2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-2014 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 * Width:: How wide a character or string is on the screen.
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 vertical scroll bars.
27 * Display Property:: Enabling special display features.
28 * Images:: Displaying images in Emacs buffers.
29 * Buttons:: Adding clickable buttons to Emacs buffers.
30 * Abstract Display:: Emacs's Widget for Object Collections.
31 * Blinking:: How Emacs shows the matching open parenthesis.
32 * Character Display:: How Emacs displays individual characters.
33 * Beeping:: Audible signal to the user.
34 * Window Systems:: Which window system is being used.
35 * Bidirectional Display:: Display of bidirectional scripts, such as
40 @section Refreshing the Screen
42 The function @code{redraw-frame} clears and redisplays the entire
43 contents of a given frame (@pxref{Frames}). This is useful if the
46 @defun redraw-frame frame
47 This function clears and redisplays frame @var{frame}.
50 Even more powerful is @code{redraw-display}:
52 @deffn Command redraw-display
53 This function clears and redisplays all visible frames.
56 In Emacs, processing user input takes priority over redisplay. If
57 you call these functions when input is available, they don't redisplay
58 immediately, but the requested redisplay does happen
59 eventually---after all the input has been processed.
61 On text terminals, suspending and resuming Emacs normally also
62 refreshes the screen. Some terminal emulators record separate
63 contents for display-oriented programs such as Emacs and for ordinary
64 sequential display. If you are using such a terminal, you might want
65 to inhibit the redisplay on resumption.
67 @defopt no-redraw-on-reenter
68 @cindex suspend (cf. @code{no-redraw-on-reenter})
69 @cindex resume (cf. @code{no-redraw-on-reenter})
70 This variable controls whether Emacs redraws the entire screen after it
71 has been suspended and resumed. Non-@code{nil} means there is no need
72 to redraw, @code{nil} means redrawing is needed. The default is @code{nil}.
75 @node Forcing Redisplay
76 @section Forcing Redisplay
77 @cindex forcing redisplay
79 Emacs normally tries to redisplay the screen whenever it waits for
80 input. With the following function, you can request an immediate
81 attempt to redisplay, in the middle of Lisp code, without actually
84 @defun redisplay &optional force
85 This function tries immediately to redisplay. The optional argument
86 @var{force}, if non-@code{nil}, forces the redisplay to be performed,
87 instead of being preempted, even if input is pending and the variable
88 @code{redisplay-dont-pause} is @code{nil} (see below). If
89 @code{redisplay-dont-pause} is non-@code{nil} (the default), this
90 function redisplays in any case, i.e., @var{force} does nothing.
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 redisplay-dont-pause
99 If this variable is @code{nil}, arriving input events preempt
100 redisplay; Emacs avoids starting a redisplay, and stops any redisplay
101 that is in progress, until the input has been processed. In
102 particular, @code{(redisplay)} returns @code{nil} without actually
103 redisplaying, if there is pending input.
105 The default value is @code{t}, which means that pending input does not
109 @defvar redisplay-preemption-period
110 If @code{redisplay-dont-pause} is @code{nil}, this variable specifies
111 how many seconds Emacs waits between checks for new input during
112 redisplay; if input arrives during this interval, redisplay stops and
113 the input is processed. The default value is 0.1; if the value is
114 @code{nil}, Emacs does not check for input during redisplay.
116 This variable has no effect when @code{redisplay-dont-pause} is
117 non-@code{nil} (the default).
120 Although @code{redisplay} tries immediately to redisplay, it does
121 not change how Emacs decides which parts of its frame(s) to redisplay.
122 By contrast, the following function adds certain windows to the
123 pending redisplay work (as if their contents had completely changed),
124 but does not immediately try to perform redisplay.
126 @defun force-window-update &optional object
127 This function forces some or all windows to be updated the next time
128 Emacs does a redisplay. If @var{object} is a window, that window is
129 to be updated. If @var{object} is a buffer or buffer name, all
130 windows displaying that buffer are to be updated. If @var{object} is
131 @code{nil} (or omitted), all windows are to be updated.
133 This function does not do a redisplay immediately; Emacs does that as
134 it waits for input, or when the function @code{redisplay} is called.
139 @cindex line wrapping
140 @cindex line truncation
141 @cindex continuation lines
142 @cindex @samp{$} in display
143 @cindex @samp{\} in display
145 When a line of text extends beyond the right edge of a window, Emacs
146 can @dfn{continue} the line (make it ``wrap'' to the next screen
147 line), or @dfn{truncate} the line (limit it to one screen line). The
148 additional screen lines used to display a long text line are called
149 @dfn{continuation} lines. Continuation is not the same as filling;
150 continuation happens on the screen only, not in the buffer contents,
151 and it breaks a line precisely at the right margin, not at a word
152 boundary. @xref{Filling}.
154 On a graphical display, tiny arrow images in the window fringes
155 indicate truncated and continued lines (@pxref{Fringes}). On a text
156 terminal, a @samp{$} in the rightmost column of the window indicates
157 truncation; a @samp{\} on the rightmost column indicates a line that
158 ``wraps''. (The display table can specify alternate characters to use
159 for this; @pxref{Display Tables}).
161 @defopt truncate-lines
162 If this buffer-local variable is non-@code{nil}, lines that extend
163 beyond the right edge of the window are truncated; otherwise, they are
164 continued. As a special exception, the variable
165 @code{truncate-partial-width-windows} takes precedence in
166 @dfn{partial-width} windows (i.e., windows that do not occupy the
170 @defopt truncate-partial-width-windows
171 @cindex partial-width windows
172 This variable controls line truncation in @dfn{partial-width} windows.
173 A partial-width window is one that does not occupy the entire frame
174 width (@pxref{Splitting Windows}). If the value is @code{nil}, line
175 truncation is determined by the variable @code{truncate-lines} (see
176 above). If the value is an integer @var{n}, lines are truncated if
177 the partial-width window has fewer than @var{n} columns, regardless of
178 the value of @code{truncate-lines}; if the partial-width window has
179 @var{n} or more columns, line truncation is determined by
180 @code{truncate-lines}. For any other non-@code{nil} value, lines are
181 truncated in every partial-width window, regardless of the value of
182 @code{truncate-lines}.
185 When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in
186 a window, that forces truncation.
189 If this buffer-local variable is non-@code{nil}, it defines a
190 @dfn{wrap prefix} which Emacs displays at the start of every
191 continuation line. (If lines are truncated, @code{wrap-prefix} is
192 never used.) Its value may be a string or an image (@pxref{Other
193 Display Specs}), or a stretch of whitespace such as specified by the
194 @code{:width} or @code{:align-to} display properties (@pxref{Specified
195 Space}). The value is interpreted in the same way as a @code{display}
196 text property. @xref{Display Property}.
198 A wrap prefix may also be specified for regions of text, using the
199 @code{wrap-prefix} text or overlay property. This takes precedence
200 over the @code{wrap-prefix} variable. @xref{Special Properties}.
204 If this buffer-local variable is non-@code{nil}, it defines a
205 @dfn{line prefix} which Emacs displays at the start of every
206 non-continuation line. Its value may be a string or an image
207 (@pxref{Other Display Specs}), or a stretch of whitespace such as
208 specified by the @code{:width} or @code{:align-to} display properties
209 (@pxref{Specified Space}). The value is interpreted in the same way
210 as a @code{display} text property. @xref{Display Property}.
212 A line prefix may also be specified for regions of text using the
213 @code{line-prefix} text or overlay property. This takes precedence
214 over the @code{line-prefix} variable. @xref{Special Properties}.
218 If your buffer contains only very short lines, you might find it
219 advisable to set @code{cache-long-scans} to @code{nil}.
221 @defvar cache-long-scans
222 If this variable is non-@code{nil} (the default), various indentation
223 and motion functions, and Emacs redisplay, cache the results of
224 scanning the buffer, and consult the cache to avoid rescanning regions
225 of the buffer unless they are modified.
227 Turning off the cache speeds up processing of short lines somewhat.
229 This variable is automatically buffer-local in every buffer.
234 @section The Echo Area
235 @cindex error display
238 @c FIXME: Why not use @xref{Minibuffers} directly? --xfq
239 The @dfn{echo area} is used for displaying error messages
240 (@pxref{Errors}), for messages made with the @code{message} primitive,
241 and for echoing keystrokes. It is not the same as the minibuffer,
242 despite the fact that the minibuffer appears (when active) in the same
243 place on the screen as the echo area. @xref{Minibuffer,, The
244 Minibuffer, emacs, The GNU Emacs Manual}.
246 Apart from the functions documented in this section, you can print
247 Lisp objects to the echo area by specifying @code{t} as the output
248 stream. @xref{Output Streams}.
251 * Displaying Messages:: Explicitly displaying text in the echo area.
252 * Progress:: Informing user about progress of a long operation.
253 * Logging Messages:: Echo area messages are logged for the user.
254 * Echo Area Customization:: Controlling the echo area.
257 @node Displaying Messages
258 @subsection Displaying Messages in the Echo Area
259 @cindex display message in echo area
261 This section describes the standard functions for displaying
262 messages in the echo area.
264 @defun message format-string &rest arguments
265 This function displays a message in the echo area.
266 @var{format-string} is a format string, and @var{arguments} are the
267 objects for its format specifications, like in the @code{format}
268 function (@pxref{Formatting Strings}). The resulting formatted string
269 is displayed in the echo area; if it contains @code{face} text
270 properties, it is displayed with the specified faces (@pxref{Faces}).
271 The string is also added to the @file{*Messages*} buffer, but without
272 text properties (@pxref{Logging Messages}).
274 In batch mode, the message is printed to the standard error stream,
275 followed by a newline.
277 If @var{format-string} is @code{nil} or the empty string,
278 @code{message} clears the echo area; if the echo area has been
279 expanded automatically, this brings it back to its normal size. If
280 the minibuffer is active, this brings the minibuffer contents back
281 onto the screen immediately.
285 (message "Minibuffer depth is %d."
287 @print{} Minibuffer depth is 0.
288 @result{} "Minibuffer depth is 0."
292 ---------- Echo Area ----------
293 Minibuffer depth is 0.
294 ---------- Echo Area ----------
298 To automatically display a message in the echo area or in a pop-buffer,
299 depending on its size, use @code{display-message-or-buffer} (see below).
302 @defmac with-temp-message message &rest body
303 This construct displays a message in the echo area temporarily, during
304 the execution of @var{body}. It displays @var{message}, executes
305 @var{body}, then returns the value of the last body form while restoring
306 the previous echo area contents.
309 @defun message-or-box format-string &rest arguments
310 This function displays a message like @code{message}, but may display it
311 in a dialog box instead of the echo area. If this function is called in
312 a command that was invoked using the mouse---more precisely, if
313 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
314 @code{nil} or a list---then it uses a dialog box or pop-up menu to
315 display the message. Otherwise, it uses the echo area. (This is the
316 same criterion that @code{y-or-n-p} uses to make a similar decision; see
317 @ref{Yes-or-No Queries}.)
319 You can force use of the mouse or of the echo area by binding
320 @code{last-nonmenu-event} to a suitable value around the call.
323 @defun message-box format-string &rest arguments
325 This function displays a message like @code{message}, but uses a dialog
326 box (or a pop-up menu) whenever that is possible. If it is impossible
327 to use a dialog box or pop-up menu, because the terminal does not
328 support them, then @code{message-box} uses the echo area, like
332 @defun display-message-or-buffer message &optional buffer-name not-this-window frame
333 This function displays the message @var{message}, which may be either a
334 string or a buffer. If it is shorter than the maximum height of the
335 echo area, as defined by @code{max-mini-window-height}, it is displayed
336 in the echo area, using @code{message}. Otherwise,
337 @code{display-buffer} is used to show it in a pop-up buffer.
339 Returns either the string shown in the echo area, or when a pop-up
340 buffer is used, the window used to display it.
342 If @var{message} is a string, then the optional argument
343 @var{buffer-name} is the name of the buffer used to display it when a
344 pop-up buffer is used, defaulting to @file{*Message*}. In the case
345 where @var{message} is a string and displayed in the echo area, it is
346 not specified whether the contents are inserted into the buffer anyway.
348 The optional arguments @var{not-this-window} and @var{frame} are as for
349 @code{display-buffer}, and only used if a buffer is displayed.
352 @defun current-message
353 This function returns the message currently being displayed in the
354 echo area, or @code{nil} if there is none.
358 @subsection Reporting Operation Progress
359 @cindex progress reporting
361 When an operation can take a while to finish, you should inform the
362 user about the progress it makes. This way the user can estimate
363 remaining time and clearly see that Emacs is busy working, not hung.
364 A convenient way to do this is to use a @dfn{progress reporter}.
366 Here is a working example that does nothing useful:
369 (let ((progress-reporter
370 (make-progress-reporter "Collecting mana for Emacs..."
374 (progress-reporter-update progress-reporter k))
375 (progress-reporter-done progress-reporter))
378 @defun make-progress-reporter message &optional min-value max-value current-value min-change min-time
379 This function creates and returns a progress reporter object, which
380 you will use as an argument for the other functions listed below. The
381 idea is to precompute as much data as possible to make progress
384 When this progress reporter is subsequently used, it will display
385 @var{message} in the echo area, followed by progress percentage.
386 @var{message} is treated as a simple string. If you need it to depend
387 on a filename, for instance, use @code{format} before calling this
390 The arguments @var{min-value} and @var{max-value} should be numbers
391 standing for the starting and final states of the operation. For
392 instance, an operation that ``scans'' a buffer should set these to the
393 results of @code{point-min} and @code{point-max} correspondingly.
394 @var{max-value} should be greater than @var{min-value}.
396 Alternatively, you can set @var{min-value} and @var{max-value} to
397 @code{nil}. In that case, the progress reporter does not report
398 process percentages; it instead displays a ``spinner'' that rotates a
399 notch each time you update the progress reporter.
401 If @var{min-value} and @var{max-value} are numbers, you can give the
402 argument @var{current-value} a numerical value specifying the initial
403 progress; if omitted, this defaults to @var{min-value}.
405 The remaining arguments control the rate of echo area updates. The
406 progress reporter will wait for at least @var{min-change} more
407 percents of the operation to be completed before printing next
408 message; the default is one percent. @var{min-time} specifies the
409 minimum time in seconds to pass between successive prints; the default
410 is 0.2 seconds. (On some operating systems, the progress reporter may
411 handle fractions of seconds with varying precision).
413 This function calls @code{progress-reporter-update}, so the first
414 message is printed immediately.
417 @defun progress-reporter-update reporter &optional value
418 This function does the main work of reporting progress of your
419 operation. It displays the message of @var{reporter}, followed by
420 progress percentage determined by @var{value}. If percentage is zero,
421 or close enough according to the @var{min-change} and @var{min-time}
422 arguments, then it is omitted from the output.
424 @var{reporter} must be the result of a call to
425 @code{make-progress-reporter}. @var{value} specifies the current
426 state of your operation and must be between @var{min-value} and
427 @var{max-value} (inclusive) as passed to
428 @code{make-progress-reporter}. For instance, if you scan a buffer,
429 then @var{value} should be the result of a call to @code{point}.
431 This function respects @var{min-change} and @var{min-time} as passed
432 to @code{make-progress-reporter} and so does not output new messages
433 on every invocation. It is thus very fast and normally you should not
434 try to reduce the number of calls to it: resulting overhead will most
435 likely negate your effort.
438 @defun progress-reporter-force-update reporter &optional value new-message
439 This function is similar to @code{progress-reporter-update} except
440 that it prints a message in the echo area unconditionally.
442 The first two arguments have the same meaning as for
443 @code{progress-reporter-update}. Optional @var{new-message} allows
444 you to change the message of the @var{reporter}. Since this function
445 always updates the echo area, such a change will be immediately
446 presented to the user.
449 @defun progress-reporter-done reporter
450 This function should be called when the operation is finished. It
451 prints the message of @var{reporter} followed by word ``done'' in the
454 You should always call this function and not hope for
455 @code{progress-reporter-update} to print ``100%''. Firstly, it may
456 never print it, there are many good reasons for this not to happen.
457 Secondly, ``done'' is more explicit.
460 @defmac dotimes-with-progress-reporter (var count [result]) message body@dots{}
461 This is a convenience macro that works the same way as @code{dotimes}
462 does, but also reports loop progress using the functions described
463 above. It allows you to save some typing.
465 You can rewrite the example in the beginning of this node using
469 (dotimes-with-progress-reporter
471 "Collecting some mana for Emacs..."
476 @node Logging Messages
477 @subsection Logging Messages in @file{*Messages*}
478 @cindex logging echo-area messages
480 Almost all the messages displayed in the echo area are also recorded
481 in the @file{*Messages*} buffer so that the user can refer back to
482 them. This includes all the messages that are output with
483 @code{message}. By default, this buffer is read-only and uses the major
484 mode @code{messages-buffer-mode}. Nothing prevents the user from
485 killing the @file{*Messages*} buffer, but the next display of a message
486 recreates it. Any Lisp code that needs to access the
487 @file{*Messages*} buffer directly and wants to ensure that it exists
488 should use the function @code{messages-buffer}.
490 @defun messages-buffer
491 This function returns the @file{*Messages*} buffer. If it does not
492 exist, it creates it, and switches it to @code{messages-buffer-mode}.
495 @defopt message-log-max
496 This variable specifies how many lines to keep in the @file{*Messages*}
497 buffer. The value @code{t} means there is no limit on how many lines to
498 keep. The value @code{nil} disables message logging entirely. Here's
499 how to display a message and prevent it from being logged:
502 (let (message-log-max)
507 To make @file{*Messages*} more convenient for the user, the logging
508 facility combines successive identical messages. It also combines
509 successive related messages for the sake of two cases: question
510 followed by answer, and a series of progress messages.
512 A ``question followed by an answer'' means two messages like the
513 ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
514 and the second is @samp{@var{question}...@var{answer}}. The first
515 message conveys no additional information beyond what's in the second,
516 so logging the second message discards the first from the log.
518 A ``series of progress messages'' means successive messages like
519 those produced by @code{make-progress-reporter}. They have the form
520 @samp{@var{base}...@var{how-far}}, where @var{base} is the same each
521 time, while @var{how-far} varies. Logging each message in the series
522 discards the previous one, provided they are consecutive.
524 The functions @code{make-progress-reporter} and @code{y-or-n-p}
525 don't have to do anything special to activate the message log
526 combination feature. It operates whenever two consecutive messages
527 are logged that share a common prefix ending in @samp{...}.
529 @node Echo Area Customization
530 @subsection Echo Area Customization
532 These variables control details of how the echo area works.
534 @defvar cursor-in-echo-area
535 This variable controls where the cursor appears when a message is
536 displayed in the echo area. If it is non-@code{nil}, then the cursor
537 appears at the end of the message. Otherwise, the cursor appears at
538 point---not in the echo area at all.
540 The value is normally @code{nil}; Lisp programs bind it to @code{t}
541 for brief periods of time.
544 @defvar echo-area-clear-hook
545 This normal hook is run whenever the echo area is cleared---either by
546 @code{(message nil)} or for any other reason.
549 @defopt echo-keystrokes
550 This variable determines how much time should elapse before command
551 characters echo. Its value must be an integer or floating point number,
553 number of seconds to wait before echoing. If the user types a prefix
554 key (such as @kbd{C-x}) and then delays this many seconds before
555 continuing, the prefix key is echoed in the echo area. (Once echoing
556 begins in a key sequence, all subsequent characters in the same key
557 sequence are echoed immediately.)
559 If the value is zero, then command input is not echoed.
562 @defvar message-truncate-lines
563 Normally, displaying a long message resizes the echo area to display
564 the entire message. But if the variable @code{message-truncate-lines}
565 is non-@code{nil}, the echo area does not resize, and the message is
569 The variable @code{max-mini-window-height}, which specifies the
570 maximum height for resizing minibuffer windows, also applies to the
571 echo area (which is really a special use of the minibuffer window;
572 @pxref{Minibuffer Misc}).
575 @section Reporting Warnings
578 @dfn{Warnings} are a facility for a program to inform the user of a
579 possible problem, but continue running.
582 * Warning Basics:: Warnings concepts and functions to report them.
583 * Warning Variables:: Variables programs bind to customize their warnings.
584 * Warning Options:: Variables users set to control display of warnings.
585 * Delayed Warnings:: Deferring a warning until the end of a command.
589 @subsection Warning Basics
590 @cindex severity level
592 Every warning has a textual message, which explains the problem for
593 the user, and a @dfn{severity level} which is a symbol. Here are the
594 possible severity levels, in order of decreasing severity, and their
599 A problem that will seriously impair Emacs operation soon
600 if you do not attend to it promptly.
602 A report of data or circumstances that are inherently wrong.
604 A report of data or circumstances that are not inherently wrong, but
605 raise suspicion of a possible problem.
607 A report of information that may be useful if you are debugging.
610 When your program encounters invalid input data, it can either
611 signal a Lisp error by calling @code{error} or @code{signal} or report
612 a warning with severity @code{:error}. Signaling a Lisp error is the
613 easiest thing to do, but it means the program cannot continue
614 processing. If you want to take the trouble to implement a way to
615 continue processing despite the bad data, then reporting a warning of
616 severity @code{:error} is the right way to inform the user of the
617 problem. For instance, the Emacs Lisp byte compiler can report an
618 error that way and continue compiling other functions. (If the
619 program signals a Lisp error and then handles it with
620 @code{condition-case}, the user won't see the error message; it could
621 show the message to the user by reporting it as a warning.)
623 @c FIXME: Why use "(bytecomp)" instead of "'bytecomp" or simply
624 @c "bytecomp" here? The parens are part of warning-type-format but
625 @c not part of the warning type. --xfq
627 Each warning has a @dfn{warning type} to classify it. The type is a
628 list of symbols. The first symbol should be the custom group that you
629 use for the program's user options. For example, byte compiler
630 warnings use the warning type @code{(bytecomp)}. You can also
631 subcategorize the warnings, if you wish, by using more symbols in the
634 @defun display-warning type message &optional level buffer-name
635 This function reports a warning, using @var{message} as the message
636 and @var{type} as the warning type. @var{level} should be the
637 severity level, with @code{:warning} being the default.
639 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
640 for logging the warning. By default, it is @file{*Warnings*}.
643 @defun lwarn type level message &rest args
644 This function reports a warning using the value of @code{(format
645 @var{message} @var{args}...)} as the message in the @file{*Warnings*}
646 buffer. In other respects it is equivalent to @code{display-warning}.
649 @defun warn message &rest args
650 This function reports a warning using the value of @code{(format
651 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
652 type, and @code{:warning} as the severity level. It exists for
653 compatibility only; we recommend not using it, because you should
654 specify a specific warning type.
657 @node Warning Variables
658 @subsection Warning Variables
660 Programs can customize how their warnings appear by binding
661 the variables described in this section.
663 @defvar warning-levels
664 This list defines the meaning and severity order of the warning
665 severity levels. Each element defines one severity level,
666 and they are arranged in order of decreasing severity.
668 Each element has the form @code{(@var{level} @var{string}
669 @var{function})}, where @var{level} is the severity level it defines.
670 @var{string} specifies the textual description of this level.
671 @var{string} should use @samp{%s} to specify where to put the warning
672 type information, or it can omit the @samp{%s} so as not to include
675 The optional @var{function}, if non-@code{nil}, is a function to call
676 with no arguments, to get the user's attention.
678 Normally you should not change the value of this variable.
681 @defvar warning-prefix-function
682 If non-@code{nil}, the value is a function to generate prefix text for
683 warnings. Programs can bind the variable to a suitable function.
684 @code{display-warning} calls this function with the warnings buffer
685 current, and the function can insert text in it. That text becomes
686 the beginning of the warning message.
688 The function is called with two arguments, the severity level and its
689 entry in @code{warning-levels}. It should return a list to use as the
690 entry (this value need not be an actual member of
691 @code{warning-levels}). By constructing this value, the function can
692 change the severity of the warning, or specify different handling for
693 a given severity level.
695 If the variable's value is @code{nil} then there is no function
699 @defvar warning-series
700 Programs can bind this variable to @code{t} to say that the next
701 warning should begin a series. When several warnings form a series,
702 that means to leave point on the first warning of the series, rather
703 than keep moving it for each warning so that it appears on the last one.
704 The series ends when the local binding is unbound and
705 @code{warning-series} becomes @code{nil} again.
707 The value can also be a symbol with a function definition. That is
708 equivalent to @code{t}, except that the next warning will also call
709 the function with no arguments with the warnings buffer current. The
710 function can insert text which will serve as a header for the series
713 Once a series has begun, the value is a marker which points to the
714 buffer position in the warnings buffer of the start of the series.
716 The variable's normal value is @code{nil}, which means to handle
717 each warning separately.
720 @defvar warning-fill-prefix
721 When this variable is non-@code{nil}, it specifies a fill prefix to
722 use for filling each warning's text.
725 @defvar warning-type-format
726 This variable specifies the format for displaying the warning type
727 in the warning message. The result of formatting the type this way
728 gets included in the message under the control of the string in the
729 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
730 If you bind it to @code{""} then the warning type won't appear at
734 @node Warning Options
735 @subsection Warning Options
737 These variables are used by users to control what happens
738 when a Lisp program reports a warning.
740 @defopt warning-minimum-level
741 This user option specifies the minimum severity level that should be
742 shown immediately to the user. The default is @code{:warning}, which
743 means to immediately display all warnings except @code{:debug}
747 @defopt warning-minimum-log-level
748 This user option specifies the minimum severity level that should be
749 logged in the warnings buffer. The default is @code{:warning}, which
750 means to log all warnings except @code{:debug} warnings.
753 @defopt warning-suppress-types
754 This list specifies which warning types should not be displayed
755 immediately for the user. Each element of the list should be a list
756 of symbols. If its elements match the first elements in a warning
757 type, then that warning is not displayed immediately.
760 @defopt warning-suppress-log-types
761 This list specifies which warning types should not be logged in the
762 warnings buffer. Each element of the list should be a list of
763 symbols. If it matches the first few elements in a warning type, then
764 that warning is not logged.
767 @node Delayed Warnings
768 @subsection Delayed Warnings
770 Sometimes, you may wish to avoid showing a warning while a command is
771 running, and only show it only after the end of the command. You can
772 use the variable @code{delayed-warnings-list} for this.
774 @defvar delayed-warnings-list
775 The value of this variable is a list of warnings to be displayed after
776 the current command has finished. Each element must be a list
779 (@var{type} @var{message} [@var{level} [@var{buffer-name}]])
783 with the same form, and the same meanings, as the argument list of
784 @code{display-warning} (@pxref{Warning Basics}). Immediately after
785 running @code{post-command-hook} (@pxref{Command Overview}), the Emacs
786 command loop displays all the warnings specified by this variable,
787 then resets it to @code{nil}.
790 Programs which need to further customize the delayed warnings
791 mechanism can change the variable @code{delayed-warnings-hook}:
793 @defvar delayed-warnings-hook
794 This is a normal hook which is run by the Emacs command loop, after
795 @code{post-command-hook}, in order to to process and display delayed
798 Its default value is a list of two functions:
801 (collapse-delayed-warnings display-delayed-warnings)
804 @findex collapse-delayed-warnings
805 @findex display-delayed-warnings
807 The function @code{collapse-delayed-warnings} removes repeated entries
808 from @code{delayed-warnings-list}. The function
809 @code{display-delayed-warnings} calls @code{display-warning} on each
810 of the entries in @code{delayed-warnings-list}, in turn, and then sets
811 @code{delayed-warnings-list} to @code{nil}.
815 @section Invisible Text
817 @cindex invisible text
818 You can make characters @dfn{invisible}, so that they do not appear on
819 the screen, with the @code{invisible} property. This can be either a
820 text property (@pxref{Text Properties}) or an overlay property
821 (@pxref{Overlays}). Cursor motion also partly ignores these
822 characters; if the command loop finds that point is inside a range of
823 invisible text after a command, it relocates point to the other side
826 In the simplest case, any non-@code{nil} @code{invisible} property makes
827 a character invisible. This is the default case---if you don't alter
828 the default value of @code{buffer-invisibility-spec}, this is how the
829 @code{invisible} property works. You should normally use @code{t}
830 as the value of the @code{invisible} property if you don't plan
831 to set @code{buffer-invisibility-spec} yourself.
833 More generally, you can use the variable @code{buffer-invisibility-spec}
834 to control which values of the @code{invisible} property make text
835 invisible. This permits you to classify the text into different subsets
836 in advance, by giving them different @code{invisible} values, and
837 subsequently make various subsets visible or invisible by changing the
838 value of @code{buffer-invisibility-spec}.
840 Controlling visibility with @code{buffer-invisibility-spec} is
841 especially useful in a program to display the list of entries in a
842 database. It permits the implementation of convenient filtering
843 commands to view just a part of the entries in the database. Setting
844 this variable is very fast, much faster than scanning all the text in
845 the buffer looking for properties to change.
