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 * Size of Displayed Text:: How large displayed text is.
22 * Line Height:: Controlling the height of lines.
23 * Faces:: A face defines a graphics style for text characters:
25 * Fringes:: Controlling window fringes.
26 * Scroll Bars:: Controlling vertical scroll bars.
27 * Window Dividers:: Separating windows visually.
28 * Display Property:: Enabling special display features.
29 * Images:: Displaying images in Emacs buffers.
30 * Buttons:: Adding clickable buttons to Emacs buffers.
31 * Abstract Display:: Emacs's Widget for Object Collections.
32 * Blinking:: How Emacs shows the matching open parenthesis.
33 * Character Display:: How Emacs displays individual characters.
34 * Beeping:: Audible signal to the user.
35 * Window Systems:: Which window system is being used.
36 * Bidirectional Display:: Display of bidirectional scripts, such as
41 @section Refreshing the Screen
43 The function @code{redraw-frame} clears and redisplays the entire
44 contents of a given frame (@pxref{Frames}). This is useful if the
47 @defun redraw-frame frame
48 This function clears and redisplays frame @var{frame}.
51 Even more powerful is @code{redraw-display}:
53 @deffn Command redraw-display
54 This function clears and redisplays all visible frames.
57 In Emacs, processing user input takes priority over redisplay. If
58 you call these functions when input is available, they don't redisplay
59 immediately, but the requested redisplay does happen
60 eventually---after all the input has been processed.
62 On text terminals, suspending and resuming Emacs normally also
63 refreshes the screen. Some terminal emulators record separate
64 contents for display-oriented programs such as Emacs and for ordinary
65 sequential display. If you are using such a terminal, you might want
66 to inhibit the redisplay on resumption.
68 @defopt no-redraw-on-reenter
69 @cindex suspend (cf. @code{no-redraw-on-reenter})
70 @cindex resume (cf. @code{no-redraw-on-reenter})
71 This variable controls whether Emacs redraws the entire screen after it
72 has been suspended and resumed. Non-@code{nil} means there is no need
73 to redraw, @code{nil} means redrawing is needed. The default is @code{nil}.
76 @node Forcing Redisplay
77 @section Forcing Redisplay
78 @cindex forcing redisplay
80 Emacs normally tries to redisplay the screen whenever it waits for
81 input. With the following function, you can request an immediate
82 attempt to redisplay, in the middle of Lisp code, without actually
85 @defun redisplay &optional force
86 This function tries immediately to redisplay. The optional argument
87 @var{force}, if non-@code{nil}, forces the redisplay to be performed,
88 instead of being preempted, even if input is pending and the variable
89 @code{redisplay-dont-pause} is @code{nil} (see below). If
90 @code{redisplay-dont-pause} is non-@code{nil} (the default), this
91 function redisplays in any case, i.e., @var{force} does nothing.
93 The function returns @code{t} if it actually tried to redisplay, and
94 @code{nil} otherwise. A value of @code{t} does not mean that
95 redisplay proceeded to completion; it could have been preempted by
99 @defvar redisplay-dont-pause
100 If this variable is @code{nil}, arriving input events preempt
101 redisplay; Emacs avoids starting a redisplay, and stops any redisplay
102 that is in progress, until the input has been processed. In
103 particular, @code{(redisplay)} returns @code{nil} without actually
104 redisplaying, if there is pending input.
106 The default value is @code{t}, which means that pending input does not
110 @defvar redisplay-preemption-period
111 If @code{redisplay-dont-pause} is @code{nil}, this variable specifies
112 how many seconds Emacs waits between checks for new input during
113 redisplay; if input arrives during this interval, redisplay stops and
114 the input is processed. The default value is 0.1; if the value is
115 @code{nil}, Emacs does not check for input during redisplay.
117 This variable has no effect when @code{redisplay-dont-pause} is
118 non-@code{nil} (the default).
121 @defvar pre-redisplay-function
122 A function run just before redisplay. It is called with one argument,
123 the set of windows to redisplay.
126 Although @code{redisplay} tries immediately to redisplay, it does
127 not change how Emacs decides which parts of its frame(s) to redisplay.
128 By contrast, the following function adds certain windows to the
129 pending redisplay work (as if their contents had completely changed),
130 but does not immediately try to perform redisplay.
132 @defun force-window-update &optional object
133 This function forces some or all windows to be updated the next time
134 Emacs does a redisplay. If @var{object} is a window, that window is
135 to be updated. If @var{object} is a buffer or buffer name, all
136 windows displaying that buffer are to be updated. If @var{object} is
137 @code{nil} (or omitted), all windows are to be updated.
139 This function does not do a redisplay immediately; Emacs does that as
140 it waits for input, or when the function @code{redisplay} is called.
145 @cindex line wrapping
146 @cindex line truncation
147 @cindex continuation lines
148 @cindex @samp{$} in display
149 @cindex @samp{\} in display
151 When a line of text extends beyond the right edge of a window, Emacs
152 can @dfn{continue} the line (make it ``wrap'' to the next screen
153 line), or @dfn{truncate} the line (limit it to one screen line). The
154 additional screen lines used to display a long text line are called
155 @dfn{continuation} lines. Continuation is not the same as filling;
156 continuation happens on the screen only, not in the buffer contents,
157 and it breaks a line precisely at the right margin, not at a word
158 boundary. @xref{Filling}.
160 On a graphical display, tiny arrow images in the window fringes
161 indicate truncated and continued lines (@pxref{Fringes}). On a text
162 terminal, a @samp{$} in the rightmost column of the window indicates
163 truncation; a @samp{\} on the rightmost column indicates a line that
164 ``wraps''. (The display table can specify alternate characters to use
165 for this; @pxref{Display Tables}).
167 @defopt truncate-lines
168 If this buffer-local variable is non-@code{nil}, lines that extend
169 beyond the right edge of the window are truncated; otherwise, they are
170 continued. As a special exception, the variable
171 @code{truncate-partial-width-windows} takes precedence in
172 @dfn{partial-width} windows (i.e., windows that do not occupy the
176 @defopt truncate-partial-width-windows
177 @cindex partial-width windows
178 This variable controls line truncation in @dfn{partial-width} windows.
179 A partial-width window is one that does not occupy the entire frame
180 width (@pxref{Splitting Windows}). If the value is @code{nil}, line
181 truncation is determined by the variable @code{truncate-lines} (see
182 above). If the value is an integer @var{n}, lines are truncated if
183 the partial-width window has fewer than @var{n} columns, regardless of
184 the value of @code{truncate-lines}; if the partial-width window has
185 @var{n} or more columns, line truncation is determined by
186 @code{truncate-lines}. For any other non-@code{nil} value, lines are
187 truncated in every partial-width window, regardless of the value of
188 @code{truncate-lines}.
191 When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in
192 a window, that forces truncation.
195 If this buffer-local variable is non-@code{nil}, it defines a
196 @dfn{wrap prefix} which Emacs displays at the start of every
197 continuation line. (If lines are truncated, @code{wrap-prefix} is
198 never used.) Its value may be a string or an image (@pxref{Other
199 Display Specs}), or a stretch of whitespace such as specified by the
200 @code{:width} or @code{:align-to} display properties (@pxref{Specified
201 Space}). The value is interpreted in the same way as a @code{display}
202 text property. @xref{Display Property}.
204 A wrap prefix may also be specified for regions of text, using the
205 @code{wrap-prefix} text or overlay property. This takes precedence
206 over the @code{wrap-prefix} variable. @xref{Special Properties}.
210 If this buffer-local variable is non-@code{nil}, it defines a
211 @dfn{line prefix} which Emacs displays at the start of every
212 non-continuation line. Its value may be a string or an image
213 (@pxref{Other Display Specs}), or a stretch of whitespace such as
214 specified by the @code{:width} or @code{:align-to} display properties
215 (@pxref{Specified Space}). The value is interpreted in the same way
216 as a @code{display} text property. @xref{Display Property}.
218 A line prefix may also be specified for regions of text using the
219 @code{line-prefix} text or overlay property. This takes precedence
220 over the @code{line-prefix} variable. @xref{Special Properties}.
224 If your buffer contains only very short lines, you might find it
225 advisable to set @code{cache-long-scans} to @code{nil}.
227 @defvar cache-long-scans
228 If this variable is non-@code{nil} (the default), various indentation
229 and motion functions, and Emacs redisplay, cache the results of
230 scanning the buffer, and consult the cache to avoid rescanning regions
231 of the buffer unless they are modified.
233 Turning off the cache speeds up processing of short lines somewhat.
235 This variable is automatically buffer-local in every buffer.
240 @section The Echo Area
241 @cindex error display
244 @c FIXME: Why not use @xref{Minibuffers} directly? --xfq
245 The @dfn{echo area} is used for displaying error messages
246 (@pxref{Errors}), for messages made with the @code{message} primitive,
247 and for echoing keystrokes. It is not the same as the minibuffer,
248 despite the fact that the minibuffer appears (when active) in the same
249 place on the screen as the echo area. @xref{Minibuffer,, The
250 Minibuffer, emacs, The GNU Emacs Manual}.
252 Apart from the functions documented in this section, you can print
253 Lisp objects to the echo area by specifying @code{t} as the output
254 stream. @xref{Output Streams}.
257 * Displaying Messages:: Explicitly displaying text in the echo area.
258 * Progress:: Informing user about progress of a long operation.
259 * Logging Messages:: Echo area messages are logged for the user.
260 * Echo Area Customization:: Controlling the echo area.
263 @node Displaying Messages
264 @subsection Displaying Messages in the Echo Area
265 @cindex display message in echo area
267 This section describes the standard functions for displaying
268 messages in the echo area.
270 @defun message format-string &rest arguments
271 This function displays a message in the echo area.
272 @var{format-string} is a format string, and @var{arguments} are the
273 objects for its format specifications, like in the @code{format}
274 function (@pxref{Formatting Strings}). The resulting formatted string
275 is displayed in the echo area; if it contains @code{face} text
276 properties, it is displayed with the specified faces (@pxref{Faces}).
277 The string is also added to the @file{*Messages*} buffer, but without
278 text properties (@pxref{Logging Messages}).
280 In batch mode, the message is printed to the standard error stream,
281 followed by a newline.
283 If @var{format-string} is @code{nil} or the empty string,
284 @code{message} clears the echo area; if the echo area has been
285 expanded automatically, this brings it back to its normal size. If
286 the minibuffer is active, this brings the minibuffer contents back
287 onto the screen immediately.
291 (message "Minibuffer depth is %d."
293 @print{} Minibuffer depth is 0.
294 @result{} "Minibuffer depth is 0."
298 ---------- Echo Area ----------
299 Minibuffer depth is 0.
300 ---------- Echo Area ----------
304 To automatically display a message in the echo area or in a pop-buffer,
305 depending on its size, use @code{display-message-or-buffer} (see below).
308 @defmac with-temp-message message &rest body
309 This construct displays a message in the echo area temporarily, during
310 the execution of @var{body}. It displays @var{message}, executes
311 @var{body}, then returns the value of the last body form while restoring
312 the previous echo area contents.
315 @defun message-or-box format-string &rest arguments
316 This function displays a message like @code{message}, but may display it
317 in a dialog box instead of the echo area. If this function is called in
318 a command that was invoked using the mouse---more precisely, if
319 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
320 @code{nil} or a list---then it uses a dialog box or pop-up menu to
321 display the message. Otherwise, it uses the echo area. (This is the
322 same criterion that @code{y-or-n-p} uses to make a similar decision; see
323 @ref{Yes-or-No Queries}.)
325 You can force use of the mouse or of the echo area by binding
326 @code{last-nonmenu-event} to a suitable value around the call.
329 @defun message-box format-string &rest arguments
331 This function displays a message like @code{message}, but uses a dialog
332 box (or a pop-up menu) whenever that is possible. If it is impossible
333 to use a dialog box or pop-up menu, because the terminal does not
334 support them, then @code{message-box} uses the echo area, like
338 @defun display-message-or-buffer message &optional buffer-name not-this-window frame
339 This function displays the message @var{message}, which may be either a
340 string or a buffer. If it is shorter than the maximum height of the
341 echo area, as defined by @code{max-mini-window-height}, it is displayed
342 in the echo area, using @code{message}. Otherwise,
343 @code{display-buffer} is used to show it in a pop-up buffer.
345 Returns either the string shown in the echo area, or when a pop-up
346 buffer is used, the window used to display it.
348 If @var{message} is a string, then the optional argument
349 @var{buffer-name} is the name of the buffer used to display it when a
350 pop-up buffer is used, defaulting to @file{*Message*}. In the case
351 where @var{message} is a string and displayed in the echo area, it is
352 not specified whether the contents are inserted into the buffer anyway.
354 The optional arguments @var{not-this-window} and @var{frame} are as for
355 @code{display-buffer}, and only used if a buffer is displayed.
358 @defun current-message
359 This function returns the message currently being displayed in the
360 echo area, or @code{nil} if there is none.
364 @subsection Reporting Operation Progress
365 @cindex progress reporting
367 When an operation can take a while to finish, you should inform the
368 user about the progress it makes. This way the user can estimate
369 remaining time and clearly see that Emacs is busy working, not hung.
370 A convenient way to do this is to use a @dfn{progress reporter}.
372 Here is a working example that does nothing useful:
375 (let ((progress-reporter
376 (make-progress-reporter "Collecting mana for Emacs..."
380 (progress-reporter-update progress-reporter k))
381 (progress-reporter-done progress-reporter))
384 @defun make-progress-reporter message &optional min-value max-value current-value min-change min-time
385 This function creates and returns a progress reporter object, which
386 you will use as an argument for the other functions listed below. The
387 idea is to precompute as much data as possible to make progress
390 When this progress reporter is subsequently used, it will display
391 @var{message} in the echo area, followed by progress percentage.
392 @var{message} is treated as a simple string. If you need it to depend
393 on a filename, for instance, use @code{format} before calling this
396 The arguments @var{min-value} and @var{max-value} should be numbers
397 standing for the starting and final states of the operation. For
398 instance, an operation that ``scans'' a buffer should set these to the
399 results of @code{point-min} and @code{point-max} correspondingly.
400 @var{max-value} should be greater than @var{min-value}.
402 Alternatively, you can set @var{min-value} and @var{max-value} to
403 @code{nil}. In that case, the progress reporter does not report
404 process percentages; it instead displays a ``spinner'' that rotates a
405 notch each time you update the progress reporter.
407 If @var{min-value} and @var{max-value} are numbers, you can give the
408 argument @var{current-value} a numerical value specifying the initial
409 progress; if omitted, this defaults to @var{min-value}.
411 The remaining arguments control the rate of echo area updates. The
412 progress reporter will wait for at least @var{min-change} more
413 percents of the operation to be completed before printing next
414 message; the default is one percent. @var{min-time} specifies the
415 minimum time in seconds to pass between successive prints; the default
416 is 0.2 seconds. (On some operating systems, the progress reporter may
417 handle fractions of seconds with varying precision).
419 This function calls @code{progress-reporter-update}, so the first
420 message is printed immediately.
423 @defun progress-reporter-update reporter &optional value
424 This function does the main work of reporting progress of your
425 operation. It displays the message of @var{reporter}, followed by
426 progress percentage determined by @var{value}. If percentage is zero,
427 or close enough according to the @var{min-change} and @var{min-time}
428 arguments, then it is omitted from the output.
430 @var{reporter} must be the result of a call to
431 @code{make-progress-reporter}. @var{value} specifies the current
432 state of your operation and must be between @var{min-value} and
433 @var{max-value} (inclusive) as passed to
434 @code{make-progress-reporter}. For instance, if you scan a buffer,
435 then @var{value} should be the result of a call to @code{point}.
437 This function respects @var{min-change} and @var{min-time} as passed
438 to @code{make-progress-reporter} and so does not output new messages
439 on every invocation. It is thus very fast and normally you should not
440 try to reduce the number of calls to it: resulting overhead will most
441 likely negate your effort.
444 @defun progress-reporter-force-update reporter &optional value new-message
445 This function is similar to @code{progress-reporter-update} except
446 that it prints a message in the echo area unconditionally.
448 The first two arguments have the same meaning as for
449 @code{progress-reporter-update}. Optional @var{new-message} allows
450 you to change the message of the @var{reporter}. Since this function
451 always updates the echo area, such a change will be immediately
452 presented to the user.
455 @defun progress-reporter-done reporter
456 This function should be called when the operation is finished. It
457 prints the message of @var{reporter} followed by word ``done'' in the
460 You should always call this function and not hope for
461 @code{progress-reporter-update} to print ``100%''. Firstly, it may
462 never print it, there are many good reasons for this not to happen.
463 Secondly, ``done'' is more explicit.
466 @defmac dotimes-with-progress-reporter (var count [result]) message body@dots{}
467 This is a convenience macro that works the same way as @code{dotimes}
468 does, but also reports loop progress using the functions described
469 above. It allows you to save some typing.
471 You can rewrite the example in the beginning of this node using
475 (dotimes-with-progress-reporter
477 "Collecting some mana for Emacs..."
482 @node Logging Messages
483 @subsection Logging Messages in @file{*Messages*}
484 @cindex logging echo-area messages
486 Almost all the messages displayed in the echo area are also recorded
487 in the @file{*Messages*} buffer so that the user can refer back to
488 them. This includes all the messages that are output with
489 @code{message}. By default, this buffer is read-only and uses the major
490 mode @code{messages-buffer-mode}. Nothing prevents the user from
491 killing the @file{*Messages*} buffer, but the next display of a message
492 recreates it. Any Lisp code that needs to access the
493 @file{*Messages*} buffer directly and wants to ensure that it exists
494 should use the function @code{messages-buffer}.
496 @defun messages-buffer
497 This function returns the @file{*Messages*} buffer. If it does not
498 exist, it creates it, and switches it to @code{messages-buffer-mode}.
501 @defopt message-log-max
502 This variable specifies how many lines to keep in the @file{*Messages*}
503 buffer. The value @code{t} means there is no limit on how many lines to
504 keep. The value @code{nil} disables message logging entirely. Here's
505 how to display a message and prevent it from being logged:
508 (let (message-log-max)
513 To make @file{*Messages*} more convenient for the user, the logging
514 facility combines successive identical messages. It also combines
515 successive related messages for the sake of two cases: question
516 followed by answer, and a series of progress messages.
518 A ``question followed by an answer'' means two messages like the
519 ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
520 and the second is @samp{@var{question}...@var{answer}}. The first
521 message conveys no additional information beyond what's in the second,
522 so logging the second message discards the first from the log.
524 A ``series of progress messages'' means successive messages like
525 those produced by @code{make-progress-reporter}. They have the form
526 @samp{@var{base}...@var{how-far}}, where @var{base} is the same each
527 time, while @var{how-far} varies. Logging each message in the series
528 discards the previous one, provided they are consecutive.
530 The functions @code{make-progress-reporter} and @code{y-or-n-p}
531 don't have to do anything special to activate the message log
532 combination feature. It operates whenever two consecutive messages
533 are logged that share a common prefix ending in @samp{...}.
535 @node Echo Area Customization
536 @subsection Echo Area Customization
538 These variables control details of how the echo area works.
540 @defvar cursor-in-echo-area
541 This variable controls where the cursor appears when a message is
542 displayed in the echo area. If it is non-@code{nil}, then the cursor
543 appears at the end of the message. Otherwise, the cursor appears at
544 point---not in the echo area at all.
546 The value is normally @code{nil}; Lisp programs bind it to @code{t}
547 for brief periods of time.
550 @defvar echo-area-clear-hook
551 This normal hook is run whenever the echo area is cleared---either by
552 @code{(message nil)} or for any other reason.
555 @defopt echo-keystrokes
556 This variable determines how much time should elapse before command
557 characters echo. Its value must be a number, and specifies the
558 number of seconds to wait before echoing. If the user types a prefix
559 key (such as @kbd{C-x}) and then delays this many seconds before
560 continuing, the prefix key is echoed in the echo area. (Once echoing
561 begins in a key sequence, all subsequent characters in the same key
562 sequence are echoed immediately.)
564 If the value is zero, then command input is not echoed.
567 @defvar message-truncate-lines
568 Normally, displaying a long message resizes the echo area to display
569 the entire message. But if the variable @code{message-truncate-lines}
570 is non-@code{nil}, the echo area does not resize, and the message is
574 The variable @code{max-mini-window-height}, which specifies the
575 maximum height for resizing minibuffer windows, also applies to the
576 echo area (which is really a special use of the minibuffer window;
577 @pxref{Minibuffer Misc}).
580 @section Reporting Warnings
583 @dfn{Warnings} are a facility for a program to inform the user of a
584 possible problem, but continue running.
587 * Warning Basics:: Warnings concepts and functions to report them.
588 * Warning Variables:: Variables programs bind to customize their warnings.
589 * Warning Options:: Variables users set to control display of warnings.
590 * Delayed Warnings:: Deferring a warning until the end of a command.
594 @subsection Warning Basics
595 @cindex severity level
597 Every warning has a textual message, which explains the problem for
598 the user, and a @dfn{severity level} which is a symbol. Here are the
599 possible severity levels, in order of decreasing severity, and their
604 A problem that will seriously impair Emacs operation soon
605 if you do not attend to it promptly.
607 A report of data or circumstances that are inherently wrong.
609 A report of data or circumstances that are not inherently wrong, but
610 raise suspicion of a possible problem.
612 A report of information that may be useful if you are debugging.
615 When your program encounters invalid input data, it can either
616 signal a Lisp error by calling @code{error} or @code{signal} or report
617 a warning with severity @code{:error}. Signaling a Lisp error is the
618 easiest thing to do, but it means the program cannot continue
619 processing. If you want to take the trouble to implement a way to
620 continue processing despite the bad data, then reporting a warning of
621 severity @code{:error} is the right way to inform the user of the
622 problem. For instance, the Emacs Lisp byte compiler can report an
623 error that way and continue compiling other functions. (If the
624 program signals a Lisp error and then handles it with
625 @code{condition-case}, the user won't see the error message; it could
626 show the message to the user by reporting it as a warning.)
628 @c FIXME: Why use "(bytecomp)" instead of "'bytecomp" or simply
629 @c "bytecomp" here? The parens are part of warning-type-format but
630 @c not part of the warning type. --xfq
632 Each warning has a @dfn{warning type} to classify it. The type is a
633 list of symbols. The first symbol should be the custom group that you
634 use for the program's user options. For example, byte compiler
635 warnings use the warning type @code{(bytecomp)}. You can also
636 subcategorize the warnings, if you wish, by using more symbols in the
639 @defun display-warning type message &optional level buffer-name
640 This function reports a warning, using @var{message} as the message
641 and @var{type} as the warning type. @var{level} should be the
642 severity level, with @code{:warning} being the default.
644 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
645 for logging the warning. By default, it is @file{*Warnings*}.
648 @defun lwarn type level message &rest args
649 This function reports a warning using the value of @code{(format
650 @var{message} @var{args}...)} as the message in the @file{*Warnings*}
651 buffer. In other respects it is equivalent to @code{display-warning}.
654 @defun warn message &rest args
655 This function reports a warning using the value of @code{(format
656 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
657 type, and @code{:warning} as the severity level. It exists for
658 compatibility only; we recommend not using it, because you should
659 specify a specific warning type.
662 @node Warning Variables
663 @subsection Warning Variables
665 Programs can customize how their warnings appear by binding
666 the variables described in this section.
668 @defvar warning-levels
669 This list defines the meaning and severity order of the warning
670 severity levels. Each element defines one severity level,
671 and they are arranged in order of decreasing severity.
673 Each element has the form @code{(@var{level} @var{string}
674 @var{function})}, where @var{level} is the severity level it defines.
675 @var{string} specifies the textual description of this level.
676 @var{string} should use @samp{%s} to specify where to put the warning
677 type information, or it can omit the @samp{%s} so as not to include
680 The optional @var{function}, if non-@code{nil}, is a function to call
681 with no arguments, to get the user's attention.
683 Normally you should not change the value of this variable.
686 @defvar warning-prefix-function
687 If non-@code{nil}, the value is a function to generate prefix text for
688 warnings. Programs can bind the variable to a suitable function.
689 @code{display-warning} calls this function with the warnings buffer
690 current, and the function can insert text in it. That text becomes
691 the beginning of the warning message.
693 The function is called with two arguments, the severity level and its
694 entry in @code{warning-levels}. It should return a list to use as the
695 entry (this value need not be an actual member of
696 @code{warning-levels}). By constructing this value, the function can
697 change the severity of the warning, or specify different handling for
698 a given severity level.
700 If the variable's value is @code{nil} then there is no function
704 @defvar warning-series
705 Programs can bind this variable to @code{t} to say that the next
706 warning should begin a series. When several warnings form a series,
707 that means to leave point on the first warning of the series, rather
708 than keep moving it for each warning so that it appears on the last one.
709 The series ends when the local binding is unbound and
710 @code{warning-series} becomes @code{nil} again.
712 The value can also be a symbol with a function definition. That is
713 equivalent to @code{t}, except that the next warning will also call
714 the function with no arguments with the warnings buffer current. The
715 function can insert text which will serve as a header for the series
718 Once a series has begun, the value is a marker which points to the
719 buffer position in the warnings buffer of the start of the series.
721 The variable's normal value is @code{nil}, which means to handle
722 each warning separately.
725 @defvar warning-fill-prefix
726 When this variable is non-@code{nil}, it specifies a fill prefix to
727 use for filling each warning's text.
730 @defvar warning-type-format
731 This variable specifies the format for displaying the warning type
732 in the warning message. The result of formatting the type this way
733 gets included in the message under the control of the string in the
734 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
735 If you bind it to @code{""} then the warning type won't appear at
739 @node Warning Options
740 @subsection Warning Options
742 These variables are used by users to control what happens
743 when a Lisp program reports a warning.
745 @defopt warning-minimum-level
746 This user option specifies the minimum severity level that should be
747 shown immediately to the user. The default is @code{:warning}, which
748 means to immediately display all warnings except @code{:debug}
752 @defopt warning-minimum-log-level
753 This user option specifies the minimum severity level that should be
754 logged in the warnings buffer. The default is @code{:warning}, which
755 means to log all warnings except @code{:debug} warnings.
758 @defopt warning-suppress-types
759 This list specifies which warning types should not be displayed
760 immediately for the user. Each element of the list should be a list
761 of symbols. If its elements match the first elements in a warning
762 type, then that warning is not displayed immediately.
765 @defopt warning-suppress-log-types
766 This list specifies which warning types should not be logged in the
767 warnings buffer. Each element of the list should be a list of
768 symbols. If it matches the first few elements in a warning type, then
769 that warning is not logged.
772 @node Delayed Warnings
773 @subsection Delayed Warnings
775 Sometimes, you may wish to avoid showing a warning while a command is
776 running, and only show it only after the end of the command. You can
777 use the variable @code{delayed-warnings-list} for this.
779 @defvar delayed-warnings-list
780 The value of this variable is a list of warnings to be displayed after
781 the current command has finished. Each element must be a list
784 (@var{type} @var{message} [@var{level} [@var{buffer-name}]])
788 with the same form, and the same meanings, as the argument list of
789 @code{display-warning} (@pxref{Warning Basics}). Immediately after
790 running @code{post-command-hook} (@pxref{Command Overview}), the Emacs
791 command loop displays all the warnings specified by this variable,
792 then resets it to @code{nil}.
795 Programs which need to further customize the delayed warnings
796 mechanism can change the variable @code{delayed-warnings-hook}:
798 @defvar delayed-warnings-hook
799 This is a normal hook which is run by the Emacs command loop, after
800 @code{post-command-hook}, in order to to process and display delayed
803 Its default value is a list of two functions:
806 (collapse-delayed-warnings display-delayed-warnings)
809 @findex collapse-delayed-warnings
810 @findex display-delayed-warnings
812 The function @code{collapse-delayed-warnings} removes repeated entries
813 from @code{delayed-warnings-list}. The function
814 @code{display-delayed-warnings} calls @code{display-warning} on each
815 of the entries in @code{delayed-warnings-list}, in turn, and then sets
816 @code{delayed-warnings-list} to @code{nil}.
820 @section Invisible Text
822 @cindex invisible text
823 You can make characters @dfn{invisible}, so that they do not appear on
824 the screen, with the @code{invisible} property. This can be either a
825 text property (@pxref{Text Properties}) or an overlay property
826 (@pxref{Overlays}). Cursor motion also partly ignores these
827 characters; if the command loop finds that point is inside a range of
828 invisible text after a command, it relocates point to the other side
831 In the simplest case, any non-@code{nil} @code{invisible} property makes
832 a character invisible. This is the default case---if you don't alter
833 the default value of @code{buffer-invisibility-spec}, this is how the
834 @code{invisible} property works. You should normally use @code{t}
835 as the value of the @code{invisible} property if you don't plan
836 to set @code{buffer-invisibility-spec} yourself.
838 More generally, you can use the variable @code{buffer-invisibility-spec}
839 to control which values of the @code{invisible} property make text
840 invisible. This permits you to classify the text into different subsets
841 in advance, by giving them different @code{invisible} values, and
842 subsequently make various subsets visible or invisible by changing the
843 value of @code{buffer-invisibility-spec}.
845 Controlling visibility with @code{buffer-invisibility-spec} is
846 especially useful in a program to display the list of entries in a
847 database. It permits the implementation of convenient filtering
848 commands to view just a part of the entries in the database. Setting
849 this variable is very fast, much faster than scanning all the text in
850 the buffer looking for properties to change.
852 @defvar buffer-invisibility-spec
853 This variable specifies which kinds of @code{invisible} properties
854 actually make a character invisible. Setting this variable makes it
859 A character is invisible if its @code{invisible} property is
860 non-@code{nil}. This is the default.
