD
3436 name of a font, if it is non-empty. On MS-Windows, fonts matching the
3437 spec are required to support codepages needed for the language.
3438 Currently, only a small set of CJK languages is supported with this
3439 property: @samp{ja}, @samp{ko}, and @samp{zh}.
3442 @cindex OpenType font
3443 The font must be an OpenType font that supports these OpenType
3444 features, provided Emacs is compiled with a library, such as
3445 @samp{libotf} on GNU/Linux, that supports complex text layout for
3446 scripts which need that. The value must be a list of the form
3449 @code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
3452 where @var{script-tag} is the OpenType script tag symbol;
3453 @var{langsys-tag} is the OpenType language system tag symbol, or
3454 @code{nil} to use the default language system; @code{gsub} is a list
3455 of OpenType GSUB feature tag symbols, or @code{nil} if none is
3456 required; and @code{gpos} is a list of OpenType GPOS feature tag
3457 symbols, or @code{nil} if none is required. If @code{gsub} or
3458 @code{gpos} is a list, a @code{nil} element in that list means that
3459 the font must not match any of the remaining tag symbols. The
3460 @code{gpos} element may be omitted.
3464 @defun font-put font-spec property value
3465 Set the font property @var{property} in the font-spec @var{font-spec}
3470 A font entity is a reference to a font that need not be open. Its
3471 properties are intermediate between a font object and a font spec:
3472 like a font object, and unlike a font spec, it refers to a single,
3473 specific font. Unlike a font object, creating a font entity does not
3474 load the contents of that font into computer memory. Emacs may open
3475 multiple font objects of different sizes from a single font entity
3476 referring to a scalable font.
3478 @defun find-font font-spec &optional frame
3479 This function returns a font entity that best matches the font spec
3480 @var{font-spec} on frame @var{frame}. If @var{frame} is @code{nil},
3481 it defaults to the selected frame.
3484 @defun list-fonts font-spec &optional frame num prefer
3485 This function returns a list of all font entities that match the font
3486 spec @var{font-spec}.
3488 The optional argument @var{frame}, if non-@code{nil}, specifies the
3489 frame on which the fonts are to be displayed. The optional argument
3490 @var{num}, if non-@code{nil}, should be an integer that specifies the
3491 maximum length of the returned list. The optional argument
3492 @var{prefer}, if non-@code{nil}, should be another font spec, which is
3493 used to control the order of the returned list; the returned font
3494 entities are sorted in order of decreasing closeness to that font
3498 If you call @code{set-face-attribute} and pass a font spec, font
3499 entity, or font name string as the value of the @code{:font}
3500 attribute, Emacs opens the best matching font that is available
3501 for display. It then stores the corresponding font object as the
3502 actual value of the @code{:font} attribute for that face.
3504 The following functions can be used to obtain information about a
3505 font. For these functions, the @var{font} argument can be a font
3506 object, a font entity, or a font spec.
3508 @defun font-get font property
3509 This function returns the value of the font property @var{property}
3512 If @var{font} is a font spec and the font spec does not specify
3513 @var{property}, the return value is @code{nil}. If @var{font} is a
3514 font object or font entity, the value for the @var{:script} property
3515 may be a list of scripts supported by the font.
3518 @defun font-face-attributes font &optional frame
3519 This function returns a list of face attributes corresponding to
3520 @var{font}. The optional argument @var{frame} specifies the frame on
3521 which the font is to be displayed. If it is @code{nil}, the selected
3522 frame is used. The return value has the form
3525 (:family @var{family} :height @var{height} :weight @var{weight}
3526 :slant @var{slant} :width @var{width})
3529 where the values of @var{family}, @var{height}, @var{weight},
3530 @var{slant}, and @var{width} are face attribute values. Some of these
3531 key-attribute pairs may be omitted from the list if they are not
3532 specified by @var{font}.
3535 @defun font-xlfd-name font &optional fold-wildcards
3536 This function returns the XLFD (X Logical Font Descriptor), a string,
3537 matching @var{font}. @xref{Fonts,,, emacs, The GNU Emacs Manual}, for
3538 information about XLFDs. If the name is too long for an XLFD (which
3539 can contain at most 255 characters), the function returns @code{nil}.
3541 If the optional argument @var{fold-wildcards} is non-@code{nil},
3542 consecutive wildcards in the XLFD are folded into one.
3545 The following two functions return important information about a font.
3547 @defun font-info name &optional frame
3548 This function returns information about a font specified by its
3549 @var{name}, a string, as it is used on @var{frame}. If @var{frame} is
3550 omitted or @code{nil}, it defaults to the selected frame.
3552 The value returned by the function is a vector of the form
3553 @code{[@var{opened-name} @var{full-name} @var{size} @var{height}
3554 @var{baseline-offset} @var{relative-compose} @var{default-ascent}
3555 @var{max-width} @var{ascent} @var{descent} @var{space-width}
3556 @var{average-width} @var{filename} @var{capability}]}. Here's the
3557 description of each components of this vector:
3561 The name used to open the font, a string.
3564 The full name of the font, a string.
3567 The pixel size of the font.
3570 The height of the font in pixels.
3572 @item baseline-offset
3573 The offset in pixels from the @acronym{ASCII} baseline, positive
3576 @item relative-compose
3577 @itemx default-ascent
3578 Numbers controlling how to compose characters.
3582 The ascent and descent of this font. The sum of these two numbers
3583 should be equal to the value of @var{height} above.
3586 The width, in pixels, of the font's space character.
3589 The average width of the font characters. If this is zero, Emacs uses
3590 the value of @var{space-width} instead, when it calculates text layout
3594 The file name of the font as a string. This can be @code{nil} if the
3595 font back-end does not provide a way to find out the font's file name.
3598 A list whose first element is a symbol representing the font type, one
3599 of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
3600 @code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
3601 additional elements describing the @sc{gsub} and @sc{gpos} features
3602 supported by the font. Each of these elements is a list of the form
3603 @code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
3604 @dots{})}, where @var{script} is a symbol representing an OpenType
3605 script tag, @var{langsys} is a symbol representing an OpenType langsys
3606 tag (or @code{nil}, which stands for the default langsys), and each
3607 @var{feature} is a symbol representing an OpenType feature tag.
3611 @defun query-font font-object
3612 This function returns information about a @var{font-object}. (This is
3613 in contrast to @code{font-info}, which takes the font name, a string,
3616 The value returned by the function is a vector of the form
3617 @code{[@var{name} @var{filename} @var{pixel-size} @var{max-width}
3618 @var{ascent} @var{descent} @var{space-width} @var{average-width}
3619 @var{capability}]}. Here's the description of each components of this
3624 The font name, a string.
3627 The file name of the font as a string. This can be @code{nil} if the
3628 font back-end does not provide a way to find out the font's file name.
3631 The pixel size of the font used to open the font.
3634 The maximum advance width of the font.
3638 The ascent and descent of this font. The sum of these two numbers
3639 gives the font height.
3642 The width, in pixels, of the font's space character.
3645 The average width of the font characters. If this is zero, Emacs uses
3646 the value of @var{space-width} instead, when it calculates text layout
3650 A list whose first element is a symbol representing the font type, one
3651 of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
3652 @code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
3653 additional elements describing the @sc{gsub} and @sc{gpos} features
3654 supported by the font. Each of these elements is a list of the form
3655 @code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
3656 @dots{})}, where @var{script} is a symbol representing an OpenType
3657 script tag, @var{langsys} is a symbol representing an OpenType langsys
3658 tag (or @code{nil}, which stands for the default langsys), and each
3659 @var{feature} is a symbol representing an OpenType feature tag.
3663 @cindex font information for layout
3664 The following four functions return size information about fonts used
3665 by various faces, allowing various layout considerations in Lisp
3666 programs. These functions take face remapping into consideration,
3667 returning information about the remapped face, if the face in question
3668 was remapped. @xref{Face Remapping}.
3670 @defun default-font-width
3671 This function returns the average width in pixels of the font used by
3672 the current buffer's default face.
3675 @defun default-font-height
3676 This function returns the height in pixels of the font used by the
3677 current buffer's default face.
3680 @defun window-font-width &optional window face
3681 This function returns the average width in pixels for the font used by
3682 @var{face} in @var{window}. The specified @var{window} must be a live
3683 window. If @code{nil} or omitted, @var{window} defaults to the
3684 selected window, and @var{face} defaults to the default face in
3688 @defun window-font-height &optional window face
3689 This function returns the height in pixels for the font used by
3690 @var{face} in @var{window}. The specified @var{window} must be a live
3691 window. If @code{nil} or omitted, @var{window} defaults to the
3692 selected window, and @var{face} defaults to the default face in
3700 On graphical displays, Emacs draws @dfn{fringes} next to each
3701 window: thin vertical strips down the sides which can display bitmaps
3702 indicating truncation, continuation, horizontal scrolling, and so on.
3705 * Fringe Size/Pos:: Specifying where to put the window fringes.
3706 * Fringe Indicators:: Displaying indicator icons in the window fringes.
3707 * Fringe Cursors:: Displaying cursors in the right fringe.
3708 * Fringe Bitmaps:: Specifying bitmaps for fringe indicators.
3709 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
3710 * Overlay Arrow:: Display of an arrow to indicate position.
3713 @node Fringe Size/Pos
3714 @subsection Fringe Size and Position
3716 The following buffer-local variables control the position and width
3717 of fringes in windows showing that buffer.
3719 @defvar fringes-outside-margins
3720 The fringes normally appear between the display margins and the window
3721 text. If the value is non-@code{nil}, they appear outside the display
3722 margins. @xref{Display Margins}.
3725 @defvar left-fringe-width
3726 This variable, if non-@code{nil}, specifies the width of the left
3727 fringe in pixels. A value of @code{nil} means to use the left fringe
3728 width from the window's frame.
3731 @defvar right-fringe-width
3732 This variable, if non-@code{nil}, specifies the width of the right
3733 fringe in pixels. A value of @code{nil} means to use the right fringe
3734 width from the window's frame.
3737 Any buffer which does not specify values for these variables uses
3738 the values specified by the @code{left-fringe} and @code{right-fringe}
3739 frame parameters (@pxref{Layout Parameters}).
3741 The above variables actually take effect via the function
3742 @code{set-window-buffer} (@pxref{Buffers and Windows}), which calls
3743 @code{set-window-fringes} as a subroutine. If you change one of these
3744 variables, the fringe display is not updated in existing windows
3745 showing the buffer, unless you call @code{set-window-buffer} again in
3746 each affected window. You can also use @code{set-window-fringes} to
3747 control the fringe display in individual windows.
3749 @defun set-window-fringes window left &optional right outside-margins
3750 This function sets the fringe widths of window @var{window}.
3751 If @var{window} is @code{nil}, the selected window is used.
3753 The argument @var{left} specifies the width in pixels of the left
3754 fringe, and likewise @var{right} for the right fringe. A value of
3755 @code{nil} for either one stands for the default width. If
3756 @var{outside-margins} is non-@code{nil}, that specifies that fringes
3757 should appear outside of the display margins.
3760 @defun window-fringes &optional window
3761 This function returns information about the fringes of a window
3762 @var{window}. If @var{window} is omitted or @code{nil}, the selected
3763 window is used. The value has the form @code{(@var{left-width}
3764 @var{right-width} @var{outside-margins})}.
3768 @node Fringe Indicators
3769 @subsection Fringe Indicators
3770 @cindex fringe indicators
3771 @cindex indicators, fringe
3773 @dfn{Fringe indicators} are tiny icons displayed in the window
3774 fringe to indicate truncated or continued lines, buffer boundaries,
3777 @defopt indicate-empty-lines
3778 @cindex fringes, and empty line indication
3779 @cindex empty lines, indicating
3780 When this is non-@code{nil}, Emacs displays a special glyph in the
3781 fringe of each empty line at the end of the buffer, on graphical
3782 displays. @xref{Fringes}. This variable is automatically
3783 buffer-local in every buffer.
3786 @defopt indicate-buffer-boundaries
3787 @cindex buffer boundaries, indicating
3788 This buffer-local variable controls how the buffer boundaries and
3789 window scrolling are indicated in the window fringes.
3791 Emacs can indicate the buffer boundaries---that is, the first and last
3792 line in the buffer---with angle icons when they appear on the screen.
3793 In addition, Emacs can display an up-arrow in the fringe to show
3794 that there is text above the screen, and a down-arrow to show
3795 there is text below the screen.
3797 There are three kinds of basic values:
3801 Don't display any of these fringe icons.
3803 Display the angle icons and arrows in the left fringe.
3805 Display the angle icons and arrows in the right fringe.
3807 Display the angle icons in the left fringe
3808 and don't display the arrows.
3811 Otherwise the value should be an alist that specifies which fringe
3812 indicators to display and where. Each element of the alist should
3813 have the form @code{(@var{indicator} . @var{position})}. Here,
3814 @var{indicator} is one of @code{top}, @code{bottom}, @code{up},
3815 @code{down}, and @code{t} (which covers all the icons not yet
3816 specified), while @var{position} is one of @code{left}, @code{right}
3819 For example, @code{((top . left) (t . right))} places the top angle
3820 bitmap in left fringe, and the bottom angle bitmap as well as both
3821 arrow bitmaps in right fringe. To show the angle bitmaps in the left
3822 fringe, and no arrow bitmaps, use @code{((top . left) (bottom . left))}.
3825 @defvar fringe-indicator-alist
3826 This buffer-local variable specifies the mapping from logical fringe
3827 indicators to the actual bitmaps displayed in the window fringes. The
3828 value is an alist of elements @code{(@var{indicator}
3829 . @var{bitmaps})}, where @var{indicator} specifies a logical indicator
3830 type and @var{bitmaps} specifies the fringe bitmaps to use for that
3833 Each @var{indicator} should be one of the following symbols:
3836 @item @code{truncation}, @code{continuation}.
3837 Used for truncation and continuation lines.
3839 @item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom}
3840 Used when @code{indicate-buffer-boundaries} is non-@code{nil}:
3841 @code{up} and @code{down} indicate a buffer boundary lying above or
3842 below the window edge; @code{top} and @code{bottom} indicate the
3843 topmost and bottommost buffer text line; and @code{top-bottom}
3844 indicates where there is just one line of text in the buffer.
3846 @item @code{empty-line}
3847 Used to indicate empty lines when @code{indicate-empty-lines} is
3850 @item @code{overlay-arrow}
3851 Used for overlay arrows (@pxref{Overlay Arrow}).
3852 @c Is this used anywhere?
3853 @c @item Unknown bitmap indicator:
3857 Each @var{bitmaps} value may be a list of symbols @code{(@var{left}
3858 @var{right} [@var{left1} @var{right1}])}. The @var{left} and
3859 @var{right} symbols specify the bitmaps shown in the left and/or right
3860 fringe, for the specific indicator. @var{left1} and @var{right1} are
3861 specific to the @code{bottom} and @code{top-bottom} indicators, and
3862 are used to indicate that the last text line has no final newline.
3863 Alternatively, @var{bitmaps} may be a single symbol which is used in
3864 both left and right fringes.
3866 @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how
3867 to define your own. In addition, @code{nil} represents the empty
3868 bitmap (i.e., an indicator that is not shown).
3870 When @code{fringe-indicator-alist} has a buffer-local value, and
3871 there is no bitmap defined for a logical indicator, or the bitmap is
3872 @code{t}, the corresponding value from the default value of
3873 @code{fringe-indicator-alist} is used.
3876 @node Fringe Cursors
3877 @subsection Fringe Cursors
3878 @cindex fringe cursors
3879 @cindex cursor, fringe
3881 When a line is exactly as wide as the window, Emacs displays the
3882 cursor in the right fringe instead of using two lines. Different
3883 bitmaps are used to represent the cursor in the fringe depending on
3884 the current buffer's cursor type.
3886 @defopt overflow-newline-into-fringe
3887 If this is non-@code{nil}, lines exactly as wide as the window (not
3888 counting the final newline character) are not continued. Instead,
3889 when point is at the end of the line, the cursor appears in the right
3893 @defvar fringe-cursor-alist
3894 This variable specifies the mapping from logical cursor type to the
3895 actual fringe bitmaps displayed in the right fringe. The value is an
3896 alist where each element has the form @code{(@var{cursor-type}
3897 . @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to
3898 display cursors of type @var{cursor-type}.
3900 Each @var{cursor-type} should be one of @code{box}, @code{hollow},
3901 @code{bar}, @code{hbar}, or @code{hollow-small}. The first four have
3902 the same meanings as in the @code{cursor-type} frame parameter
3903 (@pxref{Cursor Parameters}). The @code{hollow-small} type is used
3904 instead of @code{hollow} when the normal @code{hollow-rectangle}
3905 bitmap is too tall to fit on a specific display line.