847 @defvar buffer-invisibility-spec
848 This variable specifies which kinds of @code{invisible} properties
849 actually make a character invisible. Setting this variable makes it
854 A character is invisible if its @code{invisible} property is
855 non-@code{nil}. This is the default.
858 Each element of the list specifies a criterion for invisibility; if a
859 character's @code{invisible} property fits any one of these criteria,
860 the character is invisible. The list can have two kinds of elements:
864 A character is invisible if its @code{invisible} property value is
865 @var{atom} or if it is a list with @var{atom} as a member; comparison
866 is done with @code{eq}.
868 @item (@var{atom} . t)
869 A character is invisible if its @code{invisible} property value is
870 @var{atom} or if it is a list with @var{atom} as a member; comparison
871 is done with @code{eq}. Moreover, a sequence of such characters
872 displays as an ellipsis.
877 Two functions are specifically provided for adding elements to
878 @code{buffer-invisibility-spec} and removing elements from it.
880 @defun add-to-invisibility-spec element
881 This function adds the element @var{element} to
882 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
883 was @code{t}, it changes to a list, @code{(t)}, so that text whose
884 @code{invisible} property is @code{t} remains invisible.
887 @defun remove-from-invisibility-spec element
888 This removes the element @var{element} from
889 @code{buffer-invisibility-spec}. This does nothing if @var{element}
893 A convention for use of @code{buffer-invisibility-spec} is that a
894 major mode should use the mode's own name as an element of
895 @code{buffer-invisibility-spec} and as the value of the
896 @code{invisible} property:
899 ;; @r{If you want to display an ellipsis:}
900 (add-to-invisibility-spec '(my-symbol . t))
901 ;; @r{If you don't want ellipsis:}
902 (add-to-invisibility-spec 'my-symbol)
904 (overlay-put (make-overlay beginning end)
905 'invisible 'my-symbol)
907 ;; @r{When done with the invisibility:}
908 (remove-from-invisibility-spec '(my-symbol . t))
909 ;; @r{Or respectively:}
910 (remove-from-invisibility-spec 'my-symbol)
913 You can check for invisibility using the following function:
915 @defun invisible-p pos-or-prop
916 If @var{pos-or-prop} is a marker or number, this function returns a
917 non-@code{nil} value if the text at that position is invisible.
919 If @var{pos-or-prop} is any other kind of Lisp object, that is taken
920 to mean a possible value of the @code{invisible} text or overlay
921 property. In that case, this function returns a non-@code{nil} value
922 if that value would cause text to become invisible, based on the
923 current value of @code{buffer-invisibility-spec}.
926 @vindex line-move-ignore-invisible
927 Ordinarily, functions that operate on text or move point do not care
928 whether the text is invisible. The user-level line motion commands
929 ignore invisible newlines if @code{line-move-ignore-invisible} is
930 non-@code{nil} (the default), but only because they are explicitly
933 However, if a command ends with point inside or at the boundary of
934 invisible text, the main editing loop relocates point to one of the
935 two ends of the invisible text. Emacs chooses the direction of
936 relocation so that it is the same as the overall movement direction of
937 the command; if in doubt, it prefers a position where an inserted char
938 would not inherit the @code{invisible} property. Additionally, if the
939 text is not replaced by an ellipsis and the command only moved within
940 the invisible text, then point is moved one extra character so as to
941 try and reflect the command's movement by a visible movement of the
944 Thus, if the command moved point back to an invisible range (with the usual
945 stickiness), Emacs moves point back to the beginning of that range. If the
946 command moved point forward into an invisible range, Emacs moves point forward
947 to the first visible character that follows the invisible text and then forward
950 Incremental search can make invisible overlays visible temporarily
951 and/or permanently when a match includes invisible text. To enable
952 this, the overlay should have a non-@code{nil}
953 @code{isearch-open-invisible} property. The property value should be a
954 function to be called with the overlay as an argument. This function
955 should make the overlay visible permanently; it is used when the match
956 overlaps the overlay on exit from the search.
958 During the search, such overlays are made temporarily visible by
959 temporarily modifying their invisible and intangible properties. If you
960 want this to be done differently for a certain overlay, give it an
961 @code{isearch-open-invisible-temporary} property which is a function.
962 The function is called with two arguments: the first is the overlay, and
963 the second is @code{nil} to make the overlay visible, or @code{t} to
964 make it invisible again.
966 @node Selective Display
967 @section Selective Display
968 @c @cindex selective display Duplicates selective-display
970 @dfn{Selective display} refers to a pair of related features for
971 hiding certain lines on the screen.
973 @cindex explicit selective display
974 The first variant, explicit selective display, was designed for use in a Lisp
975 program: it controls which lines are hidden by altering the text. This kind of
976 hiding is now obsolete; instead you can get the same effect with the
977 @code{invisible} property (@pxref{Invisible Text}).
979 In the second variant, the choice of lines to hide is made
980 automatically based on indentation. This variant is designed to be a
983 The way you control explicit selective display is by replacing a
984 newline (control-j) with a carriage return (control-m). The text that
985 was formerly a line following that newline is now hidden. Strictly
986 speaking, it is temporarily no longer a line at all, since only
987 newlines can separate lines; it is now part of the previous line.
989 Selective display does not directly affect editing commands. For
990 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
991 into hidden text. However, the replacement of newline characters with
992 carriage return characters affects some editing commands. For
993 example, @code{next-line} skips hidden lines, since it searches only
994 for newlines. Modes that use selective display can also define
995 commands that take account of the newlines, or that control which
996 parts of the text are hidden.
998 When you write a selectively displayed buffer into a file, all the
999 control-m's are output as newlines. This means that when you next read
1000 in the file, it looks OK, with nothing hidden. The selective display
1001 effect is seen only within Emacs.
1003 @defvar selective-display
1004 This buffer-local variable enables selective display. This means that
1005 lines, or portions of lines, may be made hidden.
1009 If the value of @code{selective-display} is @code{t}, then the character
1010 control-m marks the start of hidden text; the control-m, and the rest
1011 of the line following it, are not displayed. This is explicit selective
1015 If the value of @code{selective-display} is a positive integer, then
1016 lines that start with more than that many columns of indentation are not
1020 When some portion of a buffer is hidden, the vertical movement
1021 commands operate as if that portion did not exist, allowing a single
1022 @code{next-line} command to skip any number of hidden lines.
1023 However, character movement commands (such as @code{forward-char}) do
1024 not skip the hidden portion, and it is possible (if tricky) to insert
1025 or delete text in an hidden portion.
1027 In the examples below, we show the @emph{display appearance} of the
1028 buffer @code{foo}, which changes with the value of
1029 @code{selective-display}. The @emph{contents} of the buffer do not
1034 (setq selective-display nil)
1037 ---------- Buffer: foo ----------
1044 ---------- Buffer: foo ----------
1048 (setq selective-display 2)
1051 ---------- Buffer: foo ----------
1056 ---------- Buffer: foo ----------
1061 @defopt selective-display-ellipses
1062 If this buffer-local variable is non-@code{nil}, then Emacs displays
1063 @samp{@dots{}} at the end of a line that is followed by hidden text.
1064 This example is a continuation of the previous one.
1068 (setq selective-display-ellipses t)
1071 ---------- Buffer: foo ----------
1076 ---------- Buffer: foo ----------
1080 You can use a display table to substitute other text for the ellipsis
1081 (@samp{@dots{}}). @xref{Display Tables}.
1084 @node Temporary Displays
1085 @section Temporary Displays
1087 Temporary displays are used by Lisp programs to put output into a
1088 buffer and then present it to the user for perusal rather than for
1089 editing. Many help commands use this feature.
1091 @defmac with-output-to-temp-buffer buffer-name forms@dots{}
1092 This function executes @var{forms} while arranging to insert any output
1093 they print into the buffer named @var{buffer-name}, which is first
1094 created if necessary, and put into Help mode. Finally, the buffer is
1095 displayed in some window, but not selected. (See the similar
1096 form @code{with-temp-buffer-window} below.)
1098 If the @var{forms} do not change the major mode in the output buffer,
1099 so that it is still Help mode at the end of their execution, then
1100 @code{with-output-to-temp-buffer} makes this buffer read-only at the
1101 end, and also scans it for function and variable names to make them
1102 into clickable cross-references. @xref{Docstring hyperlinks, , Tips
1103 for Documentation Strings}, in particular the item on hyperlinks in
1104 documentation strings, for more details.
1106 The string @var{buffer-name} specifies the temporary buffer, which
1107 need not already exist. The argument must be a string, not a buffer.
1108 The buffer is erased initially (with no questions asked), and it is
1109 marked as unmodified after @code{with-output-to-temp-buffer} exits.
1111 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
1112 temporary buffer, then it evaluates the forms in @var{forms}. Output
1113 using the Lisp output functions within @var{forms} goes by default to
1114 that buffer (but screen display and messages in the echo area, although
1115 they are ``output'' in the general sense of the word, are not affected).
1116 @xref{Output Functions}.
1118 Several hooks are available for customizing the behavior
1119 of this construct; they are listed below.
1121 The value of the last form in @var{forms} is returned.
1125 ---------- Buffer: foo ----------
1126 This is the contents of foo.
1127 ---------- Buffer: foo ----------
1131 (with-output-to-temp-buffer "foo"
1133 (print standard-output))
1134 @result{} #<buffer foo>
1136 ---------- Buffer: foo ----------
1142 ---------- Buffer: foo ----------
1147 @defopt temp-buffer-show-function
1148 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
1149 calls it as a function to do the job of displaying a help buffer. The
1150 function gets one argument, which is the buffer it should display.
1152 It is a good idea for this function to run @code{temp-buffer-show-hook}
1153 just as @code{with-output-to-temp-buffer} normally would, inside of
1154 @code{save-selected-window} and with the chosen window and buffer
1158 @defvar temp-buffer-setup-hook
1159 This normal hook is run by @code{with-output-to-temp-buffer} before
1160 evaluating @var{body}. When the hook runs, the temporary buffer is
1161 current. This hook is normally set up with a function to put the
1162 buffer in Help mode.
1165 @defvar temp-buffer-show-hook
1166 This normal hook is run by @code{with-output-to-temp-buffer} after
1167 displaying the temporary buffer. When the hook runs, the temporary buffer
1168 is current, and the window it was displayed in is selected.
1171 @defmac with-temp-buffer-window buffer-or-name action quit-function forms@dots{}
1172 This macro is similar to @code{with-output-to-temp-buffer}.
1173 Like that construct, it executes @var{forms} while arranging to insert
1174 any output they print into the buffer named @var{buffer-or-name}.
1175 Finally, the buffer is displayed in some window, but not selected.
1176 Unlike @code{with-output-to-temp-buffer}, this does not switch to Help
1179 The argument @var{buffer-or-name} specifies the temporary buffer.
1180 It can be either a buffer, which must already exist, or a string,
1181 in which case a buffer of that name is created if necessary.
1182 The buffer is marked as unmodified and read-only when
1183 @code{with-temp-buffer-window} exits.
1185 This macro does not call @code{temp-buffer-show-function}. Rather, it
1186 passes the @var{action} argument to @code{display-buffer} in order to
1189 The value of the last form in @var{forms} is returned, unless the
1190 argument @var{quit-function} is specified. In that case,
1191 it is called with two arguments: the window showing the buffer
1192 and the result of @var{forms}. The final return value is then
1193 whatever @var{quit-function} returns.
1195 @vindex temp-buffer-window-setup-hook
1196 @vindex temp-buffer-window-show-hook
1197 This macro uses the normal hooks @code{temp-buffer-window-setup-hook}
1198 and @code{temp-buffer-window-show-hook} in place of the analogous hooks
1199 run by @code{with-output-to-temp-buffer}.
1202 @defun momentary-string-display string position &optional char message
1203 This function momentarily displays @var{string} in the current buffer at
1204 @var{position}. It has no effect on the undo list or on the buffer's
1205 modification status.
1207 The momentary display remains until the next input event. If the next
1208 input event is @var{char}, @code{momentary-string-display} ignores it
1209 and returns. Otherwise, that event remains buffered for subsequent use
1210 as input. Thus, typing @var{char} will simply remove the string from
1211 the display, while typing (say) @kbd{C-f} will remove the string from
1212 the display and later (presumably) move point forward. The argument
1213 @var{char} is a space by default.
1215 The return value of @code{momentary-string-display} is not meaningful.
1217 If the string @var{string} does not contain control characters, you can
1218 do the same job in a more general way by creating (and then subsequently
1219 deleting) an overlay with a @code{before-string} property.
1220 @xref{Overlay Properties}.
1222 If @var{message} is non-@code{nil}, it is displayed in the echo area
1223 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1224 default message says to type @var{char} to continue.
1226 In this example, point is initially located at the beginning of the
1231 ---------- Buffer: foo ----------
1232 This is the contents of foo.
1233 @point{}Second line.
1234 ---------- Buffer: foo ----------
1238 (momentary-string-display
1239 "**** Important Message! ****"
1241 "Type RET when done reading")
1246 ---------- Buffer: foo ----------
1247 This is the contents of foo.
1248 **** Important Message! ****Second line.
1249 ---------- Buffer: foo ----------
1251 ---------- Echo Area ----------
1252 Type RET when done reading
1253 ---------- Echo Area ----------
1261 @c FIXME: mention intervals in this section?
1263 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1264 the screen, for the sake of presentation features. An overlay is an
1265 object that belongs to a particular buffer, and has a specified
1266 beginning and end. It also has properties that you can examine and set;
1267 these affect the display of the text within the overlay.
1269 @cindex scalability of overlays
1270 The visual effect of an overlay is the same as of the corresponding
1271 text property (@pxref{Text Properties}). However, due to a different
1272 implementation, overlays generally don't scale well (many operations
1273 take a time that is proportional to the number of overlays in the
1274 buffer). If you need to affect the visual appearance of many portions
1275 in the buffer, we recommend using text properties.
1277 An overlay uses markers to record its beginning and end; thus,
1278 editing the text of the buffer adjusts the beginning and end of each
1279 overlay so that it stays with the text. When you create the overlay,
1280 you can specify whether text inserted at the beginning should be
1281 inside the overlay or outside, and likewise for the end of the overlay.
1284 * Managing Overlays:: Creating and moving overlays.
1285 * Overlay Properties:: How to read and set properties.
1286 What properties do to the screen display.
1287 * Finding Overlays:: Searching for overlays.
1290 @node Managing Overlays
1291 @subsection Managing Overlays
1293 This section describes the functions to create, delete and move
1294 overlays, and to examine their contents. Overlay changes are not
1295 recorded in the buffer's undo list, since the overlays are not
1296 part of the buffer's contents.
1298 @defun overlayp object
1299 This function returns @code{t} if @var{object} is an overlay.
1302 @defun make-overlay start end &optional buffer front-advance rear-advance
1303 This function creates and returns an overlay that belongs to
1304 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1305 and @var{end} must specify buffer positions; they may be integers or
1306 markers. If @var{buffer} is omitted, the overlay is created in the
1309 The arguments @var{front-advance} and @var{rear-advance} specify the
1310 marker insertion type for the start of the overlay and for the end of
1311 the overlay, respectively. @xref{Marker Insertion Types}. If they
1312 are both @code{nil}, the default, then the overlay extends to include
1313 any text inserted at the beginning, but not text inserted at the end.
1314 If @var{front-advance} is non-@code{nil}, text inserted at the
1315 beginning of the overlay is excluded from the overlay. If
1316 @var{rear-advance} is non-@code{nil}, text inserted at the end of the
1317 overlay is included in the overlay.
1320 @defun overlay-start overlay
1321 This function returns the position at which @var{overlay} starts,
1325 @defun overlay-end overlay
1326 This function returns the position at which @var{overlay} ends,
1330 @defun overlay-buffer overlay
1331 This function returns the buffer that @var{overlay} belongs to. It
1332 returns @code{nil} if @var{overlay} has been deleted.
1335 @defun delete-overlay overlay
1336 This function deletes @var{overlay}. The overlay continues to exist as
1337 a Lisp object, and its property list is unchanged, but it ceases to be
1338 attached to the buffer it belonged to, and ceases to have any effect on
1341 A deleted overlay is not permanently disconnected. You can give it a
1342 position in a buffer again by calling @code{move-overlay}.
1345 @defun move-overlay overlay start end &optional buffer
1346 This function moves @var{overlay} to @var{buffer}, and places its bounds
1347 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1348 must specify buffer positions; they may be integers or markers.
1350 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1351 was already associated with; if @var{overlay} was deleted, it goes into
1354 The return value is @var{overlay}.
1356 This is the only valid way to change the endpoints of an overlay. Do
1357 not try modifying the markers in the overlay by hand, as that fails to
1358 update other vital data structures and can cause some overlays to be
1362 @defun remove-overlays &optional start end name value
1363 This function removes all the overlays between @var{start} and
1364 @var{end} whose property @var{name} has the value @var{value}. It can
1365 move the endpoints of the overlays in the region, or split them.
1367 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1368 the specified region. If @var{start} and/or @var{end} are omitted or
1369 @code{nil}, that means the beginning and end of the buffer respectively.
1370 Therefore, @code{(remove-overlays)} removes all the overlays in the
1374 @defun copy-overlay overlay
1375 This function returns a copy of @var{overlay}. The copy has the same
1376 endpoints and properties as @var{overlay}. However, the marker
1377 insertion type for the start of the overlay and for the end of the
1378 overlay are set to their default values (@pxref{Marker Insertion
1382 Here are some examples:
1385 ;; @r{Create an overlay.}
1386 (setq foo (make-overlay 1 10))
1387 @result{} #<overlay from 1 to 10 in display.texi>
1392 (overlay-buffer foo)
1393 @result{} #<buffer display.texi>
1394 ;; @r{Give it a property we can check later.}
1395 (overlay-put foo 'happy t)
1397 ;; @r{Verify the property is present.}
1398 (overlay-get foo 'happy)
1400 ;; @r{Move the overlay.}
1401 (move-overlay foo 5 20)
1402 @result{} #<overlay from 5 to 20 in display.texi>
1407 ;; @r{Delete the overlay.}
1408 (delete-overlay foo)
1410 ;; @r{Verify it is deleted.}
1412 @result{} #<overlay in no buffer>
1413 ;; @r{A deleted overlay has no position.}
1418 (overlay-buffer foo)
1420 ;; @r{Undelete the overlay.}
1421 (move-overlay foo 1 20)
1422 @result{} #<overlay from 1 to 20 in display.texi>
1423 ;; @r{Verify the results.}
1428 (overlay-buffer foo)
1429 @result{} #<buffer display.texi>
1430 ;; @r{Moving and deleting the overlay does not change its properties.}
1431 (overlay-get foo 'happy)
1435 Emacs stores the overlays of each buffer in two lists, divided
1436 around an arbitrary ``center position''. One list extends backwards
1437 through the buffer from that center position, and the other extends
1438 forwards from that center position. The center position can be anywhere
1441 @defun overlay-recenter pos
1442 This function recenters the overlays of the current buffer around
1443 position @var{pos}. That makes overlay lookup faster for positions
1444 near @var{pos}, but slower for positions far away from @var{pos}.
1447 A loop that scans the buffer forwards, creating overlays, can run
1448 faster if you do @code{(overlay-recenter (point-max))} first.
1450 @node Overlay Properties
1451 @subsection Overlay Properties
1453 Overlay properties are like text properties in that the properties that
1454 alter how a character is displayed can come from either source. But in
1455 most respects they are different. @xref{Text Properties}, for comparison.
1457 Text properties are considered a part of the text; overlays and
1458 their properties are specifically considered not to be part of the
1459 text. Thus, copying text between various buffers and strings
1460 preserves text properties, but does not try to preserve overlays.
1461 Changing a buffer's text properties marks the buffer as modified,
1462 while moving an overlay or changing its properties does not. Unlike
1463 text property changes, overlay property changes are not recorded in
1464 the buffer's undo list.
1466 Since more than one overlay can specify a property value for the
1467 same character, Emacs lets you specify a priority value of each
1468 overlay. You should not make assumptions about which overlay will
1469 prevail when there is a conflict and they have the same priority.
1471 These functions read and set the properties of an overlay:
1473 @defun overlay-get overlay prop
1474 This function returns the value of property @var{prop} recorded in
1475 @var{overlay}, if any. If @var{overlay} does not record any value for
1476 that property, but it does have a @code{category} property which is a
1477 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1481 @defun overlay-put overlay prop value
1482 This function sets the value of property @var{prop} recorded in
1483 @var{overlay} to @var{value}. It returns @var{value}.
1486 @defun overlay-properties overlay
1487 This returns a copy of the property list of @var{overlay}.
1490 See also the function @code{get-char-property} which checks both
1491 overlay properties and text properties for a given character.
1492 @xref{Examining Properties}.
1494 Many overlay properties have special meanings; here is a table
1499 @kindex priority @r{(overlay property)}
1500 This property's value (which should be a non-negative integer number)
1501 determines the priority of the overlay. No priority, or @code{nil},
1504 The priority matters when two or more overlays cover the same
1505 character and both specify the same property; the one whose
1506 @code{priority} value is larger overrides the other. For the
1507 @code{face} property, the higher priority overlay's value does not
1508 completely override the other value; instead, its face attributes
1509 override the face attributes of the lower priority @code{face}
1512 Currently, all overlays take priority over text properties. Please
1513 avoid using negative priority values, as we have not yet decided just
1514 what they should mean.
1517 @kindex window @r{(overlay property)}
1518 If the @code{window} property is non-@code{nil}, then the overlay
1519 applies only on that window.
1522 @kindex category @r{(overlay property)}
1523 If an overlay has a @code{category} property, we call it the
1524 @dfn{category} of the overlay. It should be a symbol. The properties
1525 of the symbol serve as defaults for the properties of the overlay.
1528 @kindex face @r{(overlay property)}
1529 This property controls the appearance of the text (@pxref{Faces}).
1530 The value of the property can be the following:
1534 A face name (a symbol or string).
1537 An anonymous face: a property list of the form @code{(@var{keyword}
1538 @var{value} @dots{})}, where each @var{keyword} is a face attribute
1539 name and @var{value} is a value for that attribute.
1542 A list of faces. Each list element should be either a face name or an
1543 anonymous face. This specifies a face which is an aggregate of the
1544 attributes of each of the listed faces. Faces occurring earlier in
1545 the list have higher priority.
1548 A cons cell of the form @code{(foreground-color . @var{color-name})}
1549 or @code{(background-color . @var{color-name})}. This specifies the
1550 foreground or background color, similar to @code{(:foreground
1551 @var{color-name})} or @code{(:background @var{color-name})}. This
1552 form is supported for backward compatibility only, and should be
1557 @kindex mouse-face @r{(overlay property)}
1558 This property is used instead of @code{face} when the mouse is within
1559 the range of the overlay. However, Emacs ignores all face attributes
1560 from this property that alter the text size (e.g., @code{:height},
1561 @code{:weight}, and @code{:slant}). Those attributes are always the
1562 same as in the unhighlighted text.
1565 @kindex display @r{(overlay property)}
1566 This property activates various features that change the
1567 way text is displayed. For example, it can make text appear taller
1568 or shorter, higher or lower, wider or narrower, or replaced with an image.
1569 @xref{Display Property}.
1572 @kindex help-echo @r{(overlay property)}
1573 If an overlay has a @code{help-echo} property, then when you move the
1574 mouse onto the text in the overlay, Emacs displays a help string in the
1575 echo area, or in the tooltip window. For details see @ref{Text
1579 @kindex field @r{(overlay property)}
1580 @c Copied from Special Properties.
1581 Consecutive characters with the same @code{field} property constitute a
1582 @emph{field}. Some motion functions including @code{forward-word} and
1583 @code{beginning-of-line} stop moving at a field boundary.
1586 @item modification-hooks
1587 @kindex modification-hooks @r{(overlay property)}
1588 This property's value is a list of functions to be called if any
1589 character within the overlay is changed or if text is inserted strictly
1592 The hook functions are called both before and after each change.
1593 If the functions save the information they receive, and compare notes
1594 between calls, they can determine exactly what change has been made
1597 When called before a change, each function receives four arguments: the
1598 overlay, @code{nil}, and the beginning and end of the text range to be
1601 When called after a change, each function receives five arguments: the
1602 overlay, @code{t}, the beginning and end of the text range just
1603 modified, and the length of the pre-change text replaced by that range.
1604 (For an insertion, the pre-change length is zero; for a deletion, that
1605 length is the number of characters deleted, and the post-change
1606 beginning and end are equal.)
1608 If these functions modify the buffer, they should bind
1609 @code{inhibit-modification-hooks} to @code{t} around doing so, to
1610 avoid confusing the internal mechanism that calls these hooks.
1612 Text properties also support the @code{modification-hooks} property,
1613 but the details are somewhat different (@pxref{Special Properties}).
1615 @item insert-in-front-hooks
1616 @kindex insert-in-front-hooks @r{(overlay property)}
1617 This property's value is a list of functions to be called before and
1618 after inserting text right at the beginning of the overlay. The calling
1619 conventions are the same as for the @code{modification-hooks} functions.
1621 @item insert-behind-hooks
1622 @kindex insert-behind-hooks @r{(overlay property)}
1623 This property's value is a list of functions to be called before and
1624 after inserting text right at the end of the overlay. The calling
1625 conventions are the same as for the @code{modification-hooks} functions.
1628 @kindex invisible @r{(overlay property)}
1629 The @code{invisible} property can make the text in the overlay
1630 invisible, which means that it does not appear on the screen.
1631 @xref{Invisible Text}, for details.
1634 @kindex intangible @r{(overlay property)}
1635 The @code{intangible} property on an overlay works just like the
1636 @code{intangible} text property. @xref{Special Properties}, for details.
1638 @item isearch-open-invisible
1639 This property tells incremental search how to make an invisible overlay
1640 visible, permanently, if the final match overlaps it. @xref{Invisible
1643 @item isearch-open-invisible-temporary
1644 This property tells incremental search how to make an invisible overlay
1645 visible, temporarily, during the search. @xref{Invisible Text}.
1648 @kindex before-string @r{(overlay property)}
1649 This property's value is a string to add to the display at the beginning
1650 of the overlay. The string does not appear in the buffer in any
1651 sense---only on the screen.
1654 @kindex after-string @r{(overlay property)}
1655 This property's value is a string to add to the display at the end of
1656 the overlay. The string does not appear in the buffer in any
1657 sense---only on the screen.
1660 This property specifies a display spec to prepend to each
1661 non-continuation line at display-time. @xref{Truncation}.
1664 This property specifies a display spec to prepend to each continuation
1665 line at display-time. @xref{Truncation}.
1668 @kindex evaporate @r{(overlay property)}
1669 If this property is non-@code{nil}, the overlay is deleted automatically
1670 if it becomes empty (i.e., if its length becomes zero). If you give
1671 an empty overlay a non-@code{nil} @code{evaporate} property, that deletes
1675 @cindex keymap of character (and overlays)
1676 @kindex keymap @r{(overlay property)}
1677 If this property is non-@code{nil}, it specifies a keymap for a portion of the
1678 text. This keymap is used when the character after point is within the
1679 overlay, and takes precedence over most other keymaps. @xref{Active Keymaps}.
1682 @kindex local-map @r{(overlay property)}
1683 The @code{local-map} property is similar to @code{keymap} but replaces the
1684 buffer's local map rather than augmenting existing keymaps. This also means it
1685 has lower precedence than minor mode keymaps.
1688 The @code{keymap} and @code{local-map} properties do not affect a
1689 string displayed by the @code{before-string}, @code{after-string}, or
1690 @code{display} properties. This is only relevant for mouse clicks and
1691 other mouse events that fall on the string, since point is never on
1692 the string. To bind special mouse events for the string, assign it a
1693 @code{keymap} or @code{local-map} text property. @xref{Special
1696 @node Finding Overlays
1697 @subsection Searching for Overlays
1699 @defun overlays-at pos
1700 This function returns a list of all the overlays that cover the
1701 character at position @var{pos} in the current buffer. The list is in
1702 no particular order. An overlay contains position @var{pos} if it
1703 begins at or before @var{pos}, and ends after @var{pos}.