863 Each element of the list specifies a criterion for invisibility; if a
864 character's @code{invisible} property fits any one of these criteria,
865 the character is invisible. The list can have two kinds of elements:
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}.
873 @item (@var{atom} . t)
874 A character is invisible if its @code{invisible} property value is
875 @var{atom} or if it is a list with @var{atom} as a member; comparison
876 is done with @code{eq}. Moreover, a sequence of such characters
877 displays as an ellipsis.
882 Two functions are specifically provided for adding elements to
883 @code{buffer-invisibility-spec} and removing elements from it.
885 @defun add-to-invisibility-spec element
886 This function adds the element @var{element} to
887 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
888 was @code{t}, it changes to a list, @code{(t)}, so that text whose
889 @code{invisible} property is @code{t} remains invisible.
892 @defun remove-from-invisibility-spec element
893 This removes the element @var{element} from
894 @code{buffer-invisibility-spec}. This does nothing if @var{element}
898 A convention for use of @code{buffer-invisibility-spec} is that a
899 major mode should use the mode's own name as an element of
900 @code{buffer-invisibility-spec} and as the value of the
901 @code{invisible} property:
904 ;; @r{If you want to display an ellipsis:}
905 (add-to-invisibility-spec '(my-symbol . t))
906 ;; @r{If you don't want ellipsis:}
907 (add-to-invisibility-spec 'my-symbol)
909 (overlay-put (make-overlay beginning end)
910 'invisible 'my-symbol)
912 ;; @r{When done with the invisibility:}
913 (remove-from-invisibility-spec '(my-symbol . t))
914 ;; @r{Or respectively:}
915 (remove-from-invisibility-spec 'my-symbol)
918 You can check for invisibility using the following function:
920 @defun invisible-p pos-or-prop
921 If @var{pos-or-prop} is a marker or number, this function returns a
922 non-@code{nil} value if the text at that position is invisible.
924 If @var{pos-or-prop} is any other kind of Lisp object, that is taken
925 to mean a possible value of the @code{invisible} text or overlay
926 property. In that case, this function returns a non-@code{nil} value
927 if that value would cause text to become invisible, based on the
928 current value of @code{buffer-invisibility-spec}.
931 @vindex line-move-ignore-invisible
932 Ordinarily, functions that operate on text or move point do not care
933 whether the text is invisible. The user-level line motion commands
934 ignore invisible newlines if @code{line-move-ignore-invisible} is
935 non-@code{nil} (the default), but only because they are explicitly
938 However, if a command ends with point inside or at the boundary of
939 invisible text, the main editing loop relocates point to one of the
940 two ends of the invisible text. Emacs chooses the direction of
941 relocation so that it is the same as the overall movement direction of
942 the command; if in doubt, it prefers a position where an inserted char
943 would not inherit the @code{invisible} property. Additionally, if the
944 text is not replaced by an ellipsis and the command only moved within
945 the invisible text, then point is moved one extra character so as to
946 try and reflect the command's movement by a visible movement of the
949 Thus, if the command moved point back to an invisible range (with the usual
950 stickiness), Emacs moves point back to the beginning of that range. If the
951 command moved point forward into an invisible range, Emacs moves point forward
952 to the first visible character that follows the invisible text and then forward
955 Incremental search can make invisible overlays visible temporarily
956 and/or permanently when a match includes invisible text. To enable
957 this, the overlay should have a non-@code{nil}
958 @code{isearch-open-invisible} property. The property value should be a
959 function to be called with the overlay as an argument. This function
960 should make the overlay visible permanently; it is used when the match
961 overlaps the overlay on exit from the search.
963 During the search, such overlays are made temporarily visible by
964 temporarily modifying their invisible and intangible properties. If you
965 want this to be done differently for a certain overlay, give it an
966 @code{isearch-open-invisible-temporary} property which is a function.
967 The function is called with two arguments: the first is the overlay, and
968 the second is @code{nil} to make the overlay visible, or @code{t} to
969 make it invisible again.
971 @node Selective Display
972 @section Selective Display
973 @c @cindex selective display Duplicates selective-display
975 @dfn{Selective display} refers to a pair of related features for
976 hiding certain lines on the screen.
978 @cindex explicit selective display
979 The first variant, explicit selective display, was designed for use in a Lisp
980 program: it controls which lines are hidden by altering the text. This kind of
981 hiding is now obsolete; instead you can get the same effect with the
982 @code{invisible} property (@pxref{Invisible Text}).
984 In the second variant, the choice of lines to hide is made
985 automatically based on indentation. This variant is designed to be a
988 The way you control explicit selective display is by replacing a
989 newline (control-j) with a carriage return (control-m). The text that
990 was formerly a line following that newline is now hidden. Strictly
991 speaking, it is temporarily no longer a line at all, since only
992 newlines can separate lines; it is now part of the previous line.
994 Selective display does not directly affect editing commands. For
995 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
996 into hidden text. However, the replacement of newline characters with
997 carriage return characters affects some editing commands. For
998 example, @code{next-line} skips hidden lines, since it searches only
999 for newlines. Modes that use selective display can also define
1000 commands that take account of the newlines, or that control which
1001 parts of the text are hidden.
1003 When you write a selectively displayed buffer into a file, all the
1004 control-m's are output as newlines. This means that when you next read
1005 in the file, it looks OK, with nothing hidden. The selective display
1006 effect is seen only within Emacs.
1008 @defvar selective-display
1009 This buffer-local variable enables selective display. This means that
1010 lines, or portions of lines, may be made hidden.
1014 If the value of @code{selective-display} is @code{t}, then the character
1015 control-m marks the start of hidden text; the control-m, and the rest
1016 of the line following it, are not displayed. This is explicit selective
1020 If the value of @code{selective-display} is a positive integer, then
1021 lines that start with more than that many columns of indentation are not
1025 When some portion of a buffer is hidden, the vertical movement
1026 commands operate as if that portion did not exist, allowing a single
1027 @code{next-line} command to skip any number of hidden lines.
1028 However, character movement commands (such as @code{forward-char}) do
1029 not skip the hidden portion, and it is possible (if tricky) to insert
1030 or delete text in an hidden portion.
1032 In the examples below, we show the @emph{display appearance} of the
1033 buffer @code{foo}, which changes with the value of
1034 @code{selective-display}. The @emph{contents} of the buffer do not
1039 (setq selective-display nil)
1042 ---------- Buffer: foo ----------
1049 ---------- Buffer: foo ----------
1053 (setq selective-display 2)
1056 ---------- Buffer: foo ----------
1061 ---------- Buffer: foo ----------
1066 @defopt selective-display-ellipses
1067 If this buffer-local variable is non-@code{nil}, then Emacs displays
1068 @samp{@dots{}} at the end of a line that is followed by hidden text.
1069 This example is a continuation of the previous one.
1073 (setq selective-display-ellipses t)
1076 ---------- Buffer: foo ----------
1081 ---------- Buffer: foo ----------
1085 You can use a display table to substitute other text for the ellipsis
1086 (@samp{@dots{}}). @xref{Display Tables}.
1089 @node Temporary Displays
1090 @section Temporary Displays
1092 Temporary displays are used by Lisp programs to put output into a
1093 buffer and then present it to the user for perusal rather than for
1094 editing. Many help commands use this feature.
1096 @defmac with-output-to-temp-buffer buffer-name body@dots{}
1097 This function executes the forms in @var{body} while arranging to insert
1098 any output they print into the buffer named @var{buffer-name}, which is
1099 first created if necessary, and put into Help mode. (See the similar
1100 form @code{with-temp-buffer-window} below.) Finally, the buffer is
1101 displayed in some window, but that window is not selected.
1103 If the forms in @var{body} do not change the major mode in the output
1104 buffer, so that it is still Help mode at the end of their execution,
1105 then @code{with-output-to-temp-buffer} makes this buffer read-only at
1106 the end, and also scans it for function and variable names to make them
1107 into clickable cross-references. @xref{Docstring hyperlinks, , Tips for
1108 Documentation Strings}, in particular the item on hyperlinks in
1109 documentation strings, for more details.
1111 The string @var{buffer-name} specifies the temporary buffer, which need
1112 not already exist. The argument must be a string, not a buffer. The
1113 buffer is erased initially (with no questions asked), and it is marked
1114 as unmodified after @code{with-output-to-temp-buffer} exits.
1116 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
1117 temporary buffer, then it evaluates the forms in @var{body}. Output
1118 using the Lisp output functions within @var{body} goes by default to
1119 that buffer (but screen display and messages in the echo area, although
1120 they are ``output'' in the general sense of the word, are not affected).
1121 @xref{Output Functions}.
1123 Several hooks are available for customizing the behavior
1124 of this construct; they are listed below.
1126 The value of the last form in @var{body} is returned.
1130 ---------- Buffer: foo ----------
1131 This is the contents of foo.
1132 ---------- Buffer: foo ----------
1136 (with-output-to-temp-buffer "foo"
1138 (print standard-output))
1139 @result{} #<buffer foo>
1141 ---------- Buffer: foo ----------
1147 ---------- Buffer: foo ----------
1152 @defopt temp-buffer-show-function
1153 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
1154 calls it as a function to do the job of displaying a help buffer. The
1155 function gets one argument, which is the buffer it should display.
1157 It is a good idea for this function to run @code{temp-buffer-show-hook}
1158 just as @code{with-output-to-temp-buffer} normally would, inside of
1159 @code{save-selected-window} and with the chosen window and buffer
1163 @defvar temp-buffer-setup-hook
1164 This normal hook is run by @code{with-output-to-temp-buffer} before
1165 evaluating @var{body}. When the hook runs, the temporary buffer is
1166 current. This hook is normally set up with a function to put the
1167 buffer in Help mode.
1170 @defvar temp-buffer-show-hook
1171 This normal hook is run by @code{with-output-to-temp-buffer} after
1172 displaying the temporary buffer. When the hook runs, the temporary buffer
1173 is current, and the window it was displayed in is selected.
1176 @defmac with-temp-buffer-window buffer-or-name action quit-function body@dots{}
1177 This macro is similar to @code{with-output-to-temp-buffer}. Like that
1178 construct, it executes @var{body} while arranging to insert any output
1179 it prints into the buffer named @var{buffer-or-name} and displays that
1180 buffer in some window. Unlike @code{with-output-to-temp-buffer},
1181 however, it does not automatically switch that buffer to Help mode.
1183 Like @code{with-output-to-temp-buffer} it neither makes the buffer
1184 specified by @var{buffer-or-name} current when executing @var{body}.
1185 @findex with-current-buffer-window
1186 The otherwise identical macro @code{with-current-buffer-window} can be
1187 used to execute @var{body} with that buffer current.
1189 The argument @var{buffer-or-name} specifies the temporary buffer. It
1190 can be either a buffer, which must already exist, or a string, in which
1191 case a buffer of that name is created, if necessary. The buffer is
1192 marked as unmodified and read-only when @code{with-temp-buffer-window}
1195 This macro does not call @code{temp-buffer-show-function}. Rather, it
1196 passes the @var{action} argument to @code{display-buffer} in order to
1199 The value of the last form in @var{body} is returned, unless the
1200 argument @var{quit-function} is specified. In that case, it is called
1201 with two arguments: the window showing the buffer and the result of
1202 @var{body}. The final return value is then whatever
1203 @var{quit-function} returns.
1205 @vindex temp-buffer-window-setup-hook
1206 @vindex temp-buffer-window-show-hook
1207 This macro uses the normal hooks @code{temp-buffer-window-setup-hook}
1208 and @code{temp-buffer-window-show-hook} in place of the analogous hooks
1209 run by @code{with-output-to-temp-buffer}.
1212 @defun momentary-string-display string position &optional char message
1213 This function momentarily displays @var{string} in the current buffer at
1214 @var{position}. It has no effect on the undo list or on the buffer's
1215 modification status.
1217 The momentary display remains until the next input event. If the next
1218 input event is @var{char}, @code{momentary-string-display} ignores it
1219 and returns. Otherwise, that event remains buffered for subsequent use
1220 as input. Thus, typing @var{char} will simply remove the string from
1221 the display, while typing (say) @kbd{C-f} will remove the string from
1222 the display and later (presumably) move point forward. The argument
1223 @var{char} is a space by default.
1225 The return value of @code{momentary-string-display} is not meaningful.
1227 If the string @var{string} does not contain control characters, you can
1228 do the same job in a more general way by creating (and then subsequently
1229 deleting) an overlay with a @code{before-string} property.
1230 @xref{Overlay Properties}.
1232 If @var{message} is non-@code{nil}, it is displayed in the echo area
1233 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1234 default message says to type @var{char} to continue.
1236 In this example, point is initially located at the beginning of the
1241 ---------- Buffer: foo ----------
1242 This is the contents of foo.
1243 @point{}Second line.
1244 ---------- Buffer: foo ----------
1248 (momentary-string-display
1249 "**** Important Message! ****"
1251 "Type RET when done reading")
1256 ---------- Buffer: foo ----------
1257 This is the contents of foo.
1258 **** Important Message! ****Second line.
1259 ---------- Buffer: foo ----------
1261 ---------- Echo Area ----------
1262 Type RET when done reading
1263 ---------- Echo Area ----------
1271 @c FIXME: mention intervals in this section?
1273 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1274 the screen, for the sake of presentation features. An overlay is an
1275 object that belongs to a particular buffer, and has a specified
1276 beginning and end. It also has properties that you can examine and set;
1277 these affect the display of the text within the overlay.
1279 @cindex scalability of overlays
1280 The visual effect of an overlay is the same as of the corresponding
1281 text property (@pxref{Text Properties}). However, due to a different
1282 implementation, overlays generally don't scale well (many operations
1283 take a time that is proportional to the number of overlays in the
1284 buffer). If you need to affect the visual appearance of many portions
1285 in the buffer, we recommend using text properties.
1287 An overlay uses markers to record its beginning and end; thus,
1288 editing the text of the buffer adjusts the beginning and end of each
1289 overlay so that it stays with the text. When you create the overlay,
1290 you can specify whether text inserted at the beginning should be
1291 inside the overlay or outside, and likewise for the end of the overlay.
1294 * Managing Overlays:: Creating and moving overlays.
1295 * Overlay Properties:: How to read and set properties.
1296 What properties do to the screen display.
1297 * Finding Overlays:: Searching for overlays.
1300 @node Managing Overlays
1301 @subsection Managing Overlays
1303 This section describes the functions to create, delete and move
1304 overlays, and to examine their contents. Overlay changes are not
1305 recorded in the buffer's undo list, since the overlays are not
1306 part of the buffer's contents.
1308 @defun overlayp object
1309 This function returns @code{t} if @var{object} is an overlay.
1312 @defun make-overlay start end &optional buffer front-advance rear-advance
1313 This function creates and returns an overlay that belongs to
1314 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1315 and @var{end} must specify buffer positions; they may be integers or
1316 markers. If @var{buffer} is omitted, the overlay is created in the
1319 The arguments @var{front-advance} and @var{rear-advance} specify the
1320 marker insertion type for the start of the overlay and for the end of
1321 the overlay, respectively. @xref{Marker Insertion Types}. If they
1322 are both @code{nil}, the default, then the overlay extends to include
1323 any text inserted at the beginning, but not text inserted at the end.
1324 If @var{front-advance} is non-@code{nil}, text inserted at the
1325 beginning of the overlay is excluded from the overlay. If
1326 @var{rear-advance} is non-@code{nil}, text inserted at the end of the
1327 overlay is included in the overlay.
1330 @defun overlay-start overlay
1331 This function returns the position at which @var{overlay} starts,
1335 @defun overlay-end overlay
1336 This function returns the position at which @var{overlay} ends,
1340 @defun overlay-buffer overlay
1341 This function returns the buffer that @var{overlay} belongs to. It
1342 returns @code{nil} if @var{overlay} has been deleted.
1345 @defun delete-overlay overlay
1346 This function deletes @var{overlay}. The overlay continues to exist as
1347 a Lisp object, and its property list is unchanged, but it ceases to be
1348 attached to the buffer it belonged to, and ceases to have any effect on
1351 A deleted overlay is not permanently disconnected. You can give it a
1352 position in a buffer again by calling @code{move-overlay}.
1355 @defun move-overlay overlay start end &optional buffer
1356 This function moves @var{overlay} to @var{buffer}, and places its bounds
1357 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1358 must specify buffer positions; they may be integers or markers.
1360 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1361 was already associated with; if @var{overlay} was deleted, it goes into
1364 The return value is @var{overlay}.
1366 This is the only valid way to change the endpoints of an overlay. Do
1367 not try modifying the markers in the overlay by hand, as that fails to
1368 update other vital data structures and can cause some overlays to be
1372 @defun remove-overlays &optional start end name value
1373 This function removes all the overlays between @var{start} and
1374 @var{end} whose property @var{name} has the value @var{value}. It can
1375 move the endpoints of the overlays in the region, or split them.
1377 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1378 the specified region. If @var{start} and/or @var{end} are omitted or
1379 @code{nil}, that means the beginning and end of the buffer respectively.
1380 Therefore, @code{(remove-overlays)} removes all the overlays in the
1384 @defun copy-overlay overlay
1385 This function returns a copy of @var{overlay}. The copy has the same
1386 endpoints and properties as @var{overlay}. However, the marker
1387 insertion type for the start of the overlay and for the end of the
1388 overlay are set to their default values (@pxref{Marker Insertion
1392 Here are some examples:
1395 ;; @r{Create an overlay.}
1396 (setq foo (make-overlay 1 10))
1397 @result{} #<overlay from 1 to 10 in display.texi>
1402 (overlay-buffer foo)
1403 @result{} #<buffer display.texi>
1404 ;; @r{Give it a property we can check later.}
1405 (overlay-put foo 'happy t)
1407 ;; @r{Verify the property is present.}
1408 (overlay-get foo 'happy)
1410 ;; @r{Move the overlay.}
1411 (move-overlay foo 5 20)
1412 @result{} #<overlay from 5 to 20 in display.texi>
1417 ;; @r{Delete the overlay.}
1418 (delete-overlay foo)
1420 ;; @r{Verify it is deleted.}
1422 @result{} #<overlay in no buffer>
1423 ;; @r{A deleted overlay has no position.}
1428 (overlay-buffer foo)
1430 ;; @r{Undelete the overlay.}
1431 (move-overlay foo 1 20)
1432 @result{} #<overlay from 1 to 20 in display.texi>
1433 ;; @r{Verify the results.}
1438 (overlay-buffer foo)
1439 @result{} #<buffer display.texi>
1440 ;; @r{Moving and deleting the overlay does not change its properties.}
1441 (overlay-get foo 'happy)
1445 Emacs stores the overlays of each buffer in two lists, divided
1446 around an arbitrary ``center position''. One list extends backwards
1447 through the buffer from that center position, and the other extends
1448 forwards from that center position. The center position can be anywhere
1451 @defun overlay-recenter pos
1452 This function recenters the overlays of the current buffer around
1453 position @var{pos}. That makes overlay lookup faster for positions
1454 near @var{pos}, but slower for positions far away from @var{pos}.
1457 A loop that scans the buffer forwards, creating overlays, can run
1458 faster if you do @code{(overlay-recenter (point-max))} first.
1460 @node Overlay Properties
1461 @subsection Overlay Properties
1463 Overlay properties are like text properties in that the properties that
1464 alter how a character is displayed can come from either source. But in
1465 most respects they are different. @xref{Text Properties}, for comparison.
1467 Text properties are considered a part of the text; overlays and
1468 their properties are specifically considered not to be part of the
1469 text. Thus, copying text between various buffers and strings
1470 preserves text properties, but does not try to preserve overlays.
1471 Changing a buffer's text properties marks the buffer as modified,
1472 while moving an overlay or changing its properties does not. Unlike
1473 text property changes, overlay property changes are not recorded in
1474 the buffer's undo list.
1476 Since more than one overlay can specify a property value for the
1477 same character, Emacs lets you specify a priority value of each
1478 overlay. You should not make assumptions about which overlay will
1479 prevail when there is a conflict and they have the same priority.
1481 These functions read and set the properties of an overlay:
1483 @defun overlay-get overlay prop
1484 This function returns the value of property @var{prop} recorded in
1485 @var{overlay}, if any. If @var{overlay} does not record any value for
1486 that property, but it does have a @code{category} property which is a
1487 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1491 @defun overlay-put overlay prop value
1492 This function sets the value of property @var{prop} recorded in
1493 @var{overlay} to @var{value}. It returns @var{value}.
1496 @defun overlay-properties overlay
1497 This returns a copy of the property list of @var{overlay}.
1500 See also the function @code{get-char-property} which checks both
1501 overlay properties and text properties for a given character.
1502 @xref{Examining Properties}.
1504 Many overlay properties have special meanings; here is a table
1509 @kindex priority @r{(overlay property)}
1510 This property's value (which should be a non-negative integer)
1511 determines the priority of the overlay. No priority, or @code{nil},
1514 The priority matters when two or more overlays cover the same
1515 character and both specify the same property; the one whose
1516 @code{priority} value is larger overrides the other. For the
1517 @code{face} property, the higher priority overlay's value does not
1518 completely override the other value; instead, its face attributes
1519 override the face attributes of the lower priority @code{face}
1522 Currently, all overlays take priority over text properties. Please
1523 avoid using negative priority values, as we have not yet decided just
1524 what they should mean.
1527 @kindex window @r{(overlay property)}
1528 If the @code{window} property is non-@code{nil}, then the overlay
1529 applies only on that window.
1532 @kindex category @r{(overlay property)}
1533 If an overlay has a @code{category} property, we call it the
1534 @dfn{category} of the overlay. It should be a symbol. The properties
1535 of the symbol serve as defaults for the properties of the overlay.
1538 @kindex face @r{(overlay property)}
1539 This property controls the appearance of the text (@pxref{Faces}).
1540 The value of the property can be the following:
1544 A face name (a symbol or string).
1547 An anonymous face: a property list of the form @code{(@var{keyword}
1548 @var{value} @dots{})}, where each @var{keyword} is a face attribute
1549 name and @var{value} is a value for that attribute.
1552 A list of faces. Each list element should be either a face name or an
1553 anonymous face. This specifies a face which is an aggregate of the
1554 attributes of each of the listed faces. Faces occurring earlier in
1555 the list have higher priority.
1558 A cons cell of the form @code{(foreground-color . @var{color-name})}
1559 or @code{(background-color . @var{color-name})}. This specifies the
1560 foreground or background color, similar to @code{(:foreground
1561 @var{color-name})} or @code{(:background @var{color-name})}. This
1562 form is supported for backward compatibility only, and should be
1567 @kindex mouse-face @r{(overlay property)}
1568 This property is used instead of @code{face} when the mouse is within
1569 the range of the overlay. However, Emacs ignores all face attributes
1570 from this property that alter the text size (e.g., @code{:height},
1571 @code{:weight}, and @code{:slant}). Those attributes are always the
1572 same as in the unhighlighted text.
1575 @kindex display @r{(overlay property)}
1576 This property activates various features that change the
1577 way text is displayed. For example, it can make text appear taller
1578 or shorter, higher or lower, wider or narrower, or replaced with an image.
1579 @xref{Display Property}.
1582 @kindex help-echo @r{(overlay property)}
1583 If an overlay has a @code{help-echo} property, then when you move the
1584 mouse onto the text in the overlay, Emacs displays a help string in the
1585 echo area, or in the tooltip window. For details see @ref{Text
1589 @kindex field @r{(overlay property)}
1590 @c Copied from Special Properties.
1591 Consecutive characters with the same @code{field} property constitute a
1592 @emph{field}. Some motion functions including @code{forward-word} and
1593 @code{beginning-of-line} stop moving at a field boundary.
1596 @item modification-hooks
1597 @kindex modification-hooks @r{(overlay property)}
1598 This property's value is a list of functions to be called if any
1599 character within the overlay is changed or if text is inserted strictly
1602 The hook functions are called both before and after each change.
1603 If the functions save the information they receive, and compare notes
1604 between calls, they can determine exactly what change has been made
1607 When called before a change, each function receives four arguments: the
1608 overlay, @code{nil}, and the beginning and end of the text range to be
1611 When called after a change, each function receives five arguments: the
1612 overlay, @code{t}, the beginning and end of the text range just
1613 modified, and the length of the pre-change text replaced by that range.
1614 (For an insertion, the pre-change length is zero; for a deletion, that
1615 length is the number of characters deleted, and the post-change
1616 beginning and end are equal.)
1618 If these functions modify the buffer, they should bind
1619 @code{inhibit-modification-hooks} to @code{t} around doing so, to
1620 avoid confusing the internal mechanism that calls these hooks.
1622 Text properties also support the @code{modification-hooks} property,
1623 but the details are somewhat different (@pxref{Special Properties}).
1625 @item insert-in-front-hooks
1626 @kindex insert-in-front-hooks @r{(overlay property)}
1627 This property's value is a list of functions to be called before and
1628 after inserting text right at the beginning of the overlay. The calling
1629 conventions are the same as for the @code{modification-hooks} functions.
1631 @item insert-behind-hooks
1632 @kindex insert-behind-hooks @r{(overlay property)}
1633 This property's value is a list of functions to be called before and
1634 after inserting text right at the end of the overlay. The calling
1635 conventions are the same as for the @code{modification-hooks} functions.
1638 @kindex invisible @r{(overlay property)}
1639 The @code{invisible} property can make the text in the overlay
1640 invisible, which means that it does not appear on the screen.
1641 @xref{Invisible Text}, for details.
1644 @kindex intangible @r{(overlay property)}
1645 The @code{intangible} property on an overlay works just like the
1646 @code{intangible} text property. @xref{Special Properties}, for details.
1648 @item isearch-open-invisible
1649 This property tells incremental search how to make an invisible overlay
1650 visible, permanently, if the final match overlaps it. @xref{Invisible
1653 @item isearch-open-invisible-temporary
1654 This property tells incremental search how to make an invisible overlay
1655 visible, temporarily, during the search. @xref{Invisible Text}.
1658 @kindex before-string @r{(overlay property)}
1659 This property's value is a string to add to the display at the beginning
1660 of the overlay. The string does not appear in the buffer in any
1661 sense---only on the screen.
1664 @kindex after-string @r{(overlay property)}
1665 This property's value is a string to add to the display at the end of
1666 the overlay. The string does not appear in the buffer in any
1667 sense---only on the screen.
1670 This property specifies a display spec to prepend to each
1671 non-continuation line at display-time. @xref{Truncation}.
1674 This property specifies a display spec to prepend to each continuation
1675 line at display-time. @xref{Truncation}.
1678 @kindex evaporate @r{(overlay property)}
1679 If this property is non-@code{nil}, the overlay is deleted automatically
1680 if it becomes empty (i.e., if its length becomes zero). If you give
1681 an empty overlay a non-@code{nil} @code{evaporate} property, that deletes
1685 @cindex keymap of character (and overlays)
1686 @kindex keymap @r{(overlay property)}
1687 If this property is non-@code{nil}, it specifies a keymap for a portion of the
1688 text. This keymap is used when the character after point is within the
1689 overlay, and takes precedence over most other keymaps. @xref{Active Keymaps}.
1692 @kindex local-map @r{(overlay property)}
1693 The @code{local-map} property is similar to @code{keymap} but replaces the
1694 buffer's local map rather than augmenting existing keymaps. This also means it
1695 has lower precedence than minor mode keymaps.
1698 The @code{keymap} and @code{local-map} properties do not affect a
1699 string displayed by the @code{before-string}, @code{after-string}, or
1700 @code{display} properties. This is only relevant for mouse clicks and
1701 other mouse events that fall on the string, since point is never on
1702 the string. To bind special mouse events for the string, assign it a
1703 @code{keymap} or @code{local-map} text property. @xref{Special
1706 @node Finding Overlays
1707 @subsection Searching for Overlays
1709 @defun overlays-at pos
1710 This function returns a list of all the overlays that cover the
1711 character at position @var{pos} in the current buffer. The list is in
1712 no particular order. An overlay contains position @var{pos} if it
1713 begins at or before @var{pos}, and ends after @var{pos}.
1715 To illustrate usage, here is a Lisp function that returns a list of the
1716 overlays that specify property @var{prop} for the character at point:
1719 (defun find-overlays-specifying (prop)
1720 (let ((overlays (overlays-at (point)))
1723 (let ((overlay (car overlays)))
1724 (if (overlay-get overlay prop)
1725 (setq found (cons overlay found))))
1726 (setq overlays (cdr overlays)))
1731 @defun overlays-in beg end
1732 This function returns a list of the overlays that overlap the region
1733 @var{beg} through @var{end}. ``Overlap'' means that at least one
1734 character is contained within the overlay and also contained within the
1735 specified region; however, empty overlays are included in the result if
1736 they are located at @var{beg}, strictly between @var{beg} and @var{end},
1737 or at @var{end} when @var{end} denotes the position at the end of the
1741 @defun next-overlay-change pos
1742 This function returns the buffer position of the next beginning or end
1743 of an overlay, after @var{pos}. If there is none, it returns
1747 @defun previous-overlay-change pos
1748 This function returns the buffer position of the previous beginning or
1749 end of an overlay, before @var{pos}. If there is none, it returns
1753 As an example, here's a simplified (and inefficient) version of the
1754 primitive function @code{next-single-char-property-change}
1755 (@pxref{Property Search}). It searches forward from position
1756 @var{pos} for the next position where the value of a given property
1757 @code{prop}, as obtained from either overlays or text properties,
1761 (defun next-single-char-property-change (position prop)
1763 (goto-char position)
1764 (let ((propval (get-char-property (point) prop)))
1765 (while (and (not (eobp))
1766 (eq (get-char-property (point) prop) propval))
1767 (goto-char (min (next-overlay-change (point))
1768 (next-single-property-change (point) prop)))))
1772 @node Size of Displayed Text
1773 @section Size of Displayed Text
1775 Since not all characters have the same width, these functions let you
1776 check the width of a character. @xref{Primitive Indent}, and
1777 @ref{Screen Lines}, for related functions.
