2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2000, 2001,
4 @c 2002, 2005 Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @setfilename ../info/display
7 @node Display, System Interface, Processes, Top
10 This chapter describes a number of features related to the display
11 that Emacs presents to the user.
14 * Refresh Screen:: Clearing the screen and redrawing everything on it.
15 * Forcing Redisplay:: Forcing redisplay.
16 * Truncation:: Folding or wrapping long text lines.
17 * The Echo Area:: Where messages are displayed.
18 * Warnings:: Displaying warning messages for the user.
19 * Progress:: Informing user about progress of a long operation.
20 * Invisible Text:: Hiding part of the buffer text.
21 * Selective Display:: Hiding part of the buffer text (the old way).
22 * Temporary Displays:: Displays that go away automatically.
23 * Overlays:: Use overlays to highlight parts of the buffer.
24 * Width:: How wide a character or string is on the screen.
25 * Line Height:: Controlling the height of lines.
26 * Faces:: A face defines a graphics style for text characters:
28 * Fringes:: Controlling window fringes.
29 * Scroll Bars:: Controlling vertical scroll bars.
30 * Pointer Shape:: Controlling the mouse pointer shape.
31 * Display Property:: Enabling special display features.
32 * Images:: Displaying images in Emacs buffers.
33 * Buttons:: Adding clickable buttons to Emacs buffers.
34 * Blinking:: How Emacs shows the matching open parenthesis.
35 * Inverse Video:: Specifying how the screen looks.
36 * Usual Display:: The usual conventions for displaying nonprinting chars.
37 * Display Tables:: How to specify other conventions.
38 * Beeping:: Audible signal to the user.
39 * Window Systems:: Which window system is being used.
43 @section Refreshing the Screen
45 The function @code{redraw-frame} clears and redisplays the entire
46 contents of a given frame (@pxref{Frames}). This is useful if the
50 @defun redraw-frame frame
51 This function clears and redisplays frame @var{frame}.
54 Even more powerful is @code{redraw-display}:
56 @deffn Command redraw-display
57 This function clears and redisplays all visible frames.
60 This function calls for redisplay of certain windows, the next time
61 redisplay is done, but does not clear them first.
63 @defun force-window-update &optional object
64 This function forces redisplay of some or all windows. If
65 @var{object} is a window, it forces redisplay of that window. If
66 @var{object} is a buffer or buffer name, it forces redisplay of all
67 windows displaying that buffer. If @var{object} is @code{nil} (or
68 omitted), it forces redisplay of all windows.
71 Processing user input takes absolute priority over redisplay. If you
72 call these functions when input is available, they do nothing
73 immediately, but a full redisplay does happen eventually---after all the
74 input has been processed.
76 Normally, suspending and resuming Emacs also refreshes the screen.
77 Some terminal emulators record separate contents for display-oriented
78 programs such as Emacs and for ordinary sequential display. If you are
79 using such a terminal, you might want to inhibit the redisplay on
82 @defvar no-redraw-on-reenter
83 @cindex suspend (cf. @code{no-redraw-on-reenter})
84 @cindex resume (cf. @code{no-redraw-on-reenter})
85 This variable controls whether Emacs redraws the entire screen after it
86 has been suspended and resumed. Non-@code{nil} means there is no need
87 to redraw, @code{nil} means redrawing is needed. The default is @code{nil}.
90 @node Forcing Redisplay
91 @section Forcing Redisplay
92 @cindex forcing redisplay
94 Emacs redisplay normally stops if input arrives, and does not happen
95 at all if input is available before it starts. Most of the time, this
96 is exactly what you want. However, you can prevent preemption by
97 binding @code{redisplay-dont-pause} to a non-@code{nil} value.
99 @tindex redisplay-dont-pause
100 @defvar redisplay-dont-pause
101 If this variable is non-@code{nil}, pending input does not
102 prevent or halt redisplay; redisplay occurs, and finishes,
103 regardless of whether input is available.
106 You can request a display update, but only if no input is pending,
107 with @code{(sit-for 0)}. To force a display update even when input is
111 (let ((redisplay-dont-pause t))
117 @cindex line wrapping
118 @cindex continuation lines
119 @cindex @samp{$} in display
120 @cindex @samp{\} in display
122 When a line of text extends beyond the right edge of a window, the
123 line can either be continued on the next screen line, or truncated to
124 one screen line. The additional screen lines used to display a long
125 text line are called @dfn{continuation} lines. Normally, a @samp{$} in
126 the rightmost column of the window indicates truncation; a @samp{\} on
127 the rightmost column indicates a line that ``wraps'' onto the next line,
128 which is also called @dfn{continuing} the line. (The display table can
129 specify alternative indicators; see @ref{Display Tables}.)