1705 To illustrate usage, here is a Lisp function that returns a list of the
1706 overlays that specify property @var{prop} for the character at point:
1709 (defun find-overlays-specifying (prop)
1710 (let ((overlays (overlays-at (point)))
1713 (let ((overlay (car overlays)))
1714 (if (overlay-get overlay prop)
1715 (setq found (cons overlay found))))
1716 (setq overlays (cdr overlays)))
1721 @defun overlays-in beg end
1722 This function returns a list of the overlays that overlap the region
1723 @var{beg} through @var{end}. ``Overlap'' means that at least one
1724 character is contained within the overlay and also contained within the
1725 specified region; however, empty overlays are included in the result if
1726 they are located at @var{beg}, strictly between @var{beg} and @var{end},
1727 or at @var{end} when @var{end} denotes the position at the end of the
1731 @defun next-overlay-change pos
1732 This function returns the buffer position of the next beginning or end
1733 of an overlay, after @var{pos}. If there is none, it returns
1737 @defun previous-overlay-change pos
1738 This function returns the buffer position of the previous beginning or
1739 end of an overlay, before @var{pos}. If there is none, it returns
1743 As an example, here's a simplified (and inefficient) version of the
1744 primitive function @code{next-single-char-property-change}
1745 (@pxref{Property Search}). It searches forward from position
1746 @var{pos} for the next position where the value of a given property
1747 @code{prop}, as obtained from either overlays or text properties,
1751 (defun next-single-char-property-change (position prop)
1753 (goto-char position)
1754 (let ((propval (get-char-property (point) prop)))
1755 (while (and (not (eobp))
1756 (eq (get-char-property (point) prop) propval))
1757 (goto-char (min (next-overlay-change (point))
1758 (next-single-property-change (point) prop)))))
1765 Since not all characters have the same width, these functions let you
1766 check the width of a character. @xref{Primitive Indent}, and
1767 @ref{Screen Lines}, for related functions.
1769 @defun char-width char
1770 This function returns the width in columns of the character
1771 @var{char}, if it were displayed in the current buffer (i.e., taking
1772 into account the buffer's display table, if any; @pxref{Display
1773 Tables}). The width of a tab character is usually @code{tab-width}
1774 (@pxref{Usual Display}).
1777 @defun string-width string
1778 This function returns the width in columns of the string @var{string},
1779 if it were displayed in the current buffer and the selected window.
1782 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1783 This function returns the part of @var{string} that fits within
1784 @var{width} columns, as a new string.
1786 If @var{string} does not reach @var{width}, then the result ends where
1787 @var{string} ends. If one multi-column character in @var{string}
1788 extends across the column @var{width}, that character is not included in
1789 the result. Thus, the result can fall short of @var{width} but cannot
1792 The optional argument @var{start-column} specifies the starting column.
1793 If this is non-@code{nil}, then the first @var{start-column} columns of
1794 the string are omitted from the value. If one multi-column character in
1795 @var{string} extends across the column @var{start-column}, that
1796 character is not included.
1798 The optional argument @var{padding}, if non-@code{nil}, is a padding
1799 character added at the beginning and end of the result string, to extend
1800 it to exactly @var{width} columns. The padding character is used at the
1801 end of the result if it falls short of @var{width}. It is also used at
1802 the beginning of the result if one multi-column character in
1803 @var{string} extends across the column @var{start-column}.
1805 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1806 replace the end of @var{string} (including any padding) if it extends
1807 beyond @var{width}, unless the display width of @var{string} is equal
1808 to or less than the display width of @var{ellipsis}. If
1809 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1813 (truncate-string-to-width "\tab\t" 12 4)
1815 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1821 @section Line Height
1823 @cindex height of a line
1825 The total height of each display line consists of the height of the
1826 contents of the line, plus optional additional vertical line spacing
1827 above or below the display line.
1829 The height of the line contents is the maximum height of any
1830 character or image on that display line, including the final newline
1831 if there is one. (A display line that is continued doesn't include a
1832 final newline.) That is the default line height, if you do nothing to
1833 specify a greater height. (In the most common case, this equals the
1834 height of the default frame font.)
1836 There are several ways to explicitly specify a larger line height,
1837 either by specifying an absolute height for the display line, or by
1838 specifying vertical space. However, no matter what you specify, the
1839 actual line height can never be less than the default.
1841 @kindex line-height @r{(text property)}
1842 A newline can have a @code{line-height} text or overlay property
1843 that controls the total height of the display line ending in that
1846 If the property value is @code{t}, the newline character has no
1847 effect on the displayed height of the line---the visible contents
1848 alone determine the height. This is useful for tiling small images
1849 (or image slices) without adding blank areas between the images.
1851 If the property value is a list of the form @code{(@var{height}
1852 @var{total})}, that adds extra space @emph{below} the display line.
1853 First Emacs uses @var{height} as a height spec to control extra space
1854 @emph{above} the line; then it adds enough space @emph{below} the line
1855 to bring the total line height up to @var{total}. In this case, the
1856 other ways to specify the line spacing are ignored.
1859 Any other kind of property value is a height spec, which translates
1860 into a number---the specified line height. There are several ways to
1861 write a height spec; here's how each of them translates into a number:
1865 If the height spec is a positive integer, the height value is that integer.
1867 If the height spec is a float, @var{float}, the numeric height value
1868 is @var{float} times the frame's default line height.
1869 @item (@var{face} . @var{ratio})
1870 If the height spec is a cons of the format shown, the numeric height
1871 is @var{ratio} times the height of face @var{face}. @var{ratio} can
1872 be any type of number, or @code{nil} which means a ratio of 1.
1873 If @var{face} is @code{t}, it refers to the current face.
1874 @item (nil . @var{ratio})
1875 If the height spec is a cons of the format shown, the numeric height
1876 is @var{ratio} times the height of the contents of the line.
1879 Thus, any valid height spec determines the height in pixels, one way
1880 or another. If the line contents' height is less than that, Emacs
1881 adds extra vertical space above the line to achieve the specified
1884 If you don't specify the @code{line-height} property, the line's
1885 height consists of the contents' height plus the line spacing.
1886 There are several ways to specify the line spacing for different
1887 parts of Emacs text.
1889 On graphical terminals, you can specify the line spacing for all
1890 lines in a frame, using the @code{line-spacing} frame parameter
1891 (@pxref{Layout Parameters}). However, if the default value of
1892 @code{line-spacing} is non-@code{nil}, it overrides the
1893 frame's @code{line-spacing} parameter. An integer value specifies the
1894 number of pixels put below lines. A floating point number specifies
1895 the spacing relative to the frame's default line height.
1897 @vindex line-spacing
1898 You can specify the line spacing for all lines in a buffer via the
1899 buffer-local @code{line-spacing} variable. An integer value specifies
1900 the number of pixels put below lines. A floating point number
1901 specifies the spacing relative to the default frame line height. This
1902 overrides line spacings specified for the frame.
1904 @kindex line-spacing @r{(text property)}
1905 Finally, a newline can have a @code{line-spacing} text or overlay
1906 property that overrides the default frame line spacing and the buffer
1907 local @code{line-spacing} variable, for the display line ending in
1910 One way or another, these mechanisms specify a Lisp value for the
1911 spacing of each line. The value is a height spec, and it translates
1912 into a Lisp value as described above. However, in this case the
1913 numeric height value specifies the line spacing, rather than the line
1916 On text terminals, the line spacing cannot be altered.
1922 A @dfn{face} is a collection of graphical attributes for displaying
1923 text: font, foreground color, background color, optional underlining,
1924 etc. Faces control how Emacs displays text in buffers, as well as
1925 other parts of the frame such as the mode line.
1927 @cindex anonymous face
1928 One way to represent a face is as a property list of attributes,
1929 like @code{(:foreground "red" :weight bold)}. Such a list is called
1930 an @dfn{anonymous face}. For example, you can assign an anonymous
1931 face as the value of the @code{face} text property, and Emacs will
1932 display the underlying text with the specified attributes.
1933 @xref{Special Properties}.
1936 More commonly, a face is referred to via a @dfn{face name}: a Lisp
1937 symbol associated with a set of face attributes@footnote{For backward
1938 compatibility, you can also use a string to specify a face name; that
1939 is equivalent to a Lisp symbol with the same name.}. Named faces are
1940 defined using the @code{defface} macro (@pxref{Defining Faces}).
1941 Emacs comes with several standard named faces (@pxref{Basic Faces}).
1943 Many parts of Emacs required named faces, and do not accept
1944 anonymous faces. These include the functions documented in
1945 @ref{Attribute Functions}, and the variable @code{font-lock-keywords}
1946 (@pxref{Search-based Fontification}). Unless otherwise stated, we
1947 will use the term @dfn{face} to refer only to named faces.
1950 This function returns a non-@code{nil} value if @var{object} is a
1951 named face: a Lisp symbol or string which serves as a face name.
1952 Otherwise, it returns @code{nil}.
1956 * Face Attributes:: What is in a face?
1957 * Defining Faces:: How to define a face.
1958 * Attribute Functions:: Functions to examine and set face attributes.
1959 * Displaying Faces:: How Emacs combines the faces specified for a character.
1960 * Face Remapping:: Remapping faces to alternative definitions.
1961 * Face Functions:: How to define and examine faces.
1962 * Auto Faces:: Hook for automatic face assignment.
1963 * Basic Faces:: Faces that are defined by default.
1964 * Font Selection:: Finding the best available font for a face.
1965 * Font Lookup:: Looking up the names of available fonts
1966 and information about them.
1967 * Fontsets:: A fontset is a collection of fonts
1968 that handle a range of character sets.
1969 * Low-Level Font:: Lisp representation for character display fonts.
1972 @node Face Attributes
1973 @subsection Face Attributes
1974 @cindex face attributes
1976 @dfn{Face attributes} determine the visual appearance of a face.
1977 The following table lists all the face attributes, their possible
1978 values, and their effects.
1980 Apart from the values given below, each face attribute can have the
1981 value @code{unspecified}. This special value means that the face
1982 doesn't specify that attribute directly. An @code{unspecified}
1983 attribute tells Emacs to refer instead to a parent face (see the
1984 description @code{:inherit} attribute below); or, failing that, to an
1985 underlying face (@pxref{Displaying Faces}). The @code{default} face
1986 must specify all attributes.
1988 Some of these attributes are meaningful only on certain kinds of
1989 displays. If your display cannot handle a certain attribute, the
1990 attribute is ignored.
1994 Font family or fontset (a string). @xref{Fonts,,, emacs, The GNU
1995 Emacs Manual}, for more information about font families. The function
1996 @code{font-family-list} (see below) returns a list of available family
1997 names. @xref{Fontsets}, for information about fontsets.
2000 The name of the @dfn{font foundry} for the font family specified by
2001 the @code{:family} attribute (a string). @xref{Fonts,,, emacs, The
2005 Relative character width. This should be one of the symbols
2006 @code{ultra-condensed}, @code{extra-condensed}, @code{condensed},
2007 @code{semi-condensed}, @code{normal}, @code{semi-expanded},
2008 @code{expanded}, @code{extra-expanded}, or @code{ultra-expanded}.
2011 The height of the font. In the simplest case, this is an integer in
2012 units of 1/10 point.
2014 The value can also be a floating point number or a function, which
2015 specifies the height relative to an @dfn{underlying face}
2016 (@pxref{Displaying Faces}). If the value is a floating point number,
2017 that specifies the amount by which to scale the height of the
2018 underlying face. If the value is a function, that function is called
2019 with one argument, the height of the underlying face, and returns the
2020 height of the new face. If the function is passed an integer
2021 argument, it must return an integer.
2023 The height of the default face must be specified using an integer;
2024 floating point and function values are not allowed.
2027 Font weight---one of the symbols (from densest to faintest)
2028 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
2029 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or
2030 @code{ultra-light}. On text terminals which support
2031 variable-brightness text, any weight greater than normal is displayed
2032 as extra bright, and any weight less than normal is displayed as
2037 Font slant---one of the symbols @code{italic}, @code{oblique},
2038 @code{normal}, @code{reverse-italic}, or @code{reverse-oblique}. On
2039 text terminals that support variable-brightness text, slanted text is
2040 displayed as half-bright.
2043 Foreground color, a string. The value can be a system-defined color
2044 name, or a hexadecimal color specification. @xref{Color Names}. On
2045 black-and-white displays, certain shades of gray are implemented by
2048 @item :distant-foreground
2049 Alternative foreground color, a string. This is like @code{:foreground}
2050 but the color is only used as a foreground when the background color is
2051 near to the foreground that would have been used. This is useful for
2052 example when marking text (i.e. the region face). If the text has a foreground
2053 that is visible with the region face, that foreground is used.
2054 If the foreground is near the region face background,
2055 @code{:distant-foreground} is used instead so the text is readable.
2058 Background color, a string. The value can be a system-defined color
2059 name, or a hexadecimal color specification. @xref{Color Names}.
2061 @cindex underlined text
2063 Whether or not characters should be underlined, and in what
2064 way. The possible values of the @code{:underline} attribute are:
2071 Underline with the foreground color of the face.
2074 Underline in color @var{color}, a string specifying a color.
2076 @item @code{(:color @var{color} :style @var{style})}
2077 @var{color} is either a string, or the symbol @code{foreground-color},
2078 meaning the foreground color of the face. Omitting the attribute
2079 @code{:color} means to use the foreground color of the face.
2080 @var{style} should be a symbol @code{line} or @code{wave}, meaning to
2081 use a straight or wavy line. Omitting the attribute @code{:style}
2082 means to use a straight line.
2085 @cindex overlined text
2087 Whether or not characters should be overlined, and in what color.
2088 If the value is @code{t}, overlining uses the foreground color of the
2089 face. If the value is a string, overlining uses that color. The
2090 value @code{nil} means do not overline.
2092 @cindex strike-through text
2093 @item :strike-through
2094 Whether or not characters should be strike-through, and in what
2095 color. The value is used like that of @code{:overline}.
2100 Whether or not a box should be drawn around characters, its color, the
2101 width of the box lines, and 3D appearance. Here are the possible
2102 values of the @code{:box} attribute, and what they mean:
2109 Draw a box with lines of width 1, in the foreground color.
2112 Draw a box with lines of width 1, in color @var{color}.
2114 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2115 This way you can explicitly specify all aspects of the box. The value
2116 @var{width} specifies the width of the lines to draw; it defaults to
2117 1. A negative width @var{-n} means to draw a line of width @var{n}
2118 that occupies the space of the underlying text, thus avoiding any
2119 increase in the character height or width.
2121 The value @var{color} specifies the color to draw with. The default is
2122 the foreground color of the face for simple boxes, and the background
2123 color of the face for 3D boxes.
2125 The value @var{style} specifies whether to draw a 3D box. If it is
2126 @code{released-button}, the box looks like a 3D button that is not being
2127 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2128 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2132 @item :inverse-video
2133 Whether or not characters should be displayed in inverse video. The
2134 value should be @code{t} (yes) or @code{nil} (no).
2137 The background stipple, a bitmap.
2139 The value can be a string; that should be the name of a file containing
2140 external-format X bitmap data. The file is found in the directories
2141 listed in the variable @code{x-bitmap-file-path}.
2143 Alternatively, the value can specify the bitmap directly, with a list
2144 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2145 @var{width} and @var{height} specify the size in pixels, and
2146 @var{data} is a string containing the raw bits of the bitmap, row by
2147 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2148 in the string (which should be a unibyte string for best results).
2149 This means that each row always occupies at least one whole byte.
2151 If the value is @code{nil}, that means use no stipple pattern.
2153 Normally you do not need to set the stipple attribute, because it is
2154 used automatically to handle certain shades of gray.
2157 The font used to display the face. Its value should be a font object.
2158 @xref{Low-Level Font}, for information about font objects, font specs,
2161 When specifying this attribute using @code{set-face-attribute}
2162 (@pxref{Attribute Functions}), you may also supply a font spec, a font
2163 entity, or a string. Emacs converts such values to an appropriate
2164 font object, and stores that font object as the actual attribute
2165 value. If you specify a string, the contents of the string should be
2166 a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the
2167 font name is an XLFD containing wildcards, Emacs chooses the first
2168 font matching those wildcards. Specifying this attribute also changes
2169 the values of the @code{:family}, @code{:foundry}, @code{:width},
2170 @code{:height}, @code{:weight}, and @code{:slant} attributes.
2173 The name of a face from which to inherit attributes, or a list of face
2174 names. Attributes from inherited faces are merged into the face like
2175 an underlying face would be, with higher priority than underlying
2176 faces (@pxref{Displaying Faces}). If a list of faces is used,
2177 attributes from faces earlier in the list override those from later
2181 @defun font-family-list &optional frame
2182 This function returns a list of available font family names. The
2183 optional argument @var{frame} specifies the frame on which the text is
2184 to be displayed; if it is @code{nil}, the selected frame is used.
2187 @defopt underline-minimum-offset
2188 This variable specifies the minimum distance between the baseline and
2189 the underline, in pixels, when displaying underlined text.
2192 @defopt x-bitmap-file-path
2193 This variable specifies a list of directories for searching
2194 for bitmap files, for the @code{:stipple} attribute.
2197 @defun bitmap-spec-p object
2198 This returns @code{t} if @var{object} is a valid bitmap specification,
2199 suitable for use with @code{:stipple} (see above). It returns
2200 @code{nil} otherwise.
2203 @node Defining Faces
2204 @subsection Defining Faces
2207 The usual way to define a face is through the @code{defface} macro.
2208 This macro associates a face name (a symbol) with a default @dfn{face
2209 spec}. A face spec is a construct which specifies what attributes a
2210 face should have on any given terminal; for example, a face spec might
2211 specify one foreground color on high-color terminals, and a different
2212 foreground color on low-color terminals.
2214 People are sometimes tempted to create a variable whose value is a
2215 face name. In the vast majority of cases, this is not necessary; the
2216 usual procedure is to define a face with @code{defface}, and then use
2219 @defmac defface face spec doc [keyword value]@dots{}
2220 This macro declares @var{face} as a named face whose default face spec
2221 is given by @var{spec}. You should not quote the symbol @var{face},
2222 and it should not end in @samp{-face} (that would be redundant). The
2223 argument @var{doc} is a documentation string for the face. The
2224 additional @var{keyword} arguments have the same meanings as in
2225 @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}).
2227 If @var{face} already has a default face spec, this macro does
2230 The default face spec determines @var{face}'s appearance when no
2231 customizations are in effect (@pxref{Customization}). If @var{face}
2232 has already been customized (via Custom themes or via customizations
2233 read from the init file), its appearance is determined by the custom
2234 face spec(s), which override the default face spec @var{spec}.
2235 However, if the customizations are subsequently removed, the
2236 appearance of @var{face} will again be determined by its default face
2239 As an exception, if you evaluate a @code{defface} form with
2240 @kbd{C-M-x} in Emacs Lisp mode (@code{eval-defun}), a special feature
2241 of @code{eval-defun} overrides any custom face specs on the face,
2242 causing the face to reflect exactly what the @code{defface} says.
2244 The @var{spec} argument is a @dfn{face spec}, which states how the
2245 face should appear on different kinds of terminals. It should be an
2246 alist whose elements each have the form
2249 (@var{display} . @var{plist})
2253 @var{display} specifies a class of terminals (see below). @var{plist}
2254 is a property list of face attributes and their values, specifying how
2255 the face appears on such terminals. For backward compatibility, you
2256 can also write an element as @code{(@var{display} @var{plist})}.
2258 The @var{display} part of an element of @var{spec} determines which
2259 terminals the element matches. If more than one element of @var{spec}
2260 matches a given terminal, the first element that matches is the one
2261 used for that terminal. There are three possibilities for
2265 @item @code{default}
2266 This element of @var{spec} doesn't match any terminal; instead, it
2267 specifies defaults that apply to all terminals. This element, if
2268 used, must be the first element of @var{spec}. Each of the following
2269 elements can override any or all of these defaults.
2272 This element of @var{spec} matches all terminals. Therefore, any
2273 subsequent elements of @var{spec} are never used. Normally @code{t}
2274 is used in the last (or only) element of @var{spec}.
2277 If @var{display} is a list, each element should have the form
2278 @code{(@var{characteristic} @var{value}@dots{})}. Here
2279 @var{characteristic} specifies a way of classifying terminals, and the
2280 @var{value}s are possible classifications which @var{display} should
2281 apply to. Here are the possible values of @var{characteristic}:
2285 The kind of window system the terminal uses---either @code{graphic}
2286 (any graphics-capable display), @code{x}, @code{pc} (for the MS-DOS
2287 console), @code{w32} (for MS Windows 9X/NT/2K/XP), or @code{tty} (a
2288 non-graphics-capable display). @xref{Window Systems, window-system}.
2291 What kinds of colors the terminal supports---either @code{color},
2292 @code{grayscale}, or @code{mono}.
2295 The kind of background---either @code{light} or @code{dark}.
2298 An integer that represents the minimum number of colors the terminal
2299 should support. This matches a terminal if its
2300 @code{display-color-cells} value is at least the specified integer.
2303 Whether or not the terminal can display the face attributes given in
2304 @var{value}@dots{} (@pxref{Face Attributes}). @xref{Display Face
2305 Attribute Testing}, for more information on exactly how this testing
2309 If an element of @var{display} specifies more than one @var{value} for
2310 a given @var{characteristic}, any of those values is acceptable. If
2311 @var{display} has more than one element, each element should specify a
2312 different @var{characteristic}; then @emph{each} characteristic of the
2313 terminal must match one of the @var{value}s specified for it in
2318 For example, here's the definition of the standard face
2323 '((((class color) (min-colors 88) (background light))
2324 :background "darkseagreen2")
2325 (((class color) (min-colors 88) (background dark))
2326 :background "darkolivegreen")
2327 (((class color) (min-colors 16) (background light))
2328 :background "darkseagreen2")
2329 (((class color) (min-colors 16) (background dark))
2330 :background "darkolivegreen")
2331 (((class color) (min-colors 8))
2332 :background "green" :foreground "black")
2333 (t :inverse-video t))
2334 "Basic face for highlighting."
2335 :group 'basic-faces)
2338 Internally, Emacs stores each face's default spec in its
2339 @code{face-defface-spec} symbol property (@pxref{Symbol Properties}).
2340 The @code{saved-face} property stores any face spec saved by the user
2341 using the customization buffer; the @code{customized-face} property
2342 stores the face spec customized for the current session, but not
2343 saved; and the @code{theme-face} property stores an alist associating
2344 the active customization settings and Custom themes with the face
2345 specs for that face. The face's documentation string is stored in the
2346 @code{face-documentation} property.
2348 Normally, a face is declared just once, using @code{defface}, and
2349 any further changes to its appearance are applied using the Customize
2350 framework (e.g., via the Customize user interface or via the
2351 @code{custom-set-faces} function; @pxref{Applying Customizations}), or
2352 by face remapping (@pxref{Face Remapping}). In the rare event that
2353 you need to change a face spec directly from Lisp, you can use the
2354 @code{face-spec-set} function.
2356 @defun face-spec-set face spec &optional spec-type
2357 This function applies @var{spec} as a face spec for @code{face}.
2358 @var{spec} should be a face spec, as described in the above
2359 documentation for @code{defface}.
2361 @cindex override spec @r{(for a face)}
2362 The argument @var{spec-type} determines which spec to set. If it is
2363 @code{nil} or @code{face-override-spec}, this function sets the
2364 @dfn{override spec}, which overrides over all other face specs on
2365 @var{face}. If it is @code{face-defface-spec}, this function sets the
2366 default face spec (the same one set by @code{defface}). If it is
2367 @code{reset}, this function clears out all customization specs and
2368 override specs from @var{face} (in this case, the value of @var{spec}
2369 is ignored). Any other value of @var{spec-type} is reserved for
2373 @node Attribute Functions
2374 @subsection Face Attribute Functions
2376 This section describes functions for directly accessing and
2377 modifying the attributes of a named face.
2379 @defun face-attribute face attribute &optional frame inherit
2380 This function returns the value of the @var{attribute} attribute for
2381 @var{face} on @var{frame}.
2383 If @var{frame} is @code{nil}, that means the selected frame
2384 (@pxref{Input Focus}). If @var{frame} is @code{t}, this function
2385 returns the value of the specified attribute for newly-created frames
2386 (this is normally @code{unspecified}, unless you have specified some
2387 value using @code{set-face-attribute}; see below).
2389 If @var{inherit} is @code{nil}, only attributes directly defined by
2390 @var{face} are considered, so the return value may be
2391 @code{unspecified}, or a relative value. If @var{inherit} is
2392 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2393 with the faces specified by its @code{:inherit} attribute; however the
2394 return value may still be @code{unspecified} or relative. If
2395 @var{inherit} is a face or a list of faces, then the result is further
2396 merged with that face (or faces), until it becomes specified and
2399 To ensure that the return value is always specified and absolute, use
2400 a value of @code{default} for @var{inherit}; this will resolve any
2401 unspecified or relative values by merging with the @code{default} face
2402 (which is always completely specified).
2407 (face-attribute 'bold :weight)
2412 @c FIXME: Add an index for "relative face attribute", maybe here? --xfq
2413 @defun face-attribute-relative-p attribute value
2414 This function returns non-@code{nil} if @var{value}, when used as the
2415 value of the face attribute @var{attribute}, is relative. This means
2416 it would modify, rather than completely override, any value that comes
2417 from a subsequent face in the face list or that is inherited from
2420 @code{unspecified} is a relative value for all attributes. For
2421 @code{:height}, floating point and function values are also relative.
2426 (face-attribute-relative-p :height 2.0)
2431 @defun face-all-attributes face &optional frame
2432 This function returns an alist of attributes of @var{face}. The
2433 elements of the result are name-value pairs of the form
2434 @w{@code{(@var{attr-name} . @var{attr-value})}}. Optional argument
2435 @var{frame} specifies the frame whose definition of @var{face} to
2436 return; if omitted or @code{nil}, the returned value describes the
2437 default attributes of @var{face} for newly created frames.
2440 @defun merge-face-attribute attribute value1 value2
2441 If @var{value1} is a relative value for the face attribute
2442 @var{attribute}, returns it merged with the underlying value
2443 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2444 face attribute @var{attribute}, returns @var{value1} unchanged.
2447 Normally, Emacs uses the face specs of each face to automatically
2448 calculate its attributes on each frame (@pxref{Defining Faces}). The
2449 function @code{set-face-attribute} can override this calculation by
2450 directly assigning attributes to a face, either on a specific frame or
2451 for all frames. This function is mostly intended for internal usage.
2453 @defun set-face-attribute face frame &rest arguments
2454 This function sets one or more attributes of @var{face} for
2455 @var{frame}. The attributes specifies in this way override the face
2456 spec(s) belonging to @var{face}.
2458 The extra arguments @var{arguments} specify the attributes to set, and
2459 the values for them. They should consist of alternating attribute
2460 names (such as @code{:family} or @code{:underline}) and values. Thus,
2463 (set-face-attribute 'foo nil :weight 'bold :slant 'italic)
2467 sets the attribute @code{:weight} to @code{bold} and the attribute
2468 @code{:slant} to @code{italic}.
2471 If @var{frame} is @code{t}, this function sets the default attributes
2472 for newly created frames. If @var{frame} is @code{nil}, this function
2473 sets the attributes for all existing frames, as well as for newly
2477 The following commands and functions mostly provide compatibility
2478 with old versions of Emacs. They work by calling
2479 @code{set-face-attribute}. Values of @code{t} and @code{nil} for
2480 their @var{frame} argument are handled just like
2481 @code{set-face-attribute} and @code{face-attribute}. The commands
2482 read their arguments using the minibuffer, if called interactively.
2484 @deffn Command set-face-foreground face color &optional frame
2485 @deffnx Command set-face-background face color &optional frame
2486 These set the @code{:foreground} attribute (or @code{:background}
2487 attribute, respectively) of @var{face} to @var{color}.
2490 @deffn Command set-face-stipple face pattern &optional frame
2491 This sets the @code{:stipple} attribute of @var{face} to
2495 @deffn Command set-face-font face font &optional frame
2496 This sets the @code{:font} attribute of @var{face} to @var{font}.
2499 @defun set-face-bold face bold-p &optional frame
2500 This sets the @code{:weight} attribute of @var{face} to @var{normal}
2501 if @var{bold-p} is @code{nil}, and to @var{bold} otherwise.
2504 @defun set-face-italic face italic-p &optional frame
2505 This sets the @code{:slant} attribute of @var{face} to @var{normal} if
2506 @var{italic-p} is @code{nil}, and to @var{italic} otherwise.
2509 @defun set-face-underline face underline &optional frame
2510 This sets the @code{:underline} attribute of @var{face} to
2514 @defun set-face-inverse-video face inverse-video-p &optional frame
2515 This sets the @code{:inverse-video} attribute of @var{face} to
2516 @var{inverse-video-p}.
2519 @deffn Command invert-face face &optional frame
2520 This swaps the foreground and background colors of face @var{face}.
2523 The following functions examine the attributes of a face. They
2524 mostly provide compatibility with old versions of Emacs. If you don't
2525 specify @var{frame}, they refer to the selected frame; @code{t} refers
2526 to the default data for new frames. They return @code{unspecified} if
2527 the face doesn't define any value for that attribute. If
2528 @var{inherit} is @code{nil}, only an attribute directly defined by the
2529 face is returned. If @var{inherit} is non-@code{nil}, any faces
2530 specified by its @code{:inherit} attribute are considered as well, and
2531 if @var{inherit} is a face or a list of faces, then they are also
2532 considered, until a specified attribute is found. To ensure that the
2533 return value is always specified, use a value of @code{default} for
2536 @defun face-font face &optional frame
2537 This function returns the name of the font of face @var{face}.
2540 @defun face-foreground face &optional frame inherit
2541 @defunx face-background face &optional frame inherit
2542 These functions return the foreground color (or background color,
2543 respectively) of face @var{face}, as a string.