1779 @defun char-width char
1780 This function returns the width in columns of the character
1781 @var{char}, if it were displayed in the current buffer (i.e., taking
1782 into account the buffer's display table, if any; @pxref{Display
1783 Tables}). The width of a tab character is usually @code{tab-width}
1784 (@pxref{Usual Display}).
1787 @defun string-width string
1788 This function returns the width in columns of the string @var{string},
1789 if it were displayed in the current buffer and the selected window.
1792 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1793 This function returns the part of @var{string} that fits within
1794 @var{width} columns, as a new string.
1796 If @var{string} does not reach @var{width}, then the result ends where
1797 @var{string} ends. If one multi-column character in @var{string}
1798 extends across the column @var{width}, that character is not included in
1799 the result. Thus, the result can fall short of @var{width} but cannot
1802 The optional argument @var{start-column} specifies the starting column.
1803 If this is non-@code{nil}, then the first @var{start-column} columns of
1804 the string are omitted from the value. If one multi-column character in
1805 @var{string} extends across the column @var{start-column}, that
1806 character is not included.
1808 The optional argument @var{padding}, if non-@code{nil}, is a padding
1809 character added at the beginning and end of the result string, to extend
1810 it to exactly @var{width} columns. The padding character is used at the
1811 end of the result if it falls short of @var{width}. It is also used at
1812 the beginning of the result if one multi-column character in
1813 @var{string} extends across the column @var{start-column}.
1815 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1816 replace the end of @var{string} (including any padding) if it extends
1817 beyond @var{width}, unless the display width of @var{string} is equal
1818 to or less than the display width of @var{ellipsis}. If
1819 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1823 (truncate-string-to-width "\tab\t" 12 4)
1825 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1830 The following function returns the size in pixels of text as if it were
1831 displayed in a given window. This function is used by
1832 @code{fit-window-to-buffer} (@pxref{Resizing Windows}) and
1833 @code{fit-frame-to-buffer} (@pxref{Size and Position}) to make a window
1834 exactly as large as the text it contains.
1836 @defun window-text-pixel-size &optional window from to x-limit y-limit mode-and-header-line
1837 This function returns the size of the text of @var{window}'s buffer in
1838 pixels. @var{window} must be a live window and defaults to the selected
1839 one. The return value is a cons of the maximum pixel-width of any text
1840 line and the maximum pixel-height of all text lines.
1842 The optional argument @var{from}, if non-@code{nil}, specifies the first
1843 text position to consider and defaults to the minimum accessible
1844 position of the buffer. If @var{from} is @code{t}, it uses the minimum
1845 accessible position that is not a newline character. The optional
1846 argument @var{to}, if non-@code{nil}, specifies the last text position
1847 to consider and defaults to the maximum accessible position of the
1848 buffer. If @var{to} is @code{t}, it uses the maximum accessible
1849 position that is not a newline character.
1851 The optional argument @var{x-limit}, if non-@code{nil}, specifies the
1852 maximum pixel-width that can be returned. @var{x-limit} @code{nil} or
1853 omitted, means to use the pixel-width of @var{window}'s body
1854 (@pxref{Window Sizes}); this is useful when the caller does not intend
1855 to change the width of @var{window}. Otherwise, the caller should
1856 specify here the maximum width @var{window}'s body may assume. Text
1857 whose x-coordinate is beyond @var{x-limit} is ignored. Since
1858 calculating the width of long lines can take some time, it's always a
1859 good idea to make this argument as small as needed; in particular, if
1860 the buffer might contain long lines that will be truncated anyway.
1862 The optional argument @var{y-limit}, if non-@code{nil}, specifies the
1863 maximum pixel-height that can be returned. Text lines whose
1864 y-coordinate is beyond @var{y-limit} are ignored. Since calculating the
1865 pixel-height of a large buffer can take some time, it makes sense to
1866 specify this argument; in particular, if the caller does not know the
1869 The optional argument @var{mode-and-header-line} @code{nil} or omitted
1870 means to not include the height of the mode- or header-line of
1871 @var{window} in the return value. If it is either the symbol
1872 @code{mode-line} or @code{header-line}, include only the height of that
1873 line, if present, in the return value. If it is @code{t}, include the
1874 height of both, if present, in the return value.
1879 @section Line Height
1881 @cindex height of a line
1883 The total height of each display line consists of the height of the
1884 contents of the line, plus optional additional vertical line spacing
1885 above or below the display line.
1887 The height of the line contents is the maximum height of any
1888 character or image on that display line, including the final newline
1889 if there is one. (A display line that is continued doesn't include a
1890 final newline.) That is the default line height, if you do nothing to
1891 specify a greater height. (In the most common case, this equals the
1892 height of the default frame font.)
1894 There are several ways to explicitly specify a larger line height,
1895 either by specifying an absolute height for the display line, or by
1896 specifying vertical space. However, no matter what you specify, the
1897 actual line height can never be less than the default.
1899 @kindex line-height @r{(text property)}
1900 A newline can have a @code{line-height} text or overlay property
1901 that controls the total height of the display line ending in that
1904 If the property value is @code{t}, the newline character has no
1905 effect on the displayed height of the line---the visible contents
1906 alone determine the height. This is useful for tiling small images
1907 (or image slices) without adding blank areas between the images.
1909 If the property value is a list of the form @code{(@var{height}
1910 @var{total})}, that adds extra space @emph{below} the display line.
1911 First Emacs uses @var{height} as a height spec to control extra space
1912 @emph{above} the line; then it adds enough space @emph{below} the line
1913 to bring the total line height up to @var{total}. In this case, the
1914 other ways to specify the line spacing are ignored.
1917 Any other kind of property value is a height spec, which translates
1918 into a number---the specified line height. There are several ways to
1919 write a height spec; here's how each of them translates into a number:
1923 If the height spec is a positive integer, the height value is that integer.
1925 If the height spec is a float, @var{float}, the numeric height value
1926 is @var{float} times the frame's default line height.
1927 @item (@var{face} . @var{ratio})
1928 If the height spec is a cons of the format shown, the numeric height
1929 is @var{ratio} times the height of face @var{face}. @var{ratio} can
1930 be any type of number, or @code{nil} which means a ratio of 1.
1931 If @var{face} is @code{t}, it refers to the current face.
1932 @item (nil . @var{ratio})
1933 If the height spec is a cons of the format shown, the numeric height
1934 is @var{ratio} times the height of the contents of the line.
1937 Thus, any valid height spec determines the height in pixels, one way
1938 or another. If the line contents' height is less than that, Emacs
1939 adds extra vertical space above the line to achieve the specified
1942 If you don't specify the @code{line-height} property, the line's
1943 height consists of the contents' height plus the line spacing.
1944 There are several ways to specify the line spacing for different
1945 parts of Emacs text.
1947 On graphical terminals, you can specify the line spacing for all
1948 lines in a frame, using the @code{line-spacing} frame parameter
1949 (@pxref{Layout Parameters}). However, if the default value of
1950 @code{line-spacing} is non-@code{nil}, it overrides the
1951 frame's @code{line-spacing} parameter. An integer specifies the
1952 number of pixels put below lines. A floating-point number specifies
1953 the spacing relative to the frame's default line height.
1955 @vindex line-spacing
1956 You can specify the line spacing for all lines in a buffer via the
1957 buffer-local @code{line-spacing} variable. An integer specifies
1958 the number of pixels put below lines. A floating-point number
1959 specifies the spacing relative to the default frame line height. This
1960 overrides line spacings specified for the frame.
1962 @kindex line-spacing @r{(text property)}
1963 Finally, a newline can have a @code{line-spacing} text or overlay
1964 property that overrides the default frame line spacing and the buffer
1965 local @code{line-spacing} variable, for the display line ending in
1968 One way or another, these mechanisms specify a Lisp value for the
1969 spacing of each line. The value is a height spec, and it translates
1970 into a Lisp value as described above. However, in this case the
1971 numeric height value specifies the line spacing, rather than the line
1974 On text terminals, the line spacing cannot be altered.
1980 A @dfn{face} is a collection of graphical attributes for displaying
1981 text: font, foreground color, background color, optional underlining,
1982 etc. Faces control how Emacs displays text in buffers, as well as
1983 other parts of the frame such as the mode line.
1985 @cindex anonymous face
1986 One way to represent a face is as a property list of attributes,
1987 like @code{(:foreground "red" :weight bold)}. Such a list is called
1988 an @dfn{anonymous face}. For example, you can assign an anonymous
1989 face as the value of the @code{face} text property, and Emacs will
1990 display the underlying text with the specified attributes.
1991 @xref{Special Properties}.
1994 More commonly, a face is referred to via a @dfn{face name}: a Lisp
1995 symbol associated with a set of face attributes@footnote{For backward
1996 compatibility, you can also use a string to specify a face name; that
1997 is equivalent to a Lisp symbol with the same name.}. Named faces are
1998 defined using the @code{defface} macro (@pxref{Defining Faces}).
1999 Emacs comes with several standard named faces (@pxref{Basic Faces}).
2001 Many parts of Emacs required named faces, and do not accept
2002 anonymous faces. These include the functions documented in
2003 @ref{Attribute Functions}, and the variable @code{font-lock-keywords}
2004 (@pxref{Search-based Fontification}). Unless otherwise stated, we
2005 will use the term @dfn{face} to refer only to named faces.
2008 This function returns a non-@code{nil} value if @var{object} is a
2009 named face: a Lisp symbol or string which serves as a face name.
2010 Otherwise, it returns @code{nil}.
2014 * Face Attributes:: What is in a face?
2015 * Defining Faces:: How to define a face.
2016 * Attribute Functions:: Functions to examine and set face attributes.
2017 * Displaying Faces:: How Emacs combines the faces specified for a character.
2018 * Face Remapping:: Remapping faces to alternative definitions.
2019 * Face Functions:: How to define and examine faces.
2020 * Auto Faces:: Hook for automatic face assignment.
2021 * Basic Faces:: Faces that are defined by default.
2022 * Font Selection:: Finding the best available font for a face.
2023 * Font Lookup:: Looking up the names of available fonts
2024 and information about them.
2025 * Fontsets:: A fontset is a collection of fonts
2026 that handle a range of character sets.
2027 * Low-Level Font:: Lisp representation for character display fonts.
2030 @node Face Attributes
2031 @subsection Face Attributes
2032 @cindex face attributes
2034 @dfn{Face attributes} determine the visual appearance of a face.
2035 The following table lists all the face attributes, their possible
2036 values, and their effects.
2038 Apart from the values given below, each face attribute can have the
2039 value @code{unspecified}. This special value means that the face
2040 doesn't specify that attribute directly. An @code{unspecified}
2041 attribute tells Emacs to refer instead to a parent face (see the
2042 description @code{:inherit} attribute below); or, failing that, to an
2043 underlying face (@pxref{Displaying Faces}). The @code{default} face
2044 must specify all attributes.
2046 Some of these attributes are meaningful only on certain kinds of
2047 displays. If your display cannot handle a certain attribute, the
2048 attribute is ignored.
2052 Font family or fontset (a string). @xref{Fonts,,, emacs, The GNU
2053 Emacs Manual}, for more information about font families. The function
2054 @code{font-family-list} (see below) returns a list of available family
2055 names. @xref{Fontsets}, for information about fontsets.
2058 The name of the @dfn{font foundry} for the font family specified by
2059 the @code{:family} attribute (a string). @xref{Fonts,,, emacs, The
2063 Relative character width. This should be one of the symbols
2064 @code{ultra-condensed}, @code{extra-condensed}, @code{condensed},
2065 @code{semi-condensed}, @code{normal}, @code{semi-expanded},
2066 @code{expanded}, @code{extra-expanded}, or @code{ultra-expanded}.
2069 The height of the font. In the simplest case, this is an integer in
2070 units of 1/10 point.
2072 The value can also be floating point or a function, which
2073 specifies the height relative to an @dfn{underlying face}
2074 (@pxref{Displaying Faces}). A floating-point value
2075 specifies the amount by which to scale the height of the
2076 underlying face. A function value is called
2077 with one argument, the height of the underlying face, and returns the
2078 height of the new face. If the function is passed an integer
2079 argument, it must return an integer.
2081 The height of the default face must be specified using an integer;
2082 floating point and function values are not allowed.
2085 Font weight---one of the symbols (from densest to faintest)
2086 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
2087 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or
2088 @code{ultra-light}. On text terminals which support
2089 variable-brightness text, any weight greater than normal is displayed
2090 as extra bright, and any weight less than normal is displayed as
2095 Font slant---one of the symbols @code{italic}, @code{oblique},
2096 @code{normal}, @code{reverse-italic}, or @code{reverse-oblique}. On
2097 text terminals that support variable-brightness text, slanted text is
2098 displayed as half-bright.
2101 Foreground color, a string. The value can be a system-defined color
2102 name, or a hexadecimal color specification. @xref{Color Names}. On
2103 black-and-white displays, certain shades of gray are implemented by
2106 @item :distant-foreground
2107 Alternative foreground color, a string. This is like @code{:foreground}
2108 but the color is only used as a foreground when the background color is
2109 near to the foreground that would have been used. This is useful for
2110 example when marking text (i.e. the region face). If the text has a foreground
2111 that is visible with the region face, that foreground is used.
2112 If the foreground is near the region face background,
2113 @code{:distant-foreground} is used instead so the text is readable.
2116 Background color, a string. The value can be a system-defined color
2117 name, or a hexadecimal color specification. @xref{Color Names}.
2119 @cindex underlined text
2121 Whether or not characters should be underlined, and in what
2122 way. The possible values of the @code{:underline} attribute are:
2129 Underline with the foreground color of the face.
2132 Underline in color @var{color}, a string specifying a color.
2134 @item @code{(:color @var{color} :style @var{style})}
2135 @var{color} is either a string, or the symbol @code{foreground-color},
2136 meaning the foreground color of the face. Omitting the attribute
2137 @code{:color} means to use the foreground color of the face.
2138 @var{style} should be a symbol @code{line} or @code{wave}, meaning to
2139 use a straight or wavy line. Omitting the attribute @code{:style}
2140 means to use a straight line.
2143 @cindex overlined text
2145 Whether or not characters should be overlined, and in what color.
2146 If the value is @code{t}, overlining uses the foreground color of the
2147 face. If the value is a string, overlining uses that color. The
2148 value @code{nil} means do not overline.
2150 @cindex strike-through text
2151 @item :strike-through
2152 Whether or not characters should be strike-through, and in what
2153 color. The value is used like that of @code{:overline}.
2158 Whether or not a box should be drawn around characters, its color, the
2159 width of the box lines, and 3D appearance. Here are the possible
2160 values of the @code{:box} attribute, and what they mean:
2167 Draw a box with lines of width 1, in the foreground color.
2170 Draw a box with lines of width 1, in color @var{color}.
2172 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2173 This way you can explicitly specify all aspects of the box. The value
2174 @var{width} specifies the width of the lines to draw; it defaults to
2175 1. A negative width @var{-n} means to draw a line of width @var{n}
2176 that occupies the space of the underlying text, thus avoiding any
2177 increase in the character height or width.
2179 The value @var{color} specifies the color to draw with. The default is
2180 the foreground color of the face for simple boxes, and the background
2181 color of the face for 3D boxes.
2183 The value @var{style} specifies whether to draw a 3D box. If it is
2184 @code{released-button}, the box looks like a 3D button that is not being
2185 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2186 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2190 @item :inverse-video
2191 Whether or not characters should be displayed in inverse video. The
2192 value should be @code{t} (yes) or @code{nil} (no).
2195 The background stipple, a bitmap.
2197 The value can be a string; that should be the name of a file containing
2198 external-format X bitmap data. The file is found in the directories
2199 listed in the variable @code{x-bitmap-file-path}.
2201 Alternatively, the value can specify the bitmap directly, with a list
2202 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2203 @var{width} and @var{height} specify the size in pixels, and
2204 @var{data} is a string containing the raw bits of the bitmap, row by
2205 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2206 in the string (which should be a unibyte string for best results).
2207 This means that each row always occupies at least one whole byte.
2209 If the value is @code{nil}, that means use no stipple pattern.
2211 Normally you do not need to set the stipple attribute, because it is
2212 used automatically to handle certain shades of gray.
2215 The font used to display the face. Its value should be a font object.
2216 @xref{Low-Level Font}, for information about font objects, font specs,
2219 When specifying this attribute using @code{set-face-attribute}
2220 (@pxref{Attribute Functions}), you may also supply a font spec, a font
2221 entity, or a string. Emacs converts such values to an appropriate
2222 font object, and stores that font object as the actual attribute
2223 value. If you specify a string, the contents of the string should be
2224 a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the
2225 font name is an XLFD containing wildcards, Emacs chooses the first
2226 font matching those wildcards. Specifying this attribute also changes
2227 the values of the @code{:family}, @code{:foundry}, @code{:width},
2228 @code{:height}, @code{:weight}, and @code{:slant} attributes.
2230 @cindex inheritance, for faces
2232 The name of a face from which to inherit attributes, or a list of face
2233 names. Attributes from inherited faces are merged into the face like
2234 an underlying face would be, with higher priority than underlying
2235 faces (@pxref{Displaying Faces}). If a list of faces is used,
2236 attributes from faces earlier in the list override those from later
2240 @defun font-family-list &optional frame
2241 This function returns a list of available font family names. The
2242 optional argument @var{frame} specifies the frame on which the text is
2243 to be displayed; if it is @code{nil}, the selected frame is used.
2246 @defopt underline-minimum-offset
2247 This variable specifies the minimum distance between the baseline and
2248 the underline, in pixels, when displaying underlined text.
2251 @defopt x-bitmap-file-path
2252 This variable specifies a list of directories for searching
2253 for bitmap files, for the @code{:stipple} attribute.
2256 @defun bitmap-spec-p object
2257 This returns @code{t} if @var{object} is a valid bitmap specification,
2258 suitable for use with @code{:stipple} (see above). It returns
2259 @code{nil} otherwise.
2262 @node Defining Faces
2263 @subsection Defining Faces
2266 The usual way to define a face is through the @code{defface} macro.
2267 This macro associates a face name (a symbol) with a default @dfn{face
2268 spec}. A face spec is a construct which specifies what attributes a
2269 face should have on any given terminal; for example, a face spec might
2270 specify one foreground color on high-color terminals, and a different
2271 foreground color on low-color terminals.
2273 People are sometimes tempted to create a variable whose value is a
2274 face name. In the vast majority of cases, this is not necessary; the
2275 usual procedure is to define a face with @code{defface}, and then use
2278 @defmac defface face spec doc [keyword value]@dots{}
2279 This macro declares @var{face} as a named face whose default face spec
2280 is given by @var{spec}. You should not quote the symbol @var{face},
2281 and it should not end in @samp{-face} (that would be redundant). The
2282 argument @var{doc} is a documentation string for the face. The
2283 additional @var{keyword} arguments have the same meanings as in
2284 @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}).
2286 If @var{face} already has a default face spec, this macro does
2289 The default face spec determines @var{face}'s appearance when no
2290 customizations are in effect (@pxref{Customization}). If @var{face}
2291 has already been customized (via Custom themes or via customizations
2292 read from the init file), its appearance is determined by the custom
2293 face spec(s), which override the default face spec @var{spec}.
2294 However, if the customizations are subsequently removed, the
2295 appearance of @var{face} will again be determined by its default face
2298 As an exception, if you evaluate a @code{defface} form with
2299 @kbd{C-M-x} in Emacs Lisp mode (@code{eval-defun}), a special feature
2300 of @code{eval-defun} overrides any custom face specs on the face,
2301 causing the face to reflect exactly what the @code{defface} says.
2303 The @var{spec} argument is a @dfn{face spec}, which states how the
2304 face should appear on different kinds of terminals. It should be an
2305 alist whose elements each have the form
2308 (@var{display} . @var{plist})
2312 @var{display} specifies a class of terminals (see below). @var{plist}
2313 is a property list of face attributes and their values, specifying how
2314 the face appears on such terminals. For backward compatibility, you
2315 can also write an element as @code{(@var{display} @var{plist})}.
2317 The @var{display} part of an element of @var{spec} determines which
2318 terminals the element matches. If more than one element of @var{spec}
2319 matches a given terminal, the first element that matches is the one
2320 used for that terminal. There are three possibilities for
2324 @item @code{default}
2325 This element of @var{spec} doesn't match any terminal; instead, it
2326 specifies defaults that apply to all terminals. This element, if
2327 used, must be the first element of @var{spec}. Each of the following
2328 elements can override any or all of these defaults.
2331 This element of @var{spec} matches all terminals. Therefore, any
2332 subsequent elements of @var{spec} are never used. Normally @code{t}
2333 is used in the last (or only) element of @var{spec}.
2336 If @var{display} is a list, each element should have the form
2337 @code{(@var{characteristic} @var{value}@dots{})}. Here
2338 @var{characteristic} specifies a way of classifying terminals, and the
2339 @var{value}s are possible classifications which @var{display} should
2340 apply to. Here are the possible values of @var{characteristic}:
2344 The kind of window system the terminal uses---either @code{graphic}
2345 (any graphics-capable display), @code{x}, @code{pc} (for the MS-DOS
2346 console), @code{w32} (for MS Windows 9X/NT/2K/XP), or @code{tty} (a
2347 non-graphics-capable display). @xref{Window Systems, window-system}.
2350 What kinds of colors the terminal supports---either @code{color},
2351 @code{grayscale}, or @code{mono}.
2354 The kind of background---either @code{light} or @code{dark}.
2357 An integer that represents the minimum number of colors the terminal
2358 should support. This matches a terminal if its
2359 @code{display-color-cells} value is at least the specified integer.
2362 Whether or not the terminal can display the face attributes given in
2363 @var{value}@dots{} (@pxref{Face Attributes}). @xref{Display Face
2364 Attribute Testing}, for more information on exactly how this testing
2368 If an element of @var{display} specifies more than one @var{value} for
2369 a given @var{characteristic}, any of those values is acceptable. If
2370 @var{display} has more than one element, each element should specify a
2371 different @var{characteristic}; then @emph{each} characteristic of the
2372 terminal must match one of the @var{value}s specified for it in
2377 For example, here's the definition of the standard face
2382 '((((class color) (min-colors 88) (background light))
2383 :background "darkseagreen2")
2384 (((class color) (min-colors 88) (background dark))
2385 :background "darkolivegreen")
2386 (((class color) (min-colors 16) (background light))
2387 :background "darkseagreen2")
2388 (((class color) (min-colors 16) (background dark))
2389 :background "darkolivegreen")
2390 (((class color) (min-colors 8))
2391 :background "green" :foreground "black")
2392 (t :inverse-video t))
2393 "Basic face for highlighting."
2394 :group 'basic-faces)
2397 Internally, Emacs stores each face's default spec in its
2398 @code{face-defface-spec} symbol property (@pxref{Symbol Properties}).
2399 The @code{saved-face} property stores any face spec saved by the user
2400 using the customization buffer; the @code{customized-face} property
2401 stores the face spec customized for the current session, but not
2402 saved; and the @code{theme-face} property stores an alist associating
2403 the active customization settings and Custom themes with the face
2404 specs for that face. The face's documentation string is stored in the
2405 @code{face-documentation} property.
2407 Normally, a face is declared just once, using @code{defface}, and
2408 any further changes to its appearance are applied using the Customize
2409 framework (e.g., via the Customize user interface or via the
2410 @code{custom-set-faces} function; @pxref{Applying Customizations}), or
2411 by face remapping (@pxref{Face Remapping}). In the rare event that
2412 you need to change a face spec directly from Lisp, you can use the
2413 @code{face-spec-set} function.
2415 @defun face-spec-set face spec &optional spec-type
2416 This function applies @var{spec} as a face spec for @code{face}.
2417 @var{spec} should be a face spec, as described in the above
2418 documentation for @code{defface}.
2420 This function also defines @var{face} as a valid face name if it is
2421 not already one, and (re)calculates its attributes on existing frames.
2423 @cindex override spec @r{(for a face)}
2424 The argument @var{spec-type} determines which spec to set. If it is
2425 @code{nil} or @code{face-override-spec}, this function sets the
2426 @dfn{override spec}, which overrides over all other face specs on
2427 @var{face}. If it is @code{customized-face} or @code{saved-face},
2428 this function sets the customized spec or the saved custom spec. If
2429 it is @code{face-defface-spec}, this function sets the default face
2430 spec (the same one set by @code{defface}). If it is @code{reset},
2431 this function clears out all customization specs and override specs
2432 from @var{face} (in this case, the value of @var{spec} is ignored).
2433 Any other value of @var{spec-type} is reserved for internal use.
2436 @node Attribute Functions
2437 @subsection Face Attribute Functions
2439 This section describes functions for directly accessing and
2440 modifying the attributes of a named face.
2442 @defun face-attribute face attribute &optional frame inherit
2443 This function returns the value of the @var{attribute} attribute for
2444 @var{face} on @var{frame}.
2446 If @var{frame} is @code{nil}, that means the selected frame
2447 (@pxref{Input Focus}). If @var{frame} is @code{t}, this function
2448 returns the value of the specified attribute for newly-created frames
2449 (this is normally @code{unspecified}, unless you have specified some
2450 value using @code{set-face-attribute}; see below).
2452 If @var{inherit} is @code{nil}, only attributes directly defined by
2453 @var{face} are considered, so the return value may be
2454 @code{unspecified}, or a relative value. If @var{inherit} is
2455 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2456 with the faces specified by its @code{:inherit} attribute; however the
2457 return value may still be @code{unspecified} or relative. If
2458 @var{inherit} is a face or a list of faces, then the result is further
2459 merged with that face (or faces), until it becomes specified and
2462 To ensure that the return value is always specified and absolute, use
2463 a value of @code{default} for @var{inherit}; this will resolve any
2464 unspecified or relative values by merging with the @code{default} face
2465 (which is always completely specified).
2470 (face-attribute 'bold :weight)
2475 @c FIXME: Add an index for "relative face attribute", maybe here? --xfq
2476 @defun face-attribute-relative-p attribute value
2477 This function returns non-@code{nil} if @var{value}, when used as the
2478 value of the face attribute @var{attribute}, is relative. This means
2479 it would modify, rather than completely override, any value that comes
2480 from a subsequent face in the face list or that is inherited from
2483 @code{unspecified} is a relative value for all attributes. For
2484 @code{:height}, floating point and function values are also relative.
2489 (face-attribute-relative-p :height 2.0)
2494 @defun face-all-attributes face &optional frame
2495 This function returns an alist of attributes of @var{face}. The
2496 elements of the result are name-value pairs of the form
2497 @w{@code{(@var{attr-name} . @var{attr-value})}}. Optional argument
2498 @var{frame} specifies the frame whose definition of @var{face} to
2499 return; if omitted or @code{nil}, the returned value describes the
2500 default attributes of @var{face} for newly created frames.
2503 @defun merge-face-attribute attribute value1 value2
2504 If @var{value1} is a relative value for the face attribute
2505 @var{attribute}, returns it merged with the underlying value
2506 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2507 face attribute @var{attribute}, returns @var{value1} unchanged.
2510 Normally, Emacs uses the face specs of each face to automatically
2511 calculate its attributes on each frame (@pxref{Defining Faces}). The
2512 function @code{set-face-attribute} can override this calculation by
2513 directly assigning attributes to a face, either on a specific frame or
2514 for all frames. This function is mostly intended for internal usage.
2516 @defun set-face-attribute face frame &rest arguments
2517 This function sets one or more attributes of @var{face} for
2518 @var{frame}. The attributes specifies in this way override the face
2519 spec(s) belonging to @var{face}.
2521 The extra arguments @var{arguments} specify the attributes to set, and
2522 the values for them. They should consist of alternating attribute
2523 names (such as @code{:family} or @code{:underline}) and values. Thus,
2526 (set-face-attribute 'foo nil :weight 'bold :slant 'italic)
2530 sets the attribute @code{:weight} to @code{bold} and the attribute
2531 @code{:slant} to @code{italic}.
2534 If @var{frame} is @code{t}, this function sets the default attributes
2535 for newly created frames. If @var{frame} is @code{nil}, this function
2536 sets the attributes for all existing frames, as well as for newly
2540 The following commands and functions mostly provide compatibility
2541 with old versions of Emacs. They work by calling
2542 @code{set-face-attribute}. Values of @code{t} and @code{nil} for
2543 their @var{frame} argument are handled just like
2544 @code{set-face-attribute} and @code{face-attribute}. The commands
2545 read their arguments using the minibuffer, if called interactively.
2547 @deffn Command set-face-foreground face color &optional frame
2548 @deffnx Command set-face-background face color &optional frame
2549 These set the @code{:foreground} attribute (or @code{:background}
2550 attribute, respectively) of @var{face} to @var{color}.
2553 @deffn Command set-face-stipple face pattern &optional frame
2554 This sets the @code{:stipple} attribute of @var{face} to
2558 @deffn Command set-face-font face font &optional frame
2559 This sets the @code{:font} attribute of @var{face} to @var{font}.
2562 @defun set-face-bold face bold-p &optional frame
2563 This sets the @code{:weight} attribute of @var{face} to @var{normal}
2564 if @var{bold-p} is @code{nil}, and to @var{bold} otherwise.
2567 @defun set-face-italic face italic-p &optional frame
2568 This sets the @code{:slant} attribute of @var{face} to @var{normal} if
2569 @var{italic-p} is @code{nil}, and to @var{italic} otherwise.
2572 @defun set-face-underline face underline &optional frame
2573 This sets the @code{:underline} attribute of @var{face} to
2577 @defun set-face-inverse-video face inverse-video-p &optional frame
2578 This sets the @code{:inverse-video} attribute of @var{face} to
2579 @var{inverse-video-p}.