131 On a window system display, the @samp{$} and @samp{\} indicators are
132 replaced with arrow images displayed in the window fringes
135 Note that continuation is different from filling; continuation happens
136 on the screen only, not in the buffer contents, and it breaks a line
137 precisely at the right margin, not at a word boundary. @xref{Filling}.
139 @defopt truncate-lines
140 This buffer-local variable controls how Emacs displays lines that extend
141 beyond the right edge of the window. The default is @code{nil}, which
142 specifies continuation. If the value is non-@code{nil}, then these
145 If the variable @code{truncate-partial-width-windows} is non-@code{nil},
146 then truncation is always used for side-by-side windows (within one
147 frame) regardless of the value of @code{truncate-lines}.
150 @defopt default-truncate-lines
151 This variable is the default value for @code{truncate-lines}, for
152 buffers that do not have buffer-local values for it.
155 @defopt truncate-partial-width-windows
156 This variable controls display of lines that extend beyond the right
157 edge of the window, in side-by-side windows (@pxref{Splitting Windows}).
158 If it is non-@code{nil}, these lines are truncated; otherwise,
159 @code{truncate-lines} says what to do with them.
162 When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in
163 a window, that forces truncation.
165 If your buffer contains @emph{very} long lines, and you use
166 continuation to display them, just thinking about them can make Emacs
167 redisplay slow. The column computation and indentation functions also
168 become slow. Then you might find it advisable to set
169 @code{cache-long-line-scans} to @code{t}.
171 @defvar cache-long-line-scans
172 If this variable is non-@code{nil}, various indentation and motion
173 functions, and Emacs redisplay, cache the results of scanning the
174 buffer, and consult the cache to avoid rescanning regions of the buffer
175 unless they are modified.
177 Turning on the cache slows down processing of short lines somewhat.
179 This variable is automatically buffer-local in every buffer.
183 @section The Echo Area
184 @cindex error display
187 The @dfn{echo area} is used for displaying error messages
188 (@pxref{Errors}), for messages made with the @code{message} primitive,
189 and for echoing keystrokes. It is not the same as the minibuffer,
190 despite the fact that the minibuffer appears (when active) in the same
191 place on the screen as the echo area. The @cite{GNU Emacs Manual}
192 specifies the rules for resolving conflicts between the echo area and
193 the minibuffer for use of that screen space (@pxref{Minibuffer,, The
194 Minibuffer, emacs, The GNU Emacs Manual}).
196 You can write output in the echo area by using the Lisp printing
197 functions with @code{t} as the stream (@pxref{Output Functions}), or as
200 @defun message string &rest arguments
201 This function displays a message in the echo area. The
202 argument @var{string} is similar to a C language @code{printf} control
203 string. See @code{format} in @ref{Formatting Strings}, for the details
204 on the conversion specifications. @code{message} returns the
207 In batch mode, @code{message} prints the message text on the standard
208 error stream, followed by a newline.
210 If @var{string}, or strings among the @var{arguments}, have @code{face}
211 text properties, these affect the way the message is displayed.
214 If @var{string} is @code{nil}, @code{message} clears the echo area; if
215 the echo area has been expanded automatically, this brings it back to
216 its normal size. If the minibuffer is active, this brings the
217 minibuffer contents back onto the screen immediately.
219 @vindex message-truncate-lines
220 Normally, displaying a long message resizes the echo area to display
221 the entire message. But if the variable @code{message-truncate-lines}
222 is non-@code{nil}, the echo area does not resize, and the message is
223 truncated to fit it, as in Emacs 20 and before.
227 (message "Minibuffer depth is %d."
229 @print{} Minibuffer depth is 0.
230 @result{} "Minibuffer depth is 0."
234 ---------- Echo Area ----------
235 Minibuffer depth is 0.
236 ---------- Echo Area ----------
240 To automatically display a message in the echo area or in a pop-buffer,
241 depending on its size, use @code{display-message-or-buffer} (see below).
244 @defopt max-mini-window-height
245 This variable specifies the maximum height for resizing minibuffer
246 windows. If a float, it specifies a fraction of the height of the
247 frame. If an integer, it specifies a number of lines.