3907 Each @var{bitmap} should be a symbol specifying the fringe bitmap to
3908 be displayed for that logical cursor type.
3910 See the next subsection for details.
3913 @xref{Fringe Bitmaps}.
3916 @c FIXME: I can't find the fringes-indicator-alist variable. Maybe
3917 @c it should be fringe-indicator-alist or fringe-cursor-alist? --xfq
3918 When @code{fringe-cursor-alist} has a buffer-local value, and there is
3919 no bitmap defined for a cursor type, the corresponding value from the
3920 default value of @code{fringes-indicator-alist} is used.
3923 @node Fringe Bitmaps
3924 @subsection Fringe Bitmaps
3925 @cindex fringe bitmaps
3926 @cindex bitmaps, fringe
3928 The @dfn{fringe bitmaps} are the actual bitmaps which represent the
3929 logical fringe indicators for truncated or continued lines, buffer
3930 boundaries, overlay arrows, etc. Each bitmap is represented by a
3933 These symbols are referred to by the variables
3934 @code{fringe-indicator-alist} and @code{fringe-cursor-alist},
3935 described in the previous subsections.
3938 These symbols are referred to by the variable
3939 @code{fringe-indicator-alist}, which maps fringe indicators to bitmaps
3940 (@pxref{Fringe Indicators}), and the variable
3941 @code{fringe-cursor-alist}, which maps fringe cursors to bitmaps
3942 (@pxref{Fringe Cursors}).
3945 Lisp programs can also directly display a bitmap in the left or
3946 right fringe, by using a @code{display} property for one of the
3947 characters appearing in the line (@pxref{Other Display Specs}). Such
3948 a display specification has the form
3951 (@var{fringe} @var{bitmap} [@var{face}])
3955 @var{fringe} is either the symbol @code{left-fringe} or
3956 @code{right-fringe}. @var{bitmap} is a symbol identifying the bitmap
3957 to display. The optional @var{face} names a face whose foreground
3958 color is used to display the bitmap; this face is automatically merged
3959 with the @code{fringe} face.
3961 Here is a list of the standard fringe bitmaps defined in Emacs, and
3962 how they are currently used in Emacs (via
3963 @code{fringe-indicator-alist} and @code{fringe-cursor-alist}):
3966 @item @code{left-arrow}, @code{right-arrow}
3967 Used to indicate truncated lines.
3969 @item @code{left-curly-arrow}, @code{right-curly-arrow}
3970 Used to indicate continued lines.
3972 @item @code{right-triangle}, @code{left-triangle}
3973 The former is used by overlay arrows. The latter is unused.
3975 @item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle}
3976 @itemx @code{bottom-left-angle}, @code{bottom-right-angle}
3977 @itemx @code{top-right-angle}, @code{top-left-angle}
3978 @itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle}
3979 Used to indicate buffer boundaries.
3981 @item @code{filled-rectangle}, @code{hollow-rectangle}
3982 @itemx @code{filled-square}, @code{hollow-square}
3983 @itemx @code{vertical-bar}, @code{horizontal-bar}
3984 Used for different types of fringe cursors.
3986 @item @code{empty-line}, @code{exclamation-mark}, @code{question-mark}, @code{exclamation-mark}
3987 Not used by core Emacs features.
3991 The next subsection describes how to define your own fringe bitmaps.
3993 @defun fringe-bitmaps-at-pos &optional pos window
3994 This function returns the fringe bitmaps of the display line
3995 containing position @var{pos} in window @var{window}. The return
3996 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
3997 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
3998 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
3999 is non-@code{nil} if there is an overlay arrow in the left fringe.
4001 The value is @code{nil} if @var{pos} is not visible in @var{window}.
4002 If @var{window} is @code{nil}, that stands for the selected window.
4003 If @var{pos} is @code{nil}, that stands for the value of point in
4007 @node Customizing Bitmaps
4008 @subsection Customizing Fringe Bitmaps
4009 @cindex fringe bitmaps, customizing
4011 @defun define-fringe-bitmap bitmap bits &optional height width align
4012 This function defines the symbol @var{bitmap} as a new fringe bitmap,
4013 or replaces an existing bitmap with that name.
4015 The argument @var{bits} specifies the image to use. It should be
4016 either a string or a vector of integers, where each element (an
4017 integer) corresponds to one row of the bitmap. Each bit of an integer
4018 corresponds to one pixel of the bitmap, where the low bit corresponds
4019 to the rightmost pixel of the bitmap.
4021 The height is normally the length of @var{bits}. However, you
4022 can specify a different height with non-@code{nil} @var{height}. The width
4023 is normally 8, but you can specify a different width with non-@code{nil}
4024 @var{width}. The width must be an integer between 1 and 16.
4026 The argument @var{align} specifies the positioning of the bitmap
4027 relative to the range of rows where it is used; the default is to
4028 center the bitmap. The allowed values are @code{top}, @code{center},
4031 The @var{align} argument may also be a list @code{(@var{align}
4032 @var{periodic})} where @var{align} is interpreted as described above.
4033 If @var{periodic} is non-@code{nil}, it specifies that the rows in
4034 @code{bits} should be repeated enough times to reach the specified
4038 @defun destroy-fringe-bitmap bitmap
4039 This function destroy the fringe bitmap identified by @var{bitmap}.
4040 If @var{bitmap} identifies a standard fringe bitmap, it actually
4041 restores the standard definition of that bitmap, instead of
4042 eliminating it entirely.
4045 @defun set-fringe-bitmap-face bitmap &optional face
4046 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
4047 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
4048 bitmap's face controls the color to draw it in.
4050 @var{face} is merged with the @code{fringe} face, so normally
4051 @var{face} should specify only the foreground color.
4055 @subsection The Overlay Arrow
4056 @c @cindex overlay arrow Duplicates variable names
4058 The @dfn{overlay arrow} is useful for directing the user's attention
4059 to a particular line in a buffer. For example, in the modes used for
4060 interface to debuggers, the overlay arrow indicates the line of code
4061 about to be executed. This feature has nothing to do with
4062 @dfn{overlays} (@pxref{Overlays}).
4064 @defvar overlay-arrow-string
4065 This variable holds the string to display to call attention to a
4066 particular line, or @code{nil} if the arrow feature is not in use.
4067 On a graphical display the contents of the string are ignored; instead a
4068 glyph is displayed in the fringe area to the left of the display area.
4071 @defvar overlay-arrow-position
4072 This variable holds a marker that indicates where to display the overlay
4073 arrow. It should point at the beginning of a line. On a non-graphical
4074 display the arrow text
4075 appears at the beginning of that line, overlaying any text that would
4076 otherwise appear. Since the arrow is usually short, and the line
4077 usually begins with indentation, normally nothing significant is
4080 The overlay-arrow string is displayed in any given buffer if the value
4081 of @code{overlay-arrow-position} in that buffer points into that
4082 buffer. Thus, it is possible to display multiple overlay arrow strings
4083 by creating buffer-local bindings of @code{overlay-arrow-position}.
4084 However, it is usually cleaner to use
4085 @code{overlay-arrow-variable-list} to achieve this result.
4086 @c !!! overlay-arrow-position: but the overlay string may remain in the display
4087 @c of some other buffer until an update is required. This should be fixed
4091 You can do a similar job by creating an overlay with a
4092 @code{before-string} property. @xref{Overlay Properties}.
4094 You can define multiple overlay arrows via the variable
4095 @code{overlay-arrow-variable-list}.
4097 @defvar overlay-arrow-variable-list
4098 This variable's value is a list of variables, each of which specifies
4099 the position of an overlay arrow. The variable
4100 @code{overlay-arrow-position} has its normal meaning because it is on
4104 Each variable on this list can have properties
4105 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
4106 specify an overlay arrow string (for text terminals) or fringe bitmap
4107 (for graphical terminals) to display at the corresponding overlay
4108 arrow position. If either property is not set, the default
4109 @code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator
4114 @section Scroll Bars
4117 Normally the frame parameter @code{vertical-scroll-bars} controls
4118 whether the windows in the frame have vertical scroll bars, and whether
4119 they are on the left or right. The frame parameter
4120 @code{scroll-bar-width} specifies how wide they are (@code{nil} meaning
4123 The frame parameter @code{horizontal-scroll-bars} controls whether
4124 the windows in the frame have horizontal scroll bars. The frame
4125 parameter @code{scroll-bar-height} specifies how high they are
4126 (@code{nil} meaning the default). @xref{Layout Parameters}.
4128 @vindex horizontal-scroll-bars-available-p
4129 Horizontal scroll bars are not available on all platforms. The
4130 function @code{horizontal-scroll-bars-available-p} which takes no
4131 argument returns non-@code{nil} if they are available on your system.
4133 The following three functions take as argument a live frame which
4134 defaults to the selected one.
4136 @defun frame-current-scroll-bars &optional frame
4137 This function reports the scroll bar types for frame @var{frame}. The
4138 value is a cons cell @code{(@var{vertical-type} .@:
4139 @var{horizontal-type})}, where @var{vertical-type} is either
4140 @code{left}, @code{right}, or @code{nil} (which means no vertical scroll
4141 bar.) @var{horizontal-type} is either @code{bottom} or @code{nil}
4142 (which means no horizontal scroll bar).
4145 @defun frame-scroll-bar-width &optional Lisp_Object &optional frame
4146 This function returns the width of vertical scroll bars of @var{frame}
4150 @defun frame-scroll-bar-height &optional Lisp_Object &optional frame
4151 This function returns the height of horizontal scroll bars of
4152 @var{frame} in pixels.
4155 You can override the frame specific settings for individual windows by
4156 using the following function:
4158 @defun set-window-scroll-bars window &optional width vertical-type height horizontal-type
4159 This function sets the width and/or height and the types of scroll bars
4160 for window @var{window}.
4162 @var{width} specifies the width of the vertical scroll bar in pixels
4163 (@code{nil} means use the width specified for the frame).
4164 @var{vertical-type} specifies whether to have a vertical scroll bar and,
4165 if so, where. The possible values are @code{left}, @code{right},
4166 @code{t}, which means to use the frame's default, and @code{nil} for no
4167 vertical scroll bar.
4169 @var{height} specifies the height of the horizontal scroll bar in pixels
4170 (@code{nil} means use the height specified for the frame).
4171 @var{horizontal-type} specifies whether to have a horizontal scroll bar.
4172 The possible values are @code{bottom}, @code{t}, which means to use the
4173 frame's default, and @code{nil} for no horizontal scroll bar.
4175 If @var{window} is @code{nil}, the selected window is used.
4178 The following four functions take as argument a live window which
4179 defaults to the selected one.
4181 @defun window-scroll-bars &optional window
4182 This function returns a list of the form @code{(@var{width}
4183 @var{columns} @var{vertical-type} @var{height} @var{lines}
4184 @var{horizontal-type})}.
4186 The value @var{width} is the value that was specified for the width of
4187 the vertical scroll bar (which may be @code{nil}); @var{columns} is the
4188 (possibly rounded) number of columns that the vertical scroll bar
4191 The value @var{height} is the value that was specified for the height of
4192 the horizontal scroll bar (which may be @code{nil}); @var{lines} is the
4193 (possibly rounded) number of lines that the horizontally scroll bar
4197 @defun window-current-scroll-bars &optional window
4198 This function reports the scroll bar type for window @var{window}. The
4199 value is a cons cell @code{(@var{vertical-type} .@:
4200 @var{horizontal-type})}. Unlike @code{window-scroll-bars}, this reports
4201 the scroll bar type actually used, once frame defaults and
4202 @code{scroll-bar-mode} are taken into account.
4205 @defun window-scroll-bar-width &optional window
4206 This function returns the width in pixels of @var{window}'s vertical
4210 @defun window-scroll-bar-height &optional window
4211 This function returns the height in pixels of @var{window}'s horizontal
4215 If you don't specify these values for a window with
4216 @code{set-window-scroll-bars}, the buffer-local variables
4217 @code{vertical-scroll-bar}, @code{horizontal-scroll-bar},
4218 @code{scroll-bar-width} and @code{scroll-bar-height} in the buffer being
4219 displayed control the window's scroll bars. The function
4220 @code{set-window-buffer} examines these variables. If you change them
4221 in a buffer that is already visible in a window, you can make the window
4222 take note of the new values by calling @code{set-window-buffer}
4223 specifying the same buffer that is already displayed.
4225 You can control the appearance of scroll bars for a particular buffer by
4226 setting the following variables which automatically become buffer-local
4229 @defvar vertical-scroll-bar
4230 This variable specifies the location of the vertical scroll bar. The
4231 possible values are @code{left}, @code{right}, @code{t}, which means to
4232 use the frame's default, and @code{nil} for no scroll bar.
4235 @defvar horizontal-scroll-bar
4236 This variable specifies the location of the horizontal scroll bar. The
4237 possible values are @code{bottom}, @code{t}, which means to use the
4238 frame's default, and @code{nil} for no scroll bar.
4241 @defvar scroll-bar-width
4242 This variable specifies the width of the buffer's vertical scroll bars,
4243 measured in pixels. A value of @code{nil} means to use the value
4244 specified by the frame.
4247 @defvar scroll-bar-height
4248 This variable specifies the height of the buffer's horizontal scroll
4249 bar, measured in pixels. A value of @code{nil} means to use the value
4250 specified by the frame.
4253 Finally you can toggle the display of scroll bars on all frames by
4254 customizing the variables @code{scroll-bar-mode} and
4255 @code{horizontal-scroll-bar-mode}.
4257 @defopt scroll-bar-mode
4258 This variable controls whether and where to put vertical scroll bars in
4259 all frames. The possible values are @code{nil} for no scroll bars,
4260 @code{left} to put scroll bars on the left and @code{right} to put
4261 scroll bars on the right.
4264 @defopt horizontal-scroll-bar-mode
4265 This variable controls whether to display horizontal scroll bars on all
4270 @node Window Dividers
4271 @section Window Dividers
4272 @cindex window dividers
4273 @cindex right dividers
4274 @cindex bottom dividers
4276 Window dividers are bars drawn between a frame's windows. A right
4277 divider is drawn between a window and any adjacent windows on the right.
4278 Its width (thickness) is specified by the frame parameter
4279 @code{right-divider-width}. A bottom divider is drawn between a
4280 window and adjacent windows on the bottom or the echo area. Its width
4281 is specified by the frame parameter @code{bottom-divider-width}. In
4282 either case, specifying a width of zero means to not draw such dividers.
4283 @xref{Layout Parameters}.
4285 Technically, a right divider belongs to the window on its left,
4286 which means that its width contributes to the total width of that
4287 window. A bottom divider belongs to the window above it, which
4288 means that its width contributes to the total height of that window.
4289 @xref{Window Sizes}. When a window has both, a right and a bottom
4290 divider, the bottom divider prevails. This means that a bottom
4291 divider is drawn over the full total width of its window while the right
4292 divider ends above the bottom divider.
4294 Dividers can be dragged with the mouse and are therefore useful for
4295 adjusting the sizes of adjacent windows with the mouse. They also serve
4296 to visually set apart adjacent windows when no scroll bars or mode lines
4297 are present. The following three faces allow to customize the
4298 appearance of dividers:
4301 @item window-divider
4302 When a divider is less than three pixels wide, it is drawn solidly with
4303 the foreground of this face. For larger dividers this face is used for
4304 the inner part only, excluding the first and last pixel.
4306 @item window-divider-first-pixel
4307 This is the face used for drawing the first pixel of a divider that is
4308 at least three pixels wide. To obtain a solid appearance, set this to
4309 the same value used for the @code{window-divider} face.
4311 @item window-divider-last-pixel
4312 This is the face used for drawing the last pixel of a divider that is at
4313 least three pixels wide. To obtain a solid appearance, set this to the
4314 same value used for the @code{window-divider} face.
4317 You can get the sizes of the dividers of a specific window with the
4318 following two functions.
4320 @defun window-right-divider-width &optional window
4321 Return the width (thickness) in pixels of @var{window}'s right divider.
4322 @var{window} must be a live window and defaults to the selected one.
4323 The return value is always zero for a rightmost window.
4326 @defun window-bottom-divider-width &optional window
4327 Return the width (thickness) in pixels of @var{window}'s bottom divider.
4328 @var{window} must be a live window and defaults to the selected one.
4329 The return value is zero for the minibuffer window or a bottommost
4330 window on a minibuffer-less frame.
4334 @node Display Property
4335 @section The @code{display} Property
4336 @cindex display specification
4337 @kindex display @r{(text property)}
4339 The @code{display} text property (or overlay property) is used to
4340 insert images into text, and to control other aspects of how text
4341 displays. The value of the @code{display} property should be a
4342 display specification, or a list or vector containing several display
4343 specifications. Display specifications in the same @code{display}
4344 property value generally apply in parallel to the text they cover.