2582 @deffn Command invert-face face &optional frame
2583 This swaps the foreground and background colors of face @var{face}.
2586 The following functions examine the attributes of a face. They
2587 mostly provide compatibility with old versions of Emacs. If you don't
2588 specify @var{frame}, they refer to the selected frame; @code{t} refers
2589 to the default data for new frames. They return @code{unspecified} if
2590 the face doesn't define any value for that attribute. If
2591 @var{inherit} is @code{nil}, only an attribute directly defined by the
2592 face is returned. If @var{inherit} is non-@code{nil}, any faces
2593 specified by its @code{:inherit} attribute are considered as well, and
2594 if @var{inherit} is a face or a list of faces, then they are also
2595 considered, until a specified attribute is found. To ensure that the
2596 return value is always specified, use a value of @code{default} for
2599 @defun face-font face &optional frame
2600 This function returns the name of the font of face @var{face}.
2603 @defun face-foreground face &optional frame inherit
2604 @defunx face-background face &optional frame inherit
2605 These functions return the foreground color (or background color,
2606 respectively) of face @var{face}, as a string.
2609 @defun face-stipple face &optional frame inherit
2610 This function returns the name of the background stipple pattern of face
2611 @var{face}, or @code{nil} if it doesn't have one.
2614 @defun face-bold-p face &optional frame inherit
2615 This function returns a non-@code{nil} value if the @code{:weight}
2616 attribute of @var{face} is bolder than normal (i.e., one of
2617 @code{semi-bold}, @code{bold}, @code{extra-bold}, or
2618 @code{ultra-bold}). Otherwise, it returns @code{nil}.
2621 @defun face-italic-p face &optional frame inherit
2622 This function returns a non-@code{nil} value if the @code{:slant}
2623 attribute of @var{face} is @code{italic} or @code{oblique}, and
2624 @code{nil} otherwise.
2627 @defun face-underline-p face &optional frame inherit
2628 This function returns non-@code{nil} if face @var{face} specifies
2629 a non-@code{nil} @code{:underline} attribute.
2632 @defun face-inverse-video-p face &optional frame inherit
2633 This function returns non-@code{nil} if face @var{face} specifies
2634 a non-@code{nil} @code{:inverse-video} attribute.
2637 @node Displaying Faces
2638 @subsection Displaying Faces
2640 When Emacs displays a given piece of text, the visual appearance of
2641 the text may be determined by faces drawn from different sources. If
2642 these various sources together specify more than one face for a
2643 particular character, Emacs merges the attributes of the various
2644 faces. Here is the order in which Emacs merges the faces, from
2645 highest to lowest priority:
2649 If the text consists of a special glyph, the glyph can specify a
2650 particular face. @xref{Glyphs}.
2653 If the text lies within an active region, Emacs highlights it using
2654 the @code{region} face. @xref{Standard Faces,,, emacs, The GNU Emacs
2658 If the text lies within an overlay with a non-@code{nil} @code{face}
2659 property, Emacs applies the face(s) specified by that property. If
2660 the overlay has a @code{mouse-face} property and the mouse is ``near
2661 enough'' to the overlay, Emacs applies the face or face attributes
2662 specified by the @code{mouse-face} property instead. @xref{Overlay
2665 When multiple overlays cover one character, an overlay with higher
2666 priority overrides those with lower priority. @xref{Overlays}.
2669 If the text contains a @code{face} or @code{mouse-face} property,
2670 Emacs applies the specified faces and face attributes. @xref{Special
2671 Properties}. (This is how Font Lock mode faces are applied.
2672 @xref{Font Lock Mode}.)
2675 If the text lies within the mode line of the selected window, Emacs
2676 applies the @code{mode-line} face. For the mode line of a
2677 non-selected window, Emacs applies the @code{mode-line-inactive} face.
2678 For a header line, Emacs applies the @code{header-line} face.
2681 If any given attribute has not been specified during the preceding
2682 steps, Emacs applies the attribute of the @code{default} face.
2685 At each stage, if a face has a valid @code{:inherit} attribute,
2686 Emacs treats any attribute with an @code{unspecified} value as having
2687 the corresponding value drawn from the parent face(s). @pxref{Face
2688 Attributes}. Note that the parent face(s) may also leave the
2689 attribute unspecified; in that case, the attribute remains unspecified
2690 at the next level of face merging.
2692 @node Face Remapping
2693 @subsection Face Remapping
2695 The variable @code{face-remapping-alist} is used for buffer-local or
2696 global changes in the appearance of a face. For instance, it is used
2697 to implement the @code{text-scale-adjust} command (@pxref{Text
2698 Scale,,, emacs, The GNU Emacs Manual}).
2700 @defvar face-remapping-alist
2701 The value of this variable is an alist whose elements have the form
2702 @code{(@var{face} . @var{remapping})}. This causes Emacs to display
2703 any text having the face @var{face} with @var{remapping}, rather than
2704 the ordinary definition of @var{face}.
2706 @var{remapping} may be any face spec suitable for a @code{face} text
2707 property: either a face (i.e., a face name or a property list of
2708 attribute/value pairs), or a list of faces. For details, see the
2709 description of the @code{face} text property in @ref{Special
2710 Properties}. @var{remapping} serves as the complete specification for
2711 the remapped face---it replaces the normal definition of @var{face},
2712 instead of modifying it.
2714 If @code{face-remapping-alist} is buffer-local, its local value takes
2715 effect only within that buffer.
2717 Note: face remapping is non-recursive. If @var{remapping} references
2718 the same face name @var{face}, either directly or via the
2719 @code{:inherit} attribute of some other face in @var{remapping}, that
2720 reference uses the normal definition of @var{face}. For instance, if
2721 the @code{mode-line} face is remapped using this entry in
2722 @code{face-remapping-alist}:
2725 (mode-line italic mode-line)
2729 then the new definition of the @code{mode-line} face inherits from the
2730 @code{italic} face, and the @emph{normal} (non-remapped) definition of
2731 @code{mode-line} face.
2734 @cindex relative remapping, faces
2735 @cindex base remapping, faces
2736 The following functions implement a higher-level interface to
2737 @code{face-remapping-alist}. Most Lisp code should use these
2738 functions instead of setting @code{face-remapping-alist} directly, to
2739 avoid trampling on remappings applied elsewhere. These functions are
2740 intended for buffer-local remappings, so they all make
2741 @code{face-remapping-alist} buffer-local as a side-effect. They manage
2742 @code{face-remapping-alist} entries of the form
2745 (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec})
2749 where, as explained above, each of the @var{relative-spec-N} and
2750 @var{base-spec} is either a face name, or a property list of
2751 attribute/value pairs. Each of the @dfn{relative remapping} entries,
2752 @var{relative-spec-N}, is managed by the
2753 @code{face-remap-add-relative} and @code{face-remap-remove-relative}
2754 functions; these are intended for simple modifications like changing
2755 the text size. The @dfn{base remapping} entry, @var{base-spec}, has
2756 the lowest priority and is managed by the @code{face-remap-set-base}
2757 and @code{face-remap-reset-base} functions; it is intended for major
2758 modes to remap faces in the buffers they control.
2760 @defun face-remap-add-relative face &rest specs
2761 This function adds the face spec in @var{specs} as relative
2762 remappings for face @var{face} in the current buffer. The remaining
2763 arguments, @var{specs}, should form either a list of face names, or a
2764 property list of attribute/value pairs.
2766 The return value is a Lisp object that serves as a ``cookie''; you can
2767 pass this object as an argument to @code{face-remap-remove-relative}
2768 if you need to remove the remapping later.
2771 ;; Remap the `escape-glyph' face into a combination
2772 ;; of the `highlight' and `italic' faces:
2773 (face-remap-add-relative 'escape-glyph 'highlight 'italic)
2775 ;; Increase the size of the `default' face by 50%:
2776 (face-remap-add-relative 'default :height 1.5)
2780 @defun face-remap-remove-relative cookie
2781 This function removes a relative remapping previously added by
2782 @code{face-remap-add-relative}. @var{cookie} should be the Lisp
2783 object returned by @code{face-remap-add-relative} when the remapping
2787 @defun face-remap-set-base face &rest specs
2788 This function sets the base remapping of @var{face} in the current
2789 buffer to @var{specs}. If @var{specs} is empty, the default base
2790 remapping is restored, similar to calling @code{face-remap-reset-base}
2791 (see below); note that this is different from @var{specs} containing a
2792 single value @code{nil}, which has the opposite result (the global
2793 definition of @var{face} is ignored).
2795 This overwrites the default @var{base-spec}, which inherits the global
2796 face definition, so it is up to the caller to add such inheritance if
2800 @defun face-remap-reset-base face
2801 This function sets the base remapping of @var{face} to its default
2802 value, which inherits from @var{face}'s global definition.
2805 @node Face Functions
2806 @subsection Functions for Working with Faces
2808 Here are additional functions for creating and working with faces.
2811 This function returns a list of all defined face names.
2815 This function returns the @dfn{face number} of face @var{face}. This
2816 is a number that uniquely identifies a face at low levels within
2817 Emacs. It is seldom necessary to refer to a face by its face number.
2820 @defun face-documentation face
2821 This function returns the documentation string of face @var{face}, or
2822 @code{nil} if none was specified for it.
2825 @defun face-equal face1 face2 &optional frame
2826 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2827 same attributes for display.
2830 @defun face-differs-from-default-p face &optional frame
2831 This returns non-@code{nil} if the face @var{face} displays
2832 differently from the default face.
2836 @cindex alias, for faces
2837 A @dfn{face alias} provides an equivalent name for a face. You can
2838 define a face alias by giving the alias symbol the @code{face-alias}
2839 property, with a value of the target face name. The following example
2840 makes @code{modeline} an alias for the @code{mode-line} face.
2843 (put 'modeline 'face-alias 'mode-line)
2846 @defmac define-obsolete-face-alias obsolete-face current-face when
2847 This macro defines @code{obsolete-face} as an alias for
2848 @var{current-face}, and also marks it as obsolete, indicating that it
2849 may be removed in future. @var{when} should be a string indicating
2850 when @code{obsolete-face} was made obsolete (usually a version number
2855 @subsection Automatic Face Assignment
2856 @cindex automatic face assignment
2857 @cindex faces, automatic choice
2859 This hook is used for automatically assigning faces to text in the
2860 buffer. It is part of the implementation of Jit-Lock mode, used by
2863 @defvar fontification-functions
2864 This variable holds a list of functions that are called by Emacs
2865 redisplay as needed, just before doing redisplay. They are called even
2866 when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this
2867 variable usually holds just one function, @code{jit-lock-function}.
2869 The functions are called in the order listed, with one argument, a
2870 buffer position @var{pos}. Collectively they should attempt to assign
2871 faces to the text in the current buffer starting at @var{pos}.
2873 The functions should record the faces they assign by setting the
2874 @code{face} property. They should also add a non-@code{nil}
2875 @code{fontified} property to all the text they have assigned faces to.
2876 That property tells redisplay that faces have been assigned to that text
2879 It is probably a good idea for the functions to do nothing if the
2880 character after @var{pos} already has a non-@code{nil} @code{fontified}
2881 property, but this is not required. If one function overrides the
2882 assignments made by a previous one, the properties after the last
2883 function finishes are the ones that really matter.
2885 For efficiency, we recommend writing these functions so that they
2886 usually assign faces to around 400 to 600 characters at each call.
2890 @subsection Basic Faces
2892 If your Emacs Lisp program needs to assign some faces to text, it is
2893 often a good idea to use certain existing faces or inherit from them,
2894 rather than defining entirely new faces. This way, if other users
2895 have customized the basic faces to give Emacs a certain look, your
2896 program will ``fit in'' without additional customization.
2898 Some of the basic faces defined in Emacs are listed below. In
2899 addition to these, you might want to make use of the Font Lock faces
2900 for syntactic highlighting, if highlighting is not already handled by
2901 Font Lock mode, or if some Font Lock faces are not in use.
2902 @xref{Faces for Font Lock}.
2906 The default face, whose attributes are all specified. All other faces
2907 implicitly inherit from it: any unspecified attribute defaults to the
2908 attribute on this face (@pxref{Face Attributes}).
2915 @itemx variable-pitch
2916 These have the attributes indicated by their names (e.g., @code{bold}
2917 has a bold @code{:weight} attribute), with all other attributes
2918 unspecified (and so given by @code{default}).
2921 For ``dimmed out'' text. For example, it is used for the ignored
2922 part of a filename in the minibuffer (@pxref{Minibuffer File,,
2923 Minibuffers for File Names, emacs, The GNU Emacs Manual}).
2927 For clickable text buttons that send the user to a different
2928 buffer or ``location''.
2931 For stretches of text that should temporarily stand out. For example,
2932 it is commonly assigned to the @code{mouse-face} property for cursor
2933 highlighting (@pxref{Special Properties}).
2936 For text matching a search command.
2941 For text concerning errors, warnings, or successes. For example,
2942 these are used for messages in @file{*Compilation*} buffers.
2945 @node Font Selection
2946 @subsection Font Selection
2947 @cindex font selection
2948 @cindex selecting a font
2950 Before Emacs can draw a character on a graphical display, it must
2951 select a @dfn{font} for that character@footnote{In this context, the
2952 term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock
2953 Mode}).}. @xref{Fonts,,, emacs, The GNU Emacs Manual}. Normally,
2954 Emacs automatically chooses a font based on the faces assigned to that
2955 character---specifically, the face attributes @code{:family},
2956 @code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face
2957 Attributes}). The choice of font also depends on the character to be
2958 displayed; some fonts can only display a limited set of characters.
2959 If no available font exactly fits the requirements, Emacs looks for
2960 the @dfn{closest matching font}. The variables in this section
2961 control how Emacs makes this selection.
2963 @defopt face-font-family-alternatives
2964 If a given family is specified but does not exist, this variable
2965 specifies alternative font families to try. Each element should have
2969 (@var{family} @var{alternate-families}@dots{})
2972 If @var{family} is specified but not available, Emacs will try the other
2973 families given in @var{alternate-families}, one by one, until it finds a
2974 family that does exist.
2977 @defopt face-font-selection-order
2978 If there is no font that exactly matches all desired face attributes
2979 (@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}),
2980 this variable specifies the order in which these attributes should be
2981 considered when selecting the closest matching font. The value should
2982 be a list containing those four attribute symbols, in order of
2983 decreasing importance. The default is @code{(:width :height :weight
2986 Font selection first finds the best available matches for the first
2987 attribute in the list; then, among the fonts which are best in that
2988 way, it searches for the best matches in the second attribute, and so
2991 The attributes @code{:weight} and @code{:width} have symbolic values in
2992 a range centered around @code{normal}. Matches that are more extreme
2993 (farther from @code{normal}) are somewhat preferred to matches that are
2994 less extreme (closer to @code{normal}); this is designed to ensure that
2995 non-normal faces contrast with normal ones, whenever possible.
2997 One example of a case where this variable makes a difference is when the
2998 default font has no italic equivalent. With the default ordering, the
2999 @code{italic} face will use a non-italic font that is similar to the
3000 default one. But if you put @code{:slant} before @code{:height}, the
3001 @code{italic} face will use an italic font, even if its height is not
3005 @defopt face-font-registry-alternatives
3006 This variable lets you specify alternative font registries to try, if a
3007 given registry is specified and doesn't exist. Each element should have
3011 (@var{registry} @var{alternate-registries}@dots{})
3014 If @var{registry} is specified but not available, Emacs will try the
3015 other registries given in @var{alternate-registries}, one by one,
3016 until it finds a registry that does exist.
3019 @cindex scalable fonts
3020 Emacs can make use of scalable fonts, but by default it does not use
3023 @defopt scalable-fonts-allowed
3024 This variable controls which scalable fonts to use. A value of
3025 @code{nil}, the default, means do not use scalable fonts. @code{t}
3026 means to use any scalable font that seems appropriate for the text.
3028 Otherwise, the value must be a list of regular expressions. Then a
3029 scalable font is enabled for use if its name matches any regular
3030 expression in the list. For example,
3033 (setq scalable-fonts-allowed '("iso10646-1$"))
3037 allows the use of scalable fonts with registry @code{iso10646-1}.
3040 @defvar face-font-rescale-alist
3041 This variable specifies scaling for certain faces. Its value should
3042 be a list of elements of the form
3045 (@var{fontname-regexp} . @var{scale-factor})
3048 If @var{fontname-regexp} matches the font name that is about to be
3049 used, this says to choose a larger similar font according to the
3050 factor @var{scale-factor}. You would use this feature to normalize
3051 the font size if certain fonts are bigger or smaller than their
3052 nominal heights and widths would suggest.
3056 @subsection Looking Up Fonts
3058 @defun x-list-fonts name &optional reference-face frame maximum width
3059 This function returns a list of available font names that match
3060 @var{name}. @var{name} should be a string containing a font name in
3061 either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The
3062 GNU Emacs Manual}). Within an XLFD string, wildcard characters may be
3063 used: the @samp{*} character matches any substring, and the @samp{?}
3064 character matches any single character. Case is ignored when matching
3067 If the optional arguments @var{reference-face} and @var{frame} are
3068 specified, the returned list includes only fonts that are the same
3069 size as @var{reference-face} (a face name) currently is on the frame
3072 The optional argument @var{maximum} sets a limit on how many fonts to
3073 return. If it is non-@code{nil}, then the return value is truncated
3074 after the first @var{maximum} matching fonts. Specifying a small
3075 value for @var{maximum} can make this function much faster, in cases
3076 where many fonts match the pattern.
3078 The optional argument @var{width} specifies a desired font width. If
3079 it is non-@code{nil}, the function only returns those fonts whose
3080 characters are (on average) @var{width} times as wide as
3081 @var{reference-face}.
3084 @defun x-family-fonts &optional family frame
3085 This function returns a list describing the available fonts for family
3086 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
3087 this list applies to all families, and therefore, it contains all
3088 available fonts. Otherwise, @var{family} must be a string; it may
3089 contain the wildcards @samp{?} and @samp{*}.
3091 The list describes the display that @var{frame} is on; if @var{frame} is
3092 omitted or @code{nil}, it applies to the selected frame's display
3093 (@pxref{Input Focus}).
3095 Each element in the list is a vector of the following form:
3098 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
3099 @var{fixed-p} @var{full} @var{registry-and-encoding}]
3102 The first five elements correspond to face attributes; if you
3103 specify these attributes for a face, it will use this font.
3105 The last three elements give additional information about the font.
3106 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
3107 @var{full} is the full name of the font, and
3108 @var{registry-and-encoding} is a string giving the registry and
3109 encoding of the font.
3113 @subsection Fontsets
3115 A @dfn{fontset} is a list of fonts, each assigned to a range of
3116 character codes. An individual font cannot display the whole range of
3117 characters that Emacs supports, but a fontset can. Fontsets have names,
3118 just as fonts do, and you can use a fontset name in place of a font name
3119 when you specify the ``font'' for a frame or a face. Here is
3120 information about defining a fontset under Lisp program control.
3122 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
3123 This function defines a new fontset according to the specification
3124 string @var{fontset-spec}. The string should have this format:
3127 @var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}}
3131 Whitespace characters before and after the commas are ignored.
3133 The first part of the string, @var{fontpattern}, should have the form of
3134 a standard X font name, except that the last two fields should be
3135 @samp{fontset-@var{alias}}.
3137 The new fontset has two names, one long and one short. The long name is
3138 @var{fontpattern} in its entirety. The short name is
3139 @samp{fontset-@var{alias}}. You can refer to the fontset by either
3140 name. If a fontset with the same name already exists, an error is
3141 signaled, unless @var{noerror} is non-@code{nil}, in which case this
3142 function does nothing.
3144 If optional argument @var{style-variant-p} is non-@code{nil}, that says
3145 to create bold, italic and bold-italic variants of the fontset as well.
3146 These variant fontsets do not have a short name, only a long one, which
3147 is made by altering @var{fontpattern} to indicate the bold and/or italic
3150 The specification string also says which fonts to use in the fontset.
3151 See below for the details.
3154 The construct @samp{@var{charset}:@var{font}} specifies which font to
3155 use (in this fontset) for one particular character set. Here,
3156 @var{charset} is the name of a character set, and @var{font} is the font
3157 to use for that character set. You can use this construct any number of
3158 times in the specification string.
3160 For the remaining character sets, those that you don't specify
3161 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
3162 @samp{fontset-@var{alias}} with a value that names one character set.
3163 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
3164 with @samp{ISO8859-1}.
3166 In addition, when several consecutive fields are wildcards, Emacs
3167 collapses them into a single wildcard. This is to prevent use of
3168 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
3169 for editing, and scaling a smaller font is not useful because it is
3170 better to use the smaller font in its own size, which Emacs does.
3172 Thus if @var{fontpattern} is this,
3175 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
3179 the font specification for @acronym{ASCII} characters would be this:
3182 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
3186 and the font specification for Chinese GB2312 characters would be this:
3189 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
3192 You may not have any Chinese font matching the above font
3193 specification. Most X distributions include only Chinese fonts that
3194 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
3195 such a case, @samp{Fontset-@var{n}} can be specified as below:
3198 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
3199 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
3203 Then, the font specifications for all but Chinese GB2312 characters have
3204 @samp{fixed} in the @var{family} field, and the font specification for
3205 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
3208 @defun set-fontset-font name character font-spec &optional frame add
3209 This function modifies the existing fontset @var{name} to use the font
3210 matching with @var{font-spec} for the character @var{character}.
3212 If @var{name} is @code{nil}, this function modifies the fontset of the
3213 selected frame or that of @var{frame} if @var{frame} is not
3216 If @var{name} is @code{t}, this function modifies the default
3217 fontset, whose short name is @samp{fontset-default}.
3219 @var{character} may be a cons; @code{(@var{from} . @var{to})}, where
3220 @var{from} and @var{to} are character codepoints. In that case, use
3221 @var{font-spec} for all characters in the range @var{from} and @var{to}
3224 @var{character} may be a charset. In that case, use
3225 @var{font-spec} for all character in the charsets.
3227 @var{character} may be a script name. In that case, use
3228 @var{font-spec} for all character in the charsets.
3230 @var{font-spec} may be a cons; @code{(@var{family} . @var{registry})},
3231 where @var{family} is a family name of a font (possibly including a
3232 foundry name at the head), @var{registry} is a registry name of a font
3233 (possibly including an encoding name at the tail).
3235 @var{font-spec} may be a font name string.
3237 The optional argument @var{add}, if non-@code{nil}, specifies how to
3238 add @var{font-spec} to the font specifications previously set. If it
3239 is @code{prepend}, @var{font-spec} is prepended. If it is
3240 @code{append}, @var{font-spec} is appended. By default,
3241 @var{font-spec} overrides the previous settings.
3243 For instance, this changes the default fontset to use a font of which
3244 family name is @samp{Kochi Gothic} for all characters belonging to
3245 the charset @code{japanese-jisx0208}.
3248 (set-fontset-font t 'japanese-jisx0208
3249 (font-spec :family "Kochi Gothic"))
3253 @defun char-displayable-p char
3254 This function returns @code{t} if Emacs ought to be able to display
3255 @var{char}. More precisely, if the selected frame's fontset has a
3256 font to display the character set that @var{char} belongs to.
3258 Fontsets can specify a font on a per-character basis; when the fontset
3259 does that, this function's value may not be accurate.
3262 @node Low-Level Font
3263 @subsection Low-Level Font Representation
3264 @cindex font property
3266 Normally, it is not necessary to manipulate fonts directly. In case
3267 you need to do so, this section explains how.
3269 In Emacs Lisp, fonts are represented using three different Lisp
3270 object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font
3273 @defun fontp object &optional type
3274 Return @code{t} if @var{object} is a font object, font spec, or font
3275 entity. Otherwise, return @code{nil}.
3277 The optional argument @var{type}, if non-@code{nil}, determines the
3278 exact type of Lisp object to check for. In that case, @var{type}
3279 should be one of @code{font-object}, @code{font-spec}, or
3284 A font object is a Lisp object that represents a font that Emacs has
3285 @dfn{opened}. Font objects cannot be modified in Lisp, but they can
3288 @defun font-at position &optional window string
3289 Return the font object that is being used to display the character at
3290 position @var{position} in the window @var{window}. If @var{window}
3291 is @code{nil}, it defaults to the selected window. If @var{string} is
3292 @code{nil}, @var{position} specifies a position in the current buffer;
3293 otherwise, @var{string} should be a string, and @var{position}
3294 specifies a position in that string.
3298 A font spec is a Lisp object that contains a set of specifications
3299 that can be used to find a font. More than one font may match the
3300 specifications in a font spec.
3302 @defun font-spec &rest arguments
3303 Return a new font spec using the specifications in @var{arguments},
3304 which should come in @code{property}-@code{value} pairs. The possible
3305 specifications are as follows:
3309 The font name (a string), in either XLFD, Fontconfig, or GTK format.
3310 @xref{Fonts,,, emacs, The GNU Emacs Manual}.
3317 These have the same meanings as the face attributes of the same name.
3318 @xref{Face Attributes}.
3321 The font size---either a non-negative integer that specifies the pixel
3322 size, or a floating-point number that specifies the point size.
3325 Additional typographic style information for the font, such as
3326 @samp{sans}. The value should be a string or a symbol.
3328 @cindex font registry
3330 The charset registry and encoding of the font, such as
3331 @samp{iso8859-1}. The value should be a string or a symbol.
3334 The script that the font must support (a symbol).
3337 @cindex OpenType font
3338 The font must be an OpenType font that supports these OpenType
3339 features, provided Emacs is compiled with support for @samp{libotf} (a
3340 library for performing complex text layout in certain scripts). The
3341 value must be a list of the form
3344 @code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
3347 where @var{script-tag} is the OpenType script tag symbol;
3348 @var{langsys-tag} is the OpenType language system tag symbol, or
3349 @code{nil} to use the default language system; @code{gsub} is a list
3350 of OpenType GSUB feature tag symbols, or @code{nil} if none is
3351 required; and @code{gpos} is a list of OpenType GPOS feature tag
3352 symbols, or @code{nil} if none is required. If @code{gsub} or
3353 @code{gpos} is a list, a @code{nil} element in that list means that
3354 the font must not match any of the remaining tag symbols. The
3355 @code{gpos} element may be omitted.
3359 @defun font-put font-spec property value
3360 Set the font property @var{property} in the font-spec @var{font-spec}
3365 A font entity is a reference to a font that need not be open. Its
3366 properties are intermediate between a font object and a font spec:
3367 like a font object, and unlike a font spec, it refers to a single,
3368 specific font. Unlike a font object, creating a font entity does not
3369 load the contents of that font into computer memory. Emacs may open
3370 multiple font objects of different sizes from a single font entity
3371 referring to a scalable font.
3373 @defun find-font font-spec &optional frame
3374 This function returns a font entity that best matches the font spec
3375 @var{font-spec} on frame @var{frame}. If @var{frame} is @code{nil},
3376 it defaults to the selected frame.
3379 @defun list-fonts font-spec &optional frame num prefer
3380 This function returns a list of all font entities that match the font
3381 spec @var{font-spec}.
3383 The optional argument @var{frame}, if non-@code{nil}, specifies the
3384 frame on which the fonts are to be displayed. The optional argument
3385 @var{num}, if non-@code{nil}, should be an integer that specifies the
3386 maximum length of the returned list. The optional argument
3387 @var{prefer}, if non-@code{nil}, should be another font spec, which is
3388 used to control the order of the returned list; the returned font
3389 entities are sorted in order of decreasing ``closeness'' to that font
3393 If you call @code{set-face-attribute} and pass a font spec, font
3394 entity, or font name string as the value of the @code{:font}
3395 attribute, Emacs opens the best ``matching'' font that is available
3396 for display. It then stores the corresponding font object as the
3397 actual value of the @code{:font} attribute for that face.
3399 The following functions can be used to obtain information about a
3400 font. For these functions, the @var{font} argument can be a font
3401 object, a font entity, or a font spec.
3403 @defun font-get font property
3404 This function returns the value of the font property @var{property}
3407 If @var{font} is a font spec and the font spec does not specify
3408 @var{property}, the return value is @code{nil}. If @var{font} is a
3409 font object or font entity, the value for the @var{:script} property
3410 may be a list of scripts supported by the font.
3413 @defun font-face-attributes font &optional frame
3414 This function returns a list of face attributes corresponding to
3415 @var{font}. The optional argument @var{frame} specifies the frame on
3416 which the font is to be displayed. If it is @code{nil}, the selected
3417 frame is used. The return value has the form
3420 (:family @var{family} :height @var{height} :weight @var{weight}
3421 :slant @var{slant} :width @var{width})
3424 where the values of @var{family}, @var{height}, @var{weight},
3425 @var{slant}, and @var{width} are face attribute values. Some of these
3426 key-attribute pairs may be omitted from the list if they are not
3427 specified by @var{font}.
3430 @defun font-xlfd-name font &optional fold-wildcards
3431 This function returns the XLFD (X Logical Font Descriptor), a string,
3432 matching @var{font}. @xref{Fonts,,, emacs, The GNU Emacs Manual}, for
3433 information about XLFDs. If the name is too long for an XLFD (which
3434 can contain at most 255 characters), the function returns @code{nil}.
3436 If the optional argument @var{fold-wildcards} is non-@code{nil},
3437 consecutive wildcards in the XLFD are folded into one.
3444 On graphical displays, Emacs draws @dfn{fringes} next to each
3445 window: thin vertical strips down the sides which can display bitmaps
3446 indicating truncation, continuation, horizontal scrolling, and so on.
3449 * Fringe Size/Pos:: Specifying where to put the window fringes.
3450 * Fringe Indicators:: Displaying indicator icons in the window fringes.