250 @tindex with-temp-message
251 @defmac with-temp-message message &rest body
252 This construct displays a message in the echo area temporarily, during
253 the execution of @var{body}. It displays @var{message}, executes
254 @var{body}, then returns the value of the last body form while restoring
255 the previous echo area contents.
258 @defun message-or-box string &rest arguments
259 This function displays a message like @code{message}, but may display it
260 in a dialog box instead of the echo area. If this function is called in
261 a command that was invoked using the mouse---more precisely, if
262 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
263 @code{nil} or a list---then it uses a dialog box or pop-up menu to
264 display the message. Otherwise, it uses the echo area. (This is the
265 same criterion that @code{y-or-n-p} uses to make a similar decision; see
266 @ref{Yes-or-No Queries}.)
268 You can force use of the mouse or of the echo area by binding
269 @code{last-nonmenu-event} to a suitable value around the call.
272 @defun message-box string &rest arguments
273 This function displays a message like @code{message}, but uses a dialog
274 box (or a pop-up menu) whenever that is possible. If it is impossible
275 to use a dialog box or pop-up menu, because the terminal does not
276 support them, then @code{message-box} uses the echo area, like
280 @defun display-message-or-buffer message &optional buffer-name not-this-window frame
281 @tindex display-message-or-buffer
282 This function displays the message @var{message}, which may be either a
283 string or a buffer. If it is shorter than the maximum height of the
284 echo area, as defined by @code{max-mini-window-height}, it is displayed
285 in the echo area, using @code{message}. Otherwise,
286 @code{display-buffer} is used to show it in a pop-up buffer.
288 Returns either the string shown in the echo area, or when a pop-up
289 buffer is used, the window used to display it.
291 If @var{message} is a string, then the optional argument
292 @var{buffer-name} is the name of the buffer used to display it when a
293 pop-up buffer is used, defaulting to @samp{*Message*}. In the case
294 where @var{message} is a string and displayed in the echo area, it is
295 not specified whether the contents are inserted into the buffer anyway.
297 The optional arguments @var{not-this-window} and @var{frame} are as for
298 @code{display-buffer}, and only used if a buffer is displayed.
301 @defun current-message
302 This function returns the message currently being displayed in the
303 echo area, or @code{nil} if there is none.
306 @defvar cursor-in-echo-area
307 This variable controls where the cursor appears when a message is
308 displayed in the echo area. If it is non-@code{nil}, then the cursor
309 appears at the end of the message. Otherwise, the cursor appears at
310 point---not in the echo area at all.
312 The value is normally @code{nil}; Lisp programs bind it to @code{t}
313 for brief periods of time.
316 @defvar echo-area-clear-hook
317 This normal hook is run whenever the echo area is cleared---either by
318 @code{(message nil)} or for any other reason.
321 Almost all the messages displayed in the echo area are also recorded
322 in the @samp{*Messages*} buffer.
324 @defopt message-log-max
325 This variable specifies how many lines to keep in the @samp{*Messages*}
326 buffer. The value @code{t} means there is no limit on how many lines to
327 keep. The value @code{nil} disables message logging entirely. Here's
328 how to display a message and prevent it from being logged:
331 (let (message-log-max)
336 @defvar echo-keystrokes
337 This variable determines how much time should elapse before command
338 characters echo. Its value must be an integer or floating point number,
340 number of seconds to wait before echoing. If the user types a prefix
341 key (such as @kbd{C-x}) and then delays this many seconds before
342 continuing, the prefix key is echoed in the echo area. (Once echoing
343 begins in a key sequence, all subsequent characters in the same key
344 sequence are echoed immediately.)
346 If the value is zero, then command input is not echoed.
350 @section Reporting Warnings
353 @dfn{Warnings} are a facility for a program to inform the user of a
354 possible problem, but continue running.
357 * Warning Basics:: Warnings concepts and functions to report them.
358 * Warning Variables:: Variables programs bind to customize their warnings.
359 * Warning Options:: Variables users set to control display of warnings.
363 @subsection Warning Basics
364 @cindex severity level
366 Every warning has a textual message, which explains the problem for
367 the user, and a @dfn{severity level} which is a symbol. Here are the
368 possible severity levels, in order of decreasing severity, and their
373 A problem that will seriously impair Emacs operation soon
374 if you do not attend to it promptly.
376 A report of data or circumstances that are inherently wrong.
378 A report of data or circumstances that are not inherently wrong, but
379 raise suspicion of a possible problem.