2546 @defun face-stipple face &optional frame inherit
2547 This function returns the name of the background stipple pattern of face
2548 @var{face}, or @code{nil} if it doesn't have one.
2551 @defun face-bold-p face &optional frame inherit
2552 This function returns a non-@code{nil} value if the @code{:weight}
2553 attribute of @var{face} is bolder than normal (i.e., one of
2554 @code{semi-bold}, @code{bold}, @code{extra-bold}, or
2555 @code{ultra-bold}). Otherwise, it returns @code{nil}.
2558 @defun face-italic-p face &optional frame inherit
2559 This function returns a non-@code{nil} value if the @code{:slant}
2560 attribute of @var{face} is @code{italic} or @code{oblique}, and
2561 @code{nil} otherwise.
2564 @defun face-underline-p face &optional frame inherit
2565 This function returns non-@code{nil} if face @var{face} specifies
2566 a non-@code{nil} @code{:underline} attribute.
2569 @defun face-inverse-video-p face &optional frame inherit
2570 This function returns non-@code{nil} if face @var{face} specifies
2571 a non-@code{nil} @code{:inverse-video} attribute.
2574 @node Displaying Faces
2575 @subsection Displaying Faces
2577 When Emacs displays a given piece of text, the visual appearance of
2578 the text may be determined by faces drawn from different sources. If
2579 these various sources together specify more than one face for a
2580 particular character, Emacs merges the attributes of the various
2581 faces. Here is the order in which Emacs merges the faces, from
2582 highest to lowest priority:
2586 If the text consists of a special glyph, the glyph can specify a
2587 particular face. @xref{Glyphs}.
2590 If the text lies within an active region, Emacs highlights it using
2591 the @code{region} face. @xref{Standard Faces,,, emacs, The GNU Emacs
2595 If the text lies within an overlay with a non-@code{nil} @code{face}
2596 property, Emacs applies the face(s) specified by that property. If
2597 the overlay has a @code{mouse-face} property and the mouse is ``near
2598 enough'' to the overlay, Emacs applies the face or face attributes
2599 specified by the @code{mouse-face} property instead. @xref{Overlay
2602 When multiple overlays cover one character, an overlay with higher
2603 priority overrides those with lower priority. @xref{Overlays}.
2606 If the text contains a @code{face} or @code{mouse-face} property,
2607 Emacs applies the specified faces and face attributes. @xref{Special
2608 Properties}. (This is how Font Lock mode faces are applied.
2609 @xref{Font Lock Mode}.)
2612 If the text lies within the mode line of the selected window, Emacs
2613 applies the @code{mode-line} face. For the mode line of a
2614 non-selected window, Emacs applies the @code{mode-line-inactive} face.
2615 For a header line, Emacs applies the @code{header-line} face.
2618 If any given attribute has not been specified during the preceding
2619 steps, Emacs applies the attribute of the @code{default} face.
2622 At each stage, if a face has a valid @code{:inherit} attribute,
2623 Emacs treats any attribute with an @code{unspecified} value as having
2624 the corresponding value drawn from the parent face(s). @pxref{Face
2625 Attributes}. Note that the parent face(s) may also leave the
2626 attribute unspecified; in that case, the attribute remains unspecified
2627 at the next level of face merging.
2629 @node Face Remapping
2630 @subsection Face Remapping
2632 The variable @code{face-remapping-alist} is used for buffer-local or
2633 global changes in the appearance of a face. For instance, it is used
2634 to implement the @code{text-scale-adjust} command (@pxref{Text
2635 Scale,,, emacs, The GNU Emacs Manual}).
2637 @defvar face-remapping-alist
2638 The value of this variable is an alist whose elements have the form
2639 @code{(@var{face} . @var{remapping})}. This causes Emacs to display
2640 any text having the face @var{face} with @var{remapping}, rather than
2641 the ordinary definition of @var{face}.
2643 @var{remapping} may be any face spec suitable for a @code{face} text
2644 property: either a face (i.e., a face name or a property list of
2645 attribute/value pairs), or a list of faces. For details, see the
2646 description of the @code{face} text property in @ref{Special
2647 Properties}. @var{remapping} serves as the complete specification for
2648 the remapped face---it replaces the normal definition of @var{face},
2649 instead of modifying it.
2651 If @code{face-remapping-alist} is buffer-local, its local value takes
2652 effect only within that buffer.
2654 Note: face remapping is non-recursive. If @var{remapping} references
2655 the same face name @var{face}, either directly or via the
2656 @code{:inherit} attribute of some other face in @var{remapping}, that
2657 reference uses the normal definition of @var{face}. For instance, if
2658 the @code{mode-line} face is remapped using this entry in
2659 @code{face-remapping-alist}:
2662 (mode-line italic mode-line)
2666 then the new definition of the @code{mode-line} face inherits from the
2667 @code{italic} face, and the @emph{normal} (non-remapped) definition of
2668 @code{mode-line} face.
2671 @cindex relative remapping, faces
2672 @cindex base remapping, faces
2673 The following functions implement a higher-level interface to
2674 @code{face-remapping-alist}. Most Lisp code should use these
2675 functions instead of setting @code{face-remapping-alist} directly, to
2676 avoid trampling on remappings applied elsewhere. These functions are
2677 intended for buffer-local remappings, so they all make
2678 @code{face-remapping-alist} buffer-local as a side-effect. They manage
2679 @code{face-remapping-alist} entries of the form
2682 (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec})
2686 where, as explained above, each of the @var{relative-spec-N} and
2687 @var{base-spec} is either a face name, or a property list of
2688 attribute/value pairs. Each of the @dfn{relative remapping} entries,
2689 @var{relative-spec-N}, is managed by the
2690 @code{face-remap-add-relative} and @code{face-remap-remove-relative}
2691 functions; these are intended for simple modifications like changing
2692 the text size. The @dfn{base remapping} entry, @var{base-spec}, has
2693 the lowest priority and is managed by the @code{face-remap-set-base}
2694 and @code{face-remap-reset-base} functions; it is intended for major
2695 modes to remap faces in the buffers they control.
2697 @defun face-remap-add-relative face &rest specs
2698 This function adds the face spec in @var{specs} as relative
2699 remappings for face @var{face} in the current buffer. The remaining
2700 arguments, @var{specs}, should form either a list of face names, or a
2701 property list of attribute/value pairs.
2703 The return value is a Lisp object that serves as a ``cookie''; you can
2704 pass this object as an argument to @code{face-remap-remove-relative}
2705 if you need to remove the remapping later.
2708 ;; Remap the `escape-glyph' face into a combination
2709 ;; of the `highlight' and `italic' faces:
2710 (face-remap-add-relative 'escape-glyph 'highlight 'italic)
2712 ;; Increase the size of the `default' face by 50%:
2713 (face-remap-add-relative 'default :height 1.5)
2717 @defun face-remap-remove-relative cookie
2718 This function removes a relative remapping previously added by
2719 @code{face-remap-add-relative}. @var{cookie} should be the Lisp
2720 object returned by @code{face-remap-add-relative} when the remapping
2724 @defun face-remap-set-base face &rest specs
2725 This function sets the base remapping of @var{face} in the current
2726 buffer to @var{specs}. If @var{specs} is empty, the default base
2727 remapping is restored, similar to calling @code{face-remap-reset-base}
2728 (see below); note that this is different from @var{specs} containing a
2729 single value @code{nil}, which has the opposite result (the global
2730 definition of @var{face} is ignored).
2732 This overwrites the default @var{base-spec}, which inherits the global
2733 face definition, so it is up to the caller to add such inheritance if
2737 @defun face-remap-reset-base face
2738 This function sets the base remapping of @var{face} to its default
2739 value, which inherits from @var{face}'s global definition.
2742 @node Face Functions
2743 @subsection Functions for Working with Faces
2745 Here are additional functions for creating and working with faces.
2748 This function returns a list of all defined face names.
2752 This function returns the @dfn{face number} of face @var{face}. This
2753 is a number that uniquely identifies a face at low levels within
2754 Emacs. It is seldom necessary to refer to a face by its face number.
2757 @defun face-documentation face
2758 This function returns the documentation string of face @var{face}, or
2759 @code{nil} if none was specified for it.
2762 @defun face-equal face1 face2 &optional frame
2763 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2764 same attributes for display.
2767 @defun face-differs-from-default-p face &optional frame
2768 This returns non-@code{nil} if the face @var{face} displays
2769 differently from the default face.
2773 @cindex alias, for faces
2774 A @dfn{face alias} provides an equivalent name for a face. You can
2775 define a face alias by giving the alias symbol the @code{face-alias}
2776 property, with a value of the target face name. The following example
2777 makes @code{modeline} an alias for the @code{mode-line} face.
2780 (put 'modeline 'face-alias 'mode-line)
2783 @defmac define-obsolete-face-alias obsolete-face current-face when
2784 This macro defines @code{obsolete-face} as an alias for
2785 @var{current-face}, and also marks it as obsolete, indicating that it
2786 may be removed in future. @var{when} should be a string indicating
2787 when @code{obsolete-face} was made obsolete (usually a version number
2792 @subsection Automatic Face Assignment
2793 @cindex automatic face assignment
2794 @cindex faces, automatic choice
2796 This hook is used for automatically assigning faces to text in the
2797 buffer. It is part of the implementation of Jit-Lock mode, used by
2800 @defvar fontification-functions
2801 This variable holds a list of functions that are called by Emacs
2802 redisplay as needed, just before doing redisplay. They are called even
2803 when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this
2804 variable usually holds just one function, @code{jit-lock-function}.
2806 The functions are called in the order listed, with one argument, a
2807 buffer position @var{pos}. Collectively they should attempt to assign
2808 faces to the text in the current buffer starting at @var{pos}.
2810 The functions should record the faces they assign by setting the
2811 @code{face} property. They should also add a non-@code{nil}
2812 @code{fontified} property to all the text they have assigned faces to.
2813 That property tells redisplay that faces have been assigned to that text
2816 It is probably a good idea for the functions to do nothing if the
2817 character after @var{pos} already has a non-@code{nil} @code{fontified}
2818 property, but this is not required. If one function overrides the
2819 assignments made by a previous one, the properties after the last
2820 function finishes are the ones that really matter.
2822 For efficiency, we recommend writing these functions so that they
2823 usually assign faces to around 400 to 600 characters at each call.
2827 @subsection Basic Faces
2829 If your Emacs Lisp program needs to assign some faces to text, it is
2830 often a good idea to use certain existing faces or inherit from them,
2831 rather than defining entirely new faces. This way, if other users
2832 have customized the basic faces to give Emacs a certain look, your
2833 program will ``fit in'' without additional customization.
2835 Some of the basic faces defined in Emacs are listed below. In
2836 addition to these, you might want to make use of the Font Lock faces
2837 for syntactic highlighting, if highlighting is not already handled by
2838 Font Lock mode, or if some Font Lock faces are not in use.
2839 @xref{Faces for Font Lock}.
2843 The default face, whose attributes are all specified. All other faces
2844 implicitly inherit from it: any unspecified attribute defaults to the
2845 attribute on this face (@pxref{Face Attributes}).
2852 @itemx variable-pitch
2853 These have the attributes indicated by their names (e.g., @code{bold}
2854 has a bold @code{:weight} attribute), with all other attributes
2855 unspecified (and so given by @code{default}).
2858 For ``dimmed out'' text. For example, it is used for the ignored
2859 part of a filename in the minibuffer (@pxref{Minibuffer File,,
2860 Minibuffers for File Names, emacs, The GNU Emacs Manual}).
2864 For clickable text buttons that send the user to a different
2865 buffer or ``location''.
2868 For stretches of text that should temporarily stand out. For example,
2869 it is commonly assigned to the @code{mouse-face} property for cursor
2870 highlighting (@pxref{Special Properties}).
2873 For text matching a search command.
2878 For text concerning errors, warnings, or successes. For example,
2879 these are used for messages in @file{*Compilation*} buffers.
2882 @node Font Selection
2883 @subsection Font Selection
2884 @cindex font selection
2885 @cindex selecting a font
2887 Before Emacs can draw a character on a graphical display, it must
2888 select a @dfn{font} for that character@footnote{In this context, the
2889 term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock
2890 Mode}).}. @xref{Fonts,,, emacs, The GNU Emacs Manual}. Normally,
2891 Emacs automatically chooses a font based on the faces assigned to that
2892 character---specifically, the face attributes @code{:family},
2893 @code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face
2894 Attributes}). The choice of font also depends on the character to be
2895 displayed; some fonts can only display a limited set of characters.
2896 If no available font exactly fits the requirements, Emacs looks for
2897 the @dfn{closest matching font}. The variables in this section
2898 control how Emacs makes this selection.
2900 @defopt face-font-family-alternatives
2901 If a given family is specified but does not exist, this variable
2902 specifies alternative font families to try. Each element should have
2906 (@var{family} @var{alternate-families}@dots{})
2909 If @var{family} is specified but not available, Emacs will try the other
2910 families given in @var{alternate-families}, one by one, until it finds a
2911 family that does exist.
2914 @defopt face-font-selection-order
2915 If there is no font that exactly matches all desired face attributes
2916 (@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}),
2917 this variable specifies the order in which these attributes should be
2918 considered when selecting the closest matching font. The value should
2919 be a list containing those four attribute symbols, in order of
2920 decreasing importance. The default is @code{(:width :height :weight
2923 Font selection first finds the best available matches for the first
2924 attribute in the list; then, among the fonts which are best in that
2925 way, it searches for the best matches in the second attribute, and so
2928 The attributes @code{:weight} and @code{:width} have symbolic values in
2929 a range centered around @code{normal}. Matches that are more extreme
2930 (farther from @code{normal}) are somewhat preferred to matches that are
2931 less extreme (closer to @code{normal}); this is designed to ensure that
2932 non-normal faces contrast with normal ones, whenever possible.
2934 One example of a case where this variable makes a difference is when the
2935 default font has no italic equivalent. With the default ordering, the
2936 @code{italic} face will use a non-italic font that is similar to the
2937 default one. But if you put @code{:slant} before @code{:height}, the
2938 @code{italic} face will use an italic font, even if its height is not
2942 @defopt face-font-registry-alternatives
2943 This variable lets you specify alternative font registries to try, if a
2944 given registry is specified and doesn't exist. Each element should have
2948 (@var{registry} @var{alternate-registries}@dots{})
2951 If @var{registry} is specified but not available, Emacs will try the
2952 other registries given in @var{alternate-registries}, one by one,
2953 until it finds a registry that does exist.
2956 @cindex scalable fonts
2957 Emacs can make use of scalable fonts, but by default it does not use
2960 @defopt scalable-fonts-allowed
2961 This variable controls which scalable fonts to use. A value of
2962 @code{nil}, the default, means do not use scalable fonts. @code{t}
2963 means to use any scalable font that seems appropriate for the text.
2965 Otherwise, the value must be a list of regular expressions. Then a
2966 scalable font is enabled for use if its name matches any regular
2967 expression in the list. For example,
2970 (setq scalable-fonts-allowed '("iso10646-1$"))
2974 allows the use of scalable fonts with registry @code{iso10646-1}.
2977 @defvar face-font-rescale-alist
2978 This variable specifies scaling for certain faces. Its value should
2979 be a list of elements of the form
2982 (@var{fontname-regexp} . @var{scale-factor})
2985 If @var{fontname-regexp} matches the font name that is about to be
2986 used, this says to choose a larger similar font according to the
2987 factor @var{scale-factor}. You would use this feature to normalize
2988 the font size if certain fonts are bigger or smaller than their
2989 nominal heights and widths would suggest.
2993 @subsection Looking Up Fonts
2995 @defun x-list-fonts name &optional reference-face frame maximum width
2996 This function returns a list of available font names that match
2997 @var{name}. @var{name} should be a string containing a font name in
2998 either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The
2999 GNU Emacs Manual}). Within an XLFD string, wildcard characters may be
3000 used: the @samp{*} character matches any substring, and the @samp{?}
3001 character matches any single character. Case is ignored when matching
3004 If the optional arguments @var{reference-face} and @var{frame} are
3005 specified, the returned list includes only fonts that are the same
3006 size as @var{reference-face} (a face name) currently is on the frame
3009 The optional argument @var{maximum} sets a limit on how many fonts to
3010 return. If it is non-@code{nil}, then the return value is truncated
3011 after the first @var{maximum} matching fonts. Specifying a small
3012 value for @var{maximum} can make this function much faster, in cases
3013 where many fonts match the pattern.
3015 The optional argument @var{width} specifies a desired font width. If
3016 it is non-@code{nil}, the function only returns those fonts whose
3017 characters are (on average) @var{width} times as wide as
3018 @var{reference-face}.
3021 @defun x-family-fonts &optional family frame
3022 This function returns a list describing the available fonts for family
3023 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
3024 this list applies to all families, and therefore, it contains all
3025 available fonts. Otherwise, @var{family} must be a string; it may
3026 contain the wildcards @samp{?} and @samp{*}.
3028 The list describes the display that @var{frame} is on; if @var{frame} is
3029 omitted or @code{nil}, it applies to the selected frame's display
3030 (@pxref{Input Focus}).
3032 Each element in the list is a vector of the following form:
3035 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
3036 @var{fixed-p} @var{full} @var{registry-and-encoding}]
3039 The first five elements correspond to face attributes; if you
3040 specify these attributes for a face, it will use this font.
3042 The last three elements give additional information about the font.
3043 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
3044 @var{full} is the full name of the font, and
3045 @var{registry-and-encoding} is a string giving the registry and
3046 encoding of the font.
3050 @subsection Fontsets
3052 A @dfn{fontset} is a list of fonts, each assigned to a range of
3053 character codes. An individual font cannot display the whole range of
3054 characters that Emacs supports, but a fontset can. Fontsets have names,
3055 just as fonts do, and you can use a fontset name in place of a font name
3056 when you specify the ``font'' for a frame or a face. Here is
3057 information about defining a fontset under Lisp program control.
3059 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
3060 This function defines a new fontset according to the specification
3061 string @var{fontset-spec}. The string should have this format:
3064 @var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}}
3068 Whitespace characters before and after the commas are ignored.
3070 The first part of the string, @var{fontpattern}, should have the form of
3071 a standard X font name, except that the last two fields should be
3072 @samp{fontset-@var{alias}}.
3074 The new fontset has two names, one long and one short. The long name is
3075 @var{fontpattern} in its entirety. The short name is
3076 @samp{fontset-@var{alias}}. You can refer to the fontset by either
3077 name. If a fontset with the same name already exists, an error is
3078 signaled, unless @var{noerror} is non-@code{nil}, in which case this
3079 function does nothing.
3081 If optional argument @var{style-variant-p} is non-@code{nil}, that says
3082 to create bold, italic and bold-italic variants of the fontset as well.
3083 These variant fontsets do not have a short name, only a long one, which
3084 is made by altering @var{fontpattern} to indicate the bold and/or italic
3087 The specification string also says which fonts to use in the fontset.
3088 See below for the details.
3091 The construct @samp{@var{charset}:@var{font}} specifies which font to
3092 use (in this fontset) for one particular character set. Here,
3093 @var{charset} is the name of a character set, and @var{font} is the font
3094 to use for that character set. You can use this construct any number of
3095 times in the specification string.
3097 For the remaining character sets, those that you don't specify
3098 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
3099 @samp{fontset-@var{alias}} with a value that names one character set.
3100 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
3101 with @samp{ISO8859-1}.
3103 In addition, when several consecutive fields are wildcards, Emacs
3104 collapses them into a single wildcard. This is to prevent use of
3105 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
3106 for editing, and scaling a smaller font is not useful because it is
3107 better to use the smaller font in its own size, which Emacs does.
3109 Thus if @var{fontpattern} is this,
3112 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
3116 the font specification for @acronym{ASCII} characters would be this:
3119 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
3123 and the font specification for Chinese GB2312 characters would be this:
3126 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
3129 You may not have any Chinese font matching the above font
3130 specification. Most X distributions include only Chinese fonts that
3131 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
3132 such a case, @samp{Fontset-@var{n}} can be specified as below:
3135 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
3136 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
3140 Then, the font specifications for all but Chinese GB2312 characters have
3141 @samp{fixed} in the @var{family} field, and the font specification for
3142 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
3145 @defun set-fontset-font name character font-spec &optional frame add
3146 This function modifies the existing fontset @var{name} to use the font
3147 matching with @var{font-spec} for the character @var{character}.
3149 If @var{name} is @code{nil}, this function modifies the fontset of the
3150 selected frame or that of @var{frame} if @var{frame} is not
3153 If @var{name} is @code{t}, this function modifies the default
3154 fontset, whose short name is @samp{fontset-default}.
3156 @var{character} may be a cons; @code{(@var{from} . @var{to})}, where
3157 @var{from} and @var{to} are character codepoints. In that case, use
3158 @var{font-spec} for all characters in the range @var{from} and @var{to}
3161 @var{character} may be a charset. In that case, use
3162 @var{font-spec} for all character in the charsets.
3164 @var{character} may be a script name. In that case, use
3165 @var{font-spec} for all character in the charsets.
3167 @var{font-spec} may be a cons; @code{(@var{family} . @var{registry})},
3168 where @var{family} is a family name of a font (possibly including a
3169 foundry name at the head), @var{registry} is a registry name of a font
3170 (possibly including an encoding name at the tail).
3172 @var{font-spec} may be a font name string.
3174 The optional argument @var{add}, if non-@code{nil}, specifies how to
3175 add @var{font-spec} to the font specifications previously set. If it
3176 is @code{prepend}, @var{font-spec} is prepended. If it is
3177 @code{append}, @var{font-spec} is appended. By default,
3178 @var{font-spec} overrides the previous settings.
3180 For instance, this changes the default fontset to use a font of which
3181 family name is @samp{Kochi Gothic} for all characters belonging to
3182 the charset @code{japanese-jisx0208}.
3185 (set-fontset-font t 'japanese-jisx0208
3186 (font-spec :family "Kochi Gothic"))
3190 @defun char-displayable-p char
3191 This function returns @code{t} if Emacs ought to be able to display
3192 @var{char}. More precisely, if the selected frame's fontset has a
3193 font to display the character set that @var{char} belongs to.
3195 Fontsets can specify a font on a per-character basis; when the fontset
3196 does that, this function's value may not be accurate.
3199 @node Low-Level Font
3200 @subsection Low-Level Font Representation
3201 @cindex font property
3203 Normally, it is not necessary to manipulate fonts directly. In case
3204 you need to do so, this section explains how.
3206 In Emacs Lisp, fonts are represented using three different Lisp
3207 object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font
3210 @defun fontp object &optional type
3211 Return @code{t} if @var{object} is a font object, font spec, or font
3212 entity. Otherwise, return @code{nil}.
3214 The optional argument @var{type}, if non-@code{nil}, determines the
3215 exact type of Lisp object to check for. In that case, @var{type}
3216 should be one of @code{font-object}, @code{font-spec}, or
3221 A font object is a Lisp object that represents a font that Emacs has
3222 @dfn{opened}. Font objects cannot be modified in Lisp, but they can
3225 @defun font-at position &optional window string
3226 Return the font object that is being used to display the character at
3227 position @var{position} in the window @var{window}. If @var{window}
3228 is @code{nil}, it defaults to the selected window. If @var{string} is
3229 @code{nil}, @var{position} specifies a position in the current buffer;
3230 otherwise, @var{string} should be a string, and @var{position}
3231 specifies a position in that string.
3235 A font spec is a Lisp object that contains a set of specifications
3236 that can be used to find a font. More than one font may match the
3237 specifications in a font spec.
3239 @defun font-spec &rest arguments
3240 Return a new font spec using the specifications in @var{arguments},
3241 which should come in @code{property}-@code{value} pairs. The possible
3242 specifications are as follows:
3246 The font name (a string), in either XLFD, Fontconfig, or GTK format.
3247 @xref{Fonts,,, emacs, The GNU Emacs Manual}.
3254 These have the same meanings as the face attributes of the same name.
3255 @xref{Face Attributes}.
3258 The font size---either a non-negative integer that specifies the pixel
3259 size, or a floating point number that specifies the point size.
3262 Additional typographic style information for the font, such as
3263 @samp{sans}. The value should be a string or a symbol.
3265 @cindex font registry
3267 The charset registry and encoding of the font, such as
3268 @samp{iso8859-1}. The value should be a string or a symbol.
3271 The script that the font must support (a symbol).
3274 @cindex OpenType font
3275 The font must be an OpenType font that supports these OpenType
3276 features, provided Emacs is compiled with support for @samp{libotf} (a
3277 library for performing complex text layout in certain scripts). The
3278 value must be a list of the form
3281 @code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
3284 where @var{script-tag} is the OpenType script tag symbol;
3285 @var{langsys-tag} is the OpenType language system tag symbol, or
3286 @code{nil} to use the default language system; @code{gsub} is a list
3287 of OpenType GSUB feature tag symbols, or @code{nil} if none is
3288 required; and @code{gpos} is a list of OpenType GPOS feature tag
3289 symbols, or @code{nil} if none is required. If @code{gsub} or
3290 @code{gpos} is a list, a @code{nil} element in that list means that
3291 the font must not match any of the remaining tag symbols. The
3292 @code{gpos} element may be omitted.
3296 @defun font-put font-spec property value
3297 Set the font property @var{property} in the font-spec @var{font-spec}
3302 A font entity is a reference to a font that need not be open. Its
3303 properties are intermediate between a font object and a font spec:
3304 like a font object, and unlike a font spec, it refers to a single,
3305 specific font. Unlike a font object, creating a font entity does not
3306 load the contents of that font into computer memory. Emacs may open
3307 multiple font objects of different sizes from a single font entity
3308 referring to a scalable font.
3310 @defun find-font font-spec &optional frame
3311 This function returns a font entity that best matches the font spec
3312 @var{font-spec} on frame @var{frame}. If @var{frame} is @code{nil},
3313 it defaults to the selected frame.
3316 @defun list-fonts font-spec &optional frame num prefer
3317 This function returns a list of all font entities that match the font
3318 spec @var{font-spec}.
3320 The optional argument @var{frame}, if non-@code{nil}, specifies the
3321 frame on which the fonts are to be displayed. The optional argument
3322 @var{num}, if non-@code{nil}, should be an integer that specifies the
3323 maximum length of the returned list. The optional argument
3324 @var{prefer}, if non-@code{nil}, should be another font spec, which is
3325 used to control the order of the returned list; the returned font
3326 entities are sorted in order of decreasing ``closeness'' to that font
3330 If you call @code{set-face-attribute} and pass a font spec, font
3331 entity, or font name string as the value of the @code{:font}
3332 attribute, Emacs opens the best ``matching'' font that is available
3333 for display. It then stores the corresponding font object as the
3334 actual value of the @code{:font} attribute for that face.
3336 The following functions can be used to obtain information about a
3337 font. For these functions, the @var{font} argument can be a font
3338 object, a font entity, or a font spec.
3340 @defun font-get font property
3341 This function returns the value of the font property @var{property}
3344 If @var{font} is a font spec and the font spec does not specify
3345 @var{property}, the return value is @code{nil}. If @var{font} is a
3346 font object or font entity, the value for the @var{:script} property
3347 may be a list of scripts supported by the font.
3350 @defun font-face-attributes font &optional frame
3351 This function returns a list of face attributes corresponding to
3352 @var{font}. The optional argument @var{frame} specifies the frame on
3353 which the font is to be displayed. If it is @code{nil}, the selected
3354 frame is used. The return value has the form
3357 (:family @var{family} :height @var{height} :weight @var{weight}
3358 :slant @var{slant} :width @var{width})
3361 where the values of @var{family}, @var{height}, @var{weight},
3362 @var{slant}, and @var{width} are face attribute values. Some of these
3363 key-attribute pairs may be omitted from the list if they are not
3364 specified by @var{font}.
3367 @defun font-xlfd-name font &optional fold-wildcards
3368 This function returns the XLFD (X Logical Font Descriptor), a string,
3369 matching @var{font}. @xref{Fonts,,, emacs, The GNU Emacs Manual}, for
3370 information about XLFDs. If the name is too long for an XLFD (which
3371 can contain at most 255 characters), the function returns @code{nil}.
3373 If the optional argument @var{fold-wildcards} is non-@code{nil},
3374 consecutive wildcards in the XLFD are folded into one.
3381 On graphical displays, Emacs draws @dfn{fringes} next to each
3382 window: thin vertical strips down the sides which can display bitmaps
3383 indicating truncation, continuation, horizontal scrolling, and so on.
3386 * Fringe Size/Pos:: Specifying where to put the window fringes.
3387 * Fringe Indicators:: Displaying indicator icons in the window fringes.
3388 * Fringe Cursors:: Displaying cursors in the right fringe.
3389 * Fringe Bitmaps:: Specifying bitmaps for fringe indicators.
3390 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
3391 * Overlay Arrow:: Display of an arrow to indicate position.