3451 * Fringe Cursors:: Displaying cursors in the right fringe.
3452 * Fringe Bitmaps:: Specifying bitmaps for fringe indicators.
3453 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
3454 * Overlay Arrow:: Display of an arrow to indicate position.
3457 @node Fringe Size/Pos
3458 @subsection Fringe Size and Position
3460 The following buffer-local variables control the position and width
3461 of fringes in windows showing that buffer.
3463 @defvar fringes-outside-margins
3464 The fringes normally appear between the display margins and the window
3465 text. If the value is non-@code{nil}, they appear outside the display
3466 margins. @xref{Display Margins}.
3469 @defvar left-fringe-width
3470 This variable, if non-@code{nil}, specifies the width of the left
3471 fringe in pixels. A value of @code{nil} means to use the left fringe
3472 width from the window's frame.
3475 @defvar right-fringe-width
3476 This variable, if non-@code{nil}, specifies the width of the right
3477 fringe in pixels. A value of @code{nil} means to use the right fringe
3478 width from the window's frame.
3481 Any buffer which does not specify values for these variables uses
3482 the values specified by the @code{left-fringe} and @code{right-fringe}
3483 frame parameters (@pxref{Layout Parameters}).
3485 The above variables actually take effect via the function
3486 @code{set-window-buffer} (@pxref{Buffers and Windows}), which calls
3487 @code{set-window-fringes} as a subroutine. If you change one of these
3488 variables, the fringe display is not updated in existing windows
3489 showing the buffer, unless you call @code{set-window-buffer} again in
3490 each affected window. You can also use @code{set-window-fringes} to
3491 control the fringe display in individual windows.
3493 @defun set-window-fringes window left &optional right outside-margins
3494 This function sets the fringe widths of window @var{window}.
3495 If @var{window} is @code{nil}, the selected window is used.
3497 The argument @var{left} specifies the width in pixels of the left
3498 fringe, and likewise @var{right} for the right fringe. A value of
3499 @code{nil} for either one stands for the default width. If
3500 @var{outside-margins} is non-@code{nil}, that specifies that fringes
3501 should appear outside of the display margins.
3504 @defun window-fringes &optional window
3505 This function returns information about the fringes of a window
3506 @var{window}. If @var{window} is omitted or @code{nil}, the selected
3507 window is used. The value has the form @code{(@var{left-width}
3508 @var{right-width} @var{outside-margins})}.
3512 @node Fringe Indicators
3513 @subsection Fringe Indicators
3514 @cindex fringe indicators
3515 @cindex indicators, fringe
3517 @dfn{Fringe indicators} are tiny icons displayed in the window
3518 fringe to indicate truncated or continued lines, buffer boundaries,
3521 @defopt indicate-empty-lines
3522 @cindex fringes, and empty line indication
3523 @cindex empty lines, indicating
3524 When this is non-@code{nil}, Emacs displays a special glyph in the
3525 fringe of each empty line at the end of the buffer, on graphical
3526 displays. @xref{Fringes}. This variable is automatically
3527 buffer-local in every buffer.
3530 @defopt indicate-buffer-boundaries
3531 @cindex buffer boundaries, indicating
3532 This buffer-local variable controls how the buffer boundaries and
3533 window scrolling are indicated in the window fringes.
3535 Emacs can indicate the buffer boundaries---that is, the first and last
3536 line in the buffer---with angle icons when they appear on the screen.
3537 In addition, Emacs can display an up-arrow in the fringe to show
3538 that there is text above the screen, and a down-arrow to show
3539 there is text below the screen.
3541 There are three kinds of basic values:
3545 Don't display any of these fringe icons.
3547 Display the angle icons and arrows in the left fringe.
3549 Display the angle icons and arrows in the right fringe.
3551 Display the angle icons in the left fringe
3552 and don't display the arrows.
3555 Otherwise the value should be an alist that specifies which fringe
3556 indicators to display and where. Each element of the alist should
3557 have the form @code{(@var{indicator} . @var{position})}. Here,
3558 @var{indicator} is one of @code{top}, @code{bottom}, @code{up},
3559 @code{down}, and @code{t} (which covers all the icons not yet
3560 specified), while @var{position} is one of @code{left}, @code{right}
3563 For example, @code{((top . left) (t . right))} places the top angle
3564 bitmap in left fringe, and the bottom angle bitmap as well as both
3565 arrow bitmaps in right fringe. To show the angle bitmaps in the left
3566 fringe, and no arrow bitmaps, use @code{((top . left) (bottom . left))}.
3569 @defvar fringe-indicator-alist
3570 This buffer-local variable specifies the mapping from logical fringe
3571 indicators to the actual bitmaps displayed in the window fringes. The
3572 value is an alist of elements @code{(@var{indicator}
3573 . @var{bitmaps})}, where @var{indicator} specifies a logical indicator
3574 type and @var{bitmaps} specifies the fringe bitmaps to use for that
3577 Each @var{indicator} should be one of the following symbols:
3580 @item @code{truncation}, @code{continuation}.
3581 Used for truncation and continuation lines.
3583 @item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom}
3584 Used when @code{indicate-buffer-boundaries} is non-@code{nil}:
3585 @code{up} and @code{down} indicate a buffer boundary lying above or
3586 below the window edge; @code{top} and @code{bottom} indicate the
3587 topmost and bottommost buffer text line; and @code{top-bottom}
3588 indicates where there is just one line of text in the buffer.
3590 @item @code{empty-line}
3591 Used to indicate empty lines when @code{indicate-empty-lines} is
3594 @item @code{overlay-arrow}
3595 Used for overlay arrows (@pxref{Overlay Arrow}).
3596 @c Is this used anywhere?
3597 @c @item Unknown bitmap indicator:
3601 Each @var{bitmaps} value may be a list of symbols @code{(@var{left}
3602 @var{right} [@var{left1} @var{right1}])}. The @var{left} and
3603 @var{right} symbols specify the bitmaps shown in the left and/or right
3604 fringe, for the specific indicator. @var{left1} and @var{right1} are
3605 specific to the @code{bottom} and @code{top-bottom} indicators, and
3606 are used to indicate that the last text line has no final newline.
3607 Alternatively, @var{bitmaps} may be a single symbol which is used in
3608 both left and right fringes.
3610 @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how
3611 to define your own. In addition, @code{nil} represents the empty
3612 bitmap (i.e., an indicator that is not shown).
3614 When @code{fringe-indicator-alist} has a buffer-local value, and
3615 there is no bitmap defined for a logical indicator, or the bitmap is
3616 @code{t}, the corresponding value from the default value of
3617 @code{fringe-indicator-alist} is used.
3620 @node Fringe Cursors
3621 @subsection Fringe Cursors
3622 @cindex fringe cursors
3623 @cindex cursor, fringe
3625 When a line is exactly as wide as the window, Emacs displays the
3626 cursor in the right fringe instead of using two lines. Different
3627 bitmaps are used to represent the cursor in the fringe depending on
3628 the current buffer's cursor type.
3630 @defopt overflow-newline-into-fringe
3631 If this is non-@code{nil}, lines exactly as wide as the window (not
3632 counting the final newline character) are not continued. Instead,
3633 when point is at the end of the line, the cursor appears in the right
3637 @defvar fringe-cursor-alist
3638 This variable specifies the mapping from logical cursor type to the
3639 actual fringe bitmaps displayed in the right fringe. The value is an
3640 alist where each element has the form @code{(@var{cursor-type}
3641 . @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to
3642 display cursors of type @var{cursor-type}.
3644 Each @var{cursor-type} should be one of @code{box}, @code{hollow},
3645 @code{bar}, @code{hbar}, or @code{hollow-small}. The first four have
3646 the same meanings as in the @code{cursor-type} frame parameter
3647 (@pxref{Cursor Parameters}). The @code{hollow-small} type is used
3648 instead of @code{hollow} when the normal @code{hollow-rectangle}
3649 bitmap is too tall to fit on a specific display line.
3651 Each @var{bitmap} should be a symbol specifying the fringe bitmap to
3652 be displayed for that logical cursor type.
3654 See the next subsection for details.
3657 @xref{Fringe Bitmaps}.
3660 @c FIXME: I can't find the fringes-indicator-alist variable. Maybe
3661 @c it should be fringe-indicator-alist or fringe-cursor-alist? --xfq
3662 When @code{fringe-cursor-alist} has a buffer-local value, and there is
3663 no bitmap defined for a cursor type, the corresponding value from the
3664 default value of @code{fringes-indicator-alist} is used.
3667 @node Fringe Bitmaps
3668 @subsection Fringe Bitmaps
3669 @cindex fringe bitmaps
3670 @cindex bitmaps, fringe
3672 The @dfn{fringe bitmaps} are the actual bitmaps which represent the
3673 logical fringe indicators for truncated or continued lines, buffer
3674 boundaries, overlay arrows, etc. Each bitmap is represented by a
3677 These symbols are referred to by the variables
3678 @code{fringe-indicator-alist} and @code{fringe-cursor-alist},
3679 described in the previous subsections.
3682 These symbols are referred to by the variable
3683 @code{fringe-indicator-alist}, which maps fringe indicators to bitmaps
3684 (@pxref{Fringe Indicators}), and the variable
3685 @code{fringe-cursor-alist}, which maps fringe cursors to bitmaps
3686 (@pxref{Fringe Cursors}).
3689 Lisp programs can also directly display a bitmap in the left or
3690 right fringe, by using a @code{display} property for one of the
3691 characters appearing in the line (@pxref{Other Display Specs}). Such
3692 a display specification has the form
3695 (@var{fringe} @var{bitmap} [@var{face}])
3699 @var{fringe} is either the symbol @code{left-fringe} or
3700 @code{right-fringe}. @var{bitmap} is a symbol identifying the bitmap
3701 to display. The optional @var{face} names a face whose foreground
3702 color is used to display the bitmap; this face is automatically merged
3703 with the @code{fringe} face.
3705 Here is a list of the standard fringe bitmaps defined in Emacs, and
3706 how they are currently used in Emacs (via
3707 @code{fringe-indicator-alist} and @code{fringe-cursor-alist}):
3710 @item @code{left-arrow}, @code{right-arrow}
3711 Used to indicate truncated lines.
3713 @item @code{left-curly-arrow}, @code{right-curly-arrow}
3714 Used to indicate continued lines.
3716 @item @code{right-triangle}, @code{left-triangle}
3717 The former is used by overlay arrows. The latter is unused.
3719 @item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle}
3720 @itemx @code{bottom-left-angle}, @code{bottom-right-angle}
3721 @itemx @code{top-right-angle}, @code{top-left-angle}
3722 @itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle}
3723 Used to indicate buffer boundaries.
3725 @item @code{filled-rectangle}, @code{hollow-rectangle}
3726 @itemx @code{filled-square}, @code{hollow-square}
3727 @itemx @code{vertical-bar}, @code{horizontal-bar}
3728 Used for different types of fringe cursors.
3730 @item @code{empty-line}, @code{exclamation-mark}, @code{question-mark}, @code{exclamation-mark}
3731 Not used by core Emacs features.
3735 The next subsection describes how to define your own fringe bitmaps.
3737 @defun fringe-bitmaps-at-pos &optional pos window
3738 This function returns the fringe bitmaps of the display line
3739 containing position @var{pos} in window @var{window}. The return
3740 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
3741 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
3742 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
3743 is non-@code{nil} if there is an overlay arrow in the left fringe.
3745 The value is @code{nil} if @var{pos} is not visible in @var{window}.
3746 If @var{window} is @code{nil}, that stands for the selected window.
3747 If @var{pos} is @code{nil}, that stands for the value of point in
3751 @node Customizing Bitmaps
3752 @subsection Customizing Fringe Bitmaps
3753 @cindex fringe bitmaps, customizing
3755 @defun define-fringe-bitmap bitmap bits &optional height width align
3756 This function defines the symbol @var{bitmap} as a new fringe bitmap,
3757 or replaces an existing bitmap with that name.
3759 The argument @var{bits} specifies the image to use. It should be
3760 either a string or a vector of integers, where each element (an
3761 integer) corresponds to one row of the bitmap. Each bit of an integer
3762 corresponds to one pixel of the bitmap, where the low bit corresponds
3763 to the rightmost pixel of the bitmap.
3765 The height is normally the length of @var{bits}. However, you
3766 can specify a different height with non-@code{nil} @var{height}. The width
3767 is normally 8, but you can specify a different width with non-@code{nil}
3768 @var{width}. The width must be an integer between 1 and 16.
3770 The argument @var{align} specifies the positioning of the bitmap
3771 relative to the range of rows where it is used; the default is to
3772 center the bitmap. The allowed values are @code{top}, @code{center},
3775 The @var{align} argument may also be a list @code{(@var{align}
3776 @var{periodic})} where @var{align} is interpreted as described above.
3777 If @var{periodic} is non-@code{nil}, it specifies that the rows in
3778 @code{bits} should be repeated enough times to reach the specified
3782 @defun destroy-fringe-bitmap bitmap
3783 This function destroy the fringe bitmap identified by @var{bitmap}.
3784 If @var{bitmap} identifies a standard fringe bitmap, it actually
3785 restores the standard definition of that bitmap, instead of
3786 eliminating it entirely.
3789 @defun set-fringe-bitmap-face bitmap &optional face
3790 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
3791 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
3792 bitmap's face controls the color to draw it in.
3794 @var{face} is merged with the @code{fringe} face, so normally
3795 @var{face} should specify only the foreground color.
3799 @subsection The Overlay Arrow
3800 @c @cindex overlay arrow Duplicates variable names
3802 The @dfn{overlay arrow} is useful for directing the user's attention
3803 to a particular line in a buffer. For example, in the modes used for
3804 interface to debuggers, the overlay arrow indicates the line of code
3805 about to be executed. This feature has nothing to do with
3806 @dfn{overlays} (@pxref{Overlays}).
3808 @defvar overlay-arrow-string
3809 This variable holds the string to display to call attention to a
3810 particular line, or @code{nil} if the arrow feature is not in use.
3811 On a graphical display the contents of the string are ignored; instead a
3812 glyph is displayed in the fringe area to the left of the display area.
3815 @defvar overlay-arrow-position
3816 This variable holds a marker that indicates where to display the overlay
3817 arrow. It should point at the beginning of a line. On a non-graphical
3818 display the arrow text
3819 appears at the beginning of that line, overlaying any text that would
3820 otherwise appear. Since the arrow is usually short, and the line
3821 usually begins with indentation, normally nothing significant is
3824 The overlay-arrow string is displayed in any given buffer if the value
3825 of @code{overlay-arrow-position} in that buffer points into that
3826 buffer. Thus, it is possible to display multiple overlay arrow strings
3827 by creating buffer-local bindings of @code{overlay-arrow-position}.
3828 However, it is usually cleaner to use
3829 @code{overlay-arrow-variable-list} to achieve this result.
3830 @c !!! overlay-arrow-position: but the overlay string may remain in the display
3831 @c of some other buffer until an update is required. This should be fixed
3835 You can do a similar job by creating an overlay with a
3836 @code{before-string} property. @xref{Overlay Properties}.
3838 You can define multiple overlay arrows via the variable
3839 @code{overlay-arrow-variable-list}.
3841 @defvar overlay-arrow-variable-list
3842 This variable's value is a list of variables, each of which specifies
3843 the position of an overlay arrow. The variable
3844 @code{overlay-arrow-position} has its normal meaning because it is on
3848 Each variable on this list can have properties
3849 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
3850 specify an overlay arrow string (for text terminals) or fringe bitmap
3851 (for graphical terminals) to display at the corresponding overlay
3852 arrow position. If either property is not set, the default
3853 @code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator
3857 @section Scroll Bars
3860 Normally the frame parameter @code{vertical-scroll-bars} controls
3861 whether the windows in the frame have vertical scroll bars, and
3862 whether they are on the left or right. The frame parameter
3863 @code{scroll-bar-width} specifies how wide they are (@code{nil}
3864 meaning the default). @xref{Layout Parameters}.
3866 @defun frame-current-scroll-bars &optional frame
3867 This function reports the scroll bar type settings for frame
3868 @var{frame}. The value is a cons cell
3869 @code{(@var{vertical-type} .@: @var{horizontal-type})}, where
3870 @var{vertical-type} is either @code{left}, @code{right}, or @code{nil}
3871 (which means no scroll bar.) @var{horizontal-type} is meant to
3872 specify the horizontal scroll bar type, but since they are not
3873 implemented, it is always @code{nil}.
3876 @vindex vertical-scroll-bar
3877 You can enable or disable scroll bars for a particular buffer,
3878 by setting the variable @code{vertical-scroll-bar}. This variable
3879 automatically becomes buffer-local when set. The possible values are
3880 @code{left}, @code{right}, @code{t}, which means to use the
3881 frame's default, and @code{nil} for no scroll bar.
3883 You can also control this for individual windows. Call the function
3884 @code{set-window-scroll-bars} to specify what to do for a specific window:
3886 @defun set-window-scroll-bars window width &optional vertical-type horizontal-type
3887 This function sets the width and type of scroll bars for window
3890 @var{width} specifies the scroll bar width in pixels (@code{nil} means
3891 use the width specified for the frame). @var{vertical-type} specifies
3892 whether to have a vertical scroll bar and, if so, where. The possible
3893 values are @code{left}, @code{right} and @code{nil}, just like the
3894 values of the @code{vertical-scroll-bars} frame parameter.
3896 The argument @var{horizontal-type} is meant to specify whether and
3897 where to have horizontal scroll bars, but since they are not
3898 implemented, it has no effect. If @var{window} is @code{nil}, the
3899 selected window is used.
3902 @defun window-scroll-bars &optional window
3903 Report the width and type of scroll bars specified for @var{window}.
3904 If @var{window} is omitted or @code{nil}, the selected window is used.
3905 The value is a list of the form @code{(@var{width}
3906 @var{cols} @var{vertical-type} @var{horizontal-type})}. The value
3907 @var{width} is the value that was specified for the width (which may
3908 be @code{nil}); @var{cols} is the number of columns that the scroll
3909 bar actually occupies.
3911 @var{horizontal-type} is not actually meaningful.
3914 @defun window-scroll-bar-width &optional window
3915 This function returns the width of @var{window}'s vertical scrollbar,
3916 in pixels. @var{window} must be a live window. If @var{window} is
3917 @code{nil} or omitted, it will be the selected window.
3920 If you don't specify these values for a window with
3921 @code{set-window-scroll-bars}, the buffer-local variables
3922 @code{scroll-bar-mode} and @code{scroll-bar-width} in the buffer being
3923 displayed control the window's vertical scroll bars. The function
3924 @code{set-window-buffer} examines these variables. If you change them
3925 in a buffer that is already visible in a window, you can make the
3926 window take note of the new values by calling @code{set-window-buffer}
3927 specifying the same buffer that is already displayed.
3929 @defopt scroll-bar-mode
3930 This variable, always local in all buffers, controls whether and where
3931 to put scroll bars in windows displaying the buffer. The possible values
3932 are @code{nil} for no scroll bar, @code{left} to put a scroll bar on
3933 the left, and @code{right} to put a scroll bar on the right.
3936 @defun window-current-scroll-bars &optional window
3937 This function reports the scroll bar type for window @var{window}.
3938 If @var{window} is omitted or @code{nil}, the selected window is used.
3939 The value is a cons cell
3940 @code{(@var{vertical-type} .@: @var{horizontal-type})}. Unlike
3941 @code{window-scroll-bars}, this reports the scroll bar type actually
3942 used, once frame defaults and @code{scroll-bar-mode} are taken into
3946 @defvar scroll-bar-width
3947 This variable, always local in all buffers, specifies the width of the
3948 buffer's scroll bars, measured in pixels. A value of @code{nil} means
3949 to use the value specified by the frame.
3952 @node Window Dividers
3953 @section Window Dividers
3954 @cindex window dividers
3955 @cindex right dividers
3956 @cindex bottom dividers
3958 Window dividers are bars drawn between a frame's windows. A ``right''
3959 divider is drawn between a window and any adjacent windows on the right.
3960 Its width (thickness) is specified by the frame parameter
3961 @code{right-divider-width}. A ``bottom'' divider is drawn between a
3962 window and adjacent windows on the bottom or the echo area. Its width
3963 is specified by the frame parameter @code{bottom-divider-width}. In
3964 either case, specifying a width of zero means to not draw such dividers.
3965 @xref{Layout Parameters}.
3967 Technically, a right divider ``belongs'' to the window on its left,
3968 which means that its width contributes to the total width of that
3969 window. A bottom divider ``belongs'' to the window above it, which
3970 means that its width contributes to the total height of that window.
3971 @xref{Window Sizes}. When a window has both, a right and a bottom
3972 divider, the bottom divider ``prevails''. This means that a bottom
3973 divider is drawn over the full total width of its window while the right
3974 divider ends above the bottom divider.
3976 Dividers can be dragged with the mouse and are therefore useful for
3977 adjusting the sizes of adjacent windows with the mouse. They also serve
3978 to visually set apart adjacent windows when no scroll bars or mode lines
3979 are present. The following three faces allow to customize the
3980 appearance of dividers:
3983 @item window-divider
3984 When a divider is less than three pixels wide, it is drawn solidly with
3985 the foreground of this face. For larger dividers this face is used for
3986 the inner part only, excluding the first and last pixel.
3988 @item window-divider-first-pixel
3989 This is the face used for drawing the first pixel of a divider that is
3990 at least three pixels wide. To obtain a solid appearance, set this to
3991 the same value used for the @code{window-divider} face.
3993 @item window-divider-last-pixel
3994 This is the face used for drawing the last pixel of a divider that is at
3995 least three pixels wide. To obtain a solid appearance, set this to the
3996 same value used for the @code{window-divider} face.
3999 You can get the sizes of the dividers of a specific window with the
4000 following two functions.
4002 @defun window-right-divider-width &optional window
4003 Return the width (thickness) in pixels of @var{window}'s right divider.
4004 @var{window} must be a live window and defaults to the selected one.
4005 The return value is always zero for a rightmost window.
4008 @defun window-bottom-divider-width &optional window
4009 Return the width (thickness) in pixels of @var{window}'s bottom divider.
4010 @var{window} must be a live window and defaults to the selected one.
4011 The return value is zero for the minibuffer window or a bottommost
4012 window on a minibuffer-less frame.
4016 @node Display Property
4017 @section The @code{display} Property
4018 @cindex display specification
4019 @kindex display @r{(text property)}
4021 The @code{display} text property (or overlay property) is used to
4022 insert images into text, and to control other aspects of how text
4023 displays. The value of the @code{display} property should be a
4024 display specification, or a list or vector containing several display
4025 specifications. Display specifications in the same @code{display}
4026 property value generally apply in parallel to the text they cover.
4028 If several sources (overlays and/or a text property) specify values
4029 for the @code{display} property, only one of the values takes effect,
4030 following the rules of @code{get-char-property}. @xref{Examining
4033 The rest of this section describes several kinds of
4034 display specifications and what they mean.
4037 * Replacing Specs:: Display specs that replace the text.
4038 * Specified Space:: Displaying one space with a specified width.
4039 * Pixel Specification:: Specifying space width or height in pixels.
4040 * Other Display Specs:: Displaying an image; adjusting the height,
4041 spacing, and other properties of text.
4042 * Display Margins:: Displaying text or images to the side of the main text.
4045 @node Replacing Specs
4046 @subsection Display Specs That Replace The Text
4048 Some kinds of display specifications specify something to display
4049 instead of the text that has the property. These are called
4050 @dfn{replacing} display specifications. Emacs does not allow the user
4051 to interactively move point into the middle of buffer text that is
4052 replaced in this way.
4054 If a list of display specifications includes more than one replacing
4055 display specification, the first overrides the rest. Replacing
4056 display specifications make most other display specifications
4057 irrelevant, since those don't apply to the replacement.
4059 For replacing display specifications, ``the text that has the
4060 property'' means all the consecutive characters that have the same
4061 Lisp object as their @code{display} property; these characters are
4062 replaced as a single unit. If two characters have different Lisp
4063 objects as their @code{display} properties (i.e., objects which are
4064 not @code{eq}), they are handled separately.
4066 Here is an example which illustrates this point. A string serves as
4067 a replacing display specification, which replaces the text that has
4068 the property with the specified string (@pxref{Other Display Specs}).
4069 Consider the following function:
4074 (let ((string (concat "A"))
4075 (start (+ i i (point-min))))
4076 (put-text-property start (1+ start) 'display string)
4077 (put-text-property start (+ 2 start) 'display string))))
4081 This function gives each of the first ten characters in the buffer a
4082 @code{display} property which is a string @code{"A"}, but they don't
4083 all get the same string object. The first two characters get the same
4084 string object, so they are replaced with one @samp{A}; the fact that
4085 the display property was assigned in two separate calls to
4086 @code{put-text-property} is irrelevant. Similarly, the next two
4087 characters get a second string (@code{concat} creates a new string
4088 object), so they are replaced with one @samp{A}; and so on. Thus, the
4089 ten characters appear as five A's.
4091 @node Specified Space
4092 @subsection Specified Spaces
4093 @cindex spaces, specified height or width
4094 @cindex variable-width spaces
4096 To display a space of specified width and/or height, use a display
4097 specification of the form @code{(space . @var{props})}, where
4098 @var{props} is a property list (a list of alternating properties and
4099 values). You can put this property on one or more consecutive
4100 characters; a space of the specified height and width is displayed in
4101 place of @emph{all} of those characters. These are the properties you
4102 can use in @var{props} to specify the weight of the space:
4105 @item :width @var{width}
4106 If @var{width} is a number, it specifies
4107 that the space width should be @var{width} times the normal character
4108 width. @var{width} can also be a @dfn{pixel width} specification
4109 (@pxref{Pixel Specification}).
4111 @item :relative-width @var{factor}
4112 Specifies that the width of the stretch should be computed from the
4113 first character in the group of consecutive characters that have the
4114 same @code{display} property. The space width is the width of that
4115 character, multiplied by @var{factor}.
4117 @item :align-to @var{hpos}
4118 Specifies that the space should be wide enough to reach @var{hpos}.
4119 If @var{hpos} is a number, it is measured in units of the normal
4120 character width. @var{hpos} can also be a @dfn{pixel width}
4121 specification (@pxref{Pixel Specification}).
4124 You should use one and only one of the above properties. You can
4125 also specify the height of the space, with these properties:
4128 @item :height @var{height}
4129 Specifies the height of the space.
4130 If @var{height} is a number, it specifies
4131 that the space height should be @var{height} times the normal character
4132 height. The @var{height} may also be a @dfn{pixel height} specification
4133 (@pxref{Pixel Specification}).
4135 @item :relative-height @var{factor}
4136 Specifies the height of the space, multiplying the ordinary height
4137 of the text having this display specification by @var{factor}.
4139 @item :ascent @var{ascent}
4140 If the value of @var{ascent} is a non-negative number no greater than
4141 100, it specifies that @var{ascent} percent of the height of the space
4142 should be considered as the ascent of the space---that is, the part
4143 above the baseline. The ascent may also be specified in pixel units
4144 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
4148 Don't use both @code{:height} and @code{:relative-height} together.
4150 The @code{:width} and @code{:align-to} properties are supported on
4151 non-graphic terminals, but the other space properties in this section
4154 Note that space properties are treated as paragraph separators for
4155 the purposes of reordering bidirectional text for display.
4156 @xref{Bidirectional Display}, for the details.
4158 @node Pixel Specification
4159 @subsection Pixel Specification for Spaces
4160 @cindex spaces, pixel specification
4162 The value of the @code{:width}, @code{:align-to}, @code{:height},
4163 and @code{:ascent} properties can be a special kind of expression that
4164 is evaluated during redisplay. The result of the evaluation is used
4165 as an absolute number of pixels.
4167 The following expressions are supported:
4171 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
4172 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
4173 @var{unit} ::= in | mm | cm | width | height
4176 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
4178 @var{pos} ::= left | center | right
4179 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
4184 The form @var{num} specifies a fraction of the default frame font
4185 height or width. The form @code{(@var{num})} specifies an absolute
4186 number of pixels. If @var{num} is a symbol, @var{symbol}, its
4187 buffer-local variable binding is used.
4189 The @code{in}, @code{mm}, and @code{cm} units specify the number of
4190 pixels per inch, millimeter, and centimeter, respectively. The
4191 @code{width} and @code{height} units correspond to the default width
4192 and height of the current face. An image specification @code{image}
4193 corresponds to the width or height of the image.
4195 The elements @code{left-fringe}, @code{right-fringe},
4196 @code{left-margin}, @code{right-margin}, @code{scroll-bar}, and
4197 @code{text} specify to the width of the corresponding area of the
4200 The @code{left}, @code{center}, and @code{right} positions can be
4201 used with @code{:align-to} to specify a position relative to the left
4202 edge, center, or right edge of the text area.
4204 Any of the above window elements (except @code{text}) can also be
4205 used with @code{:align-to} to specify that the position is relative to
4206 the left edge of the given area. Once the base offset for a relative
4207 position has been set (by the first occurrence of one of these
4208 symbols), further occurrences of these symbols are interpreted as the
4209 width of the specified area. For example, to align to the center of
4210 the left-margin, use
4213 :align-to (+ left-margin (0.5 . left-margin))
4216 If no specific base offset is set for alignment, it is always relative
4217 to the left edge of the text area. For example, @samp{:align-to 0} in a
4218 header-line aligns with the first text column in the text area.
4220 A value of the form @code{(@var{num} . @var{expr})} stands for the
4221 product of the values of @var{num} and @var{expr}. For example,
4222 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
4223 @var{image})} specifies half the width (or height) of the specified
4226 The form @code{(+ @var{expr} ...)} adds up the value of the
4227 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
4228 the value of the expressions.