381 A report of information that may be useful if you are debugging.
384 When your program encounters invalid input data, it can either
385 signal a Lisp error by calling @code{error} or @code{signal} or report
386 a warning with severity @code{:error}. Signaling a Lisp error is the
387 easiest thing to do, but it means the program cannot continue
388 processing. If you want to take the trouble to implement a way to
389 continue processing despite the bad data, then reporting a warning of
390 severity @code{:error} is the right way to inform the user of the
391 problem. For instance, the Emacs Lisp byte compiler can report an
392 error that way and continue compiling other functions. (If the
393 program signals a Lisp error and then handles it with
394 @code{condition-case}, the user won't see the error message; it could
395 show the message to the user by reporting it as a warning.)
398 Each warning has a @dfn{warning type} to classify it. The type is a
399 list of symbols. The first symbol should be the custom group that you
400 use for the program's user options. For example, byte compiler
401 warnings use the warning type @code{(bytecomp)}. You can also
402 subcategorize the warnings, if you wish, by using more symbols in the
405 @defun display-warning type message &optional level buffer-name
406 This function reports a warning, using @var{message} as the message
407 and @var{type} as the warning type. @var{level} should be the
408 severity level, with @code{:warning} being the default.
410 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
411 for logging the warning. By default, it is @samp{*Warnings*}.
414 @defun lwarn type level message &rest args
415 This function reports a warning using the value of @code{(format
416 @var{message} @var{args}...)} as the message. In other respects it is
417 equivalent to @code{display-warning}.
420 @defun warn message &rest args
421 This function reports a warning using the value of @code{(format
422 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
423 type, and @code{:warning} as the severity level. It exists for
424 compatibility only; we recommend not using it, because you should
425 specify a specific warning type.
428 @node Warning Variables
429 @subsection Warning Variables
431 Programs can customize how their warnings appear by binding
432 the variables described in this section.
434 @defvar warning-levels
435 This list defines the meaning and severity order of the warning
436 severity levels. Each element defines one severity level,
437 and they are arranged in order of decreasing severity.
439 Each element has the form @code{(@var{level} @var{string}
440 @var{function})}, where @var{level} is the severity level it defines.
441 @var{string} specifies the textual description of this level.
442 @var{string} should use @samp{%s} to specify where to put the warning
443 type information, or it can omit the @samp{%s} so as not to include
446 The optional @var{function}, if non-@code{nil}, is a function to call
447 with no arguments, to get the user's attention.
449 Normally you should not change the value of this variable.
452 @defvar warning-prefix-function
453 If non-@code{nil}, the value is a function to generate prefix text for
454 warnings. Programs can bind the variable to a suitable function.
455 @code{display-warning} calls this function with the warnings buffer
456 current, and the function can insert text in it. That text becomes
457 the beginning of the warning message.
459 The function is called with two arguments, the severity level and its
460 entry in @code{warning-levels}. It should return a list to use as the
461 entry (this value need not be an actual member of
462 @code{warning-levels}). By constructing this value, the function can
463 change the severity of the warning, or specify different handling for
464 a given severity level.
466 If the variable's value is @code{nil} then there is no function
470 @defvar warning-series
471 Programs can bind this variable to @code{t} to say that the next
472 warning should begin a series. When several warnings form a series,
473 that means to leave point on the first warning of the series, rather
474 than keep moving it for each warning so that it appears on the last one.
475 The series ends when the local binding is unbound and
476 @code{warning-series} becomes @code{nil} again.
478 The value can also be a symbol with a function definition. That is
479 equivalent to @code{t}, except that the next warning will also call
480 the function with no arguments with the warnings buffer current. The
481 function can insert text which will serve as a header for the series
484 Once a series has begun, the value is a marker which points to the
485 buffer position in the warnings buffer of the start of the series.
487 The variable's normal value is @code{nil}, which means to handle
488 each warning separately.
491 @defvar warning-fill-prefix
492 When this variable is non-@code{nil}, it specifies a fill prefix to
493 use for filling each warning's text.
496 @defvar warning-type-format
497 This variable specifies the format for displaying the warning type
498 in the warning message. The result of formatting the type this way
499 gets included in the message under the control of the string in the
500 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
501 If you bind it to @code{""} then the warning type won't appear at
505 @node Warning Options
506 @subsection Warning Options
508 These variables are used by users to control what happens
509 when a Lisp program reports a warning.