4346 If several sources (overlays and/or a text property) specify values
4347 for the @code{display} property, only one of the values takes effect,
4348 following the rules of @code{get-char-property}. @xref{Examining
4351 The rest of this section describes several kinds of
4352 display specifications and what they mean.
4355 * Replacing Specs:: Display specs that replace the text.
4356 * Specified Space:: Displaying one space with a specified width.
4357 * Pixel Specification:: Specifying space width or height in pixels.
4358 * Other Display Specs:: Displaying an image; adjusting the height,
4359 spacing, and other properties of text.
4360 * Display Margins:: Displaying text or images to the side of the main text.
4363 @node Replacing Specs
4364 @subsection Display Specs That Replace The Text
4365 @cindex replacing display specs
4367 Some kinds of display specifications specify something to display
4368 instead of the text that has the property. These are called
4369 @dfn{replacing} display specifications. Emacs does not allow the user
4370 to interactively move point into the middle of buffer text that is
4371 replaced in this way.
4373 If a list of display specifications includes more than one replacing
4374 display specification, the first overrides the rest. Replacing
4375 display specifications make most other display specifications
4376 irrelevant, since those don't apply to the replacement.
4378 For replacing display specifications, @dfn{the text that has the
4379 property} means all the consecutive characters that have the same
4380 Lisp object as their @code{display} property; these characters are
4381 replaced as a single unit. If two characters have different Lisp
4382 objects as their @code{display} properties (i.e., objects which are
4383 not @code{eq}), they are handled separately.
4385 Here is an example which illustrates this point. A string serves as
4386 a replacing display specification, which replaces the text that has
4387 the property with the specified string (@pxref{Other Display Specs}).
4388 Consider the following function:
4393 (let ((string (concat "A"))
4394 (start (+ i i (point-min))))
4395 (put-text-property start (1+ start) 'display string)
4396 (put-text-property start (+ 2 start) 'display string))))
4400 This function gives each of the first ten characters in the buffer a
4401 @code{display} property which is a string @code{"A"}, but they don't
4402 all get the same string object. The first two characters get the same
4403 string object, so they are replaced with one @samp{A}; the fact that
4404 the display property was assigned in two separate calls to
4405 @code{put-text-property} is irrelevant. Similarly, the next two
4406 characters get a second string (@code{concat} creates a new string
4407 object), so they are replaced with one @samp{A}; and so on. Thus, the
4408 ten characters appear as five A's.
4410 @node Specified Space
4411 @subsection Specified Spaces
4412 @cindex spaces, specified height or width
4413 @cindex variable-width spaces
4415 To display a space of specified width and/or height, use a display
4416 specification of the form @code{(space . @var{props})}, where
4417 @var{props} is a property list (a list of alternating properties and
4418 values). You can put this property on one or more consecutive
4419 characters; a space of the specified height and width is displayed in
4420 place of @emph{all} of those characters. These are the properties you
4421 can use in @var{props} to specify the weight of the space:
4424 @item :width @var{width}
4425 If @var{width} is a number, it specifies
4426 that the space width should be @var{width} times the normal character
4427 width. @var{width} can also be a @dfn{pixel width} specification
4428 (@pxref{Pixel Specification}).
4430 @item :relative-width @var{factor}
4431 Specifies that the width of the stretch should be computed from the
4432 first character in the group of consecutive characters that have the
4433 same @code{display} property. The space width is the pixel width of
4434 that character, multiplied by @var{factor}. (On text-mode terminals,
4435 the ``pixel width'' of a character is usually 1, but it could be more
4436 for TABs and double-width CJK characters.)
4438 @item :align-to @var{hpos}
4439 Specifies that the space should be wide enough to reach @var{hpos}.
4440 If @var{hpos} is a number, it is measured in units of the normal
4441 character width. @var{hpos} can also be a @dfn{pixel width}
4442 specification (@pxref{Pixel Specification}).
4445 You should use one and only one of the above properties. You can
4446 also specify the height of the space, with these properties:
4449 @item :height @var{height}
4450 Specifies the height of the space.
4451 If @var{height} is a number, it specifies
4452 that the space height should be @var{height} times the normal character
4453 height. The @var{height} may also be a @dfn{pixel height} specification
4454 (@pxref{Pixel Specification}).
4456 @item :relative-height @var{factor}
4457 Specifies the height of the space, multiplying the ordinary height
4458 of the text having this display specification by @var{factor}.
4460 @item :ascent @var{ascent}
4461 If the value of @var{ascent} is a non-negative number no greater than
4462 100, it specifies that @var{ascent} percent of the height of the space
4463 should be considered as the ascent of the space---that is, the part
4464 above the baseline. The ascent may also be specified in pixel units
4465 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
4469 Don't use both @code{:height} and @code{:relative-height} together.
4471 The @code{:width} and @code{:align-to} properties are supported on
4472 non-graphic terminals, but the other space properties in this section
4475 Note that space properties are treated as paragraph separators for
4476 the purposes of reordering bidirectional text for display.
4477 @xref{Bidirectional Display}, for the details.
4479 @node Pixel Specification
4480 @subsection Pixel Specification for Spaces
4481 @cindex spaces, pixel specification
4483 The value of the @code{:width}, @code{:align-to}, @code{:height},
4484 and @code{:ascent} properties can be a special kind of expression that
4485 is evaluated during redisplay. The result of the evaluation is used
4486 as an absolute number of pixels.
4488 The following expressions are supported:
4492 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
4493 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
4494 @var{unit} ::= in | mm | cm | width | height
4497 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
4499 @var{pos} ::= left | center | right
4500 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
4505 The form @var{num} specifies a fraction of the default frame font
4506 height or width. The form @code{(@var{num})} specifies an absolute
4507 number of pixels. If @var{num} is a symbol, @var{symbol}, its
4508 buffer-local variable binding is used.
4510 The @code{in}, @code{mm}, and @code{cm} units specify the number of
4511 pixels per inch, millimeter, and centimeter, respectively. The
4512 @code{width} and @code{height} units correspond to the default width
4513 and height of the current face. An image specification @code{image}
4514 corresponds to the width or height of the image.
4516 The elements @code{left-fringe}, @code{right-fringe},
4517 @code{left-margin}, @code{right-margin}, @code{scroll-bar}, and
4518 @code{text} specify to the width of the corresponding area of the
4521 The @code{left}, @code{center}, and @code{right} positions can be
4522 used with @code{:align-to} to specify a position relative to the left
4523 edge, center, or right edge of the text area.
4525 Any of the above window elements (except @code{text}) can also be
4526 used with @code{:align-to} to specify that the position is relative to
4527 the left edge of the given area. Once the base offset for a relative
4528 position has been set (by the first occurrence of one of these
4529 symbols), further occurrences of these symbols are interpreted as the
4530 width of the specified area. For example, to align to the center of
4531 the left-margin, use
4534 :align-to (+ left-margin (0.5 . left-margin))
4537 If no specific base offset is set for alignment, it is always relative
4538 to the left edge of the text area. For example, @samp{:align-to 0} in a
4539 header-line aligns with the first text column in the text area.
4541 A value of the form @code{(@var{num} . @var{expr})} stands for the
4542 product of the values of @var{num} and @var{expr}. For example,
4543 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
4544 @var{image})} specifies half the width (or height) of the specified
4547 The form @code{(+ @var{expr} ...)} adds up the value of the
4548 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
4549 the value of the expressions.
4551 @node Other Display Specs
4552 @subsection Other Display Specifications
4554 Here are the other sorts of display specifications that you can use
4555 in the @code{display} text property.
4559 Display @var{string} instead of the text that has this property.
4561 Recursive display specifications are not supported---@var{string}'s
4562 @code{display} properties, if any, are not used.
4564 @item (image . @var{image-props})
4565 This kind of display specification is an image descriptor (@pxref{Images}).
4566 When used as a display specification, it means to display the image
4567 instead of the text that has the display specification.
4569 @item (slice @var{x} @var{y} @var{width} @var{height})
4570 This specification together with @code{image} specifies a @dfn{slice}
4571 (a partial area) of the image to display. The elements @var{y} and
4572 @var{x} specify the top left corner of the slice, within the image;
4573 @var{width} and @var{height} specify the width and height of the
4574 slice. Integers are numbers of pixels. A floating-point number
4575 in the range 0.0--1.0 stands for that fraction of the width or height
4576 of the entire image.
4578 @item ((margin nil) @var{string})
4579 A display specification of this form means to display @var{string}
4580 instead of the text that has the display specification, at the same
4581 position as that text. It is equivalent to using just @var{string},
4582 but it is done as a special case of marginal display (@pxref{Display
4585 @item (left-fringe @var{bitmap} @r{[}@var{face}@r{]})
4586 @itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]})
4587 This display specification on any character of a line of text causes
4588 the specified @var{bitmap} be displayed in the left or right fringes
4589 for that line, instead of the characters that have the display
4590 specification. The optional @var{face} specifies the colors to be
4591 used for the bitmap. @xref{Fringe Bitmaps}, for the details.
4593 @item (space-width @var{factor})
4594 This display specification affects all the space characters within the
4595 text that has the specification. It displays all of these spaces
4596 @var{factor} times as wide as normal. The element @var{factor} should
4597 be an integer or float. Characters other than spaces are not affected
4598 at all; in particular, this has no effect on tab characters.
4600 @item (height @var{height})
4601 This display specification makes the text taller or shorter.
4602 Here are the possibilities for @var{height}:
4605 @item @code{(+ @var{n})}
4606 @c FIXME: Add an index for "step"? --xfq
4607 This means to use a font that is @var{n} steps larger. A @dfn{step} is
4608 defined by the set of available fonts---specifically, those that match
4609 what was otherwise specified for this text, in all attributes except
4610 height. Each size for which a suitable font is available counts as
4611 another step. @var{n} should be an integer.
4613 @item @code{(- @var{n})}
4614 This means to use a font that is @var{n} steps smaller.
4616 @item a number, @var{factor}
4617 A number, @var{factor}, means to use a font that is @var{factor} times
4618 as tall as the default font.
4620 @item a symbol, @var{function}
4621 A symbol is a function to compute the height. It is called with the
4622 current height as argument, and should return the new height to use.
4624 @item anything else, @var{form}
4625 If the @var{height} value doesn't fit the previous possibilities, it is
4626 a form. Emacs evaluates it to get the new height, with the symbol
4627 @code{height} bound to the current specified font height.
4630 @item (raise @var{factor})
4631 This kind of display specification raises or lowers the text
4632 it applies to, relative to the baseline of the line.
4634 @var{factor} must be a number, which is interpreted as a multiple of the
4635 height of the affected text. If it is positive, that means to display
4636 the characters raised. If it is negative, that means to display them
4639 If the text also has a @code{height} display specification, that does
4640 not affect the amount of raising or lowering, which is based on the
4641 faces used for the text.
4644 @c We put all the '@code{(when ...)}' on one line to encourage
4645 @c makeinfo's end-of-sentence heuristics to DTRT. Previously, the dot
4646 @c was at eol; the info file ended up w/ two spaces rendered after it.
4647 You can make any display specification conditional. To do that,
4648 package it in another list of the form
4649 @code{(when @var{condition} . @var{spec})}.
4650 Then the specification @var{spec} applies only when
4651 @var{condition} evaluates to a non-@code{nil} value. During the
4652 evaluation, @code{object} is bound to the string or buffer having the
4653 conditional @code{display} property. @code{position} and
4654 @code{buffer-position} are bound to the position within @code{object}
4655 and the buffer position where the @code{display} property was found,
4656 respectively. Both positions can be different when @code{object} is a
4659 @node Display Margins
4660 @subsection Displaying in the Margins
4661 @cindex display margins
4662 @cindex margins, display
4664 A buffer can have blank areas called @dfn{display margins} on the
4665 left and on the right. Ordinary text never appears in these areas,
4666 but you can put things into the display margins using the
4667 @code{display} property. There is currently no way to make text or
4668 images in the margin mouse-sensitive.
4670 The way to display something in the margins is to specify it in a
4671 margin display specification in the @code{display} property of some
4672 text. This is a replacing display specification, meaning that the
4673 text you put it on does not get displayed; the margin display appears,
4674 but that text does not.
4676 A margin display specification looks like @code{((margin
4677 right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}.
4678 Here, @var{spec} is another display specification that says what to
4679 display in the margin. Typically it is a string of text to display,
4680 or an image descriptor.
4682 To display something in the margin @emph{in association with}
4683 certain buffer text, without altering or preventing the display of
4684 that text, put a @code{before-string} property on the text and put the
4685 margin display specification on the contents of the before-string.
4687 Before the display margins can display anything, you must give
4688 them a nonzero width. The usual way to do that is to set these
4691 @defvar left-margin-width
4692 This variable specifies the width of the left margin, in character
4693 cell (a.k.a.@: ``column'') units. It is buffer-local in all buffers.
4694 A value of @code{nil} means no left marginal area.
4697 @defvar right-margin-width
4698 This variable specifies the width of the right margin, in character
4699 cell units. It is buffer-local in all buffers. A value of @code{nil}
4700 means no right marginal area.
4703 Setting these variables does not immediately affect the window. These
4704 variables are checked when a new buffer is displayed in the window.
4705 Thus, you can make changes take effect by calling
4706 @code{set-window-buffer}.
4708 You can also set the margin widths immediately.
4710 @defun set-window-margins window left &optional right
4711 This function specifies the margin widths for window @var{window}, in
4712 character cell units. The argument @var{left} controls the left
4713 margin, and @var{right} controls the right margin (default @code{0}).
4716 @defun window-margins &optional window
4717 This function returns the width of the left and right margins of
4718 @var{window} as a cons cell of the form @w{@code{(@var{left}
4719 . @var{right})}}. If one of the two marginal areas does not exist,
4720 its width is returned as @code{nil}; if neither of the two margins exist,
4721 the function returns @code{(nil)}. If @var{window} is @code{nil}, the
4722 selected window is used.
4727 @cindex images in buffers
4729 To display an image in an Emacs buffer, you must first create an image
4730 descriptor, then use it as a display specifier in the @code{display}
4731 property of text that is displayed (@pxref{Display Property}).
4733 Emacs is usually able to display images when it is run on a
4734 graphical terminal. Images cannot be displayed in a text terminal, on
4735 certain graphical terminals that lack the support for this, or if
4736 Emacs is compiled without image support. You can use the function
4737 @code{display-images-p} to determine if images can in principle be
4738 displayed (@pxref{Display Feature Testing}).
4741 * Image Formats:: Supported image formats.
4742 * Image Descriptors:: How to specify an image for use in @code{:display}.
4743 * XBM Images:: Special features for XBM format.
4744 * XPM Images:: Special features for XPM format.
4745 * PostScript Images:: Special features for PostScript format.
4746 * ImageMagick Images:: Special features available through ImageMagick.
4747 * Other Image Types:: Various other formats are supported.
4748 * Defining Images:: Convenient ways to define an image for later use.
4749 * Showing Images:: Convenient ways to display an image once it is defined.
4750 * Multi-Frame Images:: Some images contain more than one frame.
4751 * Image Cache:: Internal mechanisms of image display.
4755 @subsection Image Formats
4756 @cindex image formats
4759 Emacs can display a number of different image formats. Some of
4760 these image formats are supported only if particular support libraries
4761 are installed. On some platforms, Emacs can load support libraries on
4762 demand; if so, the variable @code{dynamic-library-alist} can be used
4763 to modify the set of known names for these dynamic libraries.
4764 @xref{Dynamic Libraries}.
4766 Supported image formats (and the required support libraries) include
4767 PBM and XBM (which do not depend on support libraries and are always
4768 available), XPM (@code{libXpm}), GIF (@code{libgif} or
4769 @code{libungif}), PostScript (@code{gs}), JPEG (@code{libjpeg}), TIFF
4770 (@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}).
4772 Each of these image formats is associated with an @dfn{image type
4773 symbol}. The symbols for the above formats are, respectively,
4774 @code{pbm}, @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
4775 @code{jpeg}, @code{tiff}, @code{png}, and @code{svg}.
4777 Furthermore, if you build Emacs with ImageMagick
4778 (@code{libMagickWand}) support, Emacs can display any image format
4779 that ImageMagick can. @xref{ImageMagick Images}. All images
4780 displayed via ImageMagick have type symbol @code{imagemagick}.
4783 This variable contains a list of type symbols for image formats which
4784 are potentially supported in the current configuration.
4786 ``Potentially'' means that Emacs knows about the image types, not
4787 necessarily that they can be used (for example, they could depend on
4788 unavailable dynamic libraries). To know which image types are really
4789 available, use @code{image-type-available-p}.
4792 @defun image-type-available-p type
4793 This function returns non-@code{nil} if images of type @var{type} can
4794 be loaded and displayed. @var{type} must be an image type symbol.