4230 @node Other Display Specs
4231 @subsection Other Display Specifications
4233 Here are the other sorts of display specifications that you can use
4234 in the @code{display} text property.
4238 Display @var{string} instead of the text that has this property.
4240 Recursive display specifications are not supported---@var{string}'s
4241 @code{display} properties, if any, are not used.
4243 @item (image . @var{image-props})
4244 This kind of display specification is an image descriptor (@pxref{Images}).
4245 When used as a display specification, it means to display the image
4246 instead of the text that has the display specification.
4248 @item (slice @var{x} @var{y} @var{width} @var{height})
4249 This specification together with @code{image} specifies a @dfn{slice}
4250 (a partial area) of the image to display. The elements @var{y} and
4251 @var{x} specify the top left corner of the slice, within the image;
4252 @var{width} and @var{height} specify the width and height of the
4253 slice. Integers are numbers of pixels. A floating-point number
4254 in the range 0.0--1.0 stands for that fraction of the width or height
4255 of the entire image.
4257 @item ((margin nil) @var{string})
4258 A display specification of this form means to display @var{string}
4259 instead of the text that has the display specification, at the same
4260 position as that text. It is equivalent to using just @var{string},
4261 but it is done as a special case of marginal display (@pxref{Display
4264 @item (left-fringe @var{bitmap} @r{[}@var{face}@r{]})
4265 @itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]})
4266 This display specification on any character of a line of text causes
4267 the specified @var{bitmap} be displayed in the left or right fringes
4268 for that line, instead of the characters that have the display
4269 specification. The optional @var{face} specifies the colors to be
4270 used for the bitmap. @xref{Fringe Bitmaps}, for the details.
4272 @item (space-width @var{factor})
4273 This display specification affects all the space characters within the
4274 text that has the specification. It displays all of these spaces
4275 @var{factor} times as wide as normal. The element @var{factor} should
4276 be an integer or float. Characters other than spaces are not affected
4277 at all; in particular, this has no effect on tab characters.
4279 @item (height @var{height})
4280 This display specification makes the text taller or shorter.
4281 Here are the possibilities for @var{height}:
4284 @item @code{(+ @var{n})}
4285 @c FIXME: Add an index for "step"? --xfq
4286 This means to use a font that is @var{n} steps larger. A ``step'' is
4287 defined by the set of available fonts---specifically, those that match
4288 what was otherwise specified for this text, in all attributes except
4289 height. Each size for which a suitable font is available counts as
4290 another step. @var{n} should be an integer.
4292 @item @code{(- @var{n})}
4293 This means to use a font that is @var{n} steps smaller.
4295 @item a number, @var{factor}
4296 A number, @var{factor}, means to use a font that is @var{factor} times
4297 as tall as the default font.
4299 @item a symbol, @var{function}
4300 A symbol is a function to compute the height. It is called with the
4301 current height as argument, and should return the new height to use.
4303 @item anything else, @var{form}
4304 If the @var{height} value doesn't fit the previous possibilities, it is
4305 a form. Emacs evaluates it to get the new height, with the symbol
4306 @code{height} bound to the current specified font height.
4309 @item (raise @var{factor})
4310 This kind of display specification raises or lowers the text
4311 it applies to, relative to the baseline of the line.
4313 @var{factor} must be a number, which is interpreted as a multiple of the
4314 height of the affected text. If it is positive, that means to display
4315 the characters raised. If it is negative, that means to display them
4318 If the text also has a @code{height} display specification, that does
4319 not affect the amount of raising or lowering, which is based on the
4320 faces used for the text.
4323 @c We put all the `@code{(when ...)}' on one line to encourage
4324 @c makeinfo's end-of-sentence heuristics to DTRT. Previously, the dot
4325 @c was at eol; the info file ended up w/ two spaces rendered after it.
4326 You can make any display specification conditional. To do that,
4327 package it in another list of the form
4328 @code{(when @var{condition} . @var{spec})}.
4329 Then the specification @var{spec} applies only when
4330 @var{condition} evaluates to a non-@code{nil} value. During the
4331 evaluation, @code{object} is bound to the string or buffer having the
4332 conditional @code{display} property. @code{position} and
4333 @code{buffer-position} are bound to the position within @code{object}
4334 and the buffer position where the @code{display} property was found,
4335 respectively. Both positions can be different when @code{object} is a
4338 @node Display Margins
4339 @subsection Displaying in the Margins
4340 @cindex display margins
4341 @cindex margins, display
4343 A buffer can have blank areas called @dfn{display margins} on the
4344 left and on the right. Ordinary text never appears in these areas,
4345 but you can put things into the display margins using the
4346 @code{display} property. There is currently no way to make text or
4347 images in the margin mouse-sensitive.
4349 The way to display something in the margins is to specify it in a
4350 margin display specification in the @code{display} property of some
4351 text. This is a replacing display specification, meaning that the
4352 text you put it on does not get displayed; the margin display appears,
4353 but that text does not.
4355 A margin display specification looks like @code{((margin
4356 right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}.
4357 Here, @var{spec} is another display specification that says what to
4358 display in the margin. Typically it is a string of text to display,
4359 or an image descriptor.
4361 To display something in the margin @emph{in association with}
4362 certain buffer text, without altering or preventing the display of
4363 that text, put a @code{before-string} property on the text and put the
4364 margin display specification on the contents of the before-string.
4366 Before the display margins can display anything, you must give
4367 them a nonzero width. The usual way to do that is to set these
4370 @defvar left-margin-width
4371 This variable specifies the width of the left margin, in character
4372 cell (a.k.a.@: ``column'') units. It is buffer-local in all buffers.
4373 A value of @code{nil} means no left marginal area.
4376 @defvar right-margin-width
4377 This variable specifies the width of the right margin, in character
4378 cell units. It is buffer-local in all buffers. A value of @code{nil}
4379 means no right marginal area.
4382 Setting these variables does not immediately affect the window. These
4383 variables are checked when a new buffer is displayed in the window.
4384 Thus, you can make changes take effect by calling
4385 @code{set-window-buffer}.
4387 You can also set the margin widths immediately.
4389 @defun set-window-margins window left &optional right
4390 This function specifies the margin widths for window @var{window}, in
4391 character cell units. The argument @var{left} controls the left
4392 margin, and @var{right} controls the right margin (default @code{0}).
4395 @defun window-margins &optional window
4396 This function returns the width of the left and right margins of
4397 @var{window} as a cons cell of the form @w{@code{(@var{left}
4398 . @var{right})}}. If one of the two marginal areas does not exist,
4399 its width is returned as @code{nil}; if neither of the two margins exist,
4400 the function returns @code{(nil)}. If @var{window} is @code{nil}, the
4401 selected window is used.
4406 @cindex images in buffers
4408 To display an image in an Emacs buffer, you must first create an image
4409 descriptor, then use it as a display specifier in the @code{display}
4410 property of text that is displayed (@pxref{Display Property}).
4412 Emacs is usually able to display images when it is run on a
4413 graphical terminal. Images cannot be displayed in a text terminal, on
4414 certain graphical terminals that lack the support for this, or if
4415 Emacs is compiled without image support. You can use the function
4416 @code{display-images-p} to determine if images can in principle be
4417 displayed (@pxref{Display Feature Testing}).
4420 * Image Formats:: Supported image formats.
4421 * Image Descriptors:: How to specify an image for use in @code{:display}.
4422 * XBM Images:: Special features for XBM format.
4423 * XPM Images:: Special features for XPM format.
4424 * PostScript Images:: Special features for PostScript format.
4425 * ImageMagick Images:: Special features available through ImageMagick.
4426 * Other Image Types:: Various other formats are supported.
4427 * Defining Images:: Convenient ways to define an image for later use.
4428 * Showing Images:: Convenient ways to display an image once it is defined.
4429 * Multi-Frame Images:: Some images contain more than one frame.
4430 * Image Cache:: Internal mechanisms of image display.
4434 @subsection Image Formats
4435 @cindex image formats
4438 Emacs can display a number of different image formats. Some of
4439 these image formats are supported only if particular support libraries
4440 are installed. On some platforms, Emacs can load support libraries on
4441 demand; if so, the variable @code{dynamic-library-alist} can be used
4442 to modify the set of known names for these dynamic libraries.
4443 @xref{Dynamic Libraries}.
4445 Supported image formats (and the required support libraries) include
4446 PBM and XBM (which do not depend on support libraries and are always
4447 available), XPM (@code{libXpm}), GIF (@code{libgif} or
4448 @code{libungif}), PostScript (@code{gs}), JPEG (@code{libjpeg}), TIFF
4449 (@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}).
4451 Each of these image formats is associated with an @dfn{image type
4452 symbol}. The symbols for the above formats are, respectively,
4453 @code{pbm}, @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
4454 @code{jpeg}, @code{tiff}, @code{png}, and @code{svg}.
4456 Furthermore, if you build Emacs with ImageMagick
4457 (@code{libMagickWand}) support, Emacs can display any image format
4458 that ImageMagick can. @xref{ImageMagick Images}. All images
4459 displayed via ImageMagick have type symbol @code{imagemagick}.
4462 This variable contains a list of type symbols for image formats which
4463 are potentially supported in the current configuration.
4465 ``Potentially'' means that Emacs knows about the image types, not
4466 necessarily that they can be used (for example, they could depend on
4467 unavailable dynamic libraries). To know which image types are really
4468 available, use @code{image-type-available-p}.
4471 @defun image-type-available-p type
4472 This function returns non-@code{nil} if images of type @var{type} can
4473 be loaded and displayed. @var{type} must be an image type symbol.
4475 For image types whose support libraries are statically linked, this
4476 function always returns @code{t}. For image types whose support
4477 libraries are dynamically loaded, it returns @code{t} if the library
4478 could be loaded and @code{nil} otherwise.
4481 @node Image Descriptors
4482 @subsection Image Descriptors
4483 @cindex image descriptor
4485 An @dfn{image descriptor} is a list which specifies the underlying
4486 data for an image, and how to display it. It is typically used as the
4487 value of a @code{display} overlay or text property (@pxref{Other
4488 Display Specs}); but @xref{Showing Images}, for convenient helper
4489 functions to insert images into buffers.
4491 Each image descriptor has the form @code{(image . @var{props})},
4492 where @var{props} is a property list of alternating keyword symbols
4493 and values, including at least the pair @code{:type @var{TYPE}} which
4494 specifies the image type.
4496 The following is a list of properties that are meaningful for all
4497 image types (there are also properties which are meaningful only for
4498 certain image types, as documented in the following subsections):
4501 @item :type @var{type}
4504 @xref{Image Formats}.
4506 Every image descriptor must include this property.
4508 @item :file @var{file}
4509 This says to load the image from file @var{file}. If @var{file} is
4510 not an absolute file name, it is expanded in @code{data-directory}.
4512 @item :data @var{data}
4513 This specifies the raw image data. Each image descriptor must have
4514 either @code{:data} or @code{:file}, but not both.
4516 For most image types, the value of a @code{:data} property should be a
4517 string containing the image data. Some image types do not support
4518 @code{:data}; for some others, @code{:data} alone is not enough, so
4519 you need to use other image properties along with @code{:data}. See
4520 the following subsections for details.
4522 @item :margin @var{margin}
4523 This specifies how many pixels to add as an extra margin around the
4524 image. The value, @var{margin}, must be a non-negative number, or a
4525 pair @code{(@var{x} . @var{y})} of such numbers. If it is a pair,
4526 @var{x} specifies how many pixels to add horizontally, and @var{y}
4527 specifies how many pixels to add vertically. If @code{:margin} is not
4528 specified, the default is zero.
4530 @item :ascent @var{ascent}
4531 This specifies the amount of the image's height to use for its
4532 ascent---that is, the part above the baseline. The value,
4533 @var{ascent}, must be a number in the range 0 to 100, or the symbol
4536 If @var{ascent} is a number, that percentage of the image's height is
4537 used for its ascent.
4539 If @var{ascent} is @code{center}, the image is vertically centered
4540 around a centerline which would be the vertical centerline of text drawn
4541 at the position of the image, in the manner specified by the text
4542 properties and overlays that apply to the image.
4544 If this property is omitted, it defaults to 50.
4546 @item :relief @var{relief}
4547 This adds a shadow rectangle around the image. The value,
4548 @var{relief}, specifies the width of the shadow lines, in pixels. If
4549 @var{relief} is negative, shadows are drawn so that the image appears
4550 as a pressed button; otherwise, it appears as an unpressed button.
4552 @item :conversion @var{algorithm}
4553 This specifies a conversion algorithm that should be applied to the
4554 image before it is displayed; the value, @var{algorithm}, specifies
4560 Specifies the Laplace edge detection algorithm, which blurs out small
4561 differences in color while highlighting larger differences. People
4562 sometimes consider this useful for displaying the image for a
4563 ``disabled'' button.
4565 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
4566 @cindex edge detection, images
4567 Specifies a general edge-detection algorithm. @var{matrix} must be
4568 either a nine-element list or a nine-element vector of numbers. A pixel
4569 at position @math{x/y} in the transformed image is computed from
4570 original pixels around that position. @var{matrix} specifies, for each
4571 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
4572 will influence the transformed pixel; element @math{0} specifies the
4573 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
4574 the pixel at @math{x/y-1} etc., as shown below:
4577 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
4578 x-1/y & x/y & x+1/y \cr
4579 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
4584 (x-1/y-1 x/y-1 x+1/y-1
4586 x-1/y+1 x/y+1 x+1/y+1)
4590 The resulting pixel is computed from the color intensity of the color
4591 resulting from summing up the RGB values of surrounding pixels,
4592 multiplied by the specified factors, and dividing that sum by the sum
4593 of the factors' absolute values.
4595 Laplace edge-detection currently uses a matrix of
4598 $$\pmatrix{1 & 0 & 0 \cr
4611 Emboss edge-detection uses a matrix of
4614 $$\pmatrix{ 2 & -1 & 0 \cr
4628 Specifies transforming the image so that it looks ``disabled''.
4631 @item :mask @var{mask}
4632 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
4633 a clipping mask for the image, so that the background of a frame is
4634 visible behind the image. If @var{bg} is not specified, or if @var{bg}
4635 is @code{t}, determine the background color of the image by looking at
4636 the four corners of the image, assuming the most frequently occurring
4637 color from the corners is the background color of the image. Otherwise,
4638 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
4639 specifying the color to assume for the background of the image.
4641 If @var{mask} is @code{nil}, remove a mask from the image, if it has
4642 one. Images in some formats include a mask which can be removed by
4643 specifying @code{:mask nil}.
4645 @item :pointer @var{shape}
4646 This specifies the pointer shape when the mouse pointer is over this
4647 image. @xref{Pointer Shape}, for available pointer shapes.
4649 @item :map @var{map}
4651 This associates an image map of @dfn{hot spots} with this image.
4653 An image map is an alist where each element has the format
4654 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
4655 as either a rectangle, a circle, or a polygon.
4657 A rectangle is a cons
4658 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
4659 which specifies the pixel coordinates of the upper left and bottom right
4660 corners of the rectangle area.
4663 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
4664 which specifies the center and the radius of the circle; @var{r} may
4665 be a float or integer.
4668 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
4669 where each pair in the vector describes one corner in the polygon.
4671 When the mouse pointer lies on a hot-spot area of an image, the
4672 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
4673 property, that defines a tool-tip for the hot-spot, and if it contains
4674 a @code{pointer} property, that defines the shape of the mouse cursor when
4675 it is on the hot-spot.
4676 @xref{Pointer Shape}, for available pointer shapes.
4678 When you click the mouse when the mouse pointer is over a hot-spot, an
4679 event is composed by combining the @var{id} of the hot-spot with the
4680 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
4681 @var{id} is @code{area4}.
4684 @defun image-mask-p spec &optional frame
4685 This function returns @code{t} if image @var{spec} has a mask bitmap.
4686 @var{frame} is the frame on which the image will be displayed.
4687 @var{frame} @code{nil} or omitted means to use the selected frame
4688 (@pxref{Input Focus}).
4692 @subsection XBM Images
4695 To use XBM format, specify @code{xbm} as the image type. This image
4696 format doesn't require an external library, so images of this type are
4699 Additional image properties supported for the @code{xbm} image type are:
4702 @item :foreground @var{foreground}
4703 The value, @var{foreground}, should be a string specifying the image
4704 foreground color, or @code{nil} for the default color. This color is
4705 used for each pixel in the XBM that is 1. The default is the frame's
4708 @item :background @var{background}
4709 The value, @var{background}, should be a string specifying the image
4710 background color, or @code{nil} for the default color. This color is
4711 used for each pixel in the XBM that is 0. The default is the frame's
4715 If you specify an XBM image using data within Emacs instead of an
4716 external file, use the following three properties:
4719 @item :data @var{data}
4720 The value, @var{data}, specifies the contents of the image.
4721 There are three formats you can use for @var{data}:
4725 A vector of strings or bool-vectors, each specifying one line of the
4726 image. Do specify @code{:height} and @code{:width}.
4729 A string containing the same byte sequence as an XBM file would contain.
4730 You must not specify @code{:height} and @code{:width} in this case,
4731 because omitting them is what indicates the data has the format of an
4732 XBM file. The file contents specify the height and width of the image.
4735 A string or a bool-vector containing the bits of the image (plus perhaps
4736 some extra bits at the end that will not be used). It should contain at
4737 least @var{width} * @code{height} bits. In this case, you must specify
4738 @code{:height} and @code{:width}, both to indicate that the string
4739 contains just the bits rather than a whole XBM file, and to specify the
4743 @item :width @var{width}
4744 The value, @var{width}, specifies the width of the image, in pixels.
4746 @item :height @var{height}
4747 The value, @var{height}, specifies the height of the image, in pixels.
4751 @subsection XPM Images
4754 To use XPM format, specify @code{xpm} as the image type. The
4755 additional image property @code{:color-symbols} is also meaningful with
4756 the @code{xpm} image type:
4759 @item :color-symbols @var{symbols}
4760 The value, @var{symbols}, should be an alist whose elements have the
4761 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
4762 the name of a color as it appears in the image file, and @var{color}
4763 specifies the actual color to use for displaying that name.
4766 @node PostScript Images
4767 @subsection PostScript Images
4768 @cindex postscript images
4770 To use PostScript for an image, specify image type @code{postscript}.
4771 This works only if you have Ghostscript installed. You must always use
4772 these three properties:
4775 @item :pt-width @var{width}
4776 The value, @var{width}, specifies the width of the image measured in
4777 points (1/72 inch). @var{width} must be an integer.
4779 @item :pt-height @var{height}
4780 The value, @var{height}, specifies the height of the image in points
4781 (1/72 inch). @var{height} must be an integer.
4783 @item :bounding-box @var{box}
4784 The value, @var{box}, must be a list or vector of four integers, which
4785 specifying the bounding box of the PostScript image, analogous to the
4786 @samp{BoundingBox} comment found in PostScript files.
4789 %%BoundingBox: 22 171 567 738
4793 @node ImageMagick Images
4794 @subsection ImageMagick Images
4795 @cindex ImageMagick images
4796 @cindex images, support for more formats
4798 If you build Emacs with ImageMagick support, you can use the
4799 ImageMagick library to load many image formats (@pxref{File
4800 Conveniences,,, emacs, The GNU Emacs Manual}). The image type symbol
4801 for images loaded via ImageMagick is @code{imagemagick}, regardless of
4802 the actual underlying image format.
4804 @defun imagemagick-types
4805 This function returns a list of image file extensions supported by the
4806 current ImageMagick installation. Each list element is a symbol
4807 representing an internal ImageMagick name for an image type, such as
4808 @code{BMP} for @file{.bmp} images.
4811 @defopt imagemagick-enabled-types
4812 The value of this variable is a list of ImageMagick image types which
4813 Emacs may attempt to render using ImageMagick. Each list element
4814 should be one of the symbols in the list returned by
4815 @code{imagemagick-types}, or an equivalent string. Alternatively, a
4816 value of @code{t} enables ImageMagick for all possible image types.
4817 Regardless of the value of this variable,
4818 @code{imagemagick-types-inhibit} (see below) takes precedence.
4821 @defopt imagemagick-types-inhibit
4822 The value of this variable lists the ImageMagick image types which
4823 should never be rendered using ImageMagick, regardless of the value of
4824 @code{imagemagick-enabled-types}. A value of @code{t} disables
4825 ImageMagick entirely.
4828 @defvar image-format-suffixes
4829 This variable is an alist mapping image types to file name extensions.
4830 Emacs uses this in conjunction with the @code{:format} image property
4831 (see below) to give a hint to the ImageMagick library as to the type
4832 of an image. Each element has the form @code{(@var{type}
4833 @var{extension})}, where @var{type} is a symbol specifying an image
4834 content-type, and @var{extension} is a string that specifies the
4835 associated file name extension.
4838 Images loaded with ImageMagick support the following additional
4839 image descriptor properties:
4842 @item :background @var{background}
4843 @var{background}, if non-@code{nil}, should be a string specifying a
4844 color, which is used as the image's background color if the image
4845 supports transparency. If the value is @code{nil}, it defaults to the
4846 frame's background color.
4848 @item :width @var{width}, :height @var{height}
4849 The @code{:width} and @code{:height} keywords are used for scaling the
4850 image. If only one of them is specified, the other one will be
4851 calculated so as to preserve the aspect ratio. If both are specified,
4852 aspect ratio may not be preserved.
4854 @item :max-width @var{max-width}, :max-height @var{max-height}
4855 The @code{:max-width} and @code{:max-height} keywords are used for
4856 scaling if the size of the image of the image exceeds these values.
4857 If @code{:width} is set it will have precedence over @code{max-width},
4858 and if @code{:height} is set it will have precedence over
4859 @code{max-height}, but you can otherwise mix these keywords as you
4860 wish. @code{:max-width} and @code{:max-height} will always preserve
4863 @item :format @var{type}
4864 The value, @var{type}, should be a symbol specifying the type of the
4865 image data, as found in @code{image-format-suffixes}. This is used
4866 when the image does not have an associated file name, to provide a
4867 hint to ImageMagick to help it detect the image type.
4869 @item :rotation @var{angle}
4870 Specifies a rotation angle in degrees.
4872 @item :index @var{frame}
4873 @c Doesn't work: http://debbugs.gnu.org/7978
4874 @xref{Multi-Frame Images}.
4877 @node Other Image Types
4878 @subsection Other Image Types
4881 For PBM images, specify image type @code{pbm}. Color, gray-scale and
4882 monochromatic images are supported. For mono PBM images, two additional
4883 image properties are supported.
4886 @item :foreground @var{foreground}
4887 The value, @var{foreground}, should be a string specifying the image
4888 foreground color, or @code{nil} for the default color. This color is
4889 used for each pixel in the PBM that is 1. The default is the frame's
4892 @item :background @var{background}
4893 The value, @var{background}, should be a string specifying the image
4894 background color, or @code{nil} for the default color. This color is
4895 used for each pixel in the PBM that is 0. The default is the frame's
4900 The remaining image types that Emacs can support are:
4904 Image type @code{gif}.
4905 Supports the @code{:index} property. @xref{Multi-Frame Images}.
4908 Image type @code{jpeg}.
4911 Image type @code{png}.
4914 Image type @code{svg}.
4917 Image type @code{tiff}.
4918 Supports the @code{:index} property. @xref{Multi-Frame Images}.
4921 @node Defining Images
4922 @subsection Defining Images
4924 The functions @code{create-image}, @code{defimage} and
4925 @code{find-image} provide convenient ways to create image descriptors.
4927 @defun create-image file-or-data &optional type data-p &rest props
4928 This function creates and returns an image descriptor which uses the
4929 data in @var{file-or-data}. @var{file-or-data} can be a file name or
4930 a string containing the image data; @var{data-p} should be @code{nil}
4931 for the former case, non-@code{nil} for the latter case.
4933 The optional argument @var{type} is a symbol specifying the image type.
4934 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
4935 determine the image type from the file's first few bytes, or else
4936 from the file's name.
4938 The remaining arguments, @var{props}, specify additional image
4939 properties---for example,
4941 @c ':heuristic-mask' is not documented?
4943 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
4946 The function returns @code{nil} if images of this type are not
4947 supported. Otherwise it returns an image descriptor.
4950 @defmac defimage symbol specs &optional doc
4951 This macro defines @var{symbol} as an image name. The arguments
4952 @var{specs} is a list which specifies how to display the image.
4953 The third argument, @var{doc}, is an optional documentation string.
4955 Each argument in @var{specs} has the form of a property list, and each
4956 one should specify at least the @code{:type} property and either the
4957 @code{:file} or the @code{:data} property. The value of @code{:type}
4958 should be a symbol specifying the image type, the value of
4959 @code{:file} is the file to load the image from, and the value of
4960 @code{:data} is a string containing the actual image data. Here is an
4964 (defimage test-image
4965 ((:type xpm :file "~/test1.xpm")
4966 (:type xbm :file "~/test1.xbm")))
4969 @code{defimage} tests each argument, one by one, to see if it is
4970 usable---that is, if the type is supported and the file exists. The
4971 first usable argument is used to make an image descriptor which is
4972 stored in @var{symbol}.
4974 If none of the alternatives will work, then @var{symbol} is defined
4978 @defun find-image specs
4979 This function provides a convenient way to find an image satisfying one
4980 of a list of image specifications @var{specs}.
4982 Each specification in @var{specs} is a property list with contents
4983 depending on image type. All specifications must at least contain the
4984 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
4985 or @w{@code{:data @var{DATA}}}, where @var{type} is a symbol specifying
4986 the image type, e.g., @code{xbm}, @var{file} is the file to load the
4987 image from, and @var{data} is a string containing the actual image data.
4988 The first specification in the list whose @var{type} is supported, and
4989 @var{file} exists, is used to construct the image specification to be
4990 returned. If no specification is satisfied, @code{nil} is returned.
4992 The image is looked for in @code{image-load-path}.
4995 @defvar image-load-path
4996 This variable's value is a list of locations in which to search for
4997 image files. If an element is a string or a variable symbol whose
4998 value is a string, the string is taken to be the name of a directory
4999 to search. If an element is a variable symbol whose value is a list,
5000 that is taken to be a list of directory names to search.
5002 The default is to search in the @file{images} subdirectory of the
5003 directory specified by @code{data-directory}, then the directory
5004 specified by @code{data-directory}, and finally in the directories in
5005 @code{load-path}. Subdirectories are not automatically included in
5006 the search, so if you put an image file in a subdirectory, you have to
5007 supply the subdirectory name explicitly. For example, to find the
5008 image @file{images/foo/bar.xpm} within @code{data-directory}, you
5009 should specify the image as follows:
5012 (defimage foo-image '((:type xpm :file "foo/bar.xpm")))
5016 @defun image-load-path-for-library library image &optional path no-error
5017 This function returns a suitable search path for images used by the
5018 Lisp package @var{library}.
5020 The function searches for @var{image} first using @code{image-load-path},
5021 excluding @file{@code{data-directory}/images}, and then in
5022 @code{load-path}, followed by a path suitable for @var{library}, which
5023 includes @file{../../etc/images} and @file{../etc/images} relative to
5024 the library file itself, and finally in
5025 @file{@code{data-directory}/images}.
5027 Then this function returns a list of directories which contains first
5028 the directory in which @var{image} was found, followed by the value of
5029 @code{load-path}. If @var{path} is given, it is used instead of
5032 If @var{no-error} is non-@code{nil} and a suitable path can't be
5033 found, don't signal an error. Instead, return a list of directories as
5034 before, except that @code{nil} appears in place of the image directory.
5036 Here is an example of using @code{image-load-path-for-library}:
5039 (defvar image-load-path) ; shush compiler
5040 (let* ((load-path (image-load-path-for-library
5041 "mh-e" "mh-logo.xpm"))
5042 (image-load-path (cons (car load-path)
5044 (mh-tool-bar-folder-buttons-init))
5048 @node Showing Images
5049 @subsection Showing Images
5051 You can use an image descriptor by setting up the @code{display}
5052 property yourself, but it is easier to use the functions in this
5055 @defun insert-image image &optional string area slice
5056 This function inserts @var{image} in the current buffer at point. The
5057 value @var{image} should be an image descriptor; it could be a value
5058 returned by @code{create-image}, or the value of a symbol defined with
5059 @code{defimage}. The argument @var{string} specifies the text to put
5060 in the buffer to hold the image. If it is omitted or @code{nil},
5061 @code{insert-image} uses @code{" "} by default.
5063 The argument @var{area} specifies whether to put the image in a margin.
5064 If it is @code{left-margin}, the image appears in the left margin;
5065 @code{right-margin} specifies the right margin. If @var{area} is
5066 @code{nil} or omitted, the image is displayed at point within the
5069 The argument @var{slice} specifies a slice of the image to insert. If
5070 @var{slice} is @code{nil} or omitted the whole image is inserted.
5071 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
5072 @var{height})} which specifies the @var{x} and @var{y} positions and
5073 @var{width} and @var{height} of the image area to insert. Integer
5074 values are in units of pixels. A floating-point number in the range
5075 0.0--1.0 stands for that fraction of the width or height of the entire
5078 Internally, this function inserts @var{string} in the buffer, and gives
5079 it a @code{display} property which specifies @var{image}. @xref{Display
5083 @cindex slice, image
5085 @defun insert-sliced-image image &optional string area rows cols
5086 This function inserts @var{image} in the current buffer at point, like
5087 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
5088 equally sized slices.
5090 If an image is inserted ``sliced'', Emacs displays each slice as a
5091 separate image, and allow more intuitive scrolling up/down, instead of
5092 jumping up/down the entire image when paging through a buffer that
5093 displays (large) images.
5096 @defun put-image image pos &optional string area
5097 This function puts image @var{image} in front of @var{pos} in the
5098 current buffer. The argument @var{pos} should be an integer or a
5099 marker. It specifies the buffer position where the image should appear.