3394 @node Fringe Size/Pos
3395 @subsection Fringe Size and Position
3397 The following buffer-local variables control the position and width
3398 of fringes in windows showing that buffer.
3400 @defvar fringes-outside-margins
3401 The fringes normally appear between the display margins and the window
3402 text. If the value is non-@code{nil}, they appear outside the display
3403 margins. @xref{Display Margins}.
3406 @defvar left-fringe-width
3407 This variable, if non-@code{nil}, specifies the width of the left
3408 fringe in pixels. A value of @code{nil} means to use the left fringe
3409 width from the window's frame.
3412 @defvar right-fringe-width
3413 This variable, if non-@code{nil}, specifies the width of the right
3414 fringe in pixels. A value of @code{nil} means to use the right fringe
3415 width from the window's frame.
3418 Any buffer which does not specify values for these variables uses
3419 the values specified by the @code{left-fringe} and @code{right-fringe}
3420 frame parameters (@pxref{Layout Parameters}).
3422 The above variables actually take effect via the function
3423 @code{set-window-buffer} (@pxref{Buffers and Windows}), which calls
3424 @code{set-window-fringes} as a subroutine. If you change one of these
3425 variables, the fringe display is not updated in existing windows
3426 showing the buffer, unless you call @code{set-window-buffer} again in
3427 each affected window. You can also use @code{set-window-fringes} to
3428 control the fringe display in individual windows.
3430 @defun set-window-fringes window left &optional right outside-margins
3431 This function sets the fringe widths of window @var{window}.
3432 If @var{window} is @code{nil}, the selected window is used.
3434 The argument @var{left} specifies the width in pixels of the left
3435 fringe, and likewise @var{right} for the right fringe. A value of
3436 @code{nil} for either one stands for the default width. If
3437 @var{outside-margins} is non-@code{nil}, that specifies that fringes
3438 should appear outside of the display margins.
3441 @defun window-fringes &optional window
3442 This function returns information about the fringes of a window
3443 @var{window}. If @var{window} is omitted or @code{nil}, the selected
3444 window is used. The value has the form @code{(@var{left-width}
3445 @var{right-width} @var{outside-margins})}.
3449 @node Fringe Indicators
3450 @subsection Fringe Indicators
3451 @cindex fringe indicators
3452 @cindex indicators, fringe
3454 @dfn{Fringe indicators} are tiny icons displayed in the window
3455 fringe to indicate truncated or continued lines, buffer boundaries,
3458 @defopt indicate-empty-lines
3459 @cindex fringes, and empty line indication
3460 @cindex empty lines, indicating
3461 When this is non-@code{nil}, Emacs displays a special glyph in the
3462 fringe of each empty line at the end of the buffer, on graphical
3463 displays. @xref{Fringes}. This variable is automatically
3464 buffer-local in every buffer.
3467 @defopt indicate-buffer-boundaries
3468 @cindex buffer boundaries, indicating
3469 This buffer-local variable controls how the buffer boundaries and
3470 window scrolling are indicated in the window fringes.
3472 Emacs can indicate the buffer boundaries---that is, the first and last
3473 line in the buffer---with angle icons when they appear on the screen.
3474 In addition, Emacs can display an up-arrow in the fringe to show
3475 that there is text above the screen, and a down-arrow to show
3476 there is text below the screen.
3478 There are three kinds of basic values:
3482 Don't display any of these fringe icons.
3484 Display the angle icons and arrows in the left fringe.
3486 Display the angle icons and arrows in the right fringe.
3488 Display the angle icons in the left fringe
3489 and don't display the arrows.
3492 Otherwise the value should be an alist that specifies which fringe
3493 indicators to display and where. Each element of the alist should
3494 have the form @code{(@var{indicator} . @var{position})}. Here,
3495 @var{indicator} is one of @code{top}, @code{bottom}, @code{up},
3496 @code{down}, and @code{t} (which covers all the icons not yet
3497 specified), while @var{position} is one of @code{left}, @code{right}
3500 For example, @code{((top . left) (t . right))} places the top angle
3501 bitmap in left fringe, and the bottom angle bitmap as well as both
3502 arrow bitmaps in right fringe. To show the angle bitmaps in the left
3503 fringe, and no arrow bitmaps, use @code{((top . left) (bottom . left))}.
3506 @defvar fringe-indicator-alist
3507 This buffer-local variable specifies the mapping from logical fringe
3508 indicators to the actual bitmaps displayed in the window fringes. The
3509 value is an alist of elements @code{(@var{indicator}
3510 . @var{bitmaps})}, where @var{indicator} specifies a logical indicator
3511 type and @var{bitmaps} specifies the fringe bitmaps to use for that
3514 Each @var{indicator} should be one of the following symbols:
3517 @item @code{truncation}, @code{continuation}.
3518 Used for truncation and continuation lines.
3520 @item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom}
3521 Used when @code{indicate-buffer-boundaries} is non-@code{nil}:
3522 @code{up} and @code{down} indicate a buffer boundary lying above or
3523 below the window edge; @code{top} and @code{bottom} indicate the
3524 topmost and bottommost buffer text line; and @code{top-bottom}
3525 indicates where there is just one line of text in the buffer.
3527 @item @code{empty-line}
3528 Used to indicate empty lines when @code{indicate-empty-lines} is
3531 @item @code{overlay-arrow}
3532 Used for overlay arrows (@pxref{Overlay Arrow}).
3533 @c Is this used anywhere?
3534 @c @item Unknown bitmap indicator:
3538 Each @var{bitmaps} value may be a list of symbols @code{(@var{left}
3539 @var{right} [@var{left1} @var{right1}])}. The @var{left} and
3540 @var{right} symbols specify the bitmaps shown in the left and/or right
3541 fringe, for the specific indicator. @var{left1} and @var{right1} are
3542 specific to the @code{bottom} and @code{top-bottom} indicators, and
3543 are used to indicate that the last text line has no final newline.
3544 Alternatively, @var{bitmaps} may be a single symbol which is used in
3545 both left and right fringes.
3547 @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how
3548 to define your own. In addition, @code{nil} represents the empty
3549 bitmap (i.e., an indicator that is not shown).
3551 When @code{fringe-indicator-alist} has a buffer-local value, and
3552 there is no bitmap defined for a logical indicator, or the bitmap is
3553 @code{t}, the corresponding value from the default value of
3554 @code{fringe-indicator-alist} is used.
3557 @node Fringe Cursors
3558 @subsection Fringe Cursors
3559 @cindex fringe cursors
3560 @cindex cursor, fringe
3562 When a line is exactly as wide as the window, Emacs displays the
3563 cursor in the right fringe instead of using two lines. Different
3564 bitmaps are used to represent the cursor in the fringe depending on
3565 the current buffer's cursor type.
3567 @defopt overflow-newline-into-fringe
3568 If this is non-@code{nil}, lines exactly as wide as the window (not
3569 counting the final newline character) are not continued. Instead,
3570 when point is at the end of the line, the cursor appears in the right
3574 @defvar fringe-cursor-alist
3575 This variable specifies the mapping from logical cursor type to the
3576 actual fringe bitmaps displayed in the right fringe. The value is an
3577 alist where each element has the form @code{(@var{cursor-type}
3578 . @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to
3579 display cursors of type @var{cursor-type}.
3581 Each @var{cursor-type} should be one of @code{box}, @code{hollow},
3582 @code{bar}, @code{hbar}, or @code{hollow-small}. The first four have
3583 the same meanings as in the @code{cursor-type} frame parameter
3584 (@pxref{Cursor Parameters}). The @code{hollow-small} type is used
3585 instead of @code{hollow} when the normal @code{hollow-rectangle}
3586 bitmap is too tall to fit on a specific display line.
3588 Each @var{bitmap} should be a symbol specifying the fringe bitmap to
3589 be displayed for that logical cursor type.
3591 See the next subsection for details.
3594 @xref{Fringe Bitmaps}.
3597 @c FIXME: I can't find the fringes-indicator-alist variable. Maybe
3598 @c it should be fringe-indicator-alist or fringe-cursor-alist? --xfq
3599 When @code{fringe-cursor-alist} has a buffer-local value, and there is
3600 no bitmap defined for a cursor type, the corresponding value from the
3601 default value of @code{fringes-indicator-alist} is used.
3604 @node Fringe Bitmaps
3605 @subsection Fringe Bitmaps
3606 @cindex fringe bitmaps
3607 @cindex bitmaps, fringe
3609 The @dfn{fringe bitmaps} are the actual bitmaps which represent the
3610 logical fringe indicators for truncated or continued lines, buffer
3611 boundaries, overlay arrows, etc. Each bitmap is represented by a
3614 These symbols are referred to by the variables
3615 @code{fringe-indicator-alist} and @code{fringe-cursor-alist},
3616 described in the previous subsections.
3619 These symbols are referred to by the variable
3620 @code{fringe-indicator-alist}, which maps fringe indicators to bitmaps
3621 (@pxref{Fringe Indicators}), and the variable
3622 @code{fringe-cursor-alist}, which maps fringe cursors to bitmaps
3623 (@pxref{Fringe Cursors}).
3626 Lisp programs can also directly display a bitmap in the left or
3627 right fringe, by using a @code{display} property for one of the
3628 characters appearing in the line (@pxref{Other Display Specs}). Such
3629 a display specification has the form
3632 (@var{fringe} @var{bitmap} [@var{face}])
3636 @var{fringe} is either the symbol @code{left-fringe} or
3637 @code{right-fringe}. @var{bitmap} is a symbol identifying the bitmap
3638 to display. The optional @var{face} names a face whose foreground
3639 color is used to display the bitmap; this face is automatically merged
3640 with the @code{fringe} face.
3642 Here is a list of the standard fringe bitmaps defined in Emacs, and
3643 how they are currently used in Emacs (via
3644 @code{fringe-indicator-alist} and @code{fringe-cursor-alist}):
3647 @item @code{left-arrow}, @code{right-arrow}
3648 Used to indicate truncated lines.
3650 @item @code{left-curly-arrow}, @code{right-curly-arrow}
3651 Used to indicate continued lines.
3653 @item @code{right-triangle}, @code{left-triangle}
3654 The former is used by overlay arrows. The latter is unused.
3656 @item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle}
3657 @itemx @code{bottom-left-angle}, @code{bottom-right-angle}
3658 @itemx @code{top-right-angle}, @code{top-left-angle}
3659 @itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle}
3660 Used to indicate buffer boundaries.
3662 @item @code{filled-rectangle}, @code{hollow-rectangle}
3663 @itemx @code{filled-square}, @code{hollow-square}
3664 @itemx @code{vertical-bar}, @code{horizontal-bar}
3665 Used for different types of fringe cursors.
3667 @item @code{empty-line}, @code{exclamation-mark}, @code{question-mark}, @code{exclamation-mark}
3668 Not used by core Emacs features.
3672 The next subsection describes how to define your own fringe bitmaps.
3674 @defun fringe-bitmaps-at-pos &optional pos window
3675 This function returns the fringe bitmaps of the display line
3676 containing position @var{pos} in window @var{window}. The return
3677 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
3678 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
3679 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
3680 is non-@code{nil} if there is an overlay arrow in the left fringe.
3682 The value is @code{nil} if @var{pos} is not visible in @var{window}.
3683 If @var{window} is @code{nil}, that stands for the selected window.
3684 If @var{pos} is @code{nil}, that stands for the value of point in
3688 @node Customizing Bitmaps
3689 @subsection Customizing Fringe Bitmaps
3690 @cindex fringe bitmaps, customizing
3692 @defun define-fringe-bitmap bitmap bits &optional height width align
3693 This function defines the symbol @var{bitmap} as a new fringe bitmap,
3694 or replaces an existing bitmap with that name.
3696 The argument @var{bits} specifies the image to use. It should be
3697 either a string or a vector of integers, where each element (an
3698 integer) corresponds to one row of the bitmap. Each bit of an integer
3699 corresponds to one pixel of the bitmap, where the low bit corresponds
3700 to the rightmost pixel of the bitmap.
3702 The height is normally the length of @var{bits}. However, you
3703 can specify a different height with non-@code{nil} @var{height}. The width
3704 is normally 8, but you can specify a different width with non-@code{nil}
3705 @var{width}. The width must be an integer between 1 and 16.
3707 The argument @var{align} specifies the positioning of the bitmap
3708 relative to the range of rows where it is used; the default is to
3709 center the bitmap. The allowed values are @code{top}, @code{center},
3712 The @var{align} argument may also be a list @code{(@var{align}
3713 @var{periodic})} where @var{align} is interpreted as described above.
3714 If @var{periodic} is non-@code{nil}, it specifies that the rows in
3715 @code{bits} should be repeated enough times to reach the specified
3719 @defun destroy-fringe-bitmap bitmap
3720 This function destroy the fringe bitmap identified by @var{bitmap}.
3721 If @var{bitmap} identifies a standard fringe bitmap, it actually
3722 restores the standard definition of that bitmap, instead of
3723 eliminating it entirely.
3726 @defun set-fringe-bitmap-face bitmap &optional face
3727 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
3728 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
3729 bitmap's face controls the color to draw it in.
3731 @var{face} is merged with the @code{fringe} face, so normally
3732 @var{face} should specify only the foreground color.
3736 @subsection The Overlay Arrow
3737 @c @cindex overlay arrow Duplicates variable names
3739 The @dfn{overlay arrow} is useful for directing the user's attention
3740 to a particular line in a buffer. For example, in the modes used for
3741 interface to debuggers, the overlay arrow indicates the line of code
3742 about to be executed. This feature has nothing to do with
3743 @dfn{overlays} (@pxref{Overlays}).
3745 @defvar overlay-arrow-string
3746 This variable holds the string to display to call attention to a
3747 particular line, or @code{nil} if the arrow feature is not in use.
3748 On a graphical display the contents of the string are ignored; instead a
3749 glyph is displayed in the fringe area to the left of the display area.
3752 @defvar overlay-arrow-position
3753 This variable holds a marker that indicates where to display the overlay
3754 arrow. It should point at the beginning of a line. On a non-graphical
3755 display the arrow text
3756 appears at the beginning of that line, overlaying any text that would
3757 otherwise appear. Since the arrow is usually short, and the line
3758 usually begins with indentation, normally nothing significant is
3761 The overlay-arrow string is displayed in any given buffer if the value
3762 of @code{overlay-arrow-position} in that buffer points into that
3763 buffer. Thus, it is possible to display multiple overlay arrow strings
3764 by creating buffer-local bindings of @code{overlay-arrow-position}.
3765 However, it is usually cleaner to use
3766 @code{overlay-arrow-variable-list} to achieve this result.
3767 @c !!! overlay-arrow-position: but the overlay string may remain in the display
3768 @c of some other buffer until an update is required. This should be fixed
3772 You can do a similar job by creating an overlay with a
3773 @code{before-string} property. @xref{Overlay Properties}.
3775 You can define multiple overlay arrows via the variable
3776 @code{overlay-arrow-variable-list}.
3778 @defvar overlay-arrow-variable-list
3779 This variable's value is a list of variables, each of which specifies
3780 the position of an overlay arrow. The variable
3781 @code{overlay-arrow-position} has its normal meaning because it is on
3785 Each variable on this list can have properties
3786 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
3787 specify an overlay arrow string (for text terminals) or fringe bitmap
3788 (for graphical terminals) to display at the corresponding overlay
3789 arrow position. If either property is not set, the default
3790 @code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator
3794 @section Scroll Bars
3797 Normally the frame parameter @code{vertical-scroll-bars} controls
3798 whether the windows in the frame have vertical scroll bars, and
3799 whether they are on the left or right. The frame parameter
3800 @code{scroll-bar-width} specifies how wide they are (@code{nil}
3801 meaning the default). @xref{Layout Parameters}.
3803 @defun frame-current-scroll-bars &optional frame
3804 This function reports the scroll bar type settings for frame
3805 @var{frame}. The value is a cons cell
3806 @code{(@var{vertical-type} .@: @var{horizontal-type})}, where
3807 @var{vertical-type} is either @code{left}, @code{right}, or @code{nil}
3808 (which means no scroll bar.) @var{horizontal-type} is meant to
3809 specify the horizontal scroll bar type, but since they are not
3810 implemented, it is always @code{nil}.
3813 @vindex vertical-scroll-bar
3814 You can enable or disable scroll bars for a particular buffer,
3815 by setting the variable @code{vertical-scroll-bar}. This variable
3816 automatically becomes buffer-local when set. The possible values are
3817 @code{left}, @code{right}, @code{t}, which means to use the
3818 frame's default, and @code{nil} for no scroll bar.
3820 You can also control this for individual windows. Call the function
3821 @code{set-window-scroll-bars} to specify what to do for a specific window:
3823 @defun set-window-scroll-bars window width &optional vertical-type horizontal-type
3824 This function sets the width and type of scroll bars for window
3827 @var{width} specifies the scroll bar width in pixels (@code{nil} means
3828 use the width specified for the frame). @var{vertical-type} specifies
3829 whether to have a vertical scroll bar and, if so, where. The possible
3830 values are @code{left}, @code{right} and @code{nil}, just like the
3831 values of the @code{vertical-scroll-bars} frame parameter.
3833 The argument @var{horizontal-type} is meant to specify whether and
3834 where to have horizontal scroll bars, but since they are not
3835 implemented, it has no effect. If @var{window} is @code{nil}, the
3836 selected window is used.
3839 @defun window-scroll-bars &optional window
3840 Report the width and type of scroll bars specified for @var{window}.
3841 If @var{window} is omitted or @code{nil}, the selected window is used.
3842 The value is a list of the form @code{(@var{width}
3843 @var{cols} @var{vertical-type} @var{horizontal-type})}. The value
3844 @var{width} is the value that was specified for the width (which may
3845 be @code{nil}); @var{cols} is the number of columns that the scroll
3846 bar actually occupies.
3848 @var{horizontal-type} is not actually meaningful.
3851 If you don't specify these values for a window with
3852 @code{set-window-scroll-bars}, the buffer-local variables
3853 @code{scroll-bar-mode} and @code{scroll-bar-width} in the buffer being
3854 displayed control the window's vertical scroll bars. The function
3855 @code{set-window-buffer} examines these variables. If you change them
3856 in a buffer that is already visible in a window, you can make the
3857 window take note of the new values by calling @code{set-window-buffer}
3858 specifying the same buffer that is already displayed.
3860 @defopt scroll-bar-mode
3861 This variable, always local in all buffers, controls whether and where
3862 to put scroll bars in windows displaying the buffer. The possible values
3863 are @code{nil} for no scroll bar, @code{left} to put a scroll bar on
3864 the left, and @code{right} to put a scroll bar on the right.
3867 @defun window-current-scroll-bars &optional window
3868 This function reports the scroll bar type for window @var{window}.
3869 If @var{window} is omitted or @code{nil}, the selected window is used.
3870 The value is a cons cell
3871 @code{(@var{vertical-type} .@: @var{horizontal-type})}. Unlike
3872 @code{window-scroll-bars}, this reports the scroll bar type actually
3873 used, once frame defaults and @code{scroll-bar-mode} are taken into
3877 @defvar scroll-bar-width
3878 This variable, always local in all buffers, specifies the width of the
3879 buffer's scroll bars, measured in pixels. A value of @code{nil} means
3880 to use the value specified by the frame.
3883 @node Display Property
3884 @section The @code{display} Property
3885 @cindex display specification
3886 @kindex display @r{(text property)}
3888 The @code{display} text property (or overlay property) is used to
3889 insert images into text, and to control other aspects of how text
3890 displays. The value of the @code{display} property should be a
3891 display specification, or a list or vector containing several display
3892 specifications. Display specifications in the same @code{display}
3893 property value generally apply in parallel to the text they cover.
3895 If several sources (overlays and/or a text property) specify values
3896 for the @code{display} property, only one of the values takes effect,
3897 following the rules of @code{get-char-property}. @xref{Examining
3900 The rest of this section describes several kinds of
3901 display specifications and what they mean.
3904 * Replacing Specs:: Display specs that replace the text.
3905 * Specified Space:: Displaying one space with a specified width.
3906 * Pixel Specification:: Specifying space width or height in pixels.
3907 * Other Display Specs:: Displaying an image; adjusting the height,
3908 spacing, and other properties of text.
3909 * Display Margins:: Displaying text or images to the side of the main text.
3912 @node Replacing Specs
3913 @subsection Display Specs That Replace The Text
3915 Some kinds of display specifications specify something to display
3916 instead of the text that has the property. These are called
3917 @dfn{replacing} display specifications. Emacs does not allow the user
3918 to interactively move point into the middle of buffer text that is
3919 replaced in this way.
3921 If a list of display specifications includes more than one replacing
3922 display specification, the first overrides the rest. Replacing
3923 display specifications make most other display specifications
3924 irrelevant, since those don't apply to the replacement.
3926 For replacing display specifications, ``the text that has the
3927 property'' means all the consecutive characters that have the same
3928 Lisp object as their @code{display} property; these characters are
3929 replaced as a single unit. If two characters have different Lisp
3930 objects as their @code{display} properties (i.e., objects which are
3931 not @code{eq}), they are handled separately.
3933 Here is an example which illustrates this point. A string serves as
3934 a replacing display specification, which replaces the text that has
3935 the property with the specified string (@pxref{Other Display Specs}).
3936 Consider the following function:
3941 (let ((string (concat "A"))
3942 (start (+ i i (point-min))))
3943 (put-text-property start (1+ start) 'display string)
3944 (put-text-property start (+ 2 start) 'display string))))
3948 This function gives each of the first ten characters in the buffer a
3949 @code{display} property which is a string @code{"A"}, but they don't
3950 all get the same string object. The first two characters get the same
3951 string object, so they are replaced with one @samp{A}; the fact that
3952 the display property was assigned in two separate calls to
3953 @code{put-text-property} is irrelevant. Similarly, the next two
3954 characters get a second string (@code{concat} creates a new string
3955 object), so they are replaced with one @samp{A}; and so on. Thus, the
3956 ten characters appear as five A's.
3958 @node Specified Space
3959 @subsection Specified Spaces
3960 @cindex spaces, specified height or width
3961 @cindex variable-width spaces
3963 To display a space of specified width and/or height, use a display
3964 specification of the form @code{(space . @var{props})}, where
3965 @var{props} is a property list (a list of alternating properties and
3966 values). You can put this property on one or more consecutive
3967 characters; a space of the specified height and width is displayed in
3968 place of @emph{all} of those characters. These are the properties you
3969 can use in @var{props} to specify the weight of the space:
3972 @item :width @var{width}
3973 If @var{width} is an integer or floating point number, it specifies
3974 that the space width should be @var{width} times the normal character
3975 width. @var{width} can also be a @dfn{pixel width} specification
3976 (@pxref{Pixel Specification}).
3978 @item :relative-width @var{factor}
3979 Specifies that the width of the stretch should be computed from the
3980 first character in the group of consecutive characters that have the
3981 same @code{display} property. The space width is the width of that
3982 character, multiplied by @var{factor}.
3984 @item :align-to @var{hpos}
3985 Specifies that the space should be wide enough to reach @var{hpos}.
3986 If @var{hpos} is a number, it is measured in units of the normal
3987 character width. @var{hpos} can also be a @dfn{pixel width}
3988 specification (@pxref{Pixel Specification}).
3991 You should use one and only one of the above properties. You can
3992 also specify the height of the space, with these properties:
3995 @item :height @var{height}
3996 Specifies the height of the space.
3997 If @var{height} is an integer or floating point number, it specifies
3998 that the space height should be @var{height} times the normal character
3999 height. The @var{height} may also be a @dfn{pixel height} specification
4000 (@pxref{Pixel Specification}).
4002 @item :relative-height @var{factor}
4003 Specifies the height of the space, multiplying the ordinary height
4004 of the text having this display specification by @var{factor}.
4006 @item :ascent @var{ascent}
4007 If the value of @var{ascent} is a non-negative number no greater than
4008 100, it specifies that @var{ascent} percent of the height of the space
4009 should be considered as the ascent of the space---that is, the part
4010 above the baseline. The ascent may also be specified in pixel units
4011 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
4015 Don't use both @code{:height} and @code{:relative-height} together.
4017 The @code{:width} and @code{:align-to} properties are supported on
4018 non-graphic terminals, but the other space properties in this section
4021 Note that space properties are treated as paragraph separators for
4022 the purposes of reordering bidirectional text for display.
4023 @xref{Bidirectional Display}, for the details.
4025 @node Pixel Specification
4026 @subsection Pixel Specification for Spaces
4027 @cindex spaces, pixel specification
4029 The value of the @code{:width}, @code{:align-to}, @code{:height},
4030 and @code{:ascent} properties can be a special kind of expression that
4031 is evaluated during redisplay. The result of the evaluation is used
4032 as an absolute number of pixels.
4034 The following expressions are supported:
4038 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
4039 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
4040 @var{unit} ::= in | mm | cm | width | height
4043 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
4045 @var{pos} ::= left | center | right
4046 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
4051 The form @var{num} specifies a fraction of the default frame font
4052 height or width. The form @code{(@var{num})} specifies an absolute
4053 number of pixels. If @var{num} is a symbol, @var{symbol}, its
4054 buffer-local variable binding is used.
4056 The @code{in}, @code{mm}, and @code{cm} units specify the number of
4057 pixels per inch, millimeter, and centimeter, respectively. The
4058 @code{width} and @code{height} units correspond to the default width
4059 and height of the current face. An image specification @code{image}
4060 corresponds to the width or height of the image.
4062 The elements @code{left-fringe}, @code{right-fringe},
4063 @code{left-margin}, @code{right-margin}, @code{scroll-bar}, and
4064 @code{text} specify to the width of the corresponding area of the
4067 The @code{left}, @code{center}, and @code{right} positions can be
4068 used with @code{:align-to} to specify a position relative to the left
4069 edge, center, or right edge of the text area.
4071 Any of the above window elements (except @code{text}) can also be
4072 used with @code{:align-to} to specify that the position is relative to
4073 the left edge of the given area. Once the base offset for a relative
4074 position has been set (by the first occurrence of one of these
4075 symbols), further occurrences of these symbols are interpreted as the
4076 width of the specified area. For example, to align to the center of
4077 the left-margin, use
4080 :align-to (+ left-margin (0.5 . left-margin))
4083 If no specific base offset is set for alignment, it is always relative
4084 to the left edge of the text area. For example, @samp{:align-to 0} in a
4085 header-line aligns with the first text column in the text area.
4087 A value of the form @code{(@var{num} . @var{expr})} stands for the
4088 product of the values of @var{num} and @var{expr}. For example,
4089 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
4090 @var{image})} specifies half the width (or height) of the specified
4093 The form @code{(+ @var{expr} ...)} adds up the value of the
4094 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
4095 the value of the expressions.
4097 @node Other Display Specs
4098 @subsection Other Display Specifications
4100 Here are the other sorts of display specifications that you can use
4101 in the @code{display} text property.
4105 Display @var{string} instead of the text that has this property.
4107 Recursive display specifications are not supported---@var{string}'s
4108 @code{display} properties, if any, are not used.
4110 @item (image . @var{image-props})
4111 This kind of display specification is an image descriptor (@pxref{Images}).
4112 When used as a display specification, it means to display the image
4113 instead of the text that has the display specification.
4115 @item (slice @var{x} @var{y} @var{width} @var{height})
4116 This specification together with @code{image} specifies a @dfn{slice}
4117 (a partial area) of the image to display. The elements @var{y} and
4118 @var{x} specify the top left corner of the slice, within the image;
4119 @var{width} and @var{height} specify the width and height of the
4120 slice. Integer values are numbers of pixels. A floating point number
4121 in the range 0.0--1.0 stands for that fraction of the width or height
4122 of the entire image.
4124 @item ((margin nil) @var{string})
4125 A display specification of this form means to display @var{string}
4126 instead of the text that has the display specification, at the same
4127 position as that text. It is equivalent to using just @var{string},
4128 but it is done as a special case of marginal display (@pxref{Display
4131 @item (left-fringe @var{bitmap} @r{[}@var{face}@r{]})
4132 @itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]})
4133 This display specification on any character of a line of text causes
4134 the specified @var{bitmap} be displayed in the left or right fringes
4135 for that line, instead of the characters that have the display
4136 specification. The optional @var{face} specifies the colors to be
4137 used for the bitmap. @xref{Fringe Bitmaps}, for the details.
4139 @item (space-width @var{factor})
4140 This display specification affects all the space characters within the
4141 text that has the specification. It displays all of these spaces
4142 @var{factor} times as wide as normal. The element @var{factor} should
4143 be an integer or float. Characters other than spaces are not affected
4144 at all; in particular, this has no effect on tab characters.
4146 @item (height @var{height})
4147 This display specification makes the text taller or shorter.
4148 Here are the possibilities for @var{height}:
4151 @item @code{(+ @var{n})}
4152 @c FIXME: Add an index for "step"? --xfq
4153 This means to use a font that is @var{n} steps larger. A ``step'' is
4154 defined by the set of available fonts---specifically, those that match
4155 what was otherwise specified for this text, in all attributes except
4156 height. Each size for which a suitable font is available counts as
4157 another step. @var{n} should be an integer.