511 @defopt warning-minimum-level
512 This user option specifies the minimum severity level that should be
513 shown immediately to the user. The default is @code{:warning}, which
514 means to immediately display all warnings except @code{:debug}
518 @defopt warning-minimum-log-level
519 This user option specifies the minimum severity level that should be
520 logged in the warnings buffer. The default is @code{:warning}, which
521 means to log all warnings except @code{:debug} warnings.
524 @defopt warning-suppress-types
525 This list specifies which warning types should not be displayed
526 immediately for the user. Each element of the list should be a list
527 of symbols. If its elements match the first elements in a warning
528 type, then that warning is not displayed immediately.
531 @defopt warning-suppress-log-types
532 This list specifies which warning types should not be logged in the
533 warnings buffer. Each element of the list should be a list of
534 symbols. If it matches the first few elements in a warning type, then
535 that warning is not logged.
539 @section Reporting Operation Progress
540 @cindex progress reporting
542 When an operation can take a while to finish, you should inform the
543 user about the progress it makes. This way the user can estimate
544 remaining time and clearly see that Emacs is busy working, not hung.
546 Functions listed in this section provide simple and efficient way of
547 reporting operation progress. Here is a working example that does
551 (let ((progress-reporter
552 (make-progress-reporter "Collecting mana for Emacs..."
556 (progress-reporter-update progress-reporter k))
557 (progress-reporter-done progress-reporter))
560 @defun make-progress-reporter message min-value max-value &optional current-value min-change min-time
561 This function creates and returns a @dfn{progress reporter}---an
562 object you will use as an argument for all other functions listed
563 here. The idea is to precompute as much data as possible to make
564 progress reporting very fast.
566 When this progress reporter is subsequently used, it will display
567 @var{message} in the echo area, followed by progress percentage.
568 @var{message} is treated as a simple string. If you need it to depend
569 on a filename, for instance, use @code{format} before calling this
572 @var{min-value} and @var{max-value} arguments stand for starting and
573 final states of your operation. For instance, if you scan a buffer,
574 they should be the results of @code{point-min} and @code{point-max}
575 correspondingly. It is required that @var{max-value} is greater than
576 @var{min-value}. If you create progress reporter when some part of
577 the operation has already been completed, then specify
578 @var{current-value} argument. But normally you should omit it or set
579 it to @code{nil}---it will default to @var{min-value} then.
581 Remaining arguments control the rate of echo area updates. Progress
582 reporter will wait for at least @var{min-change} more percents of the
583 operation to be completed before printing next message.
584 @var{min-time} specifies the minimum time in seconds to pass between
585 successive prints. It can be fractional. Depending on Emacs and
586 system capabilities, progress reporter may or may not respect this
587 last argument or do it with varying precision. Default value for
588 @var{min-change} is 1 (one percent), for @var{min-time}---0.2
591 This function calls @code{progress-reporter-update}, so the first
592 message is printed immediately.
595 @defun progress-reporter-update reporter value
596 This function does the main work of reporting progress of your
597 operation. It displays the message of @var{reporter}, followed by
598 progress percentage determined by @var{value}. If percentage is zero,
599 or close enough according to the @var{min-change} and @var{min-time}
600 arguments, then it is omitted from the output.
602 @var{reporter} must be the result of a call to
603 @code{make-progress-reporter}. @var{value} specifies the current
604 state of your operation and must be between @var{min-value} and
605 @var{max-value} (inclusive) as passed to
606 @code{make-progress-reporter}. For instance, if you scan a buffer,
607 then @var{value} should be the result of a call to @code{point}.
609 This function respects @var{min-change} and @var{min-time} as passed
610 to @code{make-progress-reporter} and so does not output new messages
611 on every invocation. It is thus very fast and normally you should not
612 try to reduce the number of calls to it: resulting overhead will most
613 likely negate your effort.
616 @defun progress-reporter-force-update reporter value &optional new-message
617 This function is similar to @code{progress-reporter-update} except
618 that it prints a message in the echo area unconditionally.
620 The first two arguments have the same meaning as for
621 @code{progress-reporter-update}. Optional @var{new-message} allows
622 you to change the message of the @var{reporter}. Since this functions
623 always updates the echo area, such a change will be immediately
624 presented to the user.
627 @defun progress-reporter-done reporter
628 This function should be called when the operation is finished. It
629 prints the message of @var{reporter} followed by word ``done'' in the
632 You should always call this function and not hope for
633 @code{progress-reporter-update} to print ``100%.'' Firstly, it may
634 never print it, there are many good reasons for this not to happen.
635 Secondly, ``done'' is more explicit.
638 @defmac dotimes-with-progress-reporter (var count [result]) message body...