5100 The argument @var{string} specifies the text that should hold the image
5101 as an alternative to the default.
5103 The argument @var{image} must be an image descriptor, perhaps returned
5104 by @code{create-image} or stored by @code{defimage}.
5106 The argument @var{area} specifies whether to put the image in a margin.
5107 If it is @code{left-margin}, the image appears in the left margin;
5108 @code{right-margin} specifies the right margin. If @var{area} is
5109 @code{nil} or omitted, the image is displayed at point within the
5112 Internally, this function creates an overlay, and gives it a
5113 @code{before-string} property containing text that has a @code{display}
5114 property whose value is the image. (Whew!)
5117 @defun remove-images start end &optional buffer
5118 This function removes images in @var{buffer} between positions
5119 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
5120 images are removed from the current buffer.
5122 This removes only images that were put into @var{buffer} the way
5123 @code{put-image} does it, not images that were inserted with
5124 @code{insert-image} or in other ways.
5127 @defun image-size spec &optional pixels frame
5128 @cindex size of image
5129 This function returns the size of an image as a pair
5130 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
5131 specification. @var{pixels} non-@code{nil} means return sizes
5132 measured in pixels, otherwise return sizes measured in canonical
5133 character units (fractions of the width/height of the frame's default
5134 font). @var{frame} is the frame on which the image will be displayed.
5135 @var{frame} null or omitted means use the selected frame (@pxref{Input
5139 @defvar max-image-size
5140 This variable is used to define the maximum size of image that Emacs
5141 will load. Emacs will refuse to load (and display) any image that is
5142 larger than this limit.
5144 If the value is an integer, it directly specifies the maximum
5145 image height and width, measured in pixels. If it is floating
5146 point, it specifies the maximum image height and width
5147 as a ratio to the frame height and width. If the value is
5148 non-numeric, there is no explicit limit on the size of images.
5150 The purpose of this variable is to prevent unreasonably large images
5151 from accidentally being loaded into Emacs. It only takes effect the
5152 first time an image is loaded. Once an image is placed in the image
5153 cache, it can always be displayed, even if the value of
5154 @code{max-image-size} is subsequently changed (@pxref{Image Cache}).
5157 @node Multi-Frame Images
5158 @subsection Multi-Frame Images
5159 @cindex multi-frame images
5162 @cindex image animation
5163 @cindex image frames
5164 Some image files can contain more than one image. We say that there
5165 are multiple ``frames'' in the image. At present, Emacs supports
5166 multiple frames for GIF, TIFF, and certain ImageMagick formats such as
5169 The frames can be used either to represent multiple ``pages'' (this is
5170 usually the case with multi-frame TIFF files, for example), or to
5171 create animation (usually the case with multi-frame GIF files).
5173 A multi-frame image has a property @code{:index}, whose value is an
5174 integer (counting from 0) that specifies which frame is being displayed.
5176 @defun image-multi-frame-p image
5177 This function returns non-@code{nil} if @var{image} contains more than
5178 one frame. The actual return value is a cons @code{(@var{nimages}
5179 . @var{delay})}, where @var{nimages} is the number of frames and
5180 @var{delay} is the delay in seconds between them, or @code{nil}
5181 if the image does not specify a delay. Images that are intended to be
5182 animated usually specify a frame delay, whereas ones that are intended
5183 to be treated as multiple pages do not.
5186 @defun image-current-frame image
5187 This function returns the index of the current frame number for
5188 @var{image}, counting from 0.
5191 @defun image-show-frame image n &optional nocheck
5192 This function switches @var{image} to frame number @var{n}. It
5193 replaces a frame number outside the valid range with that of the end
5194 of the range, unless @var{nocheck} is non-@code{nil}. If @var{image}
5195 does not contain a frame with the specified number, the image displays
5199 @defun image-animate image &optional index limit
5200 This function animates @var{image}. The optional integer @var{index}
5201 specifies the frame from which to start (default 0). The optional
5202 argument @var{limit} controls the length of the animation. If omitted
5203 or @code{nil}, the image animates once only; if @code{t} it loops
5204 forever; if a number animation stops after that many seconds.
5207 @vindex image-minimum-frame-delay
5208 @vindex image-default-frame-delay
5209 @noindent Animation operates by means of a timer. Note that Emacs imposes a
5210 minimum frame delay of 0.01 (@code{image-minimum-frame-delay}) seconds.
5211 If the image itself does not specify a delay, Emacs uses
5212 @code{image-default-frame-delay}.
5214 @defun image-animate-timer image
5215 This function returns the timer responsible for animating @var{image},
5221 @subsection Image Cache
5224 Emacs caches images so that it can display them again more
5225 efficiently. When Emacs displays an image, it searches the image
5226 cache for an existing image specification @code{equal} to the desired
5227 specification. If a match is found, the image is displayed from the
5228 cache. Otherwise, Emacs loads the image normally.
5230 @defun image-flush spec &optional frame
5231 This function removes the image with specification @var{spec} from the
5232 image cache of frame @var{frame}. Image specifications are compared
5233 using @code{equal}. If @var{frame} is @code{nil}, it defaults to the
5234 selected frame. If @var{frame} is @code{t}, the image is flushed on
5235 all existing frames.
5237 In Emacs's current implementation, each graphical terminal possesses an
5238 image cache, which is shared by all the frames on that terminal
5239 (@pxref{Multiple Terminals}). Thus, refreshing an image in one frame
5240 also refreshes it in all other frames on the same terminal.
5243 One use for @code{image-flush} is to tell Emacs about a change in an
5244 image file. If an image specification contains a @code{:file}
5245 property, the image is cached based on the file's contents when the
5246 image is first displayed. Even if the file subsequently changes,
5247 Emacs continues displaying the old version of the image. Calling
5248 @code{image-flush} flushes the image from the cache, forcing Emacs to
5249 re-read the file the next time it needs to display that image.
5251 Another use for @code{image-flush} is for memory conservation. If
5252 your Lisp program creates a large number of temporary images over a
5253 period much shorter than @code{image-cache-eviction-delay} (see
5254 below), you can opt to flush unused images yourself, instead of
5255 waiting for Emacs to do it automatically.
5257 @defun clear-image-cache &optional filter
5258 This function clears an image cache, removing all the images stored in
5259 it. If @var{filter} is omitted or @code{nil}, it clears the cache for
5260 the selected frame. If @var{filter} is a frame, it clears the cache
5261 for that frame. If @var{filter} is @code{t}, all image caches are
5262 cleared. Otherwise, @var{filter} is taken to be a file name, and all
5263 images associated with that file name are removed from all image
5267 If an image in the image cache has not been displayed for a specified
5268 period of time, Emacs removes it from the cache and frees the
5271 @defvar image-cache-eviction-delay
5272 This variable specifies the number of seconds an image can remain in
5273 the cache without being displayed. When an image is not displayed for
5274 this length of time, Emacs removes it from the image cache.
5276 Under some circumstances, if the number of images in the cache grows
5277 too large, the actual eviction delay may be shorter than this.
5279 If the value is @code{nil}, Emacs does not remove images from the cache
5280 except when you explicitly clear it. This mode can be useful for
5286 @cindex buttons in buffers
5287 @cindex clickable buttons in buffers
5289 The Button package defines functions for inserting and manipulating
5290 @dfn{buttons} that can be activated with the mouse or via keyboard
5291 commands. These buttons are typically used for various kinds of
5294 A button is essentially a set of text or overlay properties,
5295 attached to a stretch of text in a buffer. These properties are
5296 called @dfn{button properties}. One of these properties, the
5297 @dfn{action property}, specifies a function which is called when the
5298 user invokes the button using the keyboard or the mouse. The action
5299 function may examine the button and use its other properties as
5302 In some ways, the Button package duplicates the functionality in the
5303 Widget package. @xref{Top, , Introduction, widget, The Emacs Widget
5304 Library}. The advantage of the Button package is that it is faster,
5305 smaller, and simpler to program. From the point of view of the user,
5306 the interfaces produced by the two packages are very similar.
5309 * Button Properties:: Button properties with special meanings.
5310 * Button Types:: Defining common properties for classes of buttons.
5311 * Making Buttons:: Adding buttons to Emacs buffers.
5312 * Manipulating Buttons:: Getting and setting properties of buttons.
5313 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
5316 @node Button Properties
5317 @subsection Button Properties
5318 @cindex button properties
5320 Each button has an associated list of properties defining its
5321 appearance and behavior, and other arbitrary properties may be used
5322 for application specific purposes. The following properties have
5323 special meaning to the Button package:
5327 @kindex action @r{(button property)}
5328 The function to call when the user invokes the button, which is passed
5329 the single argument @var{button}. By default this is @code{ignore},
5333 @kindex mouse-action @r{(button property)}
5334 This is similar to @code{action}, and when present, will be used
5335 instead of @code{action} for button invocations resulting from
5336 mouse-clicks (instead of the user hitting @key{RET}). If not
5337 present, mouse-clicks use @code{action} instead.
5340 @kindex face @r{(button property)}
5341 This is an Emacs face controlling how buttons of this type are
5342 displayed; by default this is the @code{button} face.
5345 @kindex mouse-face @r{(button property)}
5346 This is an additional face which controls appearance during
5347 mouse-overs (merged with the usual button face); by default this is
5348 the usual Emacs @code{highlight} face.
5351 @kindex keymap @r{(button property)}
5352 The button's keymap, defining bindings active within the button
5353 region. By default this is the usual button region keymap, stored
5354 in the variable @code{button-map}, which defines @key{RET} and
5355 @key{mouse-2} to invoke the button.
5358 @kindex type @r{(button property)}
5359 The button type. @xref{Button Types}.
5362 @kindex help-index @r{(button property)}
5363 A string displayed by the Emacs tool-tip help system; by default,
5364 @code{"mouse-2, RET: Push this button"}.
5367 @kindex follow-link @r{(button property)}
5368 The follow-link property, defining how a @key{Mouse-1} click behaves
5369 on this button, @xref{Clickable Text}.
5372 @kindex button @r{(button property)}
5373 All buttons have a non-@code{nil} @code{button} property, which may be useful
5374 in finding regions of text that comprise buttons (which is what the
5375 standard button functions do).
5378 There are other properties defined for the regions of text in a
5379 button, but these are not generally interesting for typical uses.
5382 @subsection Button Types
5383 @cindex button types
5385 Every button has a @dfn{button type}, which defines default values
5386 for the button's properties. Button types are arranged in a
5387 hierarchy, with specialized types inheriting from more general types,
5388 so that it's easy to define special-purpose types of buttons for
5391 @defun define-button-type name &rest properties
5392 Define a `button type' called @var{name} (a symbol).
5393 The remaining arguments
5394 form a sequence of @var{property value} pairs, specifying default
5395 property values for buttons with this type (a button's type may be set
5396 by giving it a @code{type} property when creating the button, using
5397 the @code{:type} keyword argument).
5399 In addition, the keyword argument @code{:supertype} may be used to
5400 specify a button-type from which @var{name} inherits its default
5401 property values. Note that this inheritance happens only when
5402 @var{name} is defined; subsequent changes to a supertype are not
5403 reflected in its subtypes.
5406 Using @code{define-button-type} to define default properties for
5407 buttons is not necessary---buttons without any specified type use the
5408 built-in button-type @code{button}---but it is encouraged, since
5409 doing so usually makes the resulting code clearer and more efficient.
5411 @node Making Buttons
5412 @subsection Making Buttons
5413 @cindex making buttons
5415 Buttons are associated with a region of text, using an overlay or
5416 text properties to hold button-specific information, all of which are
5417 initialized from the button's type (which defaults to the built-in
5418 button type @code{button}). Like all Emacs text, the appearance of
5419 the button is governed by the @code{face} property; by default (via
5420 the @code{face} property inherited from the @code{button} button-type)
5421 this is a simple underline, like a typical web-page link.
5423 For convenience, there are two sorts of button-creation functions,
5424 those that add button properties to an existing region of a buffer,
5425 called @code{make-...button}, and those that also insert the button
5426 text, called @code{insert-...button}.
5428 The button-creation functions all take the @code{&rest} argument
5429 @var{properties}, which should be a sequence of @var{property value}
5430 pairs, specifying properties to add to the button; see @ref{Button
5431 Properties}. In addition, the keyword argument @code{:type} may be
5432 used to specify a button-type from which to inherit other properties;
5433 see @ref{Button Types}. Any properties not explicitly specified
5434 during creation will be inherited from the button's type (if the type
5435 defines such a property).
5437 The following functions add a button using an overlay
5438 (@pxref{Overlays}) to hold the button properties:
5440 @defun make-button beg end &rest properties
5441 This makes a button from @var{beg} to @var{end} in the
5442 current buffer, and returns it.
5445 @defun insert-button label &rest properties
5446 This insert a button with the label @var{label} at point,
5450 The following functions are similar, but using text properties
5451 (@pxref{Text Properties}) to hold the button properties. Such buttons
5452 do not add markers to the buffer, so editing in the buffer does not
5453 slow down if there is an extremely large numbers of buttons. However,
5454 if there is an existing face text property on the text (e.g., a face
5455 assigned by Font Lock mode), the button face may not be visible. Both
5456 of these functions return the starting position of the new button.
5458 @defun make-text-button beg end &rest properties
5459 This makes a button from @var{beg} to @var{end} in the current buffer,
5460 using text properties.
5463 @defun insert-text-button label &rest properties
5464 This inserts a button with the label @var{label} at point, using text
5468 @node Manipulating Buttons
5469 @subsection Manipulating Buttons
5470 @cindex manipulating buttons
5472 These are functions for getting and setting properties of buttons.
5473 Often these are used by a button's invocation function to determine
5476 Where a @var{button} parameter is specified, it means an object
5477 referring to a specific button, either an overlay (for overlay
5478 buttons), or a buffer-position or marker (for text property buttons).
5479 Such an object is passed as the first argument to a button's
5480 invocation function when it is invoked.
5482 @defun button-start button
5483 Return the position at which @var{button} starts.
5486 @defun button-end button
5487 Return the position at which @var{button} ends.
5490 @defun button-get button prop
5491 Get the property of button @var{button} named @var{prop}.
5494 @defun button-put button prop val
5495 Set @var{button}'s @var{prop} property to @var{val}.
5498 @defun button-activate button &optional use-mouse-action
5499 Call @var{button}'s @code{action} property (i.e., invoke it). If
5500 @var{use-mouse-action} is non-@code{nil}, try to invoke the button's
5501 @code{mouse-action} property instead of @code{action}; if the button
5502 has no @code{mouse-action} property, use @code{action} as normal.
5505 @defun button-label button
5506 Return @var{button}'s text label.
5509 @defun button-type button
5510 Return @var{button}'s button-type.
5513 @defun button-has-type-p button type
5514 Return @code{t} if @var{button} has button-type @var{type}, or one of
5515 @var{type}'s subtypes.
5518 @defun button-at pos
5519 Return the button at position @var{pos} in the current buffer, or
5520 @code{nil}. If the button at @var{pos} is a text property button, the
5521 return value is a marker pointing to @var{pos}.
5524 @defun button-type-put type prop val
5525 Set the button-type @var{type}'s @var{prop} property to @var{val}.
5528 @defun button-type-get type prop
5529 Get the property of button-type @var{type} named @var{prop}.
5532 @defun button-type-subtype-p type supertype
5533 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
5536 @node Button Buffer Commands
5537 @subsection Button Buffer Commands
5538 @cindex button buffer commands
5540 These are commands and functions for locating and operating on
5541 buttons in an Emacs buffer.
5543 @code{push-button} is the command that a user uses to actually `push'
5544 a button, and is bound by default in the button itself to @key{RET}
5545 and to @key{mouse-2} using a local keymap in the button's overlay or
5546 text properties. Commands that are useful outside the buttons itself,
5547 such as @code{forward-button} and @code{backward-button} are
5548 additionally available in the keymap stored in
5549 @code{button-buffer-map}; a mode which uses buttons may want to use
5550 @code{button-buffer-map} as a parent keymap for its keymap.
5552 If the button has a non-@code{nil} @code{follow-link} property, and
5553 @code{mouse-1-click-follows-link} is set, a quick @key{Mouse-1} click
5554 will also activate the @code{push-button} command.
5555 @xref{Clickable Text}.
5557 @deffn Command push-button &optional pos use-mouse-action
5558 Perform the action specified by a button at location @var{pos}.
5559 @var{pos} may be either a buffer position or a mouse-event. If
5560 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
5561 mouse-event (@pxref{Mouse Events}), try to invoke the button's
5562 @code{mouse-action} property instead of @code{action}; if the button
5563 has no @code{mouse-action} property, use @code{action} as normal.
5564 @var{pos} defaults to point, except when @code{push-button} is invoked
5565 interactively as the result of a mouse-event, in which case, the mouse
5566 event's position is used. If there's no button at @var{pos}, do
5567 nothing and return @code{nil}, otherwise return @code{t}.
5570 @deffn Command forward-button n &optional wrap display-message
5571 Move to the @var{n}th next button, or @var{n}th previous button if
5572 @var{n} is negative. If @var{n} is zero, move to the start of any
5573 button at point. If @var{wrap} is non-@code{nil}, moving past either
5574 end of the buffer continues from the other end. If
5575 @var{display-message} is non-@code{nil}, the button's help-echo string
5576 is displayed. Any button with a non-@code{nil} @code{skip} property
5577 is skipped over. Returns the button found.
5580 @deffn Command backward-button n &optional wrap display-message
5581 Move to the @var{n}th previous button, or @var{n}th next button if
5582 @var{n} is negative. If @var{n} is zero, move to the start of any
5583 button at point. If @var{wrap} is non-@code{nil}, moving past either
5584 end of the buffer continues from the other end. If
5585 @var{display-message} is non-@code{nil}, the button's help-echo string
5586 is displayed. Any button with a non-@code{nil} @code{skip} property
5587 is skipped over. Returns the button found.
5590 @defun next-button pos &optional count-current
5591 @defunx previous-button pos &optional count-current
5592 Return the next button after (for @code{next-button}) or before (for
5593 @code{previous-button}) position @var{pos} in the current buffer. If
5594 @var{count-current} is non-@code{nil}, count any button at @var{pos}
5595 in the search, instead of starting at the next button.
5598 @node Abstract Display
5599 @section Abstract Display
5601 @cindex display, abstract
5602 @cindex display, arbitrary objects
5603 @cindex model/view/controller
5604 @cindex view part, model/view/controller
5606 The Ewoc package constructs buffer text that represents a structure
5607 of Lisp objects, and updates the text to follow changes in that
5608 structure. This is like the ``view'' component in the
5609 ``model/view/controller'' design paradigm. Ewoc means ``Emacs's
5610 Widget for Object Collections''.
5612 An @dfn{ewoc} is a structure that organizes information required to
5613 construct buffer text that represents certain Lisp data. The buffer
5614 text of the ewoc has three parts, in order: first, fixed @dfn{header}
5615 text; next, textual descriptions of a series of data elements (Lisp
5616 objects that you specify); and last, fixed @dfn{footer} text.
5617 Specifically, an ewoc contains information on:
5621 The buffer which its text is generated in.
5624 The text's start position in the buffer.
5627 The header and footer strings.
5631 @c or "@cindex node, abstract display"?
5632 A doubly-linked chain of @dfn{nodes}, each of which contains:
5636 A @dfn{data element}, a single Lisp object.
5639 Links to the preceding and following nodes in the chain.
5643 A @dfn{pretty-printer} function which is responsible for
5644 inserting the textual representation of a data
5645 element value into the current buffer.
5648 Typically, you define an ewoc with @code{ewoc-create}, and then pass
5649 the resulting ewoc structure to other functions in the Ewoc package to
5650 build nodes within it, and display it in the buffer. Once it is
5651 displayed in the buffer, other functions determine the correspondence
5652 between buffer positions and nodes, move point from one node's textual
5653 representation to another, and so forth. @xref{Abstract Display
5656 @cindex encapsulation, ewoc
5657 @c or "@cindex encapsulation, abstract display"?
5658 A node @dfn{encapsulates} a data element much the way a variable
5659 holds a value. Normally, encapsulation occurs as a part of adding a
5660 node to the ewoc. You can retrieve the data element value and place a
5661 new value in its place, like so:
5664 (ewoc-data @var{node})
5667 (ewoc-set-data @var{node} @var{new-value})
5668 @result{} @var{new-value}
5672 You can also use, as the data element value, a Lisp object (list or
5673 vector) that is a container for the ``real'' value, or an index into
5674 some other structure. The example (@pxref{Abstract Display Example})
5675 uses the latter approach.
5677 When the data changes, you will want to update the text in the
5678 buffer. You can update all nodes by calling @code{ewoc-refresh}, or
5679 just specific nodes using @code{ewoc-invalidate}, or all nodes
5680 satisfying a predicate using @code{ewoc-map}. Alternatively, you can
5681 delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter},
5682 and add new nodes in their place. Deleting a node from an ewoc deletes
5683 its associated textual description from buffer, as well.
5686 * Abstract Display Functions:: Functions in the Ewoc package.
5687 * Abstract Display Example:: Example of using Ewoc.
5690 @node Abstract Display Functions
5691 @subsection Abstract Display Functions
5693 In this subsection, @var{ewoc} and @var{node} stand for the
5694 structures described above (@pxref{Abstract Display}), while
5695 @var{data} stands for an arbitrary Lisp object used as a data element.
5697 @defun ewoc-create pretty-printer &optional header footer nosep
5698 This constructs and returns a new ewoc, with no nodes (and thus no data
5699 elements). @var{pretty-printer} should be a function that takes one
5700 argument, a data element of the sort you plan to use in this ewoc, and
5701 inserts its textual description at point using @code{insert} (and never
5702 @code{insert-before-markers}, because that would interfere with the
5703 Ewoc package's internal mechanisms).
5705 Normally, a newline is automatically inserted after the header,
5706 the footer and every node's textual description. If @var{nosep}
5707 is non-@code{nil}, no newline is inserted. This may be useful for
5708 displaying an entire ewoc on a single line, for example, or for
5709 making nodes ``invisible'' by arranging for @var{pretty-printer}
5710 to do nothing for those nodes.
5712 An ewoc maintains its text in the buffer that is current when
5713 you create it, so switch to the intended buffer before calling
5717 @defun ewoc-buffer ewoc
5718 This returns the buffer where @var{ewoc} maintains its text.
5721 @defun ewoc-get-hf ewoc
5722 This returns a cons cell @code{(@var{header} . @var{footer})}
5723 made from @var{ewoc}'s header and footer.
5726 @defun ewoc-set-hf ewoc header footer
5727 This sets the header and footer of @var{ewoc} to the strings
5728 @var{header} and @var{footer}, respectively.
5731 @defun ewoc-enter-first ewoc data
5732 @defunx ewoc-enter-last ewoc data
5733 These add a new node encapsulating @var{data}, putting it, respectively,
5734 at the beginning or end of @var{ewoc}'s chain of nodes.
5737 @defun ewoc-enter-before ewoc node data
5738 @defunx ewoc-enter-after ewoc node data
5739 These add a new node encapsulating @var{data}, adding it to
5740 @var{ewoc} before or after @var{node}, respectively.
5743 @defun ewoc-prev ewoc node
5744 @defunx ewoc-next ewoc node
5745 These return, respectively, the previous node and the next node of @var{node}
5749 @defun ewoc-nth ewoc n
5750 This returns the node in @var{ewoc} found at zero-based index @var{n}.
5751 A negative @var{n} means count from the end. @code{ewoc-nth} returns
5752 @code{nil} if @var{n} is out of range.
5755 @defun ewoc-data node
5756 This extracts the data encapsulated by @var{node} and returns it.
5759 @defun ewoc-set-data node data
5760 This sets the data encapsulated by @var{node} to @var{data}.
5763 @defun ewoc-locate ewoc &optional pos guess
5764 This determines the node in @var{ewoc} which contains point (or
5765 @var{pos} if specified), and returns that node. If @var{ewoc} has no
5766 nodes, it returns @code{nil}. If @var{pos} is before the first node,
5767 it returns the first node; if @var{pos} is after the last node, it returns
5768 the last node. The optional third arg @var{guess}
5769 should be a node that is likely to be near @var{pos}; this doesn't
5770 alter the result, but makes the function run faster.
5773 @defun ewoc-location node
5774 This returns the start position of @var{node}.
5777 @defun ewoc-goto-prev ewoc arg
5778 @defunx ewoc-goto-next ewoc arg
5779 These move point to the previous or next, respectively, @var{arg}th node
5780 in @var{ewoc}. @code{ewoc-goto-prev} does not move if it is already at
5781 the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next}
5782 moves past the last node, returning @code{nil}. Excepting this special
5783 case, these functions return the node moved to.
5786 @defun ewoc-goto-node ewoc node
5787 This moves point to the start of @var{node} in @var{ewoc}.
5790 @defun ewoc-refresh ewoc
5791 This function regenerates the text of @var{ewoc}. It works by
5792 deleting the text between the header and the footer, i.e., all the
5793 data elements' representations, and then calling the pretty-printer
5794 function for each node, one by one, in order.
5797 @defun ewoc-invalidate ewoc &rest nodes
5798 This is similar to @code{ewoc-refresh}, except that only @var{nodes} in
5799 @var{ewoc} are updated instead of the entire set.
5802 @defun ewoc-delete ewoc &rest nodes
5803 This deletes each node in @var{nodes} from @var{ewoc}.
5806 @defun ewoc-filter ewoc predicate &rest args
5807 This calls @var{predicate} for each data element in @var{ewoc} and
5808 deletes those nodes for which @var{predicate} returns @code{nil}.
5809 Any @var{args} are passed to @var{predicate}.
5812 @defun ewoc-collect ewoc predicate &rest args
5813 This calls @var{predicate} for each data element in @var{ewoc}
5814 and returns a list of those elements for which @var{predicate}
5815 returns non-@code{nil}. The elements in the list are ordered
5816 as in the buffer. Any @var{args} are passed to @var{predicate}.
5819 @defun ewoc-map map-function ewoc &rest args
5820 This calls @var{map-function} for each data element in @var{ewoc} and
5821 updates those nodes for which @var{map-function} returns non-@code{nil}.
5822 Any @var{args} are passed to @var{map-function}.
5825 @node Abstract Display Example
5826 @subsection Abstract Display Example
5828 Here is a simple example using functions of the ewoc package to
5829 implement a ``color components display'', an area in a buffer that
5830 represents a vector of three integers (itself representing a 24-bit RGB
5831 value) in various ways.
5834 (setq colorcomp-ewoc nil
5836 colorcomp-mode-map nil
5837 colorcomp-labels ["Red" "Green" "Blue"])
5839 (defun colorcomp-pp (data)
5841 (let ((comp (aref colorcomp-data data)))
5842 (insert (aref colorcomp-labels data) "\t: #x"
5843 (format "%02X" comp) " "
5844 (make-string (ash comp -2) ?#) "\n"))
5845 (let ((cstr (format "#%02X%02X%02X"
5846 (aref colorcomp-data 0)
5847 (aref colorcomp-data 1)
5848 (aref colorcomp-data 2)))
5849 (samp " (sample text) "))
5851 (propertize samp 'face
5852 `(foreground-color . ,cstr))
5853 (propertize samp 'face
5854 `(background-color . ,cstr))
5857 (defun colorcomp (color)
5858 "Allow fiddling with COLOR in a new buffer.
5859 The buffer is in Color Components mode."
5860 (interactive "sColor (name or #RGB or #RRGGBB): ")
5861 (when (string= "" color)
5862 (setq color "green"))
5863 (unless (color-values color)
5864 (error "No such color: %S" color))
5866 (generate-new-buffer (format "originally: %s" color)))
5867 (kill-all-local-variables)
5868 (setq major-mode 'colorcomp-mode
5869 mode-name "Color Components")
5870 (use-local-map colorcomp-mode-map)
5872 (buffer-disable-undo)
5873 (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
5874 (color-values color))))
5875 (ewoc (ewoc-create 'colorcomp-pp
5876 "\nColor Components\n\n"
5877 (substitute-command-keys
5878 "\n\\@{colorcomp-mode-map@}"))))
5879 (set (make-local-variable 'colorcomp-data) data)
5880 (set (make-local-variable 'colorcomp-ewoc) ewoc)
5881 (ewoc-enter-last ewoc 0)
5882 (ewoc-enter-last ewoc 1)
5883 (ewoc-enter-last ewoc 2)
5884 (ewoc-enter-last ewoc nil)))
5887 @cindex controller part, model/view/controller
5888 This example can be extended to be a ``color selection widget'' (in
5889 other words, the controller part of the ``model/view/controller''
5890 design paradigm) by defining commands to modify @code{colorcomp-data}
5891 and to ``finish'' the selection process, and a keymap to tie it all
5892 together conveniently.
5895 (defun colorcomp-mod (index limit delta)
5896 (let ((cur (aref colorcomp-data index)))
5897 (unless (= limit cur)
5898 (aset colorcomp-data index (+ cur delta)))
5901 (ewoc-nth colorcomp-ewoc index)
5902 (ewoc-nth colorcomp-ewoc -1))))
5904 (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
5905 (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
5906 (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
5907 (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
5908 (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
5909 (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
5911 (defun colorcomp-copy-as-kill-and-exit ()
5912 "Copy the color components into the kill ring and kill the buffer.