4796 For image types whose support libraries are statically linked, this
4797 function always returns @code{t}. For image types whose support
4798 libraries are dynamically loaded, it returns @code{t} if the library
4799 could be loaded and @code{nil} otherwise.
4802 @node Image Descriptors
4803 @subsection Image Descriptors
4804 @cindex image descriptor
4806 An @dfn{image descriptor} is a list which specifies the underlying
4807 data for an image, and how to display it. It is typically used as the
4808 value of a @code{display} overlay or text property (@pxref{Other
4809 Display Specs}); but @xref{Showing Images}, for convenient helper
4810 functions to insert images into buffers.
4812 Each image descriptor has the form @code{(image . @var{props})},
4813 where @var{props} is a property list of alternating keyword symbols
4814 and values, including at least the pair @code{:type @var{type}} that
4815 specifies the image type.
4817 The following is a list of properties that are meaningful for all
4818 image types (there are also properties which are meaningful only for
4819 certain image types, as documented in the following subsections):
4822 @item :type @var{type}
4825 @xref{Image Formats}.
4827 Every image descriptor must include this property.
4829 @item :file @var{file}
4830 This says to load the image from file @var{file}. If @var{file} is
4831 not an absolute file name, it is expanded in @code{data-directory}.
4833 @item :data @var{data}
4834 This specifies the raw image data. Each image descriptor must have
4835 either @code{:data} or @code{:file}, but not both.
4837 For most image types, the value of a @code{:data} property should be a
4838 string containing the image data. Some image types do not support
4839 @code{:data}; for some others, @code{:data} alone is not enough, so
4840 you need to use other image properties along with @code{:data}. See
4841 the following subsections for details.
4843 @item :margin @var{margin}
4844 This specifies how many pixels to add as an extra margin around the
4845 image. The value, @var{margin}, must be a non-negative number, or a
4846 pair @code{(@var{x} . @var{y})} of such numbers. If it is a pair,
4847 @var{x} specifies how many pixels to add horizontally, and @var{y}
4848 specifies how many pixels to add vertically. If @code{:margin} is not
4849 specified, the default is zero.
4851 @item :ascent @var{ascent}
4852 This specifies the amount of the image's height to use for its
4853 ascent---that is, the part above the baseline. The value,
4854 @var{ascent}, must be a number in the range 0 to 100, or the symbol
4857 If @var{ascent} is a number, that percentage of the image's height is
4858 used for its ascent.
4860 If @var{ascent} is @code{center}, the image is vertically centered
4861 around a centerline which would be the vertical centerline of text drawn
4862 at the position of the image, in the manner specified by the text
4863 properties and overlays that apply to the image.
4865 If this property is omitted, it defaults to 50.
4867 @item :relief @var{relief}
4868 This adds a shadow rectangle around the image. The value,
4869 @var{relief}, specifies the width of the shadow lines, in pixels. If
4870 @var{relief} is negative, shadows are drawn so that the image appears
4871 as a pressed button; otherwise, it appears as an unpressed button.
4873 @item :conversion @var{algorithm}
4874 This specifies a conversion algorithm that should be applied to the
4875 image before it is displayed; the value, @var{algorithm}, specifies
4881 Specifies the Laplace edge detection algorithm, which blurs out small
4882 differences in color while highlighting larger differences. People
4883 sometimes consider this useful for displaying the image for a
4886 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
4887 @cindex edge detection, images
4888 Specifies a general edge-detection algorithm. @var{matrix} must be
4889 either a nine-element list or a nine-element vector of numbers. A pixel
4890 at position @math{x/y} in the transformed image is computed from
4891 original pixels around that position. @var{matrix} specifies, for each
4892 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
4893 will influence the transformed pixel; element @math{0} specifies the
4894 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
4895 the pixel at @math{x/y-1} etc., as shown below:
4898 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
4899 x-1/y & x/y & x+1/y \cr
4900 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
4905 (x-1/y-1 x/y-1 x+1/y-1
4907 x-1/y+1 x/y+1 x+1/y+1)
4911 The resulting pixel is computed from the color intensity of the color
4912 resulting from summing up the RGB values of surrounding pixels,
4913 multiplied by the specified factors, and dividing that sum by the sum
4914 of the factors' absolute values.
4916 Laplace edge-detection currently uses a matrix of
4919 $$\pmatrix{1 & 0 & 0 \cr
4932 Emboss edge-detection uses a matrix of
4935 $$\pmatrix{ 2 & -1 & 0 \cr
4949 Specifies transforming the image so that it looks disabled.
4952 @item :mask @var{mask}
4953 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
4954 a clipping mask for the image, so that the background of a frame is
4955 visible behind the image. If @var{bg} is not specified, or if @var{bg}
4956 is @code{t}, determine the background color of the image by looking at
4957 the four corners of the image, assuming the most frequently occurring
4958 color from the corners is the background color of the image. Otherwise,
4959 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
4960 specifying the color to assume for the background of the image.
4962 If @var{mask} is @code{nil}, remove a mask from the image, if it has
4963 one. Images in some formats include a mask which can be removed by
4964 specifying @code{:mask nil}.
4966 @item :pointer @var{shape}
4967 This specifies the pointer shape when the mouse pointer is over this
4968 image. @xref{Pointer Shape}, for available pointer shapes.
4970 @item :map @var{map}
4972 This associates an image map of @dfn{hot spots} with this image.
4974 An image map is an alist where each element has the format
4975 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
4976 as either a rectangle, a circle, or a polygon.
4978 A rectangle is a cons
4979 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
4980 which specifies the pixel coordinates of the upper left and bottom right
4981 corners of the rectangle area.
4984 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
4985 which specifies the center and the radius of the circle; @var{r} may
4986 be a float or integer.
4989 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
4990 where each pair in the vector describes one corner in the polygon.
4992 When the mouse pointer lies on a hot-spot area of an image, the
4993 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
4994 property, that defines a tool-tip for the hot-spot, and if it contains
4995 a @code{pointer} property, that defines the shape of the mouse cursor when
4996 it is on the hot-spot.
4997 @xref{Pointer Shape}, for available pointer shapes.
4999 When you click the mouse when the mouse pointer is over a hot-spot, an
5000 event is composed by combining the @var{id} of the hot-spot with the
5001 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
5002 @var{id} is @code{area4}.
5005 @defun image-mask-p spec &optional frame
5006 This function returns @code{t} if image @var{spec} has a mask bitmap.
5007 @var{frame} is the frame on which the image will be displayed.
5008 @var{frame} @code{nil} or omitted means to use the selected frame
5009 (@pxref{Input Focus}).
5013 @subsection XBM Images
5016 To use XBM format, specify @code{xbm} as the image type. This image
5017 format doesn't require an external library, so images of this type are
5020 Additional image properties supported for the @code{xbm} image type are:
5023 @item :foreground @var{foreground}
5024 The value, @var{foreground}, should be a string specifying the image
5025 foreground color, or @code{nil} for the default color. This color is
5026 used for each pixel in the XBM that is 1. The default is the frame's
5029 @item :background @var{background}
5030 The value, @var{background}, should be a string specifying the image
5031 background color, or @code{nil} for the default color. This color is
5032 used for each pixel in the XBM that is 0. The default is the frame's
5036 If you specify an XBM image using data within Emacs instead of an
5037 external file, use the following three properties:
5040 @item :data @var{data}
5041 The value, @var{data}, specifies the contents of the image.
5042 There are three formats you can use for @var{data}:
5046 A vector of strings or bool-vectors, each specifying one line of the
5047 image. Do specify @code{:height} and @code{:width}.
5050 A string containing the same byte sequence as an XBM file would contain.
5051 You must not specify @code{:height} and @code{:width} in this case,
5052 because omitting them is what indicates the data has the format of an
5053 XBM file. The file contents specify the height and width of the image.
5056 A string or a bool-vector containing the bits of the image (plus perhaps
5057 some extra bits at the end that will not be used). It should contain at
5058 least @var{width} * @code{height} bits. In this case, you must specify
5059 @code{:height} and @code{:width}, both to indicate that the string
5060 contains just the bits rather than a whole XBM file, and to specify the
5064 @item :width @var{width}
5065 The value, @var{width}, specifies the width of the image, in pixels.
5067 @item :height @var{height}
5068 The value, @var{height}, specifies the height of the image, in pixels.
5072 @subsection XPM Images
5075 To use XPM format, specify @code{xpm} as the image type. The
5076 additional image property @code{:color-symbols} is also meaningful with
5077 the @code{xpm} image type:
5080 @item :color-symbols @var{symbols}
5081 The value, @var{symbols}, should be an alist whose elements have the
5082 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
5083 the name of a color as it appears in the image file, and @var{color}
5084 specifies the actual color to use for displaying that name.
5087 @node PostScript Images
5088 @subsection PostScript Images
5089 @cindex postscript images
5091 To use PostScript for an image, specify image type @code{postscript}.
5092 This works only if you have Ghostscript installed. You must always use
5093 these three properties:
5096 @item :pt-width @var{width}
5097 The value, @var{width}, specifies the width of the image measured in
5098 points (1/72 inch). @var{width} must be an integer.
5100 @item :pt-height @var{height}
5101 The value, @var{height}, specifies the height of the image in points
5102 (1/72 inch). @var{height} must be an integer.
5104 @item :bounding-box @var{box}
5105 The value, @var{box}, must be a list or vector of four integers, which
5106 specifying the bounding box of the PostScript image, analogous to the
5107 @samp{BoundingBox} comment found in PostScript files.
5110 %%BoundingBox: 22 171 567 738
5114 @node ImageMagick Images
5115 @subsection ImageMagick Images
5116 @cindex ImageMagick images
5117 @cindex images, support for more formats
5119 If you build Emacs with ImageMagick support, you can use the
5120 ImageMagick library to load many image formats (@pxref{File
5121 Conveniences,,, emacs, The GNU Emacs Manual}). The image type symbol
5122 for images loaded via ImageMagick is @code{imagemagick}, regardless of
5123 the actual underlying image format.
5125 @defun imagemagick-types
5126 This function returns a list of image file extensions supported by the
5127 current ImageMagick installation. Each list element is a symbol
5128 representing an internal ImageMagick name for an image type, such as
5129 @code{BMP} for @file{.bmp} images.
5132 @defopt imagemagick-enabled-types
5133 The value of this variable is a list of ImageMagick image types which
5134 Emacs may attempt to render using ImageMagick. Each list element
5135 should be one of the symbols in the list returned by
5136 @code{imagemagick-types}, or an equivalent string. Alternatively, a
5137 value of @code{t} enables ImageMagick for all possible image types.
5138 Regardless of the value of this variable,
5139 @code{imagemagick-types-inhibit} (see below) takes precedence.
5142 @defopt imagemagick-types-inhibit
5143 The value of this variable lists the ImageMagick image types which
5144 should never be rendered using ImageMagick, regardless of the value of
5145 @code{imagemagick-enabled-types}. A value of @code{t} disables
5146 ImageMagick entirely.
5149 @defvar image-format-suffixes
5150 This variable is an alist mapping image types to file name extensions.
5151 Emacs uses this in conjunction with the @code{:format} image property
5152 (see below) to give a hint to the ImageMagick library as to the type
5153 of an image. Each element has the form @code{(@var{type}
5154 @var{extension})}, where @var{type} is a symbol specifying an image
5155 content-type, and @var{extension} is a string that specifies the
5156 associated file name extension.
5159 Images loaded with ImageMagick support the following additional
5160 image descriptor properties:
5163 @item :background @var{background}
5164 @var{background}, if non-@code{nil}, should be a string specifying a
5165 color, which is used as the image's background color if the image
5166 supports transparency. If the value is @code{nil}, it defaults to the
5167 frame's background color.
5169 @item :width @var{width}, :height @var{height}
5170 The @code{:width} and @code{:height} keywords are used for scaling the
5171 image. If only one of them is specified, the other one will be
5172 calculated so as to preserve the aspect ratio. If both are specified,
5173 aspect ratio may not be preserved.
5175 @item :max-width @var{max-width}, :max-height @var{max-height}
5176 The @code{:max-width} and @code{:max-height} keywords are used for
5177 scaling if the size of the image of the image exceeds these values.
5178 If @code{:width} is set it will have precedence over @code{max-width},
5179 and if @code{:height} is set it will have precedence over
5180 @code{max-height}, but you can otherwise mix these keywords as you
5181 wish. @code{:max-width} and @code{:max-height} will always preserve
5184 @item :format @var{type}
5185 The value, @var{type}, should be a symbol specifying the type of the
5186 image data, as found in @code{image-format-suffixes}. This is used
5187 when the image does not have an associated file name, to provide a
5188 hint to ImageMagick to help it detect the image type.
5190 @item :rotation @var{angle}
5191 Specifies a rotation angle in degrees.
5193 @item :index @var{frame}
5194 @c Doesn't work: http://debbugs.gnu.org/7978
5195 @xref{Multi-Frame Images}.
5198 @node Other Image Types
5199 @subsection Other Image Types
5202 For PBM images, specify image type @code{pbm}. Color, gray-scale and
5203 monochromatic images are supported. For mono PBM images, two additional
5204 image properties are supported.
5207 @item :foreground @var{foreground}
5208 The value, @var{foreground}, should be a string specifying the image
5209 foreground color, or @code{nil} for the default color. This color is
5210 used for each pixel in the PBM that is 1. The default is the frame's
5213 @item :background @var{background}
5214 The value, @var{background}, should be a string specifying the image
5215 background color, or @code{nil} for the default color. This color is
5216 used for each pixel in the PBM that is 0. The default is the frame's
5221 The remaining image types that Emacs can support are:
5225 Image type @code{gif}.
5226 Supports the @code{:index} property. @xref{Multi-Frame Images}.
5229 Image type @code{jpeg}.
5232 Image type @code{png}.
5235 Image type @code{svg}.
5238 Image type @code{tiff}.
5239 Supports the @code{:index} property. @xref{Multi-Frame Images}.
5242 @node Defining Images
5243 @subsection Defining Images
5244 @cindex define image
5246 The functions @code{create-image}, @code{defimage} and
5247 @code{find-image} provide convenient ways to create image descriptors.
5249 @defun create-image file-or-data &optional type data-p &rest props
5250 This function creates and returns an image descriptor which uses the
5251 data in @var{file-or-data}. @var{file-or-data} can be a file name or
5252 a string containing the image data; @var{data-p} should be @code{nil}
5253 for the former case, non-@code{nil} for the latter case.
5255 The optional argument @var{type} is a symbol specifying the image type.
5256 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
5257 determine the image type from the file's first few bytes, or else
5258 from the file's name.
5260 The remaining arguments, @var{props}, specify additional image
5261 properties---for example,
5263 @c ':heuristic-mask' is not documented?
5265 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
5268 The function returns @code{nil} if images of this type are not
5269 supported. Otherwise it returns an image descriptor.
5272 @defmac defimage symbol specs &optional doc
5273 This macro defines @var{symbol} as an image name. The arguments
5274 @var{specs} is a list which specifies how to display the image.
5275 The third argument, @var{doc}, is an optional documentation string.
5277 Each argument in @var{specs} has the form of a property list, and each
5278 one should specify at least the @code{:type} property and either the
5279 @code{:file} or the @code{:data} property. The value of @code{:type}
5280 should be a symbol specifying the image type, the value of
5281 @code{:file} is the file to load the image from, and the value of
5282 @code{:data} is a string containing the actual image data. Here is an
5286 (defimage test-image
5287 ((:type xpm :file "~/test1.xpm")
5288 (:type xbm :file "~/test1.xbm")))
5291 @code{defimage} tests each argument, one by one, to see if it is
5292 usable---that is, if the type is supported and the file exists. The
5293 first usable argument is used to make an image descriptor which is
5294 stored in @var{symbol}.
5296 If none of the alternatives will work, then @var{symbol} is defined
5300 @defun find-image specs
5301 This function provides a convenient way to find an image satisfying one
5302 of a list of image specifications @var{specs}.
5304 Each specification in @var{specs} is a property list with contents
5305 depending on image type. All specifications must at least contain the
5306 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
5307 or @w{@code{:data @var{data}}}, where @var{type} is a symbol specifying
5308 the image type, e.g., @code{xbm}, @var{file} is the file to load the
5309 image from, and @var{data} is a string containing the actual image data.
5310 The first specification in the list whose @var{type} is supported, and
5311 @var{file} exists, is used to construct the image specification to be
5312 returned. If no specification is satisfied, @code{nil} is returned.
5314 The image is looked for in @code{image-load-path}.
5317 @defvar image-load-path
5318 This variable's value is a list of locations in which to search for
5319 image files. If an element is a string or a variable symbol whose
5320 value is a string, the string is taken to be the name of a directory
5321 to search. If an element is a variable symbol whose value is a list,
5322 that is taken to be a list of directory names to search.