639 This is a convenience macro that works the same way as @code{dotimes}
640 does, but also reports loop progress using the functions described
641 above. It allows you to save some typing.
643 You can rewrite the example in the beginning of this node using
647 (dotimes-with-progress-reporter
649 "Collecting some mana for Emacs..."
655 @section Invisible Text
657 @cindex invisible text
658 You can make characters @dfn{invisible}, so that they do not appear on
659 the screen, with the @code{invisible} property. This can be either a
660 text property (@pxref{Text Properties}) or a property of an overlay
661 (@pxref{Overlays}). Cursor motion also partly ignores these
662 characters; if the command loop finds point within them, it moves
663 point to the other side of them.
665 In the simplest case, any non-@code{nil} @code{invisible} property makes
666 a character invisible. This is the default case---if you don't alter
667 the default value of @code{buffer-invisibility-spec}, this is how the
668 @code{invisible} property works. You should normally use @code{t}
669 as the value of the @code{invisible} property if you don't plan
670 to set @code{buffer-invisibility-spec} yourself.
672 More generally, you can use the variable @code{buffer-invisibility-spec}
673 to control which values of the @code{invisible} property make text
674 invisible. This permits you to classify the text into different subsets
675 in advance, by giving them different @code{invisible} values, and
676 subsequently make various subsets visible or invisible by changing the
677 value of @code{buffer-invisibility-spec}.
679 Controlling visibility with @code{buffer-invisibility-spec} is
680 especially useful in a program to display the list of entries in a
681 database. It permits the implementation of convenient filtering
682 commands to view just a part of the entries in the database. Setting
683 this variable is very fast, much faster than scanning all the text in
684 the buffer looking for properties to change.
686 @defvar buffer-invisibility-spec
687 This variable specifies which kinds of @code{invisible} properties
688 actually make a character invisible. Setting this variable makes it
693 A character is invisible if its @code{invisible} property is
694 non-@code{nil}. This is the default.
697 Each element of the list specifies a criterion for invisibility; if a
698 character's @code{invisible} property fits any one of these criteria,
699 the character is invisible. The list can have two kinds of elements:
703 A character is invisible if its @code{invisible} property value
704 is @var{atom} or if it is a list with @var{atom} as a member.
706 @item (@var{atom} . t)
707 A character is invisible if its @code{invisible} property value
708 is @var{atom} or if it is a list with @var{atom} as a member.
709 Moreover, if this character is at the end of a line and is followed
710 by a visible newline, it displays an ellipsis.
715 Two functions are specifically provided for adding elements to
716 @code{buffer-invisibility-spec} and removing elements from it.
718 @defun add-to-invisibility-spec element
719 This function adds the element @var{element} to
720 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
721 was @code{t}, it changes to a list, @code{(t)}, so that text whose
722 @code{invisible} property is @code{t} remains invisible.
725 @defun remove-from-invisibility-spec element
726 This removes the element @var{element} from
727 @code{buffer-invisibility-spec}. This does nothing if @var{element}
731 A convention for use of @code{buffer-invisibility-spec} is that a
732 major mode should use the mode's own name as an element of
733 @code{buffer-invisibility-spec} and as the value of the
734 @code{invisible} property:
737 ;; @r{If you want to display an ellipsis:}
738 (add-to-invisibility-spec '(my-symbol . t))
739 ;; @r{If you don't want ellipsis:}
740 (add-to-invisibility-spec 'my-symbol)
742 (overlay-put (make-overlay beginning end)
743 'invisible 'my-symbol)
745 ;; @r{When done with the overlays:}
746 (remove-from-invisibility-spec '(my-symbol . t))
747 ;; @r{Or respectively:}
748 (remove-from-invisibility-spec 'my-symbol)
751 @vindex line-move-ignore-invisible
752 Ordinarily, functions that operate on text or move point do not care
753 whether the text is invisible. The user-level line motion commands
754 explicitly ignore invisible newlines if
755 @code{line-move-ignore-invisible} is non-@code{nil} (the default), but
756 only because they are explicitly programmed to do so.
758 However, if a command ends with point inside or immediately after
759 invisible text, the main editing loop moves point further forward or
760 further backward (in the same direction that the command already moved
761 it) until that condition is no longer true. Thus, if the command
762 moved point back into an invisible range, Emacs moves point back to
763 the beginning of that range, following the previous visible character.