5913 The string is formatted #RRGGBB (hash followed by six hex digits)."
5915 (kill-new (format "#%02X%02X%02X"
5916 (aref colorcomp-data 0)
5917 (aref colorcomp-data 1)
5918 (aref colorcomp-data 2)))
5921 (setq colorcomp-mode-map
5922 (let ((m (make-sparse-keymap)))
5924 (define-key m "i" 'colorcomp-R-less)
5925 (define-key m "o" 'colorcomp-R-more)
5926 (define-key m "k" 'colorcomp-G-less)
5927 (define-key m "l" 'colorcomp-G-more)
5928 (define-key m "," 'colorcomp-B-less)
5929 (define-key m "." 'colorcomp-B-more)
5930 (define-key m " " 'colorcomp-copy-as-kill-and-exit)
5934 Note that we never modify the data in each node, which is fixed when the
5935 ewoc is created to be either @code{nil} or an index into the vector
5936 @code{colorcomp-data}, the actual color components.
5939 @section Blinking Parentheses
5940 @cindex parenthesis matching
5941 @cindex blinking parentheses
5942 @cindex balancing parentheses
5944 This section describes the mechanism by which Emacs shows a matching
5945 open parenthesis when the user inserts a close parenthesis.
5947 @defvar blink-paren-function
5948 The value of this variable should be a function (of no arguments) to
5949 be called whenever a character with close parenthesis syntax is inserted.
5950 The value of @code{blink-paren-function} may be @code{nil}, in which
5951 case nothing is done.
5954 @defopt blink-matching-paren
5955 If this variable is @code{nil}, then @code{blink-matching-open} does
5959 @defopt blink-matching-paren-distance
5960 This variable specifies the maximum distance to scan for a matching
5961 parenthesis before giving up.
5964 @defopt blink-matching-delay
5965 This variable specifies the number of seconds to keep indicating the
5966 matching parenthesis. A fraction of a second often gives good
5967 results, but the default is 1, which works on all systems.
5970 @deffn Command blink-matching-open
5971 This function is the default value of @code{blink-paren-function}. It
5972 assumes that point follows a character with close parenthesis syntax
5973 and applies the appropriate effect momentarily to the matching opening
5974 character. If that character is not already on the screen, it
5975 displays the character's context in the echo area. To avoid long
5976 delays, this function does not search farther than
5977 @code{blink-matching-paren-distance} characters.
5979 Here is an example of calling this function explicitly.
5983 (defun interactive-blink-matching-open ()
5984 "Indicate momentarily the start of parenthesized sexp before point."
5988 (let ((blink-matching-paren-distance
5990 (blink-matching-paren t))
5991 (blink-matching-open)))
5996 @node Character Display
5997 @section Character Display
5999 This section describes how characters are actually displayed by
6000 Emacs. Typically, a character is displayed as a @dfn{glyph} (a
6001 graphical symbol which occupies one character position on the screen),
6002 whose appearance corresponds to the character itself. For example,
6003 the character @samp{a} (character code 97) is displayed as @samp{a}.
6004 Some characters, however, are displayed specially. For example, the
6005 formfeed character (character code 12) is usually displayed as a
6006 sequence of two glyphs, @samp{^L}, while the newline character
6007 (character code 10) starts a new screen line.
6009 You can modify how each character is displayed by defining a
6010 @dfn{display table}, which maps each character code into a sequence of
6011 glyphs. @xref{Display Tables}.
6014 * Usual Display:: The usual conventions for displaying characters.
6015 * Display Tables:: What a display table consists of.
6016 * Active Display Table:: How Emacs selects a display table to use.
6017 * Glyphs:: How to define a glyph, and what glyphs mean.
6018 * Glyphless Chars:: How glyphless characters are drawn.
6022 @subsection Usual Display Conventions
6024 Here are the conventions for displaying each character code (in the
6025 absence of a display table, which can override these
6030 conventions; @pxref{Display Tables}).
6033 @cindex printable ASCII characters
6036 The @dfn{printable @acronym{ASCII} characters}, character codes 32
6037 through 126 (consisting of numerals, English letters, and symbols like
6038 @samp{#}) are displayed literally.
6041 The tab character (character code 9) displays as whitespace stretching
6042 up to the next tab stop column. @xref{Text Display,,, emacs, The GNU
6043 Emacs Manual}. The variable @code{tab-width} controls the number of
6044 spaces per tab stop (see below).
6047 The newline character (character code 10) has a special effect: it
6048 ends the preceding line and starts a new line.
6050 @cindex ASCII control characters
6052 The non-printable @dfn{@acronym{ASCII} control characters}---character
6053 codes 0 through 31, as well as the @key{DEL} character (character code
6054 127)---display in one of two ways according to the variable
6055 @code{ctl-arrow}. If this variable is non-@code{nil} (the default),
6056 these characters are displayed as sequences of two glyphs, where the
6057 first glyph is @samp{^} (a display table can specify a glyph to use
6058 instead of @samp{^}); e.g., the @key{DEL} character is displayed as
6061 If @code{ctl-arrow} is @code{nil}, these characters are displayed as
6062 octal escapes (see below).
6064 This rule also applies to carriage return (character code 13), if that
6065 character appears in the buffer. But carriage returns usually do not
6066 appear in buffer text; they are eliminated as part of end-of-line
6067 conversion (@pxref{Coding System Basics}).
6069 @cindex octal escapes
6071 @dfn{Raw bytes} are non-@acronym{ASCII} characters with codes 128
6072 through 255 (@pxref{Text Representations}). These characters display
6073 as @dfn{octal escapes}: sequences of four glyphs, where the first
6074 glyph is the @acronym{ASCII} code for @samp{\}, and the others are
6075 digit characters representing the character code in octal. (A display
6076 table can specify a glyph to use instead of @samp{\}.)
6079 Each non-@acronym{ASCII} character with code above 255 is displayed
6080 literally, if the terminal supports it. If the terminal does not
6081 support it, the character is said to be @dfn{glyphless}, and it is
6082 usually displayed using a placeholder glyph. For example, if a
6083 graphical terminal has no font for a character, Emacs usually displays
6084 a box containing the character code in hexadecimal. @xref{Glyphless
6088 The above display conventions apply even when there is a display
6089 table, for any character whose entry in the active display table is
6090 @code{nil}. Thus, when you set up a display table, you need only
6091 specify the characters for which you want special behavior.
6093 The following variables affect how certain characters are displayed
6094 on the screen. Since they change the number of columns the characters
6095 occupy, they also affect the indentation functions. They also affect
6096 how the mode line is displayed; if you want to force redisplay of the
6097 mode line using the new values, call the function
6098 @code{force-mode-line-update} (@pxref{Mode Line Format}).
6101 @cindex control characters in display
6102 This buffer-local variable controls how control characters are
6103 displayed. If it is non-@code{nil}, they are displayed as a caret
6104 followed by the character: @samp{^A}. If it is @code{nil}, they are
6105 displayed as octal escapes: a backslash followed by three octal
6106 digits, as in @samp{\001}.
6110 The value of this buffer-local variable is the spacing between tab
6111 stops used for displaying tab characters in Emacs buffers. The value
6112 is in units of columns, and the default is 8. Note that this feature
6113 is completely independent of the user-settable tab stops used by the
6114 command @code{tab-to-tab-stop}. @xref{Indent Tabs}.
6117 @node Display Tables
6118 @subsection Display Tables
6120 @cindex display table
6121 A display table is a special-purpose char-table
6122 (@pxref{Char-Tables}), with @code{display-table} as its subtype, which
6123 is used to override the usual character display conventions. This
6124 section describes how to make, inspect, and assign elements to a
6125 display table object.
6127 @defun make-display-table
6128 This creates and returns a display table. The table initially has
6129 @code{nil} in all elements.
6132 The ordinary elements of the display table are indexed by character
6133 codes; the element at index @var{c} says how to display the character
6134 code @var{c}. The value should be @code{nil} (which means to display
6135 the character @var{c} according to the usual display conventions;
6136 @pxref{Usual Display}), or a vector of glyph codes (which means to
6137 display the character @var{c} as those glyphs; @pxref{Glyphs}).
6139 @strong{Warning:} if you use the display table to change the display
6140 of newline characters, the whole buffer will be displayed as one long
6143 The display table also has six ``extra slots'' which serve special
6144 purposes. Here is a table of their meanings; @code{nil} in any slot
6145 means to use the default for that slot, as stated below.
6149 The glyph for the end of a truncated screen line (the default for this
6150 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
6151 arrows in the fringes to indicate truncation, so the display table has
6155 The glyph for the end of a continued line (the default is @samp{\}).
6156 On graphical terminals, Emacs uses curved arrows in the fringes to
6157 indicate continuation, so the display table has no effect.
6160 The glyph for indicating a character displayed as an octal character
6161 code (the default is @samp{\}).
6164 The glyph for indicating a control character (the default is @samp{^}).
6167 A vector of glyphs for indicating the presence of invisible lines (the
6168 default is @samp{...}). @xref{Selective Display}.
6171 The glyph used to draw the border between side-by-side windows (the
6172 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
6173 when there are no scroll bars; if scroll bars are supported and in use,
6174 a scroll bar separates the two windows.
6177 For example, here is how to construct a display table that mimics
6178 the effect of setting @code{ctl-arrow} to a non-@code{nil} value
6179 (@pxref{Glyphs}, for the function @code{make-glyph-code}):
6182 (setq disptab (make-display-table))
6187 (vector (make-glyph-code ?^ 'escape-glyph)
6188 (make-glyph-code (+ i 64) 'escape-glyph)))))
6190 (vector (make-glyph-code ?^ 'escape-glyph)
6191 (make-glyph-code ?? 'escape-glyph)))))
6194 @defun display-table-slot display-table slot
6195 This function returns the value of the extra slot @var{slot} of
6196 @var{display-table}. The argument @var{slot} may be a number from 0 to
6197 5 inclusive, or a slot name (symbol). Valid symbols are
6198 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6199 @code{selective-display}, and @code{vertical-border}.
6202 @defun set-display-table-slot display-table slot value
6203 This function stores @var{value} in the extra slot @var{slot} of
6204 @var{display-table}. The argument @var{slot} may be a number from 0 to
6205 5 inclusive, or a slot name (symbol). Valid symbols are
6206 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6207 @code{selective-display}, and @code{vertical-border}.
6210 @defun describe-display-table display-table
6211 This function displays a description of the display table
6212 @var{display-table} in a help buffer.
6215 @deffn Command describe-current-display-table
6216 This command displays a description of the current display table in a
6220 @node Active Display Table
6221 @subsection Active Display Table
6222 @cindex active display table
6224 Each window can specify a display table, and so can each buffer.
6225 The window's display table, if there is one, takes precedence over the
6226 buffer's display table. If neither exists, Emacs tries to use the
6227 standard display table; if that is @code{nil}, Emacs uses the usual
6228 character display conventions (@pxref{Usual Display}).
6230 Note that display tables affect how the mode line is displayed, so
6231 if you want to force redisplay of the mode line using a new display
6232 table, call @code{force-mode-line-update} (@pxref{Mode Line Format}).
6234 @defun window-display-table &optional window
6235 This function returns @var{window}'s display table, or @code{nil} if
6236 there is none. The default for @var{window} is the selected window.
6239 @defun set-window-display-table window table
6240 This function sets the display table of @var{window} to @var{table}.
6241 The argument @var{table} should be either a display table or
6245 @defvar buffer-display-table
6246 This variable is automatically buffer-local in all buffers; its value
6247 specifies the buffer's display table. If it is @code{nil}, there is
6248 no buffer display table.
6251 @defvar standard-display-table
6252 The value of this variable is the standard display table, which is
6253 used when Emacs is displaying a buffer in a window with neither a
6254 window display table nor a buffer display table defined. Its default
6258 The @file{disp-table} library defines several functions for changing
6259 the standard display table.
6266 A @dfn{glyph} is a graphical symbol which occupies a single
6267 character position on the screen. Each glyph is represented in Lisp
6268 as a @dfn{glyph code}, which specifies a character and optionally a
6269 face to display it in (@pxref{Faces}). The main use of glyph codes is
6270 as the entries of display tables (@pxref{Display Tables}). The
6271 following functions are used to manipulate glyph codes:
6273 @defun make-glyph-code char &optional face
6274 This function returns a glyph code representing char @var{char} with
6275 face @var{face}. If @var{face} is omitted or @code{nil}, the glyph
6276 uses the default face; in that case, the glyph code is an integer. If
6277 @var{face} is non-@code{nil}, the glyph code is not necessarily an
6281 @defun glyph-char glyph
6282 This function returns the character of glyph code @var{glyph}.
6285 @defun glyph-face glyph
6286 This function returns face of glyph code @var{glyph}, or @code{nil} if
6287 @var{glyph} uses the default face.
6291 You can set up a @dfn{glyph table} to change how glyph codes are
6292 actually displayed on text terminals. This feature is semi-obsolete;
6293 use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}).
6296 The value of this variable, if non-@code{nil}, is the current glyph
6297 table. It takes effect only on character terminals; on graphical
6298 displays, all glyphs are displayed literally. The glyph table should
6299 be a vector whose @var{g}th element specifies how to display glyph
6300 code @var{g}, where @var{g} is the glyph code for a glyph whose face
6301 is unspecified. Each element should be one of the following:
6305 Display this glyph literally.
6308 Display this glyph by sending the specified string to the terminal.
6311 Display the specified glyph code instead.
6314 Any integer glyph code greater than or equal to the length of the
6315 glyph table is displayed literally.
6319 @node Glyphless Chars
6320 @subsection Glyphless Character Display
6321 @cindex glyphless characters
6323 @dfn{Glyphless characters} are characters which are displayed in a
6324 special way, e.g., as a box containing a hexadecimal code, instead of
6325 being displayed literally. These include characters which are
6326 explicitly defined to be glyphless, as well as characters for which
6327 there is no available font (on a graphical display), and characters
6328 which cannot be encoded by the terminal's coding system (on a text
6331 @defvar glyphless-char-display
6332 The value of this variable is a char-table which defines glyphless
6333 characters and how they are displayed. Each entry must be one of the
6334 following display methods:
6338 Display the character in the usual way.
6340 @item @code{zero-width}
6341 Don't display the character.
6343 @item @code{thin-space}
6344 Display a thin space, 1-pixel wide on graphical displays, or
6345 1-character wide on text terminals.
6347 @item @code{empty-box}
6348 Display an empty box.
6350 @item @code{hex-code}
6351 Display a box containing the Unicode codepoint of the character, in
6352 hexadecimal notation.
6354 @item an @acronym{ASCII} string
6355 Display a box containing that string.
6357 @item a cons cell @code{(@var{graphical} . @var{text})}
6358 Display with @var{graphical} on graphical displays, and with
6359 @var{text} on text terminals. Both @var{graphical} and @var{text}
6360 must be one of the display methods described above.
6364 The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
6365 @acronym{ASCII} string display methods are drawn with the
6366 @code{glyphless-char} face.
6368 The char-table has one extra slot, which determines how to display any
6369 character that cannot be displayed with any available font, or cannot
6370 be encoded by the terminal's coding system. Its value should be one
6371 of the above display methods, except @code{zero-width} or a cons cell.
6373 If a character has a non-@code{nil} entry in an active display table,
6374 the display table takes effect; in this case, Emacs does not consult
6375 @code{glyphless-char-display} at all.
6378 @defopt glyphless-char-display-control
6379 This user option provides a convenient way to set
6380 @code{glyphless-char-display} for groups of similar characters. Do
6381 not set its value directly from Lisp code; the value takes effect only
6382 via a custom @code{:set} function (@pxref{Variable Definitions}),
6383 which updates @code{glyphless-char-display}.
6385 Its value should be an alist of elements @code{(@var{group}
6386 . @var{method})}, where @var{group} is a symbol specifying a group of
6387 characters, and @var{method} is a symbol specifying how to display
6390 @var{group} should be one of the following:
6394 @acronym{ASCII} control characters @code{U+0000} to @code{U+001F},
6395 excluding the newline and tab characters (normally displayed as escape
6396 sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed,
6397 emacs, The GNU Emacs Manual}).
6400 Non-@acronym{ASCII}, non-printing characters @code{U+0080} to
6401 @code{U+009F} (normally displayed as octal escape sequences like
6404 @item format-control
6405 Characters of Unicode General Category `Cf', such as @samp{U+200E}
6406 (Left-to-Right Mark), but excluding characters that have graphic
6407 images, such as @samp{U+00AD} (Soft Hyphen).
6410 Characters for there is no suitable font, or which cannot be encoded
6411 by the terminal's coding system.
6414 @c FIXME: this can also be `acronym', but that's not currently
6415 @c completely implemented; it applies only to the format-control
6416 @c group, and only works if the acronym is in `char-acronym-table'.
6417 The @var{method} symbol should be one of @code{zero-width},
6418 @code{thin-space}, @code{empty-box}, or @code{hex-code}. These have
6419 the same meanings as in @code{glyphless-char-display}, above.
6426 This section describes how to make Emacs ring the bell (or blink the
6427 screen) to attract the user's attention. Be conservative about how
6428 often you do this; frequent bells can become irritating. Also be
6429 careful not to use just beeping when signaling an error is more
6430 appropriate (@pxref{Errors}).
6432 @defun ding &optional do-not-terminate
6433 @cindex keyboard macro termination
6434 This function beeps, or flashes the screen (see @code{visible-bell} below).
6435 It also terminates any keyboard macro currently executing unless
6436 @var{do-not-terminate} is non-@code{nil}.
6439 @defun beep &optional do-not-terminate
6440 This is a synonym for @code{ding}.
6443 @defopt visible-bell
6444 This variable determines whether Emacs should flash the screen to
6445 represent a bell. Non-@code{nil} means yes, @code{nil} means no.
6446 This is effective on graphical displays, and on text terminals
6447 provided the terminal's Termcap entry defines the visible bell
6448 capability (@samp{vb}).
6451 @defvar ring-bell-function
6452 If this is non-@code{nil}, it specifies how Emacs should ``ring the
6453 bell''. Its value should be a function of no arguments. If this is
6454 non-@code{nil}, it takes precedence over the @code{visible-bell}
6458 @node Window Systems
6459 @section Window Systems
6461 Emacs works with several window systems, most notably the X Window
6462 System. Both Emacs and X use the term ``window'', but use it
6463 differently. An Emacs frame is a single window as far as X is
6464 concerned; the individual Emacs windows are not known to X at all.
6466 @defvar window-system
6467 This terminal-local variable tells Lisp programs what window system
6468 Emacs is using for displaying the frame. The possible values are
6472 @cindex X Window System
6473 Emacs is displaying the frame using X.
6475 Emacs is displaying the frame using native MS-Windows GUI.
6477 Emacs is displaying the frame using the Nextstep interface (used on
6478 GNUstep and Mac OS X).
6480 Emacs is displaying the frame using MS-DOS direct screen writes.
6482 Emacs is displaying the frame on a character-based terminal.
6486 @defvar initial-window-system
6487 This variable holds the value of @code{window-system} used for the
6488 first frame created by Emacs during startup. (When Emacs is invoked
6489 with the @option{--daemon} option, it does not create any initial
6490 frames, so @code{initial-window-system} is @code{nil}. @xref{Initial
6491 Options, daemon,, emacs, The GNU Emacs Manual}.)
6494 @defun window-system &optional frame
6495 This function returns a symbol whose name tells what window system is
6496 used for displaying @var{frame} (which defaults to the currently
6497 selected frame). The list of possible symbols it returns is the same
6498 one documented for the variable @code{window-system} above.
6501 Do @emph{not} use @code{window-system} and
6502 @code{initial-window-system} as predicates or boolean flag variables,
6503 if you want to write code that works differently on text terminals and
6504 graphic displays. That is because @code{window-system} is not a good
6505 indicator of Emacs capabilities on a given display type. Instead, use
6506 @code{display-graphic-p} or any of the other @code{display-*-p}
6507 predicates described in @ref{Display Feature Testing}.
6509 @defvar window-setup-hook
6510 This variable is a normal hook which Emacs runs after handling the
6511 initialization files. Emacs runs this hook after it has completed
6512 loading your init file, the default initialization file (if
6513 any), and the terminal-specific Lisp code, and running the hook
6514 @code{emacs-startup-hook}.
6516 This hook is used for internal purposes: setting up communication with
6517 the window system, and creating the initial window. Users should not
6521 @node Bidirectional Display
6522 @section Bidirectional Display
6523 @cindex bidirectional display
6524 @cindex right-to-left text
6526 Emacs can display text written in scripts, such as Arabic, Farsi,
6527 and Hebrew, whose natural ordering for horizontal text display runs
6528 from right to left. Furthermore, segments of Latin script and digits
6529 embedded in right-to-left text are displayed left-to-right, while
6530 segments of right-to-left script embedded in left-to-right text
6531 (e.g., Arabic or Hebrew text in comments or strings in a program
6532 source file) are appropriately displayed right-to-left. We call such
6533 mixtures of left-to-right and right-to-left text @dfn{bidirectional
6534 text}. This section describes the facilities and options for editing
6535 and displaying bidirectional text.
6537 @cindex logical order
6538 @cindex reading order
6539 @cindex visual order
6540 @cindex unicode bidirectional algorithm
6542 @cindex bidirectional reordering
6543 @cindex reordering, of bidirectional text
6544 Text is stored in Emacs buffers and strings in @dfn{logical} (or
6545 @dfn{reading}) order, i.e., the order in which a human would read
6546 each character. In right-to-left and bidirectional text, the order in
6547 which characters are displayed on the screen (called @dfn{visual
6548 order}) is not the same as logical order; the characters' screen
6549 positions do not increase monotonically with string or buffer
6550 position. In performing this @dfn{bidirectional reordering}, Emacs
6551 follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}),
6552 which is described in Annex #9 of the Unicode standard
6553 (@url{http://www.unicode.org/reports/tr9/}). Emacs provides a ``Full
6554 Bidirectionality'' class implementation of the @acronym{UBA}.
6556 @defvar bidi-display-reordering
6557 If the value of this buffer-local variable is non-@code{nil} (the
6558 default), Emacs performs bidirectional reordering for display. The
6559 reordering affects buffer text, as well as display strings and overlay
6560 strings from text and overlay properties in the buffer (@pxref{Overlay
6561 Properties}, and @pxref{Display Property}). If the value is
6562 @code{nil}, Emacs does not perform bidirectional reordering in the
6565 The default value of @code{bidi-display-reordering} controls the
6566 reordering of strings which are not directly supplied by a buffer,
6567 including the text displayed in mode lines (@pxref{Mode Line Format})
6568 and header lines (@pxref{Header Lines}).
6571 @cindex unibyte buffers, and bidi reordering
6572 Emacs never reorders the text of a unibyte buffer, even if
6573 @code{bidi-display-reordering} is non-@code{nil} in the buffer. This
6574 is because unibyte buffers contain raw bytes, not characters, and thus
6575 lack the directionality properties required for reordering.
6576 Therefore, to test whether text in a buffer will be reordered for
6577 display, it is not enough to test the value of
6578 @code{bidi-display-reordering} alone. The correct test is this:
6581 (if (and enable-multibyte-characters
6582 bidi-display-reordering)
6583 ;; Buffer is being reordered for display
6587 However, unibyte display and overlay strings @emph{are} reordered if
6588 their parent buffer is reordered. This is because plain-@sc{ascii}
6589 strings are stored by Emacs as unibyte strings. If a unibyte display
6590 or overlay string includes non-@sc{ascii} characters, these characters
6591 are assumed to have left-to-right direction.
6593 @cindex display properties, and bidi reordering of text
6594 Text covered by @code{display} text properties, by overlays with
6595 @code{display} properties whose value is a string, and by any other
6596 properties that replace buffer text, is treated as a single unit when
6597 it is reordered for display. That is, the entire chunk of text
6598 covered by these properties is reordered together. Moreover, the
6599 bidirectional properties of the characters in such a chunk of text are
6600 ignored, and Emacs reorders them as if they were replaced with a
6601 single character @code{U+FFFC}, known as the @dfn{Object Replacement
6602 Character}. This means that placing a display property over a portion
6603 of text may change the way that the surrounding text is reordered for
6604 display. To prevent this unexpected effect, always place such
6605 properties on text whose directionality is identical with text that
6608 @cindex base direction of a paragraph
6609 Each paragraph of bidirectional text has a @dfn{base direction},
6610 either right-to-left or left-to-right. Left-to-right paragraphs are
6611 displayed beginning at the left margin of the window, and are
6612 truncated or continued when the text reaches the right margin.
6613 Right-to-left paragraphs are displayed beginning at the right margin,
6614 and are continued or truncated at the left margin.
6616 By default, Emacs determines the base direction of each paragraph by
6617 looking at the text at its beginning. The precise method of
6618 determining the base direction is specified by the @acronym{UBA}; in a
6619 nutshell, the first character in a paragraph that has an explicit
6620 directionality determines the base direction of the paragraph.
6621 However, sometimes a buffer may need to force a certain base direction
6622 for its paragraphs. For example, buffers containing program source
6623 code should force all paragraphs to be displayed left-to-right. You
6624 can use following variable to do this:
6626 @defvar bidi-paragraph-direction
6627 If the value of this buffer-local variable is the symbol
6628 @code{right-to-left} or @code{left-to-right}, all paragraphs in the
6629 buffer are assumed to have that specified direction. Any other value
6630 is equivalent to @code{nil} (the default), which means to determine
6631 the base direction of each paragraph from its contents.
6633 @cindex @code{prog-mode}, and @code{bidi-paragraph-direction}
6634 Modes for program source code should set this to @code{left-to-right}.
6635 Prog mode does this by default, so modes derived from Prog mode do not
6636 need to set this explicitly (@pxref{Basic Major Modes}).
6639 @defun current-bidi-paragraph-direction &optional buffer
6640 This function returns the paragraph direction at point in the named
6641 @var{buffer}. The returned value is a symbol, either
6642 @code{left-to-right} or @code{right-to-left}. If @var{buffer} is
6643 omitted or @code{nil}, it defaults to the current buffer. If the
6644 buffer-local value of the variable @code{bidi-paragraph-direction} is
6645 non-@code{nil}, the returned value will be identical to that value;
6646 otherwise, the returned value reflects the paragraph direction
6647 determined dynamically by Emacs. For buffers whose value of
6648 @code{bidi-display-reordering} is @code{nil} as well as unibyte
6649 buffers, this function always returns @code{left-to-right}.
6652 @cindex visual-order cursor motion
6653 Sometimes there's a need to move point in strict visual order,
6654 either to the left or to the right of its current screen position.
6655 Emacs provides a primitive to do that.
6657 @defun move-point-visually direction
6658 This function moves point of the currently selected window to the
6659 buffer position that appears immediately to the right or to the left
6660 of point on the screen. If @var{direction} is positive, point will
6661 move one screen position to the right, otherwise it will move one
6662 screen position to the left. Note that, depending on the surrounding
6663 bidirectional context, this could potentially move point many buffer
6664 positions away. If invoked at the end of a screen line, the function
6665 moves point to the rightmost or leftmost screen position of the next
6666 or previous screen line, as appropriate for the value of
6669 The function returns the new buffer position as its value.
6672 @cindex layout on display, and bidirectional text
6673 @cindex jumbled display of bidirectional text
6674 @cindex concatenating bidirectional strings
6675 Bidirectional reordering can have surprising and unpleasant effects
6676 when two strings with bidirectional content are juxtaposed in a
6677 buffer, or otherwise programmatically concatenated into a string of
6678 text. A typical problematic case is when a buffer consists of
6679 sequences of text ``fields'' separated by whitespace or punctuation
6680 characters, like Buffer Menu mode or Rmail Summary Mode. Because the
6681 punctuation characters used as separators have @dfn{weak
6682 directionality}, they take on the directionality of surrounding text.
6683 As result, a numeric field that follows a field with bidirectional
6684 content can be displayed @emph{to the left} of the preceding field,
6685 messing up the expected layout. There are several ways to avoid this
6690 Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or
6691 @acronym{LRM}, to the end of each field that may have bidirectional
6692 content, or prepend it to the beginning of the following field. The
6693 function @code{bidi-string-mark-left-to-right}, described below, comes
6694 in handy for this purpose. (In a right-to-left paragraph, use
6695 @code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.) This
6696 is one of the solutions recommended by the UBA.
6699 Include the tab character in the field separator. The tab character
6700 plays the role of @dfn{segment separator} in bidirectional reordering,
6701 causing the text on either side to be reordered separately.
6703 @cindex @code{space} display spec, and bidirectional text
6705 Separate fields with a @code{display} property or overlay with a
6706 property value of the form @code{(space . PROPS)} (@pxref{Specified
6707 Space}). Emacs treats this display specification as a @dfn{paragraph
6708 separator}, and reorders the text on either side separately.
6711 @defun bidi-string-mark-left-to-right string
6712 This function returns its argument @var{string}, possibly modified,
6713 such that the result can be safely concatenated with another string,
6714 or juxtaposed with another string in a buffer, without disrupting the
6715 relative layout of this string and the next one on display. If the
6716 string returned by this function is displayed as part of a
6717 left-to-right paragraph, it will always appear on display to the left
6718 of the text that follows it. The function works by examining the
6719 characters of its argument, and if any of those characters could cause
6720 reordering on display, the function appends the @acronym{LRM}
6721 character to the string. The appended @acronym{LRM} character is made
6722 invisible by giving it an @code{invisible} text property of @code{t}
6723 (@pxref{Invisible Text}).
6726 The reordering algorithm uses the bidirectional properties of the
6727 characters stored as their @code{bidi-class} property
6728 (@pxref{Character Properties}). Lisp programs can change these
6729 properties by calling the @code{put-char-code-property} function.
6730 However, doing this requires a thorough understanding of the
6731 @acronym{UBA}, and is therefore not recommended. Any changes to the
6732 bidirectional properties of a character have global effect: they
6733 affect all Emacs frames and windows.
6735 Similarly, the @code{mirroring} property is used to display the
6736 appropriate mirrored character in the reordered text. Lisp programs
6737 can affect the mirrored display by changing this property. Again, any
6738 such changes affect all of Emacs display.