5324 The default is to search in the @file{images} subdirectory of the
5325 directory specified by @code{data-directory}, then the directory
5326 specified by @code{data-directory}, and finally in the directories in
5327 @code{load-path}. Subdirectories are not automatically included in
5328 the search, so if you put an image file in a subdirectory, you have to
5329 supply the subdirectory name explicitly. For example, to find the
5330 image @file{images/foo/bar.xpm} within @code{data-directory}, you
5331 should specify the image as follows:
5334 (defimage foo-image '((:type xpm :file "foo/bar.xpm")))
5338 @defun image-load-path-for-library library image &optional path no-error
5339 This function returns a suitable search path for images used by the
5340 Lisp package @var{library}.
5342 The function searches for @var{image} first using @code{image-load-path},
5343 excluding @file{@code{data-directory}/images}, and then in
5344 @code{load-path}, followed by a path suitable for @var{library}, which
5345 includes @file{../../etc/images} and @file{../etc/images} relative to
5346 the library file itself, and finally in
5347 @file{@code{data-directory}/images}.
5349 Then this function returns a list of directories which contains first
5350 the directory in which @var{image} was found, followed by the value of
5351 @code{load-path}. If @var{path} is given, it is used instead of
5354 If @var{no-error} is non-@code{nil} and a suitable path can't be
5355 found, don't signal an error. Instead, return a list of directories as
5356 before, except that @code{nil} appears in place of the image directory.
5358 Here is an example of using @code{image-load-path-for-library}:
5361 (defvar image-load-path) ; shush compiler
5362 (let* ((load-path (image-load-path-for-library
5363 "mh-e" "mh-logo.xpm"))
5364 (image-load-path (cons (car load-path)
5366 (mh-tool-bar-folder-buttons-init))
5370 @node Showing Images
5371 @subsection Showing Images
5374 You can use an image descriptor by setting up the @code{display}
5375 property yourself, but it is easier to use the functions in this
5378 @defun insert-image image &optional string area slice
5379 This function inserts @var{image} in the current buffer at point. The
5380 value @var{image} should be an image descriptor; it could be a value
5381 returned by @code{create-image}, or the value of a symbol defined with
5382 @code{defimage}. The argument @var{string} specifies the text to put
5383 in the buffer to hold the image. If it is omitted or @code{nil},
5384 @code{insert-image} uses @code{" "} by default.
5386 The argument @var{area} specifies whether to put the image in a margin.
5387 If it is @code{left-margin}, the image appears in the left margin;
5388 @code{right-margin} specifies the right margin. If @var{area} is
5389 @code{nil} or omitted, the image is displayed at point within the
5392 The argument @var{slice} specifies a slice of the image to insert. If
5393 @var{slice} is @code{nil} or omitted the whole image is inserted.
5394 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
5395 @var{height})} which specifies the @var{x} and @var{y} positions and
5396 @var{width} and @var{height} of the image area to insert. Integer
5397 values are in units of pixels. A floating-point number in the range
5398 0.0--1.0 stands for that fraction of the width or height of the entire
5401 Internally, this function inserts @var{string} in the buffer, and gives
5402 it a @code{display} property which specifies @var{image}. @xref{Display
5406 @cindex slice, image
5408 @defun insert-sliced-image image &optional string area rows cols
5409 This function inserts @var{image} in the current buffer at point, like
5410 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
5411 equally sized slices.
5413 Emacs displays each slice as a
5414 separate image, and allows more intuitive scrolling up/down, instead of
5415 jumping up/down the entire image when paging through a buffer that
5416 displays (large) images.
5419 @defun put-image image pos &optional string area
5420 This function puts image @var{image} in front of @var{pos} in the
5421 current buffer. The argument @var{pos} should be an integer or a
5422 marker. It specifies the buffer position where the image should appear.
5423 The argument @var{string} specifies the text that should hold the image
5424 as an alternative to the default.
5426 The argument @var{image} must be an image descriptor, perhaps returned
5427 by @code{create-image} or stored by @code{defimage}.
5429 The argument @var{area} specifies whether to put the image in a margin.
5430 If it is @code{left-margin}, the image appears in the left margin;
5431 @code{right-margin} specifies the right margin. If @var{area} is
5432 @code{nil} or omitted, the image is displayed at point within the
5435 Internally, this function creates an overlay, and gives it a
5436 @code{before-string} property containing text that has a @code{display}
5437 property whose value is the image. (Whew!)
5440 @defun remove-images start end &optional buffer
5441 This function removes images in @var{buffer} between positions
5442 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
5443 images are removed from the current buffer.
5445 This removes only images that were put into @var{buffer} the way
5446 @code{put-image} does it, not images that were inserted with
5447 @code{insert-image} or in other ways.
5450 @defun image-size spec &optional pixels frame
5451 @cindex size of image
5452 This function returns the size of an image as a pair
5453 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
5454 specification. @var{pixels} non-@code{nil} means return sizes measured
5455 in pixels, otherwise return sizes measured in the default character size
5456 of @var{frame} (@pxref{Frame Font}). @var{frame} is the frame on which
5457 the image will be displayed. @var{frame} null or omitted means use the
5458 selected frame (@pxref{Input Focus}).
5461 @defvar max-image-size
5462 This variable is used to define the maximum size of image that Emacs
5463 will load. Emacs will refuse to load (and display) any image that is
5464 larger than this limit.
5466 If the value is an integer, it directly specifies the maximum
5467 image height and width, measured in pixels. If it is floating
5468 point, it specifies the maximum image height and width
5469 as a ratio to the frame height and width. If the value is
5470 non-numeric, there is no explicit limit on the size of images.
5472 The purpose of this variable is to prevent unreasonably large images
5473 from accidentally being loaded into Emacs. It only takes effect the
5474 first time an image is loaded. Once an image is placed in the image
5475 cache, it can always be displayed, even if the value of
5476 @code{max-image-size} is subsequently changed (@pxref{Image Cache}).
5479 @node Multi-Frame Images
5480 @subsection Multi-Frame Images
5481 @cindex multi-frame images
5484 @cindex image animation
5485 @cindex image frames
5486 Some image files can contain more than one image. We say that there
5487 are multiple ``frames'' in the image. At present, Emacs supports
5488 multiple frames for GIF, TIFF, and certain ImageMagick formats such as
5491 The frames can be used either to represent multiple pages (this is
5492 usually the case with multi-frame TIFF files, for example), or to
5493 create animation (usually the case with multi-frame GIF files).
5495 A multi-frame image has a property @code{:index}, whose value is an
5496 integer (counting from 0) that specifies which frame is being displayed.
5498 @defun image-multi-frame-p image
5499 This function returns non-@code{nil} if @var{image} contains more than
5500 one frame. The actual return value is a cons @code{(@var{nimages}
5501 . @var{delay})}, where @var{nimages} is the number of frames and
5502 @var{delay} is the delay in seconds between them, or @code{nil}
5503 if the image does not specify a delay. Images that are intended to be
5504 animated usually specify a frame delay, whereas ones that are intended
5505 to be treated as multiple pages do not.
5508 @defun image-current-frame image
5509 This function returns the index of the current frame number for
5510 @var{image}, counting from 0.
5513 @defun image-show-frame image n &optional nocheck
5514 This function switches @var{image} to frame number @var{n}. It
5515 replaces a frame number outside the valid range with that of the end
5516 of the range, unless @var{nocheck} is non-@code{nil}. If @var{image}
5517 does not contain a frame with the specified number, the image displays
5521 @defun image-animate image &optional index limit
5522 This function animates @var{image}. The optional integer @var{index}
5523 specifies the frame from which to start (default 0). The optional
5524 argument @var{limit} controls the length of the animation. If omitted
5525 or @code{nil}, the image animates once only; if @code{t} it loops
5526 forever; if a number animation stops after that many seconds.
5529 @vindex image-minimum-frame-delay
5530 @vindex image-default-frame-delay
5531 @noindent Animation operates by means of a timer. Note that Emacs imposes a
5532 minimum frame delay of 0.01 (@code{image-minimum-frame-delay}) seconds.
5533 If the image itself does not specify a delay, Emacs uses
5534 @code{image-default-frame-delay}.
5536 @defun image-animate-timer image
5537 This function returns the timer responsible for animating @var{image},
5543 @subsection Image Cache
5546 Emacs caches images so that it can display them again more
5547 efficiently. When Emacs displays an image, it searches the image
5548 cache for an existing image specification @code{equal} to the desired
5549 specification. If a match is found, the image is displayed from the
5550 cache. Otherwise, Emacs loads the image normally.
5552 @defun image-flush spec &optional frame
5553 This function removes the image with specification @var{spec} from the
5554 image cache of frame @var{frame}. Image specifications are compared
5555 using @code{equal}. If @var{frame} is @code{nil}, it defaults to the
5556 selected frame. If @var{frame} is @code{t}, the image is flushed on
5557 all existing frames.
5559 In Emacs's current implementation, each graphical terminal possesses an
5560 image cache, which is shared by all the frames on that terminal
5561 (@pxref{Multiple Terminals}). Thus, refreshing an image in one frame
5562 also refreshes it in all other frames on the same terminal.
5565 One use for @code{image-flush} is to tell Emacs about a change in an
5566 image file. If an image specification contains a @code{:file}
5567 property, the image is cached based on the file's contents when the
5568 image is first displayed. Even if the file subsequently changes,
5569 Emacs continues displaying the old version of the image. Calling
5570 @code{image-flush} flushes the image from the cache, forcing Emacs to
5571 re-read the file the next time it needs to display that image.
5573 Another use for @code{image-flush} is for memory conservation. If
5574 your Lisp program creates a large number of temporary images over a
5575 period much shorter than @code{image-cache-eviction-delay} (see
5576 below), you can opt to flush unused images yourself, instead of
5577 waiting for Emacs to do it automatically.
5579 @defun clear-image-cache &optional filter
5580 This function clears an image cache, removing all the images stored in
5581 it. If @var{filter} is omitted or @code{nil}, it clears the cache for
5582 the selected frame. If @var{filter} is a frame, it clears the cache
5583 for that frame. If @var{filter} is @code{t}, all image caches are
5584 cleared. Otherwise, @var{filter} is taken to be a file name, and all
5585 images associated with that file name are removed from all image
5589 If an image in the image cache has not been displayed for a specified
5590 period of time, Emacs removes it from the cache and frees the
5593 @defvar image-cache-eviction-delay
5594 This variable specifies the number of seconds an image can remain in
5595 the cache without being displayed. When an image is not displayed for
5596 this length of time, Emacs removes it from the image cache.
5598 Under some circumstances, if the number of images in the cache grows
5599 too large, the actual eviction delay may be shorter than this.
5601 If the value is @code{nil}, Emacs does not remove images from the cache
5602 except when you explicitly clear it. This mode can be useful for
5608 @cindex buttons in buffers
5609 @cindex clickable buttons in buffers
5611 The Button package defines functions for inserting and manipulating
5612 @dfn{buttons} that can be activated with the mouse or via keyboard
5613 commands. These buttons are typically used for various kinds of
5616 A button is essentially a set of text or overlay properties,
5617 attached to a stretch of text in a buffer. These properties are
5618 called @dfn{button properties}. One of these properties, the
5619 @dfn{action property}, specifies a function which is called when the
5620 user invokes the button using the keyboard or the mouse. The action
5621 function may examine the button and use its other properties as
5624 In some ways, the Button package duplicates the functionality in the
5625 Widget package. @xref{Top, , Introduction, widget, The Emacs Widget
5626 Library}. The advantage of the Button package is that it is faster,
5627 smaller, and simpler to program. From the point of view of the user,
5628 the interfaces produced by the two packages are very similar.
5631 * Button Properties:: Button properties with special meanings.
5632 * Button Types:: Defining common properties for classes of buttons.
5633 * Making Buttons:: Adding buttons to Emacs buffers.
5634 * Manipulating Buttons:: Getting and setting properties of buttons.
5635 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
5638 @node Button Properties
5639 @subsection Button Properties
5640 @cindex button properties
5642 Each button has an associated list of properties defining its
5643 appearance and behavior, and other arbitrary properties may be used
5644 for application specific purposes. The following properties have
5645 special meaning to the Button package:
5649 @kindex action @r{(button property)}
5650 The function to call when the user invokes the button, which is passed
5651 the single argument @var{button}. By default this is @code{ignore},
5655 @kindex mouse-action @r{(button property)}
5656 This is similar to @code{action}, and when present, will be used
5657 instead of @code{action} for button invocations resulting from
5658 mouse-clicks (instead of the user hitting @key{RET}). If not
5659 present, mouse-clicks use @code{action} instead.
5662 @kindex face @r{(button property)}
5663 This is an Emacs face controlling how buttons of this type are
5664 displayed; by default this is the @code{button} face.
5667 @kindex mouse-face @r{(button property)}
5668 This is an additional face which controls appearance during
5669 mouse-overs (merged with the usual button face); by default this is
5670 the usual Emacs @code{highlight} face.
5673 @kindex keymap @r{(button property)}
5674 The button's keymap, defining bindings active within the button
5675 region. By default this is the usual button region keymap, stored
5676 in the variable @code{button-map}, which defines @key{RET} and
5677 @key{mouse-2} to invoke the button.
5680 @kindex type @r{(button property)}
5681 The button type. @xref{Button Types}.
5684 @kindex help-index @r{(button property)}
5685 A string displayed by the Emacs tool-tip help system; by default,
5686 @code{"mouse-2, RET: Push this button"}.
5689 @kindex follow-link @r{(button property)}
5690 The follow-link property, defining how a @key{Mouse-1} click behaves
5691 on this button, @xref{Clickable Text}.
5694 @kindex button @r{(button property)}
5695 All buttons have a non-@code{nil} @code{button} property, which may be useful
5696 in finding regions of text that comprise buttons (which is what the
5697 standard button functions do).
5700 There are other properties defined for the regions of text in a
5701 button, but these are not generally interesting for typical uses.
5704 @subsection Button Types
5705 @cindex button types
5707 Every button has a @dfn{button type}, which defines default values
5708 for the button's properties. Button types are arranged in a
5709 hierarchy, with specialized types inheriting from more general types,
5710 so that it's easy to define special-purpose types of buttons for
5713 @defun define-button-type name &rest properties
5714 Define a button type called @var{name} (a symbol).
5715 The remaining arguments
5716 form a sequence of @var{property value} pairs, specifying default
5717 property values for buttons with this type (a button's type may be set
5718 by giving it a @code{type} property when creating the button, using
5719 the @code{:type} keyword argument).
5721 In addition, the keyword argument @code{:supertype} may be used to
5722 specify a button-type from which @var{name} inherits its default
5723 property values. Note that this inheritance happens only when
5724 @var{name} is defined; subsequent changes to a supertype are not
5725 reflected in its subtypes.
5728 Using @code{define-button-type} to define default properties for
5729 buttons is not necessary---buttons without any specified type use the
5730 built-in button-type @code{button}---but it is encouraged, since
5731 doing so usually makes the resulting code clearer and more efficient.
5733 @node Making Buttons
5734 @subsection Making Buttons
5735 @cindex making buttons
5737 Buttons are associated with a region of text, using an overlay or
5738 text properties to hold button-specific information, all of which are
5739 initialized from the button's type (which defaults to the built-in
5740 button type @code{button}). Like all Emacs text, the appearance of
5741 the button is governed by the @code{face} property; by default (via
5742 the @code{face} property inherited from the @code{button} button-type)
5743 this is a simple underline, like a typical web-page link.
5745 For convenience, there are two sorts of button-creation functions,
5746 those that add button properties to an existing region of a buffer,
5747 called @code{make-...button}, and those that also insert the button
5748 text, called @code{insert-...button}.
5750 The button-creation functions all take the @code{&rest} argument
5751 @var{properties}, which should be a sequence of @var{property value}
5752 pairs, specifying properties to add to the button; see @ref{Button
5753 Properties}. In addition, the keyword argument @code{:type} may be
5754 used to specify a button-type from which to inherit other properties;
5755 see @ref{Button Types}. Any properties not explicitly specified
5756 during creation will be inherited from the button's type (if the type
5757 defines such a property).
5759 The following functions add a button using an overlay
5760 (@pxref{Overlays}) to hold the button properties:
5762 @defun make-button beg end &rest properties
5763 This makes a button from @var{beg} to @var{end} in the
5764 current buffer, and returns it.
5767 @defun insert-button label &rest properties
5768 This insert a button with the label @var{label} at point,
5772 The following functions are similar, but using text properties
5773 (@pxref{Text Properties}) to hold the button properties. Such buttons
5774 do not add markers to the buffer, so editing in the buffer does not
5775 slow down if there is an extremely large numbers of buttons. However,
5776 if there is an existing face text property on the text (e.g., a face
5777 assigned by Font Lock mode), the button face may not be visible. Both
5778 of these functions return the starting position of the new button.