764 If the command moved point forward into an invisible range, Emacs
765 moves point forward past the first visible character that follows the
768 Incremental search can make invisible overlays visible temporarily
769 and/or permanently when a match includes invisible text. To enable
770 this, the overlay should have a non-@code{nil}
771 @code{isearch-open-invisible} property. The property value should be a
772 function to be called with the overlay as an argument. This function
773 should make the overlay visible permanently; it is used when the match
774 overlaps the overlay on exit from the search.
776 During the search, such overlays are made temporarily visible by
777 temporarily modifying their invisible and intangible properties. If you
778 want this to be done differently for a certain overlay, give it an
779 @code{isearch-open-invisible-temporary} property which is a function.
780 The function is called with two arguments: the first is the overlay, and
781 the second is @code{nil} to make the overlay visible, or @code{t} to
782 make it invisible again.
784 @node Selective Display
785 @section Selective Display
786 @cindex selective display
788 @dfn{Selective display} refers to a pair of related features for
789 hiding certain lines on the screen.
791 The first variant, explicit selective display, is designed for use
792 in a Lisp program: it controls which lines are hidden by altering the
793 text. This kind of hiding in some ways resembles the effect of the
794 @code{invisible} property (@pxref{Invisible Text}), but the two
795 features are different and do not work the same way.
797 In the second variant, the choice of lines to hide is made
798 automatically based on indentation. This variant is designed to be a
801 The way you control explicit selective display is by replacing a
802 newline (control-j) with a carriage return (control-m). The text that
803 was formerly a line following that newline is now hidden. Strictly
804 speaking, it is temporarily no longer a line at all, since only
805 newlines can separate lines; it is now part of the previous line.
807 Selective display does not directly affect editing commands. For
808 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
809 into hidden text. However, the replacement of newline characters with
810 carriage return characters affects some editing commands. For
811 example, @code{next-line} skips hidden lines, since it searches only
812 for newlines. Modes that use selective display can also define
813 commands that take account of the newlines, or that control which
814 parts of the text are hidden.
816 When you write a selectively displayed buffer into a file, all the
817 control-m's are output as newlines. This means that when you next read
818 in the file, it looks OK, with nothing hidden. The selective display
819 effect is seen only within Emacs.
821 @defvar selective-display
822 This buffer-local variable enables selective display. This means that
823 lines, or portions of lines, may be made hidden.
827 If the value of @code{selective-display} is @code{t}, then the character
828 control-m marks the start of hidden text; the control-m, and the rest
829 of the line following it, are not displayed. This is explicit selective
833 If the value of @code{selective-display} is a positive integer, then
834 lines that start with more than that many columns of indentation are not
838 When some portion of a buffer is hidden, the vertical movement
839 commands operate as if that portion did not exist, allowing a single
840 @code{next-line} command to skip any number of hidden lines.
841 However, character movement commands (such as @code{forward-char}) do
842 not skip the hidden portion, and it is possible (if tricky) to insert
843 or delete text in an hidden portion.
845 In the examples below, we show the @emph{display appearance} of the
846 buffer @code{foo}, which changes with the value of
847 @code{selective-display}. The @emph{contents} of the buffer do not
852 (setq selective-display nil)
855 ---------- Buffer: foo ----------
862 ---------- Buffer: foo ----------
866 (setq selective-display 2)
869 ---------- Buffer: foo ----------
874 ---------- Buffer: foo ----------
879 @defvar selective-display-ellipses
880 If this buffer-local variable is non-@code{nil}, then Emacs displays
881 @samp{@dots{}} at the end of a line that is followed by hidden text.
882 This example is a continuation of the previous one.
886 (setq selective-display-ellipses t)
889 ---------- Buffer: foo ----------
894 ---------- Buffer: foo ----------
898 You can use a display table to substitute other text for the ellipsis
899 (@samp{@dots{}}). @xref{Display Tables}.
902 @node Temporary Displays
903 @section Temporary Displays
905 Temporary displays are used by Lisp programs to put output into a
906 buffer and then present it to the user for perusal rather than for
907 editing. Many help commands use this feature.
909 @defspec with-output-to-temp-buffer buffer-name forms@dots{}
910 This function executes @var{forms} while arranging to insert any output
911 they print into the buffer named @var{buffer-name}, which is first
912 created if necessary, and put into Help mode. Finally, the buffer is
913 displayed in some window, but not selected.