4159 @item @code{(- @var{n})}
4160 This means to use a font that is @var{n} steps smaller.
4162 @item a number, @var{factor}
4163 A number, @var{factor}, means to use a font that is @var{factor} times
4164 as tall as the default font.
4166 @item a symbol, @var{function}
4167 A symbol is a function to compute the height. It is called with the
4168 current height as argument, and should return the new height to use.
4170 @item anything else, @var{form}
4171 If the @var{height} value doesn't fit the previous possibilities, it is
4172 a form. Emacs evaluates it to get the new height, with the symbol
4173 @code{height} bound to the current specified font height.
4176 @item (raise @var{factor})
4177 This kind of display specification raises or lowers the text
4178 it applies to, relative to the baseline of the line.
4180 @var{factor} must be a number, which is interpreted as a multiple of the
4181 height of the affected text. If it is positive, that means to display
4182 the characters raised. If it is negative, that means to display them
4185 If the text also has a @code{height} display specification, that does
4186 not affect the amount of raising or lowering, which is based on the
4187 faces used for the text.
4190 @c We put all the `@code{(when ...)}' on one line to encourage
4191 @c makeinfo's end-of-sentence heuristics to DTRT. Previously, the dot
4192 @c was at eol; the info file ended up w/ two spaces rendered after it.
4193 You can make any display specification conditional. To do that,
4194 package it in another list of the form
4195 @code{(when @var{condition} . @var{spec})}.
4196 Then the specification @var{spec} applies only when
4197 @var{condition} evaluates to a non-@code{nil} value. During the
4198 evaluation, @code{object} is bound to the string or buffer having the
4199 conditional @code{display} property. @code{position} and
4200 @code{buffer-position} are bound to the position within @code{object}
4201 and the buffer position where the @code{display} property was found,
4202 respectively. Both positions can be different when @code{object} is a
4205 @node Display Margins
4206 @subsection Displaying in the Margins
4207 @cindex display margins
4208 @cindex margins, display
4210 A buffer can have blank areas called @dfn{display margins} on the
4211 left and on the right. Ordinary text never appears in these areas,
4212 but you can put things into the display margins using the
4213 @code{display} property. There is currently no way to make text or
4214 images in the margin mouse-sensitive.
4216 The way to display something in the margins is to specify it in a
4217 margin display specification in the @code{display} property of some
4218 text. This is a replacing display specification, meaning that the
4219 text you put it on does not get displayed; the margin display appears,
4220 but that text does not.
4222 A margin display specification looks like @code{((margin
4223 right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}.
4224 Here, @var{spec} is another display specification that says what to
4225 display in the margin. Typically it is a string of text to display,
4226 or an image descriptor.
4228 To display something in the margin @emph{in association with}
4229 certain buffer text, without altering or preventing the display of
4230 that text, put a @code{before-string} property on the text and put the
4231 margin display specification on the contents of the before-string.
4233 Before the display margins can display anything, you must give
4234 them a nonzero width. The usual way to do that is to set these
4237 @defvar left-margin-width
4238 This variable specifies the width of the left margin, in character
4239 cell (a.k.a.@: ``column'') units. It is buffer-local in all buffers.
4240 A value of @code{nil} means no left marginal area.
4243 @defvar right-margin-width
4244 This variable specifies the width of the right margin, in character
4245 cell units. It is buffer-local in all buffers. A value of @code{nil}
4246 means no right marginal area.
4249 Setting these variables does not immediately affect the window. These
4250 variables are checked when a new buffer is displayed in the window.
4251 Thus, you can make changes take effect by calling
4252 @code{set-window-buffer}.
4254 You can also set the margin widths immediately.
4256 @defun set-window-margins window left &optional right
4257 This function specifies the margin widths for window @var{window}, in
4258 character cell units. The argument @var{left} controls the left
4259 margin, and @var{right} controls the right margin (default @code{0}).
4262 @defun window-margins &optional window
4263 This function returns the width of the left and right margins of
4264 @var{window} as a cons cell of the form @w{@code{(@var{left}
4265 . @var{right})}}. If one of the two marginal areas does not exist,
4266 its width is returned as @code{nil}; if neither of the two margins exist,
4267 the function returns @code{(nil)}. If @var{window} is @code{nil}, the
4268 selected window is used.
4273 @cindex images in buffers
4275 To display an image in an Emacs buffer, you must first create an image
4276 descriptor, then use it as a display specifier in the @code{display}
4277 property of text that is displayed (@pxref{Display Property}).
4279 Emacs is usually able to display images when it is run on a
4280 graphical terminal. Images cannot be displayed in a text terminal, on
4281 certain graphical terminals that lack the support for this, or if
4282 Emacs is compiled without image support. You can use the function
4283 @code{display-images-p} to determine if images can in principle be
4284 displayed (@pxref{Display Feature Testing}).
4287 * Image Formats:: Supported image formats.
4288 * Image Descriptors:: How to specify an image for use in @code{:display}.
4289 * XBM Images:: Special features for XBM format.
4290 * XPM Images:: Special features for XPM format.
4291 * PostScript Images:: Special features for PostScript format.
4292 * ImageMagick Images:: Special features available through ImageMagick.
4293 * Other Image Types:: Various other formats are supported.
4294 * Defining Images:: Convenient ways to define an image for later use.
4295 * Showing Images:: Convenient ways to display an image once it is defined.
4296 * Multi-Frame Images:: Some images contain more than one frame.
4297 * Image Cache:: Internal mechanisms of image display.
4301 @subsection Image Formats
4302 @cindex image formats
4305 Emacs can display a number of different image formats. Some of
4306 these image formats are supported only if particular support libraries
4307 are installed. On some platforms, Emacs can load support libraries on
4308 demand; if so, the variable @code{dynamic-library-alist} can be used
4309 to modify the set of known names for these dynamic libraries.
4310 @xref{Dynamic Libraries}.
4312 Supported image formats (and the required support libraries) include
4313 PBM and XBM (which do not depend on support libraries and are always
4314 available), XPM (@code{libXpm}), GIF (@code{libgif} or
4315 @code{libungif}), PostScript (@code{gs}), JPEG (@code{libjpeg}), TIFF
4316 (@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}).
4318 Each of these image formats is associated with an @dfn{image type
4319 symbol}. The symbols for the above formats are, respectively,
4320 @code{pbm}, @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
4321 @code{jpeg}, @code{tiff}, @code{png}, and @code{svg}.
4323 Furthermore, if you build Emacs with ImageMagick
4324 (@code{libMagickWand}) support, Emacs can display any image format
4325 that ImageMagick can. @xref{ImageMagick Images}. All images
4326 displayed via ImageMagick have type symbol @code{imagemagick}.
4329 This variable contains a list of type symbols for image formats which
4330 are potentially supported in the current configuration.
4332 ``Potentially'' means that Emacs knows about the image types, not
4333 necessarily that they can be used (for example, they could depend on
4334 unavailable dynamic libraries). To know which image types are really
4335 available, use @code{image-type-available-p}.
4338 @defun image-type-available-p type
4339 This function returns non-@code{nil} if images of type @var{type} can
4340 be loaded and displayed. @var{type} must be an image type symbol.
4342 For image types whose support libraries are statically linked, this
4343 function always returns @code{t}. For image types whose support
4344 libraries are dynamically loaded, it returns @code{t} if the library
4345 could be loaded and @code{nil} otherwise.
4348 @node Image Descriptors
4349 @subsection Image Descriptors
4350 @cindex image descriptor
4352 An @dfn{image descriptor} is a list which specifies the underlying
4353 data for an image, and how to display it. It is typically used as the
4354 value of a @code{display} overlay or text property (@pxref{Other
4355 Display Specs}); but @xref{Showing Images}, for convenient helper
4356 functions to insert images into buffers.
4358 Each image descriptor has the form @code{(image . @var{props})},
4359 where @var{props} is a property list of alternating keyword symbols
4360 and values, including at least the pair @code{:type @var{TYPE}} which
4361 specifies the image type.
4363 The following is a list of properties that are meaningful for all
4364 image types (there are also properties which are meaningful only for
4365 certain image types, as documented in the following subsections):
4368 @item :type @var{type}
4371 @xref{Image Formats}.
4373 Every image descriptor must include this property.
4375 @item :file @var{file}
4376 This says to load the image from file @var{file}. If @var{file} is
4377 not an absolute file name, it is expanded in @code{data-directory}.
4379 @item :data @var{data}
4380 This specifies the raw image data. Each image descriptor must have
4381 either @code{:data} or @code{:file}, but not both.
4383 For most image types, the value of a @code{:data} property should be a
4384 string containing the image data. Some image types do not support
4385 @code{:data}; for some others, @code{:data} alone is not enough, so
4386 you need to use other image properties along with @code{:data}. See
4387 the following subsections for details.
4389 @item :margin @var{margin}
4390 This specifies how many pixels to add as an extra margin around the
4391 image. The value, @var{margin}, must be a non-negative number, or a
4392 pair @code{(@var{x} . @var{y})} of such numbers. If it is a pair,
4393 @var{x} specifies how many pixels to add horizontally, and @var{y}
4394 specifies how many pixels to add vertically. If @code{:margin} is not
4395 specified, the default is zero.
4397 @item :ascent @var{ascent}
4398 This specifies the amount of the image's height to use for its
4399 ascent---that is, the part above the baseline. The value,
4400 @var{ascent}, must be a number in the range 0 to 100, or the symbol
4403 If @var{ascent} is a number, that percentage of the image's height is
4404 used for its ascent.
4406 If @var{ascent} is @code{center}, the image is vertically centered
4407 around a centerline which would be the vertical centerline of text drawn
4408 at the position of the image, in the manner specified by the text
4409 properties and overlays that apply to the image.
4411 If this property is omitted, it defaults to 50.
4413 @item :relief @var{relief}
4414 This adds a shadow rectangle around the image. The value,
4415 @var{relief}, specifies the width of the shadow lines, in pixels. If
4416 @var{relief} is negative, shadows are drawn so that the image appears
4417 as a pressed button; otherwise, it appears as an unpressed button.
4419 @item :conversion @var{algorithm}
4420 This specifies a conversion algorithm that should be applied to the
4421 image before it is displayed; the value, @var{algorithm}, specifies
4427 Specifies the Laplace edge detection algorithm, which blurs out small
4428 differences in color while highlighting larger differences. People
4429 sometimes consider this useful for displaying the image for a
4430 ``disabled'' button.
4432 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
4433 @cindex edge detection, images
4434 Specifies a general edge-detection algorithm. @var{matrix} must be
4435 either a nine-element list or a nine-element vector of numbers. A pixel
4436 at position @math{x/y} in the transformed image is computed from
4437 original pixels around that position. @var{matrix} specifies, for each
4438 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
4439 will influence the transformed pixel; element @math{0} specifies the
4440 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
4441 the pixel at @math{x/y-1} etc., as shown below:
4444 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
4445 x-1/y & x/y & x+1/y \cr
4446 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
4451 (x-1/y-1 x/y-1 x+1/y-1
4453 x-1/y+1 x/y+1 x+1/y+1)
4457 The resulting pixel is computed from the color intensity of the color
4458 resulting from summing up the RGB values of surrounding pixels,
4459 multiplied by the specified factors, and dividing that sum by the sum
4460 of the factors' absolute values.
4462 Laplace edge-detection currently uses a matrix of
4465 $$\pmatrix{1 & 0 & 0 \cr
4478 Emboss edge-detection uses a matrix of
4481 $$\pmatrix{ 2 & -1 & 0 \cr
4495 Specifies transforming the image so that it looks ``disabled''.
4498 @item :mask @var{mask}
4499 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
4500 a clipping mask for the image, so that the background of a frame is
4501 visible behind the image. If @var{bg} is not specified, or if @var{bg}
4502 is @code{t}, determine the background color of the image by looking at
4503 the four corners of the image, assuming the most frequently occurring
4504 color from the corners is the background color of the image. Otherwise,
4505 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
4506 specifying the color to assume for the background of the image.
4508 If @var{mask} is @code{nil}, remove a mask from the image, if it has
4509 one. Images in some formats include a mask which can be removed by
4510 specifying @code{:mask nil}.
4512 @item :pointer @var{shape}
4513 This specifies the pointer shape when the mouse pointer is over this
4514 image. @xref{Pointer Shape}, for available pointer shapes.
4516 @item :map @var{map}
4518 This associates an image map of @dfn{hot spots} with this image.
4520 An image map is an alist where each element has the format
4521 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
4522 as either a rectangle, a circle, or a polygon.
4524 A rectangle is a cons
4525 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
4526 which specifies the pixel coordinates of the upper left and bottom right
4527 corners of the rectangle area.
4530 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
4531 which specifies the center and the radius of the circle; @var{r} may
4532 be a float or integer.
4535 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
4536 where each pair in the vector describes one corner in the polygon.
4538 When the mouse pointer lies on a hot-spot area of an image, the
4539 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
4540 property, that defines a tool-tip for the hot-spot, and if it contains
4541 a @code{pointer} property, that defines the shape of the mouse cursor when
4542 it is on the hot-spot.
4543 @xref{Pointer Shape}, for available pointer shapes.
4545 When you click the mouse when the mouse pointer is over a hot-spot, an
4546 event is composed by combining the @var{id} of the hot-spot with the
4547 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
4548 @var{id} is @code{area4}.
4551 @defun image-mask-p spec &optional frame
4552 This function returns @code{t} if image @var{spec} has a mask bitmap.
4553 @var{frame} is the frame on which the image will be displayed.
4554 @var{frame} @code{nil} or omitted means to use the selected frame
4555 (@pxref{Input Focus}).
4559 @subsection XBM Images
4562 To use XBM format, specify @code{xbm} as the image type. This image
4563 format doesn't require an external library, so images of this type are
4566 Additional image properties supported for the @code{xbm} image type are:
4569 @item :foreground @var{foreground}
4570 The value, @var{foreground}, should be a string specifying the image
4571 foreground color, or @code{nil} for the default color. This color is
4572 used for each pixel in the XBM that is 1. The default is the frame's
4575 @item :background @var{background}
4576 The value, @var{background}, should be a string specifying the image
4577 background color, or @code{nil} for the default color. This color is
4578 used for each pixel in the XBM that is 0. The default is the frame's
4582 If you specify an XBM image using data within Emacs instead of an
4583 external file, use the following three properties:
4586 @item :data @var{data}
4587 The value, @var{data}, specifies the contents of the image.
4588 There are three formats you can use for @var{data}:
4592 A vector of strings or bool-vectors, each specifying one line of the
4593 image. Do specify @code{:height} and @code{:width}.
4596 A string containing the same byte sequence as an XBM file would contain.
4597 You must not specify @code{:height} and @code{:width} in this case,
4598 because omitting them is what indicates the data has the format of an
4599 XBM file. The file contents specify the height and width of the image.
4602 A string or a bool-vector containing the bits of the image (plus perhaps
4603 some extra bits at the end that will not be used). It should contain at
4604 least @var{width} * @code{height} bits. In this case, you must specify
4605 @code{:height} and @code{:width}, both to indicate that the string
4606 contains just the bits rather than a whole XBM file, and to specify the
4610 @item :width @var{width}
4611 The value, @var{width}, specifies the width of the image, in pixels.
4613 @item :height @var{height}
4614 The value, @var{height}, specifies the height of the image, in pixels.
4618 @subsection XPM Images
4621 To use XPM format, specify @code{xpm} as the image type. The
4622 additional image property @code{:color-symbols} is also meaningful with
4623 the @code{xpm} image type:
4626 @item :color-symbols @var{symbols}
4627 The value, @var{symbols}, should be an alist whose elements have the
4628 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
4629 the name of a color as it appears in the image file, and @var{color}
4630 specifies the actual color to use for displaying that name.
4633 @node PostScript Images
4634 @subsection PostScript Images
4635 @cindex postscript images
4637 To use PostScript for an image, specify image type @code{postscript}.
4638 This works only if you have Ghostscript installed. You must always use
4639 these three properties:
4642 @item :pt-width @var{width}
4643 The value, @var{width}, specifies the width of the image measured in
4644 points (1/72 inch). @var{width} must be an integer.
4646 @item :pt-height @var{height}
4647 The value, @var{height}, specifies the height of the image in points
4648 (1/72 inch). @var{height} must be an integer.
4650 @item :bounding-box @var{box}
4651 The value, @var{box}, must be a list or vector of four integers, which
4652 specifying the bounding box of the PostScript image, analogous to the
4653 @samp{BoundingBox} comment found in PostScript files.
4656 %%BoundingBox: 22 171 567 738
4660 @node ImageMagick Images
4661 @subsection ImageMagick Images
4662 @cindex ImageMagick images
4663 @cindex images, support for more formats
4665 If you build Emacs with ImageMagick support, you can use the
4666 ImageMagick library to load many image formats (@pxref{File
4667 Conveniences,,, emacs, The GNU Emacs Manual}). The image type symbol
4668 for images loaded via ImageMagick is @code{imagemagick}, regardless of
4669 the actual underlying image format.
4671 @defun imagemagick-types
4672 This function returns a list of image file extensions supported by the
4673 current ImageMagick installation. Each list element is a symbol
4674 representing an internal ImageMagick name for an image type, such as
4675 @code{BMP} for @file{.bmp} images.
4678 @defopt imagemagick-enabled-types
4679 The value of this variable is a list of ImageMagick image types which
4680 Emacs may attempt to render using ImageMagick. Each list element
4681 should be one of the symbols in the list returned by
4682 @code{imagemagick-types}, or an equivalent string. Alternatively, a
4683 value of @code{t} enables ImageMagick for all possible image types.
4684 Regardless of the value of this variable,
4685 @code{imagemagick-types-inhibit} (see below) takes precedence.
4688 @defopt imagemagick-types-inhibit
4689 The value of this variable lists the ImageMagick image types which
4690 should never be rendered using ImageMagick, regardless of the value of
4691 @code{imagemagick-enabled-types}. A value of @code{t} disables
4692 ImageMagick entirely.
4695 @defvar image-format-suffixes
4696 This variable is an alist mapping image types to file name extensions.
4697 Emacs uses this in conjunction with the @code{:format} image property
4698 (see below) to give a hint to the ImageMagick library as to the type
4699 of an image. Each element has the form @code{(@var{type}
4700 @var{extension})}, where @var{type} is a symbol specifying an image
4701 content-type, and @var{extension} is a string that specifies the
4702 associated file name extension.
4705 Images loaded with ImageMagick support the following additional
4706 image descriptor properties:
4709 @item :background @var{background}
4710 @var{background}, if non-@code{nil}, should be a string specifying a
4711 color, which is used as the image's background color if the image
4712 supports transparency. If the value is @code{nil}, it defaults to the
4713 frame's background color.
4715 @item :width @var{width}, :height @var{height}
4716 The @code{:width} and @code{:height} keywords are used for scaling the
4717 image. If only one of them is specified, the other one will be
4718 calculated so as to preserve the aspect ratio. If both are specified,
4719 aspect ratio may not be preserved.
4721 @item :max-width @var{max-width}, :max-height @var{max-height}
4722 The @code{:max-width} and @code{:max-height} keywords are used for
4723 scaling if the size of the image of the image exceeds these values.
4724 If @code{:width} is set it will have precedence over @code{max-width},
4725 and if @code{:height} is set it will have precedence over
4726 @code{max-height}, but you can otherwise mix these keywords as you
4727 wish. @code{:max-width} and @code{:max-height} will always preserve
4730 @item :format @var{type}
4731 The value, @var{type}, should be a symbol specifying the type of the
4732 image data, as found in @code{image-format-suffixes}. This is used
4733 when the image does not have an associated file name, to provide a
4734 hint to ImageMagick to help it detect the image type.
4736 @item :rotation @var{angle}
4737 Specifies a rotation angle in degrees.
4739 @item :index @var{frame}
4740 @c Doesn't work: http://debbugs.gnu.org/7978
4741 @xref{Multi-Frame Images}.
4744 @node Other Image Types
4745 @subsection Other Image Types
4748 For PBM images, specify image type @code{pbm}. Color, gray-scale and
4749 monochromatic images are supported. For mono PBM images, two additional
4750 image properties are supported.
4753 @item :foreground @var{foreground}
4754 The value, @var{foreground}, should be a string specifying the image
4755 foreground color, or @code{nil} for the default color. This color is
4756 used for each pixel in the PBM that is 1. The default is the frame's
4759 @item :background @var{background}
4760 The value, @var{background}, should be a string specifying the image
4761 background color, or @code{nil} for the default color. This color is
4762 used for each pixel in the PBM that is 0. The default is the frame's
4767 The remaining image types that Emacs can support are:
4771 Image type @code{gif}.
4772 Supports the @code{:index} property. @xref{Multi-Frame Images}.
4775 Image type @code{jpeg}.
4778 Image type @code{png}.
4781 Image type @code{svg}.
4784 Image type @code{tiff}.
4785 Supports the @code{:index} property. @xref{Multi-Frame Images}.
4788 @node Defining Images
4789 @subsection Defining Images
4791 The functions @code{create-image}, @code{defimage} and
4792 @code{find-image} provide convenient ways to create image descriptors.
4794 @defun create-image file-or-data &optional type data-p &rest props
4795 This function creates and returns an image descriptor which uses the
4796 data in @var{file-or-data}. @var{file-or-data} can be a file name or
4797 a string containing the image data; @var{data-p} should be @code{nil}
4798 for the former case, non-@code{nil} for the latter case.
4800 The optional argument @var{type} is a symbol specifying the image type.
4801 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
4802 determine the image type from the file's first few bytes, or else
4803 from the file's name.
4805 The remaining arguments, @var{props}, specify additional image
4806 properties---for example,
4808 @c ':heuristic-mask' is not documented?
4810 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
4813 The function returns @code{nil} if images of this type are not
4814 supported. Otherwise it returns an image descriptor.
4817 @defmac defimage symbol specs &optional doc
4818 This macro defines @var{symbol} as an image name. The arguments
4819 @var{specs} is a list which specifies how to display the image.
4820 The third argument, @var{doc}, is an optional documentation string.
4822 Each argument in @var{specs} has the form of a property list, and each
4823 one should specify at least the @code{:type} property and either the
4824 @code{:file} or the @code{:data} property. The value of @code{:type}
4825 should be a symbol specifying the image type, the value of
4826 @code{:file} is the file to load the image from, and the value of
4827 @code{:data} is a string containing the actual image data. Here is an
4831 (defimage test-image
4832 ((:type xpm :file "~/test1.xpm")
4833 (:type xbm :file "~/test1.xbm")))
4836 @code{defimage} tests each argument, one by one, to see if it is
4837 usable---that is, if the type is supported and the file exists. The
4838 first usable argument is used to make an image descriptor which is
4839 stored in @var{symbol}.
4841 If none of the alternatives will work, then @var{symbol} is defined
4845 @defun find-image specs
4846 This function provides a convenient way to find an image satisfying one
4847 of a list of image specifications @var{specs}.
4849 Each specification in @var{specs} is a property list with contents
4850 depending on image type. All specifications must at least contain the
4851 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
4852 or @w{@code{:data @var{DATA}}}, where @var{type} is a symbol specifying
4853 the image type, e.g., @code{xbm}, @var{file} is the file to load the
4854 image from, and @var{data} is a string containing the actual image data.
4855 The first specification in the list whose @var{type} is supported, and
4856 @var{file} exists, is used to construct the image specification to be
4857 returned. If no specification is satisfied, @code{nil} is returned.
4859 The image is looked for in @code{image-load-path}.
4862 @defvar image-load-path
4863 This variable's value is a list of locations in which to search for
4864 image files. If an element is a string or a variable symbol whose
4865 value is a string, the string is taken to be the name of a directory
4866 to search. If an element is a variable symbol whose value is a list,
4867 that is taken to be a list of directory names to search.
4869 The default is to search in the @file{images} subdirectory of the
4870 directory specified by @code{data-directory}, then the directory
4871 specified by @code{data-directory}, and finally in the directories in
4872 @code{load-path}. Subdirectories are not automatically included in
4873 the search, so if you put an image file in a subdirectory, you have to
4874 supply the subdirectory name explicitly. For example, to find the
4875 image @file{images/foo/bar.xpm} within @code{data-directory}, you
4876 should specify the image as follows:
4879 (defimage foo-image '((:type xpm :file "foo/bar.xpm")))
4883 @defun image-load-path-for-library library image &optional path no-error
4884 This function returns a suitable search path for images used by the
4885 Lisp package @var{library}.
4887 The function searches for @var{image} first using @code{image-load-path},
4888 excluding @file{@code{data-directory}/images}, and then in
4889 @code{load-path}, followed by a path suitable for @var{library}, which
4890 includes @file{../../etc/images} and @file{../etc/images} relative to
4891 the library file itself, and finally in
4892 @file{@code{data-directory}/images}.
4894 Then this function returns a list of directories which contains first
4895 the directory in which @var{image} was found, followed by the value of
4896 @code{load-path}. If @var{path} is given, it is used instead of
4899 If @var{no-error} is non-@code{nil} and a suitable path can't be
4900 found, don't signal an error. Instead, return a list of directories as
4901 before, except that @code{nil} appears in place of the image directory.
4903 Here is an example of using @code{image-load-path-for-library}:
4906 (defvar image-load-path) ; shush compiler
4907 (let* ((load-path (image-load-path-for-library
4908 "mh-e" "mh-logo.xpm"))
4909 (image-load-path (cons (car load-path)
4911 (mh-tool-bar-folder-buttons-init))
4915 @node Showing Images
4916 @subsection Showing Images
4918 You can use an image descriptor by setting up the @code{display}
4919 property yourself, but it is easier to use the functions in this
4922 @defun insert-image image &optional string area slice
4923 This function inserts @var{image} in the current buffer at point. The
4924 value @var{image} should be an image descriptor; it could be a value
4925 returned by @code{create-image}, or the value of a symbol defined with
4926 @code{defimage}. The argument @var{string} specifies the text to put
4927 in the buffer to hold the image. If it is omitted or @code{nil},
4928 @code{insert-image} uses @code{" "} by default.
4930 The argument @var{area} specifies whether to put the image in a margin.
4931 If it is @code{left-margin}, the image appears in the left margin;
4932 @code{right-margin} specifies the right margin. If @var{area} is
4933 @code{nil} or omitted, the image is displayed at point within the
4936 The argument @var{slice} specifies a slice of the image to insert. If
4937 @var{slice} is @code{nil} or omitted the whole image is inserted.
4938 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
4939 @var{height})} which specifies the @var{x} and @var{y} positions and
4940 @var{width} and @var{height} of the image area to insert. Integer
4941 values are in units of pixels. A floating point number in the range
4942 0.0--1.0 stands for that fraction of the width or height of the entire
4945 Internally, this function inserts @var{string} in the buffer, and gives
4946 it a @code{display} property which specifies @var{image}. @xref{Display
4950 @cindex slice, image
4952 @defun insert-sliced-image image &optional string area rows cols
4953 This function inserts @var{image} in the current buffer at point, like
4954 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
4955 equally sized slices.
4957 If an image is inserted ``sliced'', Emacs displays each slice as a
4958 separate image, and allow more intuitive scrolling up/down, instead of
4959 jumping up/down the entire image when paging through a buffer that
4960 displays (large) images.
4963 @defun put-image image pos &optional string area
4964 This function puts image @var{image} in front of @var{pos} in the
4965 current buffer. The argument @var{pos} should be an integer or a
4966 marker. It specifies the buffer position where the image should appear.
4967 The argument @var{string} specifies the text that should hold the image
4968 as an alternative to the default.
4970 The argument @var{image} must be an image descriptor, perhaps returned
4971 by @code{create-image} or stored by @code{defimage}.
4973 The argument @var{area} specifies whether to put the image in a margin.
4974 If it is @code{left-margin}, the image appears in the left margin;
4975 @code{right-margin} specifies the right margin. If @var{area} is
4976 @code{nil} or omitted, the image is displayed at point within the
4979 Internally, this function creates an overlay, and gives it a
4980 @code{before-string} property containing text that has a @code{display}
4981 property whose value is the image. (Whew!)
4984 @defun remove-images start end &optional buffer
4985 This function removes images in @var{buffer} between positions
4986 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
4987 images are removed from the current buffer.
4989 This removes only images that were put into @var{buffer} the way
4990 @code{put-image} does it, not images that were inserted with
4991 @code{insert-image} or in other ways.
4994 @defun image-size spec &optional pixels frame
4995 @cindex size of image
4996 This function returns the size of an image as a pair
4997 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
4998 specification. @var{pixels} non-@code{nil} means return sizes
4999 measured in pixels, otherwise return sizes measured in canonical
5000 character units (fractions of the width/height of the frame's default
5001 font). @var{frame} is the frame on which the image will be displayed.
5002 @var{frame} null or omitted means use the selected frame (@pxref{Input
5006 @defvar max-image-size
5007 This variable is used to define the maximum size of image that Emacs
5008 will load. Emacs will refuse to load (and display) any image that is
5009 larger than this limit.