5780 @defun make-text-button beg end &rest properties
5781 This makes a button from @var{beg} to @var{end} in the current buffer,
5782 using text properties.
5785 @defun insert-text-button label &rest properties
5786 This inserts a button with the label @var{label} at point, using text
5790 @node Manipulating Buttons
5791 @subsection Manipulating Buttons
5792 @cindex manipulating buttons
5794 These are functions for getting and setting properties of buttons.
5795 Often these are used by a button's invocation function to determine
5798 Where a @var{button} parameter is specified, it means an object
5799 referring to a specific button, either an overlay (for overlay
5800 buttons), or a buffer-position or marker (for text property buttons).
5801 Such an object is passed as the first argument to a button's
5802 invocation function when it is invoked.
5804 @defun button-start button
5805 Return the position at which @var{button} starts.
5808 @defun button-end button
5809 Return the position at which @var{button} ends.
5812 @defun button-get button prop
5813 Get the property of button @var{button} named @var{prop}.
5816 @defun button-put button prop val
5817 Set @var{button}'s @var{prop} property to @var{val}.
5820 @defun button-activate button &optional use-mouse-action
5821 Call @var{button}'s @code{action} property (i.e., invoke the function
5822 that is the value of that property, passing it the single argument
5823 @var{button}). If @var{use-mouse-action} is non-@code{nil}, try to
5824 invoke the button's @code{mouse-action} property instead of
5825 @code{action}; if the button has no @code{mouse-action} property, use
5826 @code{action} as normal.
5829 @defun button-label button
5830 Return @var{button}'s text label.
5833 @defun button-type button
5834 Return @var{button}'s button-type.
5837 @defun button-has-type-p button type
5838 Return @code{t} if @var{button} has button-type @var{type}, or one of
5839 @var{type}'s subtypes.
5842 @defun button-at pos
5843 Return the button at position @var{pos} in the current buffer, or
5844 @code{nil}. If the button at @var{pos} is a text property button, the
5845 return value is a marker pointing to @var{pos}.
5848 @defun button-type-put type prop val
5849 Set the button-type @var{type}'s @var{prop} property to @var{val}.
5852 @defun button-type-get type prop
5853 Get the property of button-type @var{type} named @var{prop}.
5856 @defun button-type-subtype-p type supertype
5857 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
5860 @node Button Buffer Commands
5861 @subsection Button Buffer Commands
5862 @cindex button buffer commands
5864 These are commands and functions for locating and operating on
5865 buttons in an Emacs buffer.
5867 @code{push-button} is the command that a user uses to actually push
5868 a button, and is bound by default in the button itself to @key{RET}
5869 and to @key{mouse-2} using a local keymap in the button's overlay or
5870 text properties. Commands that are useful outside the buttons itself,
5871 such as @code{forward-button} and @code{backward-button} are
5872 additionally available in the keymap stored in
5873 @code{button-buffer-map}; a mode which uses buttons may want to use
5874 @code{button-buffer-map} as a parent keymap for its keymap.
5876 If the button has a non-@code{nil} @code{follow-link} property, and
5877 @code{mouse-1-click-follows-link} is set, a quick @key{Mouse-1} click
5878 will also activate the @code{push-button} command.
5879 @xref{Clickable Text}.
5881 @deffn Command push-button &optional pos use-mouse-action
5882 Perform the action specified by a button at location @var{pos}.
5883 @var{pos} may be either a buffer position or a mouse-event. If
5884 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
5885 mouse-event (@pxref{Mouse Events}), try to invoke the button's
5886 @code{mouse-action} property instead of @code{action}; if the button
5887 has no @code{mouse-action} property, use @code{action} as normal.
5888 @var{pos} defaults to point, except when @code{push-button} is invoked
5889 interactively as the result of a mouse-event, in which case, the mouse
5890 event's position is used. If there's no button at @var{pos}, do
5891 nothing and return @code{nil}, otherwise return @code{t}.
5894 @deffn Command forward-button n &optional wrap display-message
5895 Move to the @var{n}th next button, or @var{n}th previous button if
5896 @var{n} is negative. If @var{n} is zero, move to the start of any
5897 button at point. If @var{wrap} is non-@code{nil}, moving past either
5898 end of the buffer continues from the other end. If
5899 @var{display-message} is non-@code{nil}, the button's help-echo string
5900 is displayed. Any button with a non-@code{nil} @code{skip} property
5901 is skipped over. Returns the button found.
5904 @deffn Command backward-button n &optional wrap display-message
5905 Move to the @var{n}th previous button, or @var{n}th next button if
5906 @var{n} is negative. If @var{n} is zero, move to the start of any
5907 button at point. If @var{wrap} is non-@code{nil}, moving past either
5908 end of the buffer continues from the other end. If
5909 @var{display-message} is non-@code{nil}, the button's help-echo string
5910 is displayed. Any button with a non-@code{nil} @code{skip} property
5911 is skipped over. Returns the button found.
5914 @defun next-button pos &optional count-current
5915 @defunx previous-button pos &optional count-current
5916 Return the next button after (for @code{next-button}) or before (for
5917 @code{previous-button}) position @var{pos} in the current buffer. If
5918 @var{count-current} is non-@code{nil}, count any button at @var{pos}
5919 in the search, instead of starting at the next button.
5922 @node Abstract Display
5923 @section Abstract Display
5925 @cindex display, abstract
5926 @cindex display, arbitrary objects
5927 @cindex model/view/controller
5928 @cindex view part, model/view/controller
5930 The Ewoc package constructs buffer text that represents a structure
5931 of Lisp objects, and updates the text to follow changes in that
5932 structure. This is like the ``view'' component in the
5933 ``model--view--controller'' design paradigm. Ewoc means ``Emacs's
5934 Widget for Object Collections''.
5936 An @dfn{ewoc} is a structure that organizes information required to
5937 construct buffer text that represents certain Lisp data. The buffer
5938 text of the ewoc has three parts, in order: first, fixed @dfn{header}
5939 text; next, textual descriptions of a series of data elements (Lisp
5940 objects that you specify); and last, fixed @dfn{footer} text.
5941 Specifically, an ewoc contains information on:
5945 The buffer which its text is generated in.
5948 The text's start position in the buffer.
5951 The header and footer strings.
5955 @c or "@cindex node, abstract display"?
5956 A doubly-linked chain of @dfn{nodes}, each of which contains:
5960 A @dfn{data element}, a single Lisp object.
5963 Links to the preceding and following nodes in the chain.
5967 A @dfn{pretty-printer} function which is responsible for
5968 inserting the textual representation of a data
5969 element value into the current buffer.
5972 Typically, you define an ewoc with @code{ewoc-create}, and then pass
5973 the resulting ewoc structure to other functions in the Ewoc package to
5974 build nodes within it, and display it in the buffer. Once it is
5975 displayed in the buffer, other functions determine the correspondence
5976 between buffer positions and nodes, move point from one node's textual
5977 representation to another, and so forth. @xref{Abstract Display
5980 @cindex encapsulation, ewoc
5981 @c or "@cindex encapsulation, abstract display"?
5982 A node @dfn{encapsulates} a data element much the way a variable
5983 holds a value. Normally, encapsulation occurs as a part of adding a
5984 node to the ewoc. You can retrieve the data element value and place a
5985 new value in its place, like so:
5988 (ewoc-data @var{node})
5991 (ewoc-set-data @var{node} @var{new-value})
5992 @result{} @var{new-value}
5996 You can also use, as the data element value, a Lisp object (list or
5997 vector) that is a container for the real value, or an index into
5998 some other structure. The example (@pxref{Abstract Display Example})
5999 uses the latter approach.
6001 When the data changes, you will want to update the text in the
6002 buffer. You can update all nodes by calling @code{ewoc-refresh}, or
6003 just specific nodes using @code{ewoc-invalidate}, or all nodes
6004 satisfying a predicate using @code{ewoc-map}. Alternatively, you can
6005 delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter},
6006 and add new nodes in their place. Deleting a node from an ewoc deletes
6007 its associated textual description from buffer, as well.
6010 * Abstract Display Functions:: Functions in the Ewoc package.
6011 * Abstract Display Example:: Example of using Ewoc.
6014 @node Abstract Display Functions
6015 @subsection Abstract Display Functions
6017 In this subsection, @var{ewoc} and @var{node} stand for the
6018 structures described above (@pxref{Abstract Display}), while
6019 @var{data} stands for an arbitrary Lisp object used as a data element.
6021 @defun ewoc-create pretty-printer &optional header footer nosep
6022 This constructs and returns a new ewoc, with no nodes (and thus no data
6023 elements). @var{pretty-printer} should be a function that takes one
6024 argument, a data element of the sort you plan to use in this ewoc, and
6025 inserts its textual description at point using @code{insert} (and never
6026 @code{insert-before-markers}, because that would interfere with the
6027 Ewoc package's internal mechanisms).
6029 Normally, a newline is automatically inserted after the header,
6030 the footer and every node's textual description. If @var{nosep}
6031 is non-@code{nil}, no newline is inserted. This may be useful for
6032 displaying an entire ewoc on a single line, for example, or for
6033 making nodes invisible by arranging for @var{pretty-printer}
6034 to do nothing for those nodes.
6036 An ewoc maintains its text in the buffer that is current when
6037 you create it, so switch to the intended buffer before calling
6041 @defun ewoc-buffer ewoc
6042 This returns the buffer where @var{ewoc} maintains its text.
6045 @defun ewoc-get-hf ewoc
6046 This returns a cons cell @code{(@var{header} . @var{footer})}
6047 made from @var{ewoc}'s header and footer.
6050 @defun ewoc-set-hf ewoc header footer
6051 This sets the header and footer of @var{ewoc} to the strings
6052 @var{header} and @var{footer}, respectively.
6055 @defun ewoc-enter-first ewoc data
6056 @defunx ewoc-enter-last ewoc data
6057 These add a new node encapsulating @var{data}, putting it, respectively,
6058 at the beginning or end of @var{ewoc}'s chain of nodes.
6061 @defun ewoc-enter-before ewoc node data
6062 @defunx ewoc-enter-after ewoc node data
6063 These add a new node encapsulating @var{data}, adding it to
6064 @var{ewoc} before or after @var{node}, respectively.
6067 @defun ewoc-prev ewoc node
6068 @defunx ewoc-next ewoc node
6069 These return, respectively, the previous node and the next node of @var{node}
6073 @defun ewoc-nth ewoc n
6074 This returns the node in @var{ewoc} found at zero-based index @var{n}.
6075 A negative @var{n} means count from the end. @code{ewoc-nth} returns
6076 @code{nil} if @var{n} is out of range.
6079 @defun ewoc-data node
6080 This extracts the data encapsulated by @var{node} and returns it.
6083 @defun ewoc-set-data node data
6084 This sets the data encapsulated by @var{node} to @var{data}.
6087 @defun ewoc-locate ewoc &optional pos guess
6088 This determines the node in @var{ewoc} which contains point (or
6089 @var{pos} if specified), and returns that node. If @var{ewoc} has no
6090 nodes, it returns @code{nil}. If @var{pos} is before the first node,
6091 it returns the first node; if @var{pos} is after the last node, it returns
6092 the last node. The optional third arg @var{guess}
6093 should be a node that is likely to be near @var{pos}; this doesn't
6094 alter the result, but makes the function run faster.
6097 @defun ewoc-location node
6098 This returns the start position of @var{node}.
6101 @defun ewoc-goto-prev ewoc arg
6102 @defunx ewoc-goto-next ewoc arg
6103 These move point to the previous or next, respectively, @var{arg}th node
6104 in @var{ewoc}. @code{ewoc-goto-prev} does not move if it is already at
6105 the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next}
6106 moves past the last node, returning @code{nil}. Excepting this special
6107 case, these functions return the node moved to.
6110 @defun ewoc-goto-node ewoc node
6111 This moves point to the start of @var{node} in @var{ewoc}.
6114 @defun ewoc-refresh ewoc
6115 This function regenerates the text of @var{ewoc}. It works by
6116 deleting the text between the header and the footer, i.e., all the
6117 data elements' representations, and then calling the pretty-printer
6118 function for each node, one by one, in order.
6121 @defun ewoc-invalidate ewoc &rest nodes
6122 This is similar to @code{ewoc-refresh}, except that only @var{nodes} in
6123 @var{ewoc} are updated instead of the entire set.
6126 @defun ewoc-delete ewoc &rest nodes
6127 This deletes each node in @var{nodes} from @var{ewoc}.
6130 @defun ewoc-filter ewoc predicate &rest args
6131 This calls @var{predicate} for each data element in @var{ewoc} and
6132 deletes those nodes for which @var{predicate} returns @code{nil}.
6133 Any @var{args} are passed to @var{predicate}.
6136 @defun ewoc-collect ewoc predicate &rest args
6137 This calls @var{predicate} for each data element in @var{ewoc}
6138 and returns a list of those elements for which @var{predicate}
6139 returns non-@code{nil}. The elements in the list are ordered
6140 as in the buffer. Any @var{args} are passed to @var{predicate}.
6143 @defun ewoc-map map-function ewoc &rest args
6144 This calls @var{map-function} for each data element in @var{ewoc} and
6145 updates those nodes for which @var{map-function} returns non-@code{nil}.
6146 Any @var{args} are passed to @var{map-function}.
6149 @node Abstract Display Example
6150 @subsection Abstract Display Example
6152 Here is a simple example using functions of the ewoc package to
6153 implement a @dfn{color components} display, an area in a buffer that
6154 represents a vector of three integers (itself representing a 24-bit RGB
6155 value) in various ways.
6158 (setq colorcomp-ewoc nil
6160 colorcomp-mode-map nil
6161 colorcomp-labels ["Red" "Green" "Blue"])
6163 (defun colorcomp-pp (data)
6165 (let ((comp (aref colorcomp-data data)))
6166 (insert (aref colorcomp-labels data) "\t: #x"
6167 (format "%02X" comp) " "
6168 (make-string (ash comp -2) ?#) "\n"))
6169 (let ((cstr (format "#%02X%02X%02X"
6170 (aref colorcomp-data 0)
6171 (aref colorcomp-data 1)
6172 (aref colorcomp-data 2)))
6173 (samp " (sample text) "))
6175 (propertize samp 'face
6176 `(foreground-color . ,cstr))
6177 (propertize samp 'face
6178 `(background-color . ,cstr))
6181 (defun colorcomp (color)
6182 "Allow fiddling with COLOR in a new buffer.
6183 The buffer is in Color Components mode."
6184 (interactive "sColor (name or #RGB or #RRGGBB): ")
6185 (when (string= "" color)
6186 (setq color "green"))
6187 (unless (color-values color)
6188 (error "No such color: %S" color))
6190 (generate-new-buffer (format "originally: %s" color)))
6191 (kill-all-local-variables)
6192 (setq major-mode 'colorcomp-mode
6193 mode-name "Color Components")
6194 (use-local-map colorcomp-mode-map)
6196 (buffer-disable-undo)
6197 (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
6198 (color-values color))))
6199 (ewoc (ewoc-create 'colorcomp-pp
6200 "\nColor Components\n\n"
6201 (substitute-command-keys
6202 "\n\\@{colorcomp-mode-map@}"))))
6203 (set (make-local-variable 'colorcomp-data) data)
6204 (set (make-local-variable 'colorcomp-ewoc) ewoc)
6205 (ewoc-enter-last ewoc 0)
6206 (ewoc-enter-last ewoc 1)
6207 (ewoc-enter-last ewoc 2)
6208 (ewoc-enter-last ewoc nil)))
6211 @cindex controller part, model/view/controller
6212 This example can be extended to be a color selection widget (in
6213 other words, the ``controller'' part of the ``model--view--controller''
6214 design paradigm) by defining commands to modify @code{colorcomp-data}
6215 and to finish the selection process, and a keymap to tie it all
6216 together conveniently.
6219 (defun colorcomp-mod (index limit delta)
6220 (let ((cur (aref colorcomp-data index)))
6221 (unless (= limit cur)
6222 (aset colorcomp-data index (+ cur delta)))
6225 (ewoc-nth colorcomp-ewoc index)
6226 (ewoc-nth colorcomp-ewoc -1))))
6228 (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
6229 (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
6230 (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
6231 (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
6232 (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
6233 (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
6235 (defun colorcomp-copy-as-kill-and-exit ()
6236 "Copy the color components into the kill ring and kill the buffer.
6237 The string is formatted #RRGGBB (hash followed by six hex digits)."
6239 (kill-new (format "#%02X%02X%02X"
6240 (aref colorcomp-data 0)
6241 (aref colorcomp-data 1)
6242 (aref colorcomp-data 2)))
6245 (setq colorcomp-mode-map
6246 (let ((m (make-sparse-keymap)))
6248 (define-key m "i" 'colorcomp-R-less)
6249 (define-key m "o" 'colorcomp-R-more)
6250 (define-key m "k" 'colorcomp-G-less)
6251 (define-key m "l" 'colorcomp-G-more)
6252 (define-key m "," 'colorcomp-B-less)
6253 (define-key m "." 'colorcomp-B-more)
6254 (define-key m " " 'colorcomp-copy-as-kill-and-exit)
6258 Note that we never modify the data in each node, which is fixed when the
6259 ewoc is created to be either @code{nil} or an index into the vector
6260 @code{colorcomp-data}, the actual color components.