5011 If the value is an integer, it directly specifies the maximum
5012 image height and width, measured in pixels. If it is a floating
5013 point number, it specifies the maximum image height and width
5014 as a ratio to the frame height and width. If the value is
5015 non-numeric, there is no explicit limit on the size of images.
5017 The purpose of this variable is to prevent unreasonably large images
5018 from accidentally being loaded into Emacs. It only takes effect the
5019 first time an image is loaded. Once an image is placed in the image
5020 cache, it can always be displayed, even if the value of
5021 @code{max-image-size} is subsequently changed (@pxref{Image Cache}).
5024 @node Multi-Frame Images
5025 @subsection Multi-Frame Images
5026 @cindex multi-frame images
5029 @cindex image animation
5030 @cindex image frames
5031 Some image files can contain more than one image. We say that there
5032 are multiple ``frames'' in the image. At present, Emacs supports
5033 multiple frames for GIF, TIFF, and certain ImageMagick formats such as
5036 The frames can be used either to represent multiple ``pages'' (this is
5037 usually the case with multi-frame TIFF files, for example), or to
5038 create animation (usually the case with multi-frame GIF files).
5040 A multi-frame image has a property @code{:index}, whose value is an
5041 integer (counting from 0) that specifies which frame is being displayed.
5043 @defun image-multi-frame-p image
5044 This function returns non-@code{nil} if @var{image} contains more than
5045 one frame. The actual return value is a cons @code{(@var{nimages}
5046 . @var{delay})}, where @var{nimages} is the number of frames and
5047 @var{delay} is the delay in seconds between them, or @code{nil}
5048 if the image does not specify a delay. Images that are intended to be
5049 animated usually specify a frame delay, whereas ones that are intended
5050 to be treated as multiple pages do not.
5053 @defun image-current-frame image
5054 This function returns the index of the current frame number for
5055 @var{image}, counting from 0.
5058 @defun image-show-frame image n &optional nocheck
5059 This function switches @var{image} to frame number @var{n}. It
5060 replaces a frame number outside the valid range with that of the end
5061 of the range, unless @var{nocheck} is non-@code{nil}. If @var{image}
5062 does not contain a frame with the specified number, the image displays
5066 @defun image-animate image &optional index limit
5067 This function animates @var{image}. The optional integer @var{index}
5068 specifies the frame from which to start (default 0). The optional
5069 argument @var{limit} controls the length of the animation. If omitted
5070 or @code{nil}, the image animates once only; if @code{t} it loops
5071 forever; if a number animation stops after that many seconds.
5074 @vindex image-minimum-frame-delay
5075 @vindex image-default-frame-delay
5076 @noindent Animation operates by means of a timer. Note that Emacs imposes a
5077 minimum frame delay of 0.01 (@code{image-minimum-frame-delay}) seconds.
5078 If the image itself does not specify a delay, Emacs uses
5079 @code{image-default-frame-delay}.
5081 @defun image-animate-timer image
5082 This function returns the timer responsible for animating @var{image},
5088 @subsection Image Cache
5091 Emacs caches images so that it can display them again more
5092 efficiently. When Emacs displays an image, it searches the image
5093 cache for an existing image specification @code{equal} to the desired
5094 specification. If a match is found, the image is displayed from the
5095 cache. Otherwise, Emacs loads the image normally.
5097 @defun image-flush spec &optional frame
5098 This function removes the image with specification @var{spec} from the
5099 image cache of frame @var{frame}. Image specifications are compared
5100 using @code{equal}. If @var{frame} is @code{nil}, it defaults to the
5101 selected frame. If @var{frame} is @code{t}, the image is flushed on
5102 all existing frames.
5104 In Emacs's current implementation, each graphical terminal possesses an
5105 image cache, which is shared by all the frames on that terminal
5106 (@pxref{Multiple Terminals}). Thus, refreshing an image in one frame
5107 also refreshes it in all other frames on the same terminal.
5110 One use for @code{image-flush} is to tell Emacs about a change in an
5111 image file. If an image specification contains a @code{:file}
5112 property, the image is cached based on the file's contents when the
5113 image is first displayed. Even if the file subsequently changes,
5114 Emacs continues displaying the old version of the image. Calling
5115 @code{image-flush} flushes the image from the cache, forcing Emacs to
5116 re-read the file the next time it needs to display that image.
5118 Another use for @code{image-flush} is for memory conservation. If
5119 your Lisp program creates a large number of temporary images over a
5120 period much shorter than @code{image-cache-eviction-delay} (see
5121 below), you can opt to flush unused images yourself, instead of
5122 waiting for Emacs to do it automatically.
5124 @defun clear-image-cache &optional filter
5125 This function clears an image cache, removing all the images stored in
5126 it. If @var{filter} is omitted or @code{nil}, it clears the cache for
5127 the selected frame. If @var{filter} is a frame, it clears the cache
5128 for that frame. If @var{filter} is @code{t}, all image caches are
5129 cleared. Otherwise, @var{filter} is taken to be a file name, and all
5130 images associated with that file name are removed from all image
5134 If an image in the image cache has not been displayed for a specified
5135 period of time, Emacs removes it from the cache and frees the
5138 @defvar image-cache-eviction-delay
5139 This variable specifies the number of seconds an image can remain in
5140 the cache without being displayed. When an image is not displayed for
5141 this length of time, Emacs removes it from the image cache.
5143 Under some circumstances, if the number of images in the cache grows
5144 too large, the actual eviction delay may be shorter than this.
5146 If the value is @code{nil}, Emacs does not remove images from the cache
5147 except when you explicitly clear it. This mode can be useful for
5153 @cindex buttons in buffers
5154 @cindex clickable buttons in buffers
5156 The Button package defines functions for inserting and manipulating
5157 @dfn{buttons} that can be activated with the mouse or via keyboard
5158 commands. These buttons are typically used for various kinds of
5161 A button is essentially a set of text or overlay properties,
5162 attached to a stretch of text in a buffer. These properties are
5163 called @dfn{button properties}. One of these properties, the
5164 @dfn{action property}, specifies a function which is called when the
5165 user invokes the button using the keyboard or the mouse. The action
5166 function may examine the button and use its other properties as
5169 In some ways, the Button package duplicates the functionality in the
5170 Widget package. @xref{Top, , Introduction, widget, The Emacs Widget
5171 Library}. The advantage of the Button package is that it is faster,
5172 smaller, and simpler to program. From the point of view of the user,
5173 the interfaces produced by the two packages are very similar.
5176 * Button Properties:: Button properties with special meanings.
5177 * Button Types:: Defining common properties for classes of buttons.
5178 * Making Buttons:: Adding buttons to Emacs buffers.
5179 * Manipulating Buttons:: Getting and setting properties of buttons.
5180 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
5183 @node Button Properties
5184 @subsection Button Properties
5185 @cindex button properties
5187 Each button has an associated list of properties defining its
5188 appearance and behavior, and other arbitrary properties may be used
5189 for application specific purposes. The following properties have
5190 special meaning to the Button package:
5194 @kindex action @r{(button property)}
5195 The function to call when the user invokes the button, which is passed
5196 the single argument @var{button}. By default this is @code{ignore},
5200 @kindex mouse-action @r{(button property)}
5201 This is similar to @code{action}, and when present, will be used
5202 instead of @code{action} for button invocations resulting from
5203 mouse-clicks (instead of the user hitting @key{RET}). If not
5204 present, mouse-clicks use @code{action} instead.
5207 @kindex face @r{(button property)}
5208 This is an Emacs face controlling how buttons of this type are
5209 displayed; by default this is the @code{button} face.
5212 @kindex mouse-face @r{(button property)}
5213 This is an additional face which controls appearance during
5214 mouse-overs (merged with the usual button face); by default this is
5215 the usual Emacs @code{highlight} face.
5218 @kindex keymap @r{(button property)}
5219 The button's keymap, defining bindings active within the button
5220 region. By default this is the usual button region keymap, stored
5221 in the variable @code{button-map}, which defines @key{RET} and
5222 @key{mouse-2} to invoke the button.
5225 @kindex type @r{(button property)}
5226 The button type. @xref{Button Types}.
5229 @kindex help-index @r{(button property)}
5230 A string displayed by the Emacs tool-tip help system; by default,
5231 @code{"mouse-2, RET: Push this button"}.
5234 @kindex follow-link @r{(button property)}
5235 The follow-link property, defining how a @key{Mouse-1} click behaves
5236 on this button, @xref{Clickable Text}.
5239 @kindex button @r{(button property)}
5240 All buttons have a non-@code{nil} @code{button} property, which may be useful
5241 in finding regions of text that comprise buttons (which is what the
5242 standard button functions do).
5245 There are other properties defined for the regions of text in a
5246 button, but these are not generally interesting for typical uses.
5249 @subsection Button Types
5250 @cindex button types
5252 Every button has a @dfn{button type}, which defines default values
5253 for the button's properties. Button types are arranged in a
5254 hierarchy, with specialized types inheriting from more general types,
5255 so that it's easy to define special-purpose types of buttons for
5258 @defun define-button-type name &rest properties
5259 Define a `button type' called @var{name} (a symbol).
5260 The remaining arguments
5261 form a sequence of @var{property value} pairs, specifying default
5262 property values for buttons with this type (a button's type may be set
5263 by giving it a @code{type} property when creating the button, using
5264 the @code{:type} keyword argument).
5266 In addition, the keyword argument @code{:supertype} may be used to
5267 specify a button-type from which @var{name} inherits its default
5268 property values. Note that this inheritance happens only when
5269 @var{name} is defined; subsequent changes to a supertype are not
5270 reflected in its subtypes.
5273 Using @code{define-button-type} to define default properties for
5274 buttons is not necessary---buttons without any specified type use the
5275 built-in button-type @code{button}---but it is encouraged, since
5276 doing so usually makes the resulting code clearer and more efficient.
5278 @node Making Buttons
5279 @subsection Making Buttons
5280 @cindex making buttons
5282 Buttons are associated with a region of text, using an overlay or
5283 text properties to hold button-specific information, all of which are
5284 initialized from the button's type (which defaults to the built-in
5285 button type @code{button}). Like all Emacs text, the appearance of
5286 the button is governed by the @code{face} property; by default (via
5287 the @code{face} property inherited from the @code{button} button-type)
5288 this is a simple underline, like a typical web-page link.
5290 For convenience, there are two sorts of button-creation functions,
5291 those that add button properties to an existing region of a buffer,
5292 called @code{make-...button}, and those that also insert the button
5293 text, called @code{insert-...button}.
5295 The button-creation functions all take the @code{&rest} argument
5296 @var{properties}, which should be a sequence of @var{property value}
5297 pairs, specifying properties to add to the button; see @ref{Button
5298 Properties}. In addition, the keyword argument @code{:type} may be
5299 used to specify a button-type from which to inherit other properties;
5300 see @ref{Button Types}. Any properties not explicitly specified
5301 during creation will be inherited from the button's type (if the type
5302 defines such a property).
5304 The following functions add a button using an overlay
5305 (@pxref{Overlays}) to hold the button properties:
5307 @defun make-button beg end &rest properties
5308 This makes a button from @var{beg} to @var{end} in the
5309 current buffer, and returns it.
5312 @defun insert-button label &rest properties
5313 This insert a button with the label @var{label} at point,
5317 The following functions are similar, but using text properties
5318 (@pxref{Text Properties}) to hold the button properties. Such buttons
5319 do not add markers to the buffer, so editing in the buffer does not
5320 slow down if there is an extremely large numbers of buttons. However,
5321 if there is an existing face text property on the text (e.g., a face
5322 assigned by Font Lock mode), the button face may not be visible. Both
5323 of these functions return the starting position of the new button.
5325 @defun make-text-button beg end &rest properties
5326 This makes a button from @var{beg} to @var{end} in the current buffer,
5327 using text properties.
5330 @defun insert-text-button label &rest properties
5331 This inserts a button with the label @var{label} at point, using text
5335 @node Manipulating Buttons
5336 @subsection Manipulating Buttons
5337 @cindex manipulating buttons
5339 These are functions for getting and setting properties of buttons.
5340 Often these are used by a button's invocation function to determine
5343 Where a @var{button} parameter is specified, it means an object
5344 referring to a specific button, either an overlay (for overlay
5345 buttons), or a buffer-position or marker (for text property buttons).
5346 Such an object is passed as the first argument to a button's
5347 invocation function when it is invoked.
5349 @defun button-start button
5350 Return the position at which @var{button} starts.
5353 @defun button-end button
5354 Return the position at which @var{button} ends.
5357 @defun button-get button prop
5358 Get the property of button @var{button} named @var{prop}.
5361 @defun button-put button prop val
5362 Set @var{button}'s @var{prop} property to @var{val}.
5365 @defun button-activate button &optional use-mouse-action
5366 Call @var{button}'s @code{action} property (i.e., invoke it). If
5367 @var{use-mouse-action} is non-@code{nil}, try to invoke the button's
5368 @code{mouse-action} property instead of @code{action}; if the button
5369 has no @code{mouse-action} property, use @code{action} as normal.
5372 @defun button-label button
5373 Return @var{button}'s text label.
5376 @defun button-type button
5377 Return @var{button}'s button-type.
5380 @defun button-has-type-p button type
5381 Return @code{t} if @var{button} has button-type @var{type}, or one of
5382 @var{type}'s subtypes.
5385 @defun button-at pos
5386 Return the button at position @var{pos} in the current buffer, or
5387 @code{nil}. If the button at @var{pos} is a text property button, the
5388 return value is a marker pointing to @var{pos}.
5391 @defun button-type-put type prop val
5392 Set the button-type @var{type}'s @var{prop} property to @var{val}.
5395 @defun button-type-get type prop
5396 Get the property of button-type @var{type} named @var{prop}.
5399 @defun button-type-subtype-p type supertype
5400 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
5403 @node Button Buffer Commands
5404 @subsection Button Buffer Commands
5405 @cindex button buffer commands
5407 These are commands and functions for locating and operating on
5408 buttons in an Emacs buffer.
5410 @code{push-button} is the command that a user uses to actually `push'
5411 a button, and is bound by default in the button itself to @key{RET}
5412 and to @key{mouse-2} using a local keymap in the button's overlay or
5413 text properties. Commands that are useful outside the buttons itself,
5414 such as @code{forward-button} and @code{backward-button} are
5415 additionally available in the keymap stored in
5416 @code{button-buffer-map}; a mode which uses buttons may want to use
5417 @code{button-buffer-map} as a parent keymap for its keymap.
5419 If the button has a non-@code{nil} @code{follow-link} property, and
5420 @code{mouse-1-click-follows-link} is set, a quick @key{Mouse-1} click
5421 will also activate the @code{push-button} command.
5422 @xref{Clickable Text}.
5424 @deffn Command push-button &optional pos use-mouse-action
5425 Perform the action specified by a button at location @var{pos}.
5426 @var{pos} may be either a buffer position or a mouse-event. If
5427 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
5428 mouse-event (@pxref{Mouse Events}), try to invoke the button's
5429 @code{mouse-action} property instead of @code{action}; if the button
5430 has no @code{mouse-action} property, use @code{action} as normal.
5431 @var{pos} defaults to point, except when @code{push-button} is invoked
5432 interactively as the result of a mouse-event, in which case, the mouse
5433 event's position is used. If there's no button at @var{pos}, do
5434 nothing and return @code{nil}, otherwise return @code{t}.
5437 @deffn Command forward-button n &optional wrap display-message
5438 Move to the @var{n}th next button, or @var{n}th previous button if
5439 @var{n} is negative. If @var{n} is zero, move to the start of any
5440 button at point. If @var{wrap} is non-@code{nil}, moving past either
5441 end of the buffer continues from the other end. If
5442 @var{display-message} is non-@code{nil}, the button's help-echo string
5443 is displayed. Any button with a non-@code{nil} @code{skip} property
5444 is skipped over. Returns the button found.
5447 @deffn Command backward-button n &optional wrap display-message
5448 Move to the @var{n}th previous button, or @var{n}th next button if
5449 @var{n} is negative. If @var{n} is zero, move to the start of any
5450 button at point. If @var{wrap} is non-@code{nil}, moving past either
5451 end of the buffer continues from the other end. If
5452 @var{display-message} is non-@code{nil}, the button's help-echo string
5453 is displayed. Any button with a non-@code{nil} @code{skip} property
5454 is skipped over. Returns the button found.
5457 @defun next-button pos &optional count-current
5458 @defunx previous-button pos &optional count-current
5459 Return the next button after (for @code{next-button}) or before (for
5460 @code{previous-button}) position @var{pos} in the current buffer. If
5461 @var{count-current} is non-@code{nil}, count any button at @var{pos}
5462 in the search, instead of starting at the next button.
5465 @node Abstract Display
5466 @section Abstract Display
5468 @cindex display, abstract
5469 @cindex display, arbitrary objects
5470 @cindex model/view/controller
5471 @cindex view part, model/view/controller
5473 The Ewoc package constructs buffer text that represents a structure
5474 of Lisp objects, and updates the text to follow changes in that
5475 structure. This is like the ``view'' component in the
5476 ``model/view/controller'' design paradigm. Ewoc means ``Emacs's
5477 Widget for Object Collections''.
5479 An @dfn{ewoc} is a structure that organizes information required to
5480 construct buffer text that represents certain Lisp data. The buffer
5481 text of the ewoc has three parts, in order: first, fixed @dfn{header}
5482 text; next, textual descriptions of a series of data elements (Lisp
5483 objects that you specify); and last, fixed @dfn{footer} text.
5484 Specifically, an ewoc contains information on:
5488 The buffer which its text is generated in.
5491 The text's start position in the buffer.
5494 The header and footer strings.
5498 @c or "@cindex node, abstract display"?
5499 A doubly-linked chain of @dfn{nodes}, each of which contains:
5503 A @dfn{data element}, a single Lisp object.
5506 Links to the preceding and following nodes in the chain.
5510 A @dfn{pretty-printer} function which is responsible for
5511 inserting the textual representation of a data
5512 element value into the current buffer.
5515 Typically, you define an ewoc with @code{ewoc-create}, and then pass
5516 the resulting ewoc structure to other functions in the Ewoc package to
5517 build nodes within it, and display it in the buffer. Once it is
5518 displayed in the buffer, other functions determine the correspondence
5519 between buffer positions and nodes, move point from one node's textual
5520 representation to another, and so forth. @xref{Abstract Display
5523 @cindex encapsulation, ewoc
5524 @c or "@cindex encapsulation, abstract display"?
5525 A node @dfn{encapsulates} a data element much the way a variable
5526 holds a value. Normally, encapsulation occurs as a part of adding a
5527 node to the ewoc. You can retrieve the data element value and place a
5528 new value in its place, like so:
5531 (ewoc-data @var{node})
5534 (ewoc-set-data @var{node} @var{new-value})
5535 @result{} @var{new-value}
5539 You can also use, as the data element value, a Lisp object (list or
5540 vector) that is a container for the ``real'' value, or an index into
5541 some other structure. The example (@pxref{Abstract Display Example})
5542 uses the latter approach.
5544 When the data changes, you will want to update the text in the
5545 buffer. You can update all nodes by calling @code{ewoc-refresh}, or
5546 just specific nodes using @code{ewoc-invalidate}, or all nodes
5547 satisfying a predicate using @code{ewoc-map}. Alternatively, you can
5548 delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter},
5549 and add new nodes in their place. Deleting a node from an ewoc deletes
5550 its associated textual description from buffer, as well.
5553 * Abstract Display Functions:: Functions in the Ewoc package.
5554 * Abstract Display Example:: Example of using Ewoc.
5557 @node Abstract Display Functions
5558 @subsection Abstract Display Functions
5560 In this subsection, @var{ewoc} and @var{node} stand for the
5561 structures described above (@pxref{Abstract Display}), while
5562 @var{data} stands for an arbitrary Lisp object used as a data element.
5564 @defun ewoc-create pretty-printer &optional header footer nosep
5565 This constructs and returns a new ewoc, with no nodes (and thus no data
5566 elements). @var{pretty-printer} should be a function that takes one
5567 argument, a data element of the sort you plan to use in this ewoc, and
5568 inserts its textual description at point using @code{insert} (and never
5569 @code{insert-before-markers}, because that would interfere with the
5570 Ewoc package's internal mechanisms).
5572 Normally, a newline is automatically inserted after the header,
5573 the footer and every node's textual description. If @var{nosep}
5574 is non-@code{nil}, no newline is inserted. This may be useful for
5575 displaying an entire ewoc on a single line, for example, or for
5576 making nodes ``invisible'' by arranging for @var{pretty-printer}
5577 to do nothing for those nodes.
5579 An ewoc maintains its text in the buffer that is current when
5580 you create it, so switch to the intended buffer before calling
5584 @defun ewoc-buffer ewoc
5585 This returns the buffer where @var{ewoc} maintains its text.
5588 @defun ewoc-get-hf ewoc
5589 This returns a cons cell @code{(@var{header} . @var{footer})}
5590 made from @var{ewoc}'s header and footer.
5593 @defun ewoc-set-hf ewoc header footer
5594 This sets the header and footer of @var{ewoc} to the strings
5595 @var{header} and @var{footer}, respectively.
5598 @defun ewoc-enter-first ewoc data
5599 @defunx ewoc-enter-last ewoc data
5600 These add a new node encapsulating @var{data}, putting it, respectively,
5601 at the beginning or end of @var{ewoc}'s chain of nodes.
5604 @defun ewoc-enter-before ewoc node data
5605 @defunx ewoc-enter-after ewoc node data
5606 These add a new node encapsulating @var{data}, adding it to
5607 @var{ewoc} before or after @var{node}, respectively.
5610 @defun ewoc-prev ewoc node
5611 @defunx ewoc-next ewoc node
5612 These return, respectively, the previous node and the next node of @var{node}
5616 @defun ewoc-nth ewoc n
5617 This returns the node in @var{ewoc} found at zero-based index @var{n}.
5618 A negative @var{n} means count from the end. @code{ewoc-nth} returns
5619 @code{nil} if @var{n} is out of range.
5622 @defun ewoc-data node
5623 This extracts the data encapsulated by @var{node} and returns it.
5626 @defun ewoc-set-data node data
5627 This sets the data encapsulated by @var{node} to @var{data}.
5630 @defun ewoc-locate ewoc &optional pos guess
5631 This determines the node in @var{ewoc} which contains point (or
5632 @var{pos} if specified), and returns that node. If @var{ewoc} has no
5633 nodes, it returns @code{nil}. If @var{pos} is before the first node,
5634 it returns the first node; if @var{pos} is after the last node, it returns
5635 the last node. The optional third arg @var{guess}
5636 should be a node that is likely to be near @var{pos}; this doesn't
5637 alter the result, but makes the function run faster.
5640 @defun ewoc-location node
5641 This returns the start position of @var{node}.
5644 @defun ewoc-goto-prev ewoc arg
5645 @defunx ewoc-goto-next ewoc arg
5646 These move point to the previous or next, respectively, @var{arg}th node
5647 in @var{ewoc}. @code{ewoc-goto-prev} does not move if it is already at
5648 the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next}
5649 moves past the last node, returning @code{nil}. Excepting this special
5650 case, these functions return the node moved to.
5653 @defun ewoc-goto-node ewoc node
5654 This moves point to the start of @var{node} in @var{ewoc}.
5657 @defun ewoc-refresh ewoc
5658 This function regenerates the text of @var{ewoc}. It works by
5659 deleting the text between the header and the footer, i.e., all the
5660 data elements' representations, and then calling the pretty-printer
5661 function for each node, one by one, in order.
5664 @defun ewoc-invalidate ewoc &rest nodes
5665 This is similar to @code{ewoc-refresh}, except that only @var{nodes} in
5666 @var{ewoc} are updated instead of the entire set.
5669 @defun ewoc-delete ewoc &rest nodes
5670 This deletes each node in @var{nodes} from @var{ewoc}.
5673 @defun ewoc-filter ewoc predicate &rest args
5674 This calls @var{predicate} for each data element in @var{ewoc} and
5675 deletes those nodes for which @var{predicate} returns @code{nil}.
5676 Any @var{args} are passed to @var{predicate}.
5679 @defun ewoc-collect ewoc predicate &rest args
5680 This calls @var{predicate} for each data element in @var{ewoc}
5681 and returns a list of those elements for which @var{predicate}
5682 returns non-@code{nil}. The elements in the list are ordered
5683 as in the buffer. Any @var{args} are passed to @var{predicate}.
5686 @defun ewoc-map map-function ewoc &rest args
5687 This calls @var{map-function} for each data element in @var{ewoc} and
5688 updates those nodes for which @var{map-function} returns non-@code{nil}.
5689 Any @var{args} are passed to @var{map-function}.
5692 @node Abstract Display Example
5693 @subsection Abstract Display Example
5695 Here is a simple example using functions of the ewoc package to
5696 implement a ``color components display'', an area in a buffer that
5697 represents a vector of three integers (itself representing a 24-bit RGB
5698 value) in various ways.
5701 (setq colorcomp-ewoc nil
5703 colorcomp-mode-map nil
5704 colorcomp-labels ["Red" "Green" "Blue"])
5706 (defun colorcomp-pp (data)
5708 (let ((comp (aref colorcomp-data data)))
5709 (insert (aref colorcomp-labels data) "\t: #x"
5710 (format "%02X" comp) " "
5711 (make-string (ash comp -2) ?#) "\n"))
5712 (let ((cstr (format "#%02X%02X%02X"
5713 (aref colorcomp-data 0)
5714 (aref colorcomp-data 1)
5715 (aref colorcomp-data 2)))
5716 (samp " (sample text) "))
5718 (propertize samp 'face
5719 `(foreground-color . ,cstr))
5720 (propertize samp 'face
5721 `(background-color . ,cstr))
5724 (defun colorcomp (color)
5725 "Allow fiddling with COLOR in a new buffer.
5726 The buffer is in Color Components mode."
5727 (interactive "sColor (name or #RGB or #RRGGBB): ")
5728 (when (string= "" color)
5729 (setq color "green"))
5730 (unless (color-values color)
5731 (error "No such color: %S" color))
5733 (generate-new-buffer (format "originally: %s" color)))
5734 (kill-all-local-variables)
5735 (setq major-mode 'colorcomp-mode
5736 mode-name "Color Components")
5737 (use-local-map colorcomp-mode-map)
5739 (buffer-disable-undo)
5740 (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
5741 (color-values color))))
5742 (ewoc (ewoc-create 'colorcomp-pp
5743 "\nColor Components\n\n"
5744 (substitute-command-keys
5745 "\n\\@{colorcomp-mode-map@}"))))
5746 (set (make-local-variable 'colorcomp-data) data)
5747 (set (make-local-variable 'colorcomp-ewoc) ewoc)
5748 (ewoc-enter-last ewoc 0)
5749 (ewoc-enter-last ewoc 1)
5750 (ewoc-enter-last ewoc 2)
5751 (ewoc-enter-last ewoc nil)))
5754 @cindex controller part, model/view/controller
5755 This example can be extended to be a ``color selection widget'' (in
5756 other words, the controller part of the ``model/view/controller''
5757 design paradigm) by defining commands to modify @code{colorcomp-data}
5758 and to ``finish'' the selection process, and a keymap to tie it all
5759 together conveniently.
5762 (defun colorcomp-mod (index limit delta)
5763 (let ((cur (aref colorcomp-data index)))
5764 (unless (= limit cur)
5765 (aset colorcomp-data index (+ cur delta)))
5768 (ewoc-nth colorcomp-ewoc index)
5769 (ewoc-nth colorcomp-ewoc -1))))
5771 (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
5772 (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
5773 (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
5774 (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
5775 (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
5776 (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
5778 (defun colorcomp-copy-as-kill-and-exit ()
5779 "Copy the color components into the kill ring and kill the buffer.
5780 The string is formatted #RRGGBB (hash followed by six hex digits)."
5782 (kill-new (format "#%02X%02X%02X"
5783 (aref colorcomp-data 0)
5784 (aref colorcomp-data 1)
5785 (aref colorcomp-data 2)))
5788 (setq colorcomp-mode-map
5789 (let ((m (make-sparse-keymap)))
5791 (define-key m "i" 'colorcomp-R-less)
5792 (define-key m "o" 'colorcomp-R-more)
5793 (define-key m "k" 'colorcomp-G-less)
5794 (define-key m "l" 'colorcomp-G-more)
5795 (define-key m "," 'colorcomp-B-less)
5796 (define-key m "." 'colorcomp-B-more)
5797 (define-key m " " 'colorcomp-copy-as-kill-and-exit)
5801 Note that we never modify the data in each node, which is fixed when the
5802 ewoc is created to be either @code{nil} or an index into the vector
5803 @code{colorcomp-data}, the actual color components.
5806 @section Blinking Parentheses
5807 @cindex parenthesis matching
5808 @cindex blinking parentheses
5809 @cindex balancing parentheses
5811 This section describes the mechanism by which Emacs shows a matching
5812 open parenthesis when the user inserts a close parenthesis.
5814 @defvar blink-paren-function
5815 The value of this variable should be a function (of no arguments) to
5816 be called whenever a character with close parenthesis syntax is inserted.
5817 The value of @code{blink-paren-function} may be @code{nil}, in which
5818 case nothing is done.
5821 @defopt blink-matching-paren
5822 If this variable is @code{nil}, then @code{blink-matching-open} does
5826 @defopt blink-matching-paren-distance
5827 This variable specifies the maximum distance to scan for a matching
5828 parenthesis before giving up.
5831 @defopt blink-matching-delay
5832 This variable specifies the number of seconds for the cursor to remain
5833 at the matching parenthesis. A fraction of a second often gives
5834 good results, but the default is 1, which works on all systems.
5837 @deffn Command blink-matching-open
5838 This function is the default value of @code{blink-paren-function}. It
5839 assumes that point follows a character with close parenthesis syntax and
5840 moves the cursor momentarily to the matching opening character. If that
5841 character is not already on the screen, it displays the character's
5842 context in the echo area. To avoid long delays, this function does not
5843 search farther than @code{blink-matching-paren-distance} characters.
5845 Here is an example of calling this function explicitly.
5849 (defun interactive-blink-matching-open ()
5850 "Indicate momentarily the start of sexp before point."
5854 (let ((blink-matching-paren-distance
5856 (blink-matching-paren t))
5857 (blink-matching-open)))
5862 @node Character Display
5863 @section Character Display
5865 This section describes how characters are actually displayed by
5866 Emacs. Typically, a character is displayed as a @dfn{glyph} (a
5867 graphical symbol which occupies one character position on the screen),
5868 whose appearance corresponds to the character itself. For example,
5869 the character @samp{a} (character code 97) is displayed as @samp{a}.
5870 Some characters, however, are displayed specially. For example, the
5871 formfeed character (character code 12) is usually displayed as a
5872 sequence of two glyphs, @samp{^L}, while the newline character
5873 (character code 10) starts a new screen line.
5875 You can modify how each character is displayed by defining a
5876 @dfn{display table}, which maps each character code into a sequence of
5877 glyphs. @xref{Display Tables}.
5880 * Usual Display:: The usual conventions for displaying characters.
5881 * Display Tables:: What a display table consists of.
5882 * Active Display Table:: How Emacs selects a display table to use.
5883 * Glyphs:: How to define a glyph, and what glyphs mean.
5884 * Glyphless Chars:: How glyphless characters are drawn.
5888 @subsection Usual Display Conventions
5890 Here are the conventions for displaying each character code (in the
5891 absence of a display table, which can override these
5896 conventions; @pxref{Display Tables}).
5899 @cindex printable ASCII characters
5902 The @dfn{printable @acronym{ASCII} characters}, character codes 32
5903 through 126 (consisting of numerals, English letters, and symbols like
5904 @samp{#}) are displayed literally.
5907 The tab character (character code 9) displays as whitespace stretching
5908 up to the next tab stop column. @xref{Text Display,,, emacs, The GNU
5909 Emacs Manual}. The variable @code{tab-width} controls the number of
5910 spaces per tab stop (see below).
5913 The newline character (character code 10) has a special effect: it
5914 ends the preceding line and starts a new line.
5916 @cindex ASCII control characters
5918 The non-printable @dfn{@acronym{ASCII} control characters}---character
5919 codes 0 through 31, as well as the @key{DEL} character (character code
5920 127)---display in one of two ways according to the variable
5921 @code{ctl-arrow}. If this variable is non-@code{nil} (the default),
5922 these characters are displayed as sequences of two glyphs, where the
5923 first glyph is @samp{^} (a display table can specify a glyph to use
5924 instead of @samp{^}); e.g., the @key{DEL} character is displayed as
5927 If @code{ctl-arrow} is @code{nil}, these characters are displayed as
5928 octal escapes (see below).
5930 This rule also applies to carriage return (character code 13), if that
5931 character appears in the buffer. But carriage returns usually do not
5932 appear in buffer text; they are eliminated as part of end-of-line
5933 conversion (@pxref{Coding System Basics}).
5935 @cindex octal escapes
5937 @dfn{Raw bytes} are non-@acronym{ASCII} characters with codes 128
5938 through 255 (@pxref{Text Representations}). These characters display
5939 as @dfn{octal escapes}: sequences of four glyphs, where the first
5940 glyph is the @acronym{ASCII} code for @samp{\}, and the others are
5941 digit characters representing the character code in octal. (A display
5942 table can specify a glyph to use instead of @samp{\}.)
5945 Each non-@acronym{ASCII} character with code above 255 is displayed
5946 literally, if the terminal supports it. If the terminal does not
5947 support it, the character is said to be @dfn{glyphless}, and it is
5948 usually displayed using a placeholder glyph. For example, if a
5949 graphical terminal has no font for a character, Emacs usually displays
5950 a box containing the character code in hexadecimal. @xref{Glyphless
5954 The above display conventions apply even when there is a display
5955 table, for any character whose entry in the active display table is
5956 @code{nil}. Thus, when you set up a display table, you need only
5957 specify the characters for which you want special behavior.
5959 The following variables affect how certain characters are displayed
5960 on the screen. Since they change the number of columns the characters
5961 occupy, they also affect the indentation functions. They also affect
5962 how the mode line is displayed; if you want to force redisplay of the
5963 mode line using the new values, call the function
5964 @code{force-mode-line-update} (@pxref{Mode Line Format}).
5967 @cindex control characters in display
5968 This buffer-local variable controls how control characters are
5969 displayed. If it is non-@code{nil}, they are displayed as a caret
5970 followed by the character: @samp{^A}. If it is @code{nil}, they are
5971 displayed as octal escapes: a backslash followed by three octal
5972 digits, as in @samp{\001}.
5976 The value of this buffer-local variable is the spacing between tab
5977 stops used for displaying tab characters in Emacs buffers. The value
5978 is in units of columns, and the default is 8. Note that this feature
5979 is completely independent of the user-settable tab stops used by the
5980 command @code{tab-to-tab-stop}. @xref{Indent Tabs}.
5983 @node Display Tables
5984 @subsection Display Tables
5986 @cindex display table
5987 A display table is a special-purpose char-table
5988 (@pxref{Char-Tables}), with @code{display-table} as its subtype, which
5989 is used to override the usual character display conventions. This
5990 section describes how to make, inspect, and assign elements to a
5991 display table object.
5993 @defun make-display-table
5994 This creates and returns a display table. The table initially has
5995 @code{nil} in all elements.
5998 The ordinary elements of the display table are indexed by character
5999 codes; the element at index @var{c} says how to display the character
6000 code @var{c}. The value should be @code{nil} (which means to display
6001 the character @var{c} according to the usual display conventions;
6002 @pxref{Usual Display}), or a vector of glyph codes (which means to
6003 display the character @var{c} as those glyphs; @pxref{Glyphs}).
6005 @strong{Warning:} if you use the display table to change the display
6006 of newline characters, the whole buffer will be displayed as one long
6009 The display table also has six ``extra slots'' which serve special
6010 purposes. Here is a table of their meanings; @code{nil} in any slot
6011 means to use the default for that slot, as stated below.
6015 The glyph for the end of a truncated screen line (the default for this
6016 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
6017 arrows in the fringes to indicate truncation, so the display table has
6021 The glyph for the end of a continued line (the default is @samp{\}).
6022 On graphical terminals, Emacs uses curved arrows in the fringes to
6023 indicate continuation, so the display table has no effect.
6026 The glyph for indicating a character displayed as an octal character
6027 code (the default is @samp{\}).
6030 The glyph for indicating a control character (the default is @samp{^}).
6033 A vector of glyphs for indicating the presence of invisible lines (the
6034 default is @samp{...}). @xref{Selective Display}.
6037 The glyph used to draw the border between side-by-side windows (the
6038 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
6039 when there are no scroll bars; if scroll bars are supported and in use,
6040 a scroll bar separates the two windows.
6043 For example, here is how to construct a display table that mimics
6044 the effect of setting @code{ctl-arrow} to a non-@code{nil} value
6045 (@pxref{Glyphs}, for the function @code{make-glyph-code}):
6048 (setq disptab (make-display-table))
6053 (vector (make-glyph-code ?^ 'escape-glyph)
6054 (make-glyph-code (+ i 64) 'escape-glyph)))))
6056 (vector (make-glyph-code ?^ 'escape-glyph)
6057 (make-glyph-code ?? 'escape-glyph)))))
6060 @defun display-table-slot display-table slot
6061 This function returns the value of the extra slot @var{slot} of
6062 @var{display-table}. The argument @var{slot} may be a number from 0 to
6063 5 inclusive, or a slot name (symbol). Valid symbols are
6064 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6065 @code{selective-display}, and @code{vertical-border}.
6068 @defun set-display-table-slot display-table slot value
6069 This function stores @var{value} in the extra slot @var{slot} of
6070 @var{display-table}. The argument @var{slot} may be a number from 0 to
6071 5 inclusive, or a slot name (symbol). Valid symbols are
6072 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6073 @code{selective-display}, and @code{vertical-border}.
6076 @defun describe-display-table display-table
6077 This function displays a description of the display table
6078 @var{display-table} in a help buffer.
6081 @deffn Command describe-current-display-table
6082 This command displays a description of the current display table in a
6086 @node Active Display Table
6087 @subsection Active Display Table
6088 @cindex active display table
6090 Each window can specify a display table, and so can each buffer.
6091 The window's display table, if there is one, takes precedence over the
6092 buffer's display table. If neither exists, Emacs tries to use the
6093 standard display table; if that is @code{nil}, Emacs uses the usual
6094 character display conventions (@pxref{Usual Display}).
6096 Note that display tables affect how the mode line is displayed, so
6097 if you want to force redisplay of the mode line using a new display
6098 table, call @code{force-mode-line-update} (@pxref{Mode Line Format}).
6100 @defun window-display-table &optional window
6101 This function returns @var{window}'s display table, or @code{nil} if
6102 there is none. The default for @var{window} is the selected window.
6105 @defun set-window-display-table window table
6106 This function sets the display table of @var{window} to @var{table}.
6107 The argument @var{table} should be either a display table or
6111 @defvar buffer-display-table
6112 This variable is automatically buffer-local in all buffers; its value
6113 specifies the buffer's display table. If it is @code{nil}, there is
6114 no buffer display table.
6117 @defvar standard-display-table
6118 The value of this variable is the standard display table, which is
6119 used when Emacs is displaying a buffer in a window with neither a
6120 window display table nor a buffer display table defined. Its default
6124 The @file{disp-table} library defines several functions for changing
6125 the standard display table.
6132 A @dfn{glyph} is a graphical symbol which occupies a single
6133 character position on the screen. Each glyph is represented in Lisp
6134 as a @dfn{glyph code}, which specifies a character and optionally a
6135 face to display it in (@pxref{Faces}). The main use of glyph codes is
6136 as the entries of display tables (@pxref{Display Tables}). The
6137 following functions are used to manipulate glyph codes:
6139 @defun make-glyph-code char &optional face
6140 This function returns a glyph code representing char @var{char} with
6141 face @var{face}. If @var{face} is omitted or @code{nil}, the glyph
6142 uses the default face; in that case, the glyph code is an integer. If
6143 @var{face} is non-@code{nil}, the glyph code is not necessarily an
6147 @defun glyph-char glyph
6148 This function returns the character of glyph code @var{glyph}.
6151 @defun glyph-face glyph
6152 This function returns face of glyph code @var{glyph}, or @code{nil} if
6153 @var{glyph} uses the default face.
6157 You can set up a @dfn{glyph table} to change how glyph codes are
6158 actually displayed on text terminals. This feature is semi-obsolete;
6159 use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}).
6162 The value of this variable, if non-@code{nil}, is the current glyph
6163 table. It takes effect only on character terminals; on graphical
6164 displays, all glyphs are displayed literally. The glyph table should
6165 be a vector whose @var{g}th element specifies how to display glyph
6166 code @var{g}, where @var{g} is the glyph code for a glyph whose face
6167 is unspecified. Each element should be one of the following:
6171 Display this glyph literally.
6174 Display this glyph by sending the specified string to the terminal.
6177 Display the specified glyph code instead.
6180 Any integer glyph code greater than or equal to the length of the
6181 glyph table is displayed literally.
6185 @node Glyphless Chars
6186 @subsection Glyphless Character Display
6187 @cindex glyphless characters
6189 @dfn{Glyphless characters} are characters which are displayed in a
6190 special way, e.g., as a box containing a hexadecimal code, instead of
6191 being displayed literally. These include characters which are
6192 explicitly defined to be glyphless, as well as characters for which
6193 there is no available font (on a graphical display), and characters
6194 which cannot be encoded by the terminal's coding system (on a text
6197 @defvar glyphless-char-display
6198 The value of this variable is a char-table which defines glyphless
6199 characters and how they are displayed. Each entry must be one of the
6200 following display methods:
6204 Display the character in the usual way.
6206 @item @code{zero-width}
6207 Don't display the character.
6209 @item @code{thin-space}
6210 Display a thin space, 1-pixel wide on graphical displays, or
6211 1-character wide on text terminals.
6213 @item @code{empty-box}
6214 Display an empty box.
6216 @item @code{hex-code}
6217 Display a box containing the Unicode codepoint of the character, in
6218 hexadecimal notation.
6220 @item an @acronym{ASCII} string
6221 Display a box containing that string.
6223 @item a cons cell @code{(@var{graphical} . @var{text})}
6224 Display with @var{graphical} on graphical displays, and with
6225 @var{text} on text terminals. Both @var{graphical} and @var{text}
6226 must be one of the display methods described above.
6230 The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
6231 @acronym{ASCII} string display methods are drawn with the
6232 @code{glyphless-char} face.
6234 The char-table has one extra slot, which determines how to display any
6235 character that cannot be displayed with any available font, or cannot
6236 be encoded by the terminal's coding system. Its value should be one
6237 of the above display methods, except @code{zero-width} or a cons cell.
6239 If a character has a non-@code{nil} entry in an active display table,
6240 the display table takes effect; in this case, Emacs does not consult
6241 @code{glyphless-char-display} at all.
6244 @defopt glyphless-char-display-control
6245 This user option provides a convenient way to set
6246 @code{glyphless-char-display} for groups of similar characters. Do
6247 not set its value directly from Lisp code; the value takes effect only
6248 via a custom @code{:set} function (@pxref{Variable Definitions}),
6249 which updates @code{glyphless-char-display}.
6251 Its value should be an alist of elements @code{(@var{group}
6252 . @var{method})}, where @var{group} is a symbol specifying a group of
6253 characters, and @var{method} is a symbol specifying how to display
6256 @var{group} should be one of the following:
6260 @acronym{ASCII} control characters @code{U+0000} to @code{U+001F},
6261 excluding the newline and tab characters (normally displayed as escape
6262 sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed,
6263 emacs, The GNU Emacs Manual}).
6266 Non-@acronym{ASCII}, non-printing characters @code{U+0080} to
6267 @code{U+009F} (normally displayed as octal escape sequences like
6270 @item format-control
6271 Characters of Unicode General Category `Cf', such as @samp{U+200E}
6272 (Left-to-Right Mark), but excluding characters that have graphic
6273 images, such as @samp{U+00AD} (Soft Hyphen).
6276 Characters for there is no suitable font, or which cannot be encoded
6277 by the terminal's coding system.
6280 @c FIXME: this can also be `acronym', but that's not currently
6281 @c completely implemented; it applies only to the format-control
6282 @c group, and only works if the acronym is in `char-acronym-table'.
6283 The @var{method} symbol should be one of @code{zero-width},
6284 @code{thin-space}, @code{empty-box}, or @code{hex-code}. These have
6285 the same meanings as in @code{glyphless-char-display}, above.
6292 This section describes how to make Emacs ring the bell (or blink the
6293 screen) to attract the user's attention. Be conservative about how
6294 often you do this; frequent bells can become irritating. Also be
6295 careful not to use just beeping when signaling an error is more
6296 appropriate (@pxref{Errors}).
6298 @defun ding &optional do-not-terminate
6299 @cindex keyboard macro termination
6300 This function beeps, or flashes the screen (see @code{visible-bell} below).
6301 It also terminates any keyboard macro currently executing unless
6302 @var{do-not-terminate} is non-@code{nil}.
6305 @defun beep &optional do-not-terminate
6306 This is a synonym for @code{ding}.
6309 @defopt visible-bell
6310 This variable determines whether Emacs should flash the screen to
6311 represent a bell. Non-@code{nil} means yes, @code{nil} means no.
6312 This is effective on graphical displays, and on text terminals
6313 provided the terminal's Termcap entry defines the visible bell
6314 capability (@samp{vb}).
6317 @defvar ring-bell-function
6318 If this is non-@code{nil}, it specifies how Emacs should ``ring the
6319 bell''. Its value should be a function of no arguments. If this is
6320 non-@code{nil}, it takes precedence over the @code{visible-bell}
6324 @node Window Systems
6325 @section Window Systems
6327 Emacs works with several window systems, most notably the X Window
6328 System. Both Emacs and X use the term ``window'', but use it
6329 differently. An Emacs frame is a single window as far as X is
6330 concerned; the individual Emacs windows are not known to X at all.
6332 @defvar window-system
6333 This terminal-local variable tells Lisp programs what window system
6334 Emacs is using for displaying the frame. The possible values are
6338 @cindex X Window System
6339 Emacs is displaying the frame using X.
6341 Emacs is displaying the frame using native MS-Windows GUI.
6343 Emacs is displaying the frame using the Nextstep interface (used on
6344 GNUstep and Mac OS X).
6346 Emacs is displaying the frame using MS-DOS direct screen writes.
6348 Emacs is displaying the frame on a character-based terminal.
6352 @defvar initial-window-system
6353 This variable holds the value of @code{window-system} used for the
6354 first frame created by Emacs during startup. (When Emacs is invoked
6355 with the @option{--daemon} option, it does not create any initial
6356 frames, so @code{initial-window-system} is @code{nil}. @xref{Initial
6357 Options, daemon,, emacs, The GNU Emacs Manual}.)
6360 @defun window-system &optional frame
6361 This function returns a symbol whose name tells what window system is
6362 used for displaying @var{frame} (which defaults to the currently
6363 selected frame). The list of possible symbols it returns is the same
6364 one documented for the variable @code{window-system} above.
6367 Do @emph{not} use @code{window-system} and
6368 @code{initial-window-system} as predicates or boolean flag variables,
6369 if you want to write code that works differently on text terminals and
6370 graphic displays. That is because @code{window-system} is not a good
6371 indicator of Emacs capabilities on a given display type. Instead, use
6372 @code{display-graphic-p} or any of the other @code{display-*-p}
6373 predicates described in @ref{Display Feature Testing}.
6375 @defvar window-setup-hook
6376 This variable is a normal hook which Emacs runs after handling the
6377 initialization files. Emacs runs this hook after it has completed
6378 loading your init file, the default initialization file (if
6379 any), and the terminal-specific Lisp code, and running the hook
6380 @code{term-setup-hook}.
6382 This hook is used for internal purposes: setting up communication with
6383 the window system, and creating the initial window. Users should not
6387 @node Bidirectional Display
6388 @section Bidirectional Display
6389 @cindex bidirectional display
6390 @cindex right-to-left text
6392 Emacs can display text written in scripts, such as Arabic, Farsi,
6393 and Hebrew, whose natural ordering for horizontal text display runs
6394 from right to left. Furthermore, segments of Latin script and digits
6395 embedded in right-to-left text are displayed left-to-right, while
6396 segments of right-to-left script embedded in left-to-right text
6397 (e.g., Arabic or Hebrew text in comments or strings in a program
6398 source file) are appropriately displayed right-to-left. We call such
6399 mixtures of left-to-right and right-to-left text @dfn{bidirectional
6400 text}. This section describes the facilities and options for editing
6401 and displaying bidirectional text.
6403 @cindex logical order
6404 @cindex reading order
6405 @cindex visual order
6406 @cindex unicode bidirectional algorithm
6408 @cindex bidirectional reordering
6409 @cindex reordering, of bidirectional text
6410 Text is stored in Emacs buffers and strings in @dfn{logical} (or
6411 @dfn{reading}) order, i.e., the order in which a human would read
6412 each character. In right-to-left and bidirectional text, the order in
6413 which characters are displayed on the screen (called @dfn{visual
6414 order}) is not the same as logical order; the characters' screen
6415 positions do not increase monotonically with string or buffer
6416 position. In performing this @dfn{bidirectional reordering}, Emacs
6417 follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}),
6418 which is described in Annex #9 of the Unicode standard
6419 (@url{http://www.unicode.org/reports/tr9/}). Emacs provides a ``Full
6420 Bidirectionality'' class implementation of the @acronym{UBA}.
6422 @defvar bidi-display-reordering
6423 If the value of this buffer-local variable is non-@code{nil} (the
6424 default), Emacs performs bidirectional reordering for display. The
6425 reordering affects buffer text, as well as display strings and overlay
6426 strings from text and overlay properties in the buffer (@pxref{Overlay
6427 Properties}, and @pxref{Display Property}). If the value is
6428 @code{nil}, Emacs does not perform bidirectional reordering in the
6431 The default value of @code{bidi-display-reordering} controls the
6432 reordering of strings which are not directly supplied by a buffer,
6433 including the text displayed in mode lines (@pxref{Mode Line Format})
6434 and header lines (@pxref{Header Lines}).
6437 @cindex unibyte buffers, and bidi reordering
6438 Emacs never reorders the text of a unibyte buffer, even if
6439 @code{bidi-display-reordering} is non-@code{nil} in the buffer. This
6440 is because unibyte buffers contain raw bytes, not characters, and thus
6441 lack the directionality properties required for reordering.
6442 Therefore, to test whether text in a buffer will be reordered for
6443 display, it is not enough to test the value of
6444 @code{bidi-display-reordering} alone. The correct test is this:
6447 (if (and enable-multibyte-characters
6448 bidi-display-reordering)
6449 ;; Buffer is being reordered for display
6453 However, unibyte display and overlay strings @emph{are} reordered if
6454 their parent buffer is reordered. This is because plain-@sc{ascii}
6455 strings are stored by Emacs as unibyte strings. If a unibyte display
6456 or overlay string includes non-@sc{ascii} characters, these characters
6457 are assumed to have left-to-right direction.
6459 @cindex display properties, and bidi reordering of text
6460 Text covered by @code{display} text properties, by overlays with
6461 @code{display} properties whose value is a string, and by any other
6462 properties that replace buffer text, is treated as a single unit when
6463 it is reordered for display. That is, the entire chunk of text
6464 covered by these properties is reordered together. Moreover, the
6465 bidirectional properties of the characters in such a chunk of text are
6466 ignored, and Emacs reorders them as if they were replaced with a
6467 single character @code{U+FFFC}, known as the @dfn{Object Replacement
6468 Character}. This means that placing a display property over a portion
6469 of text may change the way that the surrounding text is reordered for
6470 display. To prevent this unexpected effect, always place such
6471 properties on text whose directionality is identical with text that
6474 @cindex base direction of a paragraph
6475 Each paragraph of bidirectional text has a @dfn{base direction},
6476 either right-to-left or left-to-right. Left-to-right paragraphs are
6477 displayed beginning at the left margin of the window, and are
6478 truncated or continued when the text reaches the right margin.
6479 Right-to-left paragraphs are displayed beginning at the right margin,
6480 and are continued or truncated at the left margin.
6482 By default, Emacs determines the base direction of each paragraph by
6483 looking at the text at its beginning. The precise method of
6484 determining the base direction is specified by the @acronym{UBA}; in a
6485 nutshell, the first character in a paragraph that has an explicit
6486 directionality determines the base direction of the paragraph.
6487 However, sometimes a buffer may need to force a certain base direction
6488 for its paragraphs. For example, buffers containing program source
6489 code should force all paragraphs to be displayed left-to-right. You
6490 can use following variable to do this:
6492 @defvar bidi-paragraph-direction
6493 If the value of this buffer-local variable is the symbol
6494 @code{right-to-left} or @code{left-to-right}, all paragraphs in the
6495 buffer are assumed to have that specified direction. Any other value
6496 is equivalent to @code{nil} (the default), which means to determine
6497 the base direction of each paragraph from its contents.
6499 @cindex @code{prog-mode}, and @code{bidi-paragraph-direction}
6500 Modes for program source code should set this to @code{left-to-right}.
6501 Prog mode does this by default, so modes derived from Prog mode do not
6502 need to set this explicitly (@pxref{Basic Major Modes}).
6505 @defun current-bidi-paragraph-direction &optional buffer
6506 This function returns the paragraph direction at point in the named
6507 @var{buffer}. The returned value is a symbol, either
6508 @code{left-to-right} or @code{right-to-left}. If @var{buffer} is
6509 omitted or @code{nil}, it defaults to the current buffer. If the
6510 buffer-local value of the variable @code{bidi-paragraph-direction} is
6511 non-@code{nil}, the returned value will be identical to that value;
6512 otherwise, the returned value reflects the paragraph direction
6513 determined dynamically by Emacs. For buffers whose value of
6514 @code{bidi-display-reordering} is @code{nil} as well as unibyte
6515 buffers, this function always returns @code{left-to-right}.
6518 @cindex visual-order cursor motion
6519 Sometimes there's a need to move point in strict visual order,
6520 either to the left or to the right of its current screen position.
6521 Emacs provides a primitive to do that.
6523 @defun move-point-visually direction
6524 This function moves point of the currently selected window to the
6525 buffer position that appears immediately to the right or to the left
6526 of point on the screen. If @var{direction} is positive, point will
6527 move one screen position to the right, otherwise it will move one
6528 screen position to the left. Note that, depending on the surrounding
6529 bidirectional context, this could potentially move point many buffer
6530 positions away. If invoked at the end of a screen line, the function
6531 moves point to the rightmost or leftmost screen position of the next
6532 or previous screen line, as appropriate for the value of
6535 The function returns the new buffer position as its value.
6538 @cindex layout on display, and bidirectional text
6539 @cindex jumbled display of bidirectional text
6540 @cindex concatenating bidirectional strings
6541 Bidirectional reordering can have surprising and unpleasant effects
6542 when two strings with bidirectional content are juxtaposed in a
6543 buffer, or otherwise programmatically concatenated into a string of
6544 text. A typical problematic case is when a buffer consists of
6545 sequences of text ``fields'' separated by whitespace or punctuation
6546 characters, like Buffer Menu mode or Rmail Summary Mode. Because the
6547 punctuation characters used as separators have @dfn{weak
6548 directionality}, they take on the directionality of surrounding text.
6549 As result, a numeric field that follows a field with bidirectional
6550 content can be displayed @emph{to the left} of the preceding field,
6551 messing up the expected layout. There are several ways to avoid this
6556 Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or
6557 @acronym{LRM}, to the end of each field that may have bidirectional
6558 content, or prepend it to the beginning of the following field. The
6559 function @code{bidi-string-mark-left-to-right}, described below, comes
6560 in handy for this purpose. (In a right-to-left paragraph, use
6561 @code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.) This
6562 is one of the solutions recommended by the UBA.
6565 Include the tab character in the field separator. The tab character
6566 plays the role of @dfn{segment separator} in bidirectional reordering,
6567 causing the text on either side to be reordered separately.
6569 @cindex @code{space} display spec, and bidirectional text
6571 Separate fields with a @code{display} property or overlay with a
6572 property value of the form @code{(space . PROPS)} (@pxref{Specified
6573 Space}). Emacs treats this display specification as a @dfn{paragraph
6574 separator}, and reorders the text on either side separately.
6577 @defun bidi-string-mark-left-to-right string
6578 This function returns its argument @var{string}, possibly modified,
6579 such that the result can be safely concatenated with another string,
6580 or juxtaposed with another string in a buffer, without disrupting the
6581 relative layout of this string and the next one on display. If the
6582 string returned by this function is displayed as part of a
6583 left-to-right paragraph, it will always appear on display to the left
6584 of the text that follows it. The function works by examining the
6585 characters of its argument, and if any of those characters could cause
6586 reordering on display, the function appends the @acronym{LRM}
6587 character to the string. The appended @acronym{LRM} character is made
6588 invisible by giving it an @code{invisible} text property of @code{t}
6589 (@pxref{Invisible Text}).
6592 The reordering algorithm uses the bidirectional properties of the
6593 characters stored as their @code{bidi-class} property
6594 (@pxref{Character Properties}). Lisp programs can change these
6595 properties by calling the @code{put-char-code-property} function.
6596 However, doing this requires a thorough understanding of the
6597 @acronym{UBA}, and is therefore not recommended. Any changes to the
6598 bidirectional properties of a character have global effect: they
6599 affect all Emacs frames and windows.
6601 Similarly, the @code{mirroring} property is used to display the
6602 appropriate mirrored character in the reordered text. Lisp programs
6603 can affect the mirrored display by changing this property. Again, any
6604 such changes affect all of Emacs display.