6263 @section Blinking Parentheses
6264 @cindex parenthesis matching
6265 @cindex blinking parentheses
6266 @cindex balancing parentheses
6268 This section describes the mechanism by which Emacs shows a matching
6269 open parenthesis when the user inserts a close parenthesis.
6271 @defvar blink-paren-function
6272 The value of this variable should be a function (of no arguments) to
6273 be called whenever a character with close parenthesis syntax is inserted.
6274 The value of @code{blink-paren-function} may be @code{nil}, in which
6275 case nothing is done.
6278 @defopt blink-matching-paren
6279 If this variable is @code{nil}, then @code{blink-matching-open} does
6283 @defopt blink-matching-paren-distance
6284 This variable specifies the maximum distance to scan for a matching
6285 parenthesis before giving up.
6288 @defopt blink-matching-delay
6289 This variable specifies the number of seconds to keep indicating the
6290 matching parenthesis. A fraction of a second often gives good
6291 results, but the default is 1, which works on all systems.
6294 @deffn Command blink-matching-open
6295 This function is the default value of @code{blink-paren-function}. It
6296 assumes that point follows a character with close parenthesis syntax
6297 and applies the appropriate effect momentarily to the matching opening
6298 character. If that character is not already on the screen, it
6299 displays the character's context in the echo area. To avoid long
6300 delays, this function does not search farther than
6301 @code{blink-matching-paren-distance} characters.
6303 Here is an example of calling this function explicitly.
6307 (defun interactive-blink-matching-open ()
6308 "Indicate momentarily the start of parenthesized sexp before point."
6312 (let ((blink-matching-paren-distance
6314 (blink-matching-paren t))
6315 (blink-matching-open)))
6320 @node Character Display
6321 @section Character Display
6323 This section describes how characters are actually displayed by
6324 Emacs. Typically, a character is displayed as a @dfn{glyph} (a
6325 graphical symbol which occupies one character position on the screen),
6326 whose appearance corresponds to the character itself. For example,
6327 the character @samp{a} (character code 97) is displayed as @samp{a}.
6328 Some characters, however, are displayed specially. For example, the
6329 formfeed character (character code 12) is usually displayed as a
6330 sequence of two glyphs, @samp{^L}, while the newline character
6331 (character code 10) starts a new screen line.
6333 You can modify how each character is displayed by defining a
6334 @dfn{display table}, which maps each character code into a sequence of
6335 glyphs. @xref{Display Tables}.
6338 * Usual Display:: The usual conventions for displaying characters.
6339 * Display Tables:: What a display table consists of.
6340 * Active Display Table:: How Emacs selects a display table to use.
6341 * Glyphs:: How to define a glyph, and what glyphs mean.
6342 * Glyphless Chars:: How glyphless characters are drawn.
6346 @subsection Usual Display Conventions
6348 Here are the conventions for displaying each character code (in the
6349 absence of a display table, which can override these
6354 conventions; @pxref{Display Tables}).
6357 @cindex printable ASCII characters
6360 The @dfn{printable @acronym{ASCII} characters}, character codes 32
6361 through 126 (consisting of numerals, English letters, and symbols like
6362 @samp{#}) are displayed literally.
6365 The tab character (character code 9) displays as whitespace stretching
6366 up to the next tab stop column. @xref{Text Display,,, emacs, The GNU
6367 Emacs Manual}. The variable @code{tab-width} controls the number of
6368 spaces per tab stop (see below).
6371 The newline character (character code 10) has a special effect: it
6372 ends the preceding line and starts a new line.
6374 @cindex ASCII control characters
6376 The non-printable @dfn{@acronym{ASCII} control characters}---character
6377 codes 0 through 31, as well as the @key{DEL} character (character code
6378 127)---display in one of two ways according to the variable
6379 @code{ctl-arrow}. If this variable is non-@code{nil} (the default),
6380 these characters are displayed as sequences of two glyphs, where the
6381 first glyph is @samp{^} (a display table can specify a glyph to use
6382 instead of @samp{^}); e.g., the @key{DEL} character is displayed as
6385 If @code{ctl-arrow} is @code{nil}, these characters are displayed as
6386 octal escapes (see below).
6388 This rule also applies to carriage return (character code 13), if that
6389 character appears in the buffer. But carriage returns usually do not
6390 appear in buffer text; they are eliminated as part of end-of-line
6391 conversion (@pxref{Coding System Basics}).
6393 @cindex octal escapes
6395 @dfn{Raw bytes} are non-@acronym{ASCII} characters with codes 128
6396 through 255 (@pxref{Text Representations}). These characters display
6397 as @dfn{octal escapes}: sequences of four glyphs, where the first
6398 glyph is the @acronym{ASCII} code for @samp{\}, and the others are
6399 digit characters representing the character code in octal. (A display
6400 table can specify a glyph to use instead of @samp{\}.)
6403 Each non-@acronym{ASCII} character with code above 255 is displayed
6404 literally, if the terminal supports it. If the terminal does not
6405 support it, the character is said to be @dfn{glyphless}, and it is
6406 usually displayed using a placeholder glyph. For example, if a
6407 graphical terminal has no font for a character, Emacs usually displays
6408 a box containing the character code in hexadecimal. @xref{Glyphless
6412 The above display conventions apply even when there is a display
6413 table, for any character whose entry in the active display table is
6414 @code{nil}. Thus, when you set up a display table, you need only
6415 specify the characters for which you want special behavior.
6417 The following variables affect how certain characters are displayed
6418 on the screen. Since they change the number of columns the characters
6419 occupy, they also affect the indentation functions. They also affect
6420 how the mode line is displayed; if you want to force redisplay of the
6421 mode line using the new values, call the function
6422 @code{force-mode-line-update} (@pxref{Mode Line Format}).
6425 @cindex control characters in display
6426 This buffer-local variable controls how control characters are
6427 displayed. If it is non-@code{nil}, they are displayed as a caret
6428 followed by the character: @samp{^A}. If it is @code{nil}, they are
6429 displayed as octal escapes: a backslash followed by three octal
6430 digits, as in @samp{\001}.
6434 The value of this buffer-local variable is the spacing between tab
6435 stops used for displaying tab characters in Emacs buffers. The value
6436 is in units of columns, and the default is 8. Note that this feature
6437 is completely independent of the user-settable tab stops used by the
6438 command @code{tab-to-tab-stop}. @xref{Indent Tabs}.
6441 @node Display Tables
6442 @subsection Display Tables
6444 @cindex display table
6445 A display table is a special-purpose char-table
6446 (@pxref{Char-Tables}), with @code{display-table} as its subtype, which
6447 is used to override the usual character display conventions. This
6448 section describes how to make, inspect, and assign elements to a
6449 display table object.
6451 @defun make-display-table
6452 This creates and returns a display table. The table initially has
6453 @code{nil} in all elements.
6456 The ordinary elements of the display table are indexed by character
6457 codes; the element at index @var{c} says how to display the character
6458 code @var{c}. The value should be @code{nil} (which means to display
6459 the character @var{c} according to the usual display conventions;
6460 @pxref{Usual Display}), or a vector of glyph codes (which means to
6461 display the character @var{c} as those glyphs; @pxref{Glyphs}).
6463 @strong{Warning:} if you use the display table to change the display
6464 of newline characters, the whole buffer will be displayed as one long
6467 The display table also has six @dfn{extra slots} which serve special
6468 purposes. Here is a table of their meanings; @code{nil} in any slot
6469 means to use the default for that slot, as stated below.
6473 The glyph for the end of a truncated screen line (the default for this
6474 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
6475 arrows in the fringes to indicate truncation, so the display table has
6479 The glyph for the end of a continued line (the default is @samp{\}).
6480 On graphical terminals, Emacs uses curved arrows in the fringes to
6481 indicate continuation, so the display table has no effect.
6484 The glyph for indicating a character displayed as an octal character
6485 code (the default is @samp{\}).
6488 The glyph for indicating a control character (the default is @samp{^}).
6491 A vector of glyphs for indicating the presence of invisible lines (the
6492 default is @samp{...}). @xref{Selective Display}.
6495 The glyph used to draw the border between side-by-side windows (the
6496 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
6497 when there are no scroll bars; if scroll bars are supported and in use,
6498 a scroll bar separates the two windows.
6501 For example, here is how to construct a display table that mimics
6502 the effect of setting @code{ctl-arrow} to a non-@code{nil} value
6503 (@pxref{Glyphs}, for the function @code{make-glyph-code}):
6506 (setq disptab (make-display-table))
6511 (vector (make-glyph-code ?^ 'escape-glyph)
6512 (make-glyph-code (+ i 64) 'escape-glyph)))))
6514 (vector (make-glyph-code ?^ 'escape-glyph)
6515 (make-glyph-code ?? 'escape-glyph)))))
6518 @defun display-table-slot display-table slot
6519 This function returns the value of the extra slot @var{slot} of
6520 @var{display-table}. The argument @var{slot} may be a number from 0 to
6521 5 inclusive, or a slot name (symbol). Valid symbols are
6522 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6523 @code{selective-display}, and @code{vertical-border}.
6526 @defun set-display-table-slot display-table slot value
6527 This function stores @var{value} in the extra slot @var{slot} of
6528 @var{display-table}. The argument @var{slot} may be a number from 0 to
6529 5 inclusive, or a slot name (symbol). Valid symbols are
6530 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6531 @code{selective-display}, and @code{vertical-border}.
6534 @defun describe-display-table display-table
6535 This function displays a description of the display table
6536 @var{display-table} in a help buffer.
6539 @deffn Command describe-current-display-table
6540 This command displays a description of the current display table in a
6544 @node Active Display Table
6545 @subsection Active Display Table
6546 @cindex active display table
6548 Each window can specify a display table, and so can each buffer.
6549 The window's display table, if there is one, takes precedence over the
6550 buffer's display table. If neither exists, Emacs tries to use the
6551 standard display table; if that is @code{nil}, Emacs uses the usual
6552 character display conventions (@pxref{Usual Display}).
6554 Note that display tables affect how the mode line is displayed, so
6555 if you want to force redisplay of the mode line using a new display
6556 table, call @code{force-mode-line-update} (@pxref{Mode Line Format}).
6558 @defun window-display-table &optional window
6559 This function returns @var{window}'s display table, or @code{nil} if
6560 there is none. The default for @var{window} is the selected window.
6563 @defun set-window-display-table window table
6564 This function sets the display table of @var{window} to @var{table}.
6565 The argument @var{table} should be either a display table or
6569 @defvar buffer-display-table
6570 This variable is automatically buffer-local in all buffers; its value
6571 specifies the buffer's display table. If it is @code{nil}, there is
6572 no buffer display table.
6575 @defvar standard-display-table
6576 The value of this variable is the standard display table, which is
6577 used when Emacs is displaying a buffer in a window with neither a
6578 window display table nor a buffer display table defined, or when Emacs
6579 is outputting text to the standard output or error streams. Although its
6580 default is typically @code{nil}, in an interactive session if the
6581 terminal cannot display curved quotes, its default maps curved quotes
6582 to ASCII approximations. @xref{Keys in Documentation}.
6585 The @file{disp-table} library defines several functions for changing
6586 the standard display table.
6593 A @dfn{glyph} is a graphical symbol which occupies a single
6594 character position on the screen. Each glyph is represented in Lisp
6595 as a @dfn{glyph code}, which specifies a character and optionally a
6596 face to display it in (@pxref{Faces}). The main use of glyph codes is
6597 as the entries of display tables (@pxref{Display Tables}). The
6598 following functions are used to manipulate glyph codes:
6600 @defun make-glyph-code char &optional face
6601 This function returns a glyph code representing char @var{char} with
6602 face @var{face}. If @var{face} is omitted or @code{nil}, the glyph
6603 uses the default face; in that case, the glyph code is an integer. If
6604 @var{face} is non-@code{nil}, the glyph code is not necessarily an
6608 @defun glyph-char glyph
6609 This function returns the character of glyph code @var{glyph}.
6612 @defun glyph-face glyph
6613 This function returns face of glyph code @var{glyph}, or @code{nil} if
6614 @var{glyph} uses the default face.
6618 You can set up a @dfn{glyph table} to change how glyph codes are
6619 actually displayed on text terminals. This feature is semi-obsolete;
6620 use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}).
6623 The value of this variable, if non-@code{nil}, is the current glyph
6624 table. It takes effect only on character terminals; on graphical
6625 displays, all glyphs are displayed literally. The glyph table should
6626 be a vector whose @var{g}th element specifies how to display glyph
6627 code @var{g}, where @var{g} is the glyph code for a glyph whose face
6628 is unspecified. Each element should be one of the following:
6632 Display this glyph literally.
6635 Display this glyph by sending the specified string to the terminal.
6638 Display the specified glyph code instead.
6641 Any integer glyph code greater than or equal to the length of the
6642 glyph table is displayed literally.
6646 @node Glyphless Chars
6647 @subsection Glyphless Character Display
6648 @cindex glyphless characters
6650 @dfn{Glyphless characters} are characters which are displayed in a
6651 special way, e.g., as a box containing a hexadecimal code, instead of
6652 being displayed literally. These include characters which are
6653 explicitly defined to be glyphless, as well as characters for which
6654 there is no available font (on a graphical display), and characters
6655 which cannot be encoded by the terminal's coding system (on a text
6658 @defvar glyphless-char-display
6659 The value of this variable is a char-table which defines glyphless
6660 characters and how they are displayed. Each entry must be one of the
6661 following display methods:
6665 Display the character in the usual way.
6667 @item @code{zero-width}
6668 Don't display the character.
6670 @item @code{thin-space}
6671 Display a thin space, 1-pixel wide on graphical displays, or
6672 1-character wide on text terminals.
6674 @item @code{empty-box}
6675 Display an empty box.
6677 @item @code{hex-code}
6678 Display a box containing the Unicode codepoint of the character, in
6679 hexadecimal notation.
6681 @item an @acronym{ASCII} string
6682 Display a box containing that string. The string should contain at
6683 most 6 @acronym{ASCII} characters.
6685 @item a cons cell @code{(@var{graphical} . @var{text})}
6686 Display with @var{graphical} on graphical displays, and with
6687 @var{text} on text terminals. Both @var{graphical} and @var{text}
6688 must be one of the display methods described above.
6692 The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
6693 @acronym{ASCII} string display methods are drawn with the
6694 @code{glyphless-char} face. On text terminals, a box is emulated by
6695 square brackets, @samp{[]}.
6697 The char-table has one extra slot, which determines how to display any
6698 character that cannot be displayed with any available font, or cannot
6699 be encoded by the terminal's coding system. Its value should be one
6700 of the above display methods, except @code{zero-width} or a cons cell.
6702 If a character has a non-@code{nil} entry in an active display table,
6703 the display table takes effect; in this case, Emacs does not consult
6704 @code{glyphless-char-display} at all.
6707 @defopt glyphless-char-display-control
6708 This user option provides a convenient way to set
6709 @code{glyphless-char-display} for groups of similar characters. Do
6710 not set its value directly from Lisp code; the value takes effect only
6711 via a custom @code{:set} function (@pxref{Variable Definitions}),
6712 which updates @code{glyphless-char-display}.
6714 Its value should be an alist of elements @code{(@var{group}
6715 . @var{method})}, where @var{group} is a symbol specifying a group of
6716 characters, and @var{method} is a symbol specifying how to display
6719 @var{group} should be one of the following:
6723 @acronym{ASCII} control characters @code{U+0000} to @code{U+001F},
6724 excluding the newline and tab characters (normally displayed as escape
6725 sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed,
6726 emacs, The GNU Emacs Manual}).
6729 Non-@acronym{ASCII}, non-printing characters @code{U+0080} to
6730 @code{U+009F} (normally displayed as octal escape sequences like
6733 @item format-control
6734 Characters of Unicode General Category [Cf], such as @samp{U+200E}
6735 (Left-to-Right Mark), but excluding characters that have graphic
6736 images, such as @samp{U+00AD} (Soft Hyphen).
6739 Characters for there is no suitable font, or which cannot be encoded
6740 by the terminal's coding system.
6743 @c FIXME: this can also be 'acronym', but that's not currently
6744 @c completely implemented; it applies only to the format-control
6745 @c group, and only works if the acronym is in 'char-acronym-table'.
6746 The @var{method} symbol should be one of @code{zero-width},
6747 @code{thin-space}, @code{empty-box}, or @code{hex-code}. These have
6748 the same meanings as in @code{glyphless-char-display}, above.
6755 This section describes how to make Emacs ring the bell (or blink the
6756 screen) to attract the user's attention. Be conservative about how
6757 often you do this; frequent bells can become irritating. Also be
6758 careful not to use just beeping when signaling an error is more
6759 appropriate (@pxref{Errors}).
6761 @defun ding &optional do-not-terminate
6762 @cindex keyboard macro termination
6763 This function beeps, or flashes the screen (see @code{visible-bell} below).
6764 It also terminates any keyboard macro currently executing unless
6765 @var{do-not-terminate} is non-@code{nil}.
6768 @defun beep &optional do-not-terminate
6769 This is a synonym for @code{ding}.
6772 @defopt visible-bell
6773 This variable determines whether Emacs should flash the screen to
6774 represent a bell. Non-@code{nil} means yes, @code{nil} means no.
6775 This is effective on graphical displays, and on text terminals
6776 provided the terminal's Termcap entry defines the visible bell
6777 capability (@samp{vb}).
6780 @defvar ring-bell-function
6781 If this is non-@code{nil}, it specifies how Emacs should ring the
6782 bell. Its value should be a function of no arguments. If this is
6783 non-@code{nil}, it takes precedence over the @code{visible-bell}
6787 @node Window Systems
6788 @section Window Systems
6790 Emacs works with several window systems, most notably the X Window
6791 System. Both Emacs and X use the term ``window'', but use it
6792 differently. An Emacs frame is a single window as far as X is
6793 concerned; the individual Emacs windows are not known to X at all.
6795 @defvar window-system
6796 This terminal-local variable tells Lisp programs what window system
6797 Emacs is using for displaying the frame. The possible values are
6801 @cindex X Window System
6802 Emacs is displaying the frame using X.
6804 Emacs is displaying the frame using native MS-Windows GUI.
6806 Emacs is displaying the frame using the Nextstep interface (used on
6807 GNUstep and Mac OS X).
6809 Emacs is displaying the frame using MS-DOS direct screen writes.
6811 Emacs is displaying the frame on a character-based terminal.
6815 @defvar initial-window-system
6816 This variable holds the value of @code{window-system} used for the
6817 first frame created by Emacs during startup. (When Emacs is invoked
6818 with the @option{--daemon} option, it does not create any initial
6819 frames, so @code{initial-window-system} is @code{nil}, except on
6820 MS-Windows, where it is still @code{w32}. @xref{Initial Options,
6821 daemon,, emacs, The GNU Emacs Manual}.)
6824 @defun window-system &optional frame
6825 This function returns a symbol whose name tells what window system is
6826 used for displaying @var{frame} (which defaults to the currently
6827 selected frame). The list of possible symbols it returns is the same
6828 one documented for the variable @code{window-system} above.
6831 Do @emph{not} use @code{window-system} and
6832 @code{initial-window-system} as predicates or boolean flag variables,
6833 if you want to write code that works differently on text terminals and
6834 graphic displays. That is because @code{window-system} is not a good
6835 indicator of Emacs capabilities on a given display type. Instead, use
6836 @code{display-graphic-p} or any of the other @code{display-*-p}
6837 predicates described in @ref{Display Feature Testing}.
6839 @node Bidirectional Display
6840 @section Bidirectional Display
6841 @cindex bidirectional display
6842 @cindex right-to-left text
6844 Emacs can display text written in scripts, such as Arabic, Farsi,
6845 and Hebrew, whose natural ordering for horizontal text display runs
6846 from right to left. Furthermore, segments of Latin script and digits
6847 embedded in right-to-left text are displayed left-to-right, while
6848 segments of right-to-left script embedded in left-to-right text
6849 (e.g., Arabic or Hebrew text in comments or strings in a program
6850 source file) are appropriately displayed right-to-left. We call such
6851 mixtures of left-to-right and right-to-left text @dfn{bidirectional
6852 text}. This section describes the facilities and options for editing
6853 and displaying bidirectional text.
6855 @cindex logical order
6856 @cindex reading order
6857 @cindex visual order
6858 @cindex unicode bidirectional algorithm
6860 @cindex bidirectional reordering
6861 @cindex reordering, of bidirectional text
6862 Text is stored in Emacs buffers and strings in @dfn{logical} (or
6863 @dfn{reading}) order, i.e., the order in which a human would read
6864 each character. In right-to-left and bidirectional text, the order in
6865 which characters are displayed on the screen (called @dfn{visual
6866 order}) is not the same as logical order; the characters' screen
6867 positions do not increase monotonically with string or buffer
6868 position. In performing this @dfn{bidirectional reordering}, Emacs
6869 follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}),
6870 which is described in Annex #9 of the Unicode standard
6871 (@url{http://www.unicode.org/reports/tr9/}). Emacs provides a ``Full
6872 Bidirectionality'' class implementation of the @acronym{UBA},
6873 consistent with the requirements of the Unicode Standard v8.0.
6875 @defvar bidi-display-reordering
6876 If the value of this buffer-local variable is non-@code{nil} (the
6877 default), Emacs performs bidirectional reordering for display. The
6878 reordering affects buffer text, as well as display strings and overlay
6879 strings from text and overlay properties in the buffer (@pxref{Overlay
6880 Properties}, and @pxref{Display Property}). If the value is
6881 @code{nil}, Emacs does not perform bidirectional reordering in the
6884 The default value of @code{bidi-display-reordering} controls the
6885 reordering of strings which are not directly supplied by a buffer,
6886 including the text displayed in mode lines (@pxref{Mode Line Format})
6887 and header lines (@pxref{Header Lines}).
6890 @cindex unibyte buffers, and bidi reordering
6891 Emacs never reorders the text of a unibyte buffer, even if
6892 @code{bidi-display-reordering} is non-@code{nil} in the buffer. This
6893 is because unibyte buffers contain raw bytes, not characters, and thus
6894 lack the directionality properties required for reordering.
6895 Therefore, to test whether text in a buffer will be reordered for
6896 display, it is not enough to test the value of
6897 @code{bidi-display-reordering} alone. The correct test is this:
6900 (if (and enable-multibyte-characters
6901 bidi-display-reordering)
6902 ;; Buffer is being reordered for display
6906 However, unibyte display and overlay strings @emph{are} reordered if
6907 their parent buffer is reordered. This is because plain-@sc{ascii}
6908 strings are stored by Emacs as unibyte strings. If a unibyte display
6909 or overlay string includes non-@sc{ascii} characters, these characters
6910 are assumed to have left-to-right direction.
6912 @cindex display properties, and bidi reordering of text
6913 Text covered by @code{display} text properties, by overlays with
6914 @code{display} properties whose value is a string, and by any other
6915 properties that replace buffer text, is treated as a single unit when
6916 it is reordered for display. That is, the entire chunk of text
6917 covered by these properties is reordered together. Moreover, the
6918 bidirectional properties of the characters in such a chunk of text are
6919 ignored, and Emacs reorders them as if they were replaced with a
6920 single character @code{U+FFFC}, known as the @dfn{Object Replacement
6921 Character}. This means that placing a display property over a portion
6922 of text may change the way that the surrounding text is reordered for
6923 display. To prevent this unexpected effect, always place such
6924 properties on text whose directionality is identical with text that
6927 @cindex base direction of a paragraph
6928 Each paragraph of bidirectional text has a @dfn{base direction},
6929 either right-to-left or left-to-right. Left-to-right paragraphs are
6930 displayed beginning at the left margin of the window, and are
6931 truncated or continued when the text reaches the right margin.
6932 Right-to-left paragraphs are displayed beginning at the right margin,
6933 and are continued or truncated at the left margin.
6935 By default, Emacs determines the base direction of each paragraph by
6936 looking at the text at its beginning. The precise method of
6937 determining the base direction is specified by the @acronym{UBA}; in a
6938 nutshell, the first character in a paragraph that has an explicit
6939 directionality determines the base direction of the paragraph.
6940 However, sometimes a buffer may need to force a certain base direction
6941 for its paragraphs. For example, buffers containing program source
6942 code should force all paragraphs to be displayed left-to-right. You
6943 can use following variable to do this:
6945 @defvar bidi-paragraph-direction
6946 If the value of this buffer-local variable is the symbol
6947 @code{right-to-left} or @code{left-to-right}, all paragraphs in the
6948 buffer are assumed to have that specified direction. Any other value
6949 is equivalent to @code{nil} (the default), which means to determine
6950 the base direction of each paragraph from its contents.
6952 @cindex @code{prog-mode}, and @code{bidi-paragraph-direction}
6953 Modes for program source code should set this to @code{left-to-right}.
6954 Prog mode does this by default, so modes derived from Prog mode do not
6955 need to set this explicitly (@pxref{Basic Major Modes}).
6958 @defun current-bidi-paragraph-direction &optional buffer
6959 This function returns the paragraph direction at point in the named
6960 @var{buffer}. The returned value is a symbol, either
6961 @code{left-to-right} or @code{right-to-left}. If @var{buffer} is
6962 omitted or @code{nil}, it defaults to the current buffer. If the
6963 buffer-local value of the variable @code{bidi-paragraph-direction} is
6964 non-@code{nil}, the returned value will be identical to that value;
6965 otherwise, the returned value reflects the paragraph direction
6966 determined dynamically by Emacs. For buffers whose value of
6967 @code{bidi-display-reordering} is @code{nil} as well as unibyte
6968 buffers, this function always returns @code{left-to-right}.
6971 @cindex visual-order cursor motion
6972 Sometimes there's a need to move point in strict visual order,
6973 either to the left or to the right of its current screen position.
6974 Emacs provides a primitive to do that.
6976 @defun move-point-visually direction
6977 This function moves point of the currently selected window to the
6978 buffer position that appears immediately to the right or to the left
6979 of point on the screen. If @var{direction} is positive, point will
6980 move one screen position to the right, otherwise it will move one
6981 screen position to the left. Note that, depending on the surrounding
6982 bidirectional context, this could potentially move point many buffer
6983 positions away. If invoked at the end of a screen line, the function
6984 moves point to the rightmost or leftmost screen position of the next
6985 or previous screen line, as appropriate for the value of
6988 The function returns the new buffer position as its value.
6991 @cindex layout on display, and bidirectional text
6992 @cindex jumbled display of bidirectional text
6993 @cindex concatenating bidirectional strings
6994 Bidirectional reordering can have surprising and unpleasant effects
6995 when two strings with bidirectional content are juxtaposed in a
6996 buffer, or otherwise programmatically concatenated into a string of
6997 text. A typical problematic case is when a buffer consists of
6998 sequences of text fields separated by whitespace or punctuation
6999 characters, like Buffer Menu mode or Rmail Summary Mode. Because the
7000 punctuation characters used as separators have @dfn{weak
7001 directionality}, they take on the directionality of surrounding text.
7002 As result, a numeric field that follows a field with bidirectional
7003 content can be displayed @emph{to the left} of the preceding field,
7004 messing up the expected layout. There are several ways to avoid this
7009 Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or
7010 @acronym{LRM}, to the end of each field that may have bidirectional
7011 content, or prepend it to the beginning of the following field. The
7012 function @code{bidi-string-mark-left-to-right}, described below, comes
7013 in handy for this purpose. (In a right-to-left paragraph, use
7014 @code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.) This
7015 is one of the solutions recommended by the UBA.
7018 Include the tab character in the field separator. The tab character
7019 plays the role of @dfn{segment separator} in bidirectional reordering,
7020 causing the text on either side to be reordered separately.
7022 @cindex @code{space} display spec, and bidirectional text
7024 Separate fields with a @code{display} property or overlay with a
7025 property value of the form @code{(space . PROPS)} (@pxref{Specified
7026 Space}). Emacs treats this display specification as a @dfn{paragraph
7027 separator}, and reorders the text on either side separately.
7030 @defun bidi-string-mark-left-to-right string
7031 This function returns its argument @var{string}, possibly modified,
7032 such that the result can be safely concatenated with another string,
7033 or juxtaposed with another string in a buffer, without disrupting the
7034 relative layout of this string and the next one on display. If the
7035 string returned by this function is displayed as part of a
7036 left-to-right paragraph, it will always appear on display to the left
7037 of the text that follows it. The function works by examining the
7038 characters of its argument, and if any of those characters could cause
7039 reordering on display, the function appends the @acronym{LRM}
7040 character to the string. The appended @acronym{LRM} character is made
7041 invisible by giving it an @code{invisible} text property of @code{t}
7042 (@pxref{Invisible Text}).
7045 The reordering algorithm uses the bidirectional properties of the
7046 characters stored as their @code{bidi-class} property
7047 (@pxref{Character Properties}). Lisp programs can change these
7048 properties by calling the @code{put-char-code-property} function.
7049 However, doing this requires a thorough understanding of the
7050 @acronym{UBA}, and is therefore not recommended. Any changes to the
7051 bidirectional properties of a character have global effect: they
7052 affect all Emacs frames and windows.
7054 Similarly, the @code{mirroring} property is used to display the
7055 appropriate mirrored character in the reordered text. Lisp programs
7056 can affect the mirrored display by changing this property. Again, any
7057 such changes affect all of Emacs display.
7059 @cindex overriding bidirectional properties
7060 @cindex directional overrides
7063 The bidirectional properties of characters can be overridden by
7064 inserting into the text special directional control characters,
7065 LEFT-TO-RIGHT OVERRIDE (@acronym{LRO}) and RIGHT-TO-LEFT OVERRIDE
7066 (@acronym{RLO}). Any characters between a @acronym{RLO} and the
7067 following newline or POP DIRECTIONAL FORMATTING (@acronym{PDF})
7068 control character, whichever comes first, will be displayed as if they
7069 were strong right-to-left characters, i.e.@: they will be reversed on
7070 display. Similarly, any characters between @acronym{LRO} and
7071 @acronym{PDF} or newline will display as if they were strong
7072 left-to-right, and will @emph{not} be reversed even if they are strong
7073 right-to-left characters.
7075 @cindex phishing using directional overrides
7076 @cindex malicious use of directional overrides
7077 These overrides are useful when you want to make some text
7078 unaffected by the reordering algorithm, and instead directly control
7079 the display order. But they can also be used for malicious purposes,
7080 known as @dfn{phishing}. Specifically, a URL on a Web page or a link
7081 in an email message can be manipulated to make its visual appearance
7082 unrecognizable, or similar to some popular benign location, while the
7083 real location, interpreted by a browser in the logical order, is very
7086 Emacs provides a primitive that applications can use to detect
7087 instances of text whose bidirectional properties were overridden so as
7088 to make a left-to-right character display as if it were a
7089 right-to-left character, or vise versa.
7091 @defun bidi-find-overridden-directionality from to &optional object
7092 This function looks at the text of the specified @var{object} between
7093 positions @var{from} (inclusive) and @var{to} (exclusive), and returns
7094 the first position where it finds a strong left-to-right character
7095 whose directional properties were forced to display the character as
7096 right-to-left, or for a strong right-to-left character that was forced
7097 to display as left-to-right. If it finds no such characters in the
7098 specified region of text, it returns @code{nil}.
7100 The optional argument @var{object} specifies which text to search, and
7101 defaults to the current buffer. If @var{object} is non-@code{nil}, it
7102 can be some other buffer, or it can be a string or a window. If it is
7103 a string, the function searches that string. If it is a window, the
7104 function searches the buffer displayed in that window. If a buffer
7105 whose text you want to examine is displayed in some window, we
7106 recommend to specify it by that window, rather than pass the buffer to
7107 the function. This is because telling the function about the window
7108 allows it to correctly account for window-specific overlays, which
7109 might change the result of the function if some text in the buffer is
7110 covered by overlays.
7113 @cindex copying bidirectional text, preserve visual order
7114 @cindex visual order, preserve when copying bidirectional text
7115 When text that includes mixed right-to-left and left-to-right
7116 characters and bidirectional controls is copied into a different
7117 location, it can change its visual appearance, and also can affect the
7118 visual appearance of the surrounding text at destination. This is
7119 because reordering of bidirectional text specified by the
7120 @acronym{UBA} has non-trivial context-dependent effects both on the
7121 copied text and on the text at copy destination that will surround it.
7123 Sometimes, a Lisp program may need to preserve the exact visual
7124 appearance of the copied text at destination, and of the text that
7125 surrounds the copy. Lisp programs can use the following function to
7126 achieve that effect.
7128 @defun buffer-substring-with-bidi-context start end &optional no-properties
7129 This function works similar to @code{buffer-substring} (@pxref{Buffer
7130 Contents}), but it prepends and appends to the copied text bidi
7131 directional control characters necessary to preserve the visual
7132 appearance of the text when it is inserted at another place. Optional
7133 argument @var{no-properties}, if non-@code{nil}, means remove the text
7134 properties from the copy of the text.