915 If the @var{forms} do not change the major mode in the output buffer,
916 so that it is still Help mode at the end of their execution, then
917 @code{with-output-to-temp-buffer} makes this buffer read-only at the
918 end, and also scans it for function and variable names to make them
919 into clickable cross-references. @xref{Docstring hyperlinks, , Tips
920 for Documentation Strings}, in particular the item on hyperlinks in
921 documentation strings, for more details.
923 The string @var{buffer-name} specifies the temporary buffer, which
924 need not already exist. The argument must be a string, not a buffer.
925 The buffer is erased initially (with no questions asked), and it is
926 marked as unmodified after @code{with-output-to-temp-buffer} exits.
928 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
929 temporary buffer, then it evaluates the forms in @var{forms}. Output
930 using the Lisp output functions within @var{forms} goes by default to
931 that buffer (but screen display and messages in the echo area, although
932 they are ``output'' in the general sense of the word, are not affected).
933 @xref{Output Functions}.
935 Several hooks are available for customizing the behavior
936 of this construct; they are listed below.
938 The value of the last form in @var{forms} is returned.
942 ---------- Buffer: foo ----------
943 This is the contents of foo.
944 ---------- Buffer: foo ----------
948 (with-output-to-temp-buffer "foo"
950 (print standard-output))
951 @result{} #<buffer foo>
953 ---------- Buffer: foo ----------
958 ---------- Buffer: foo ----------
963 @defvar temp-buffer-show-function
964 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
965 calls it as a function to do the job of displaying a help buffer. The
966 function gets one argument, which is the buffer it should display.
968 It is a good idea for this function to run @code{temp-buffer-show-hook}
969 just as @code{with-output-to-temp-buffer} normally would, inside of
970 @code{save-selected-window} and with the chosen window and buffer
974 @defvar temp-buffer-setup-hook
975 @tindex temp-buffer-setup-hook
976 This normal hook is run by @code{with-output-to-temp-buffer} before
977 evaluating @var{body}. When the hook runs, the temporary buffer is
978 current. This hook is normally set up with a function to put the
982 @defvar temp-buffer-show-hook
983 This normal hook is run by @code{with-output-to-temp-buffer} after
984 displaying the temporary buffer. When the hook runs, the temporary buffer
985 is current, and the window it was displayed in is selected. This hook
986 is normally set up with a function to make the buffer read only, and
987 find function names and variable names in it, provided the major mode
991 @defun momentary-string-display string position &optional char message
992 This function momentarily displays @var{string} in the current buffer at
993 @var{position}. It has no effect on the undo list or on the buffer's
996 The momentary display remains until the next input event. If the next
997 input event is @var{char}, @code{momentary-string-display} ignores it
998 and returns. Otherwise, that event remains buffered for subsequent use
999 as input. Thus, typing @var{char} will simply remove the string from
1000 the display, while typing (say) @kbd{C-f} will remove the string from
1001 the display and later (presumably) move point forward. The argument
1002 @var{char} is a space by default.
1004 The return value of @code{momentary-string-display} is not meaningful.
1006 If the string @var{string} does not contain control characters, you can
1007 do the same job in a more general way by creating (and then subsequently
1008 deleting) an overlay with a @code{before-string} property.
1009 @xref{Overlay Properties}.
1011 If @var{message} is non-@code{nil}, it is displayed in the echo area
1012 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1013 default message says to type @var{char} to continue.
1015 In this example, point is initially located at the beginning of the
1020 ---------- Buffer: foo ----------
1021 This is the contents of foo.
1022 @point{}Second line.
1023 ---------- Buffer: foo ----------
1027 (momentary-string-display
1028 "**** Important Message! ****"
1030 "Type RET when done reading")
1035 ---------- Buffer: foo ----------
1036 This is the contents of foo.
1037 **** Important Message! ****Second line.
1038 ---------- Buffer: foo ----------
1040 ---------- Echo Area ----------
1041 Type RET when done reading
1042 ---------- Echo Area ----------
1051 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1052 the screen, for the sake of presentation features. An overlay is an
1053 object that belongs to a particular buffer, and has a specified
1054 beginning and end. It also has properties that you can examine and set;
1055 these affect the display of the text within the overlay.
1057 An overlays uses markers to record its beginning and end; thus,
1058 editing the text of the buffer adjusts the beginning and end of each
1059 overlay so that it stays with the text. When you create the overlay,
1060 you can specify whether text inserted at the beginning should be
1061 inside the overlay or outside, and likewise for the end of the overlay.
1064 * Managing Overlays:: Creating and moving overlays.
1065 * Overlay Properties:: How to read and set properties.
1066 What properties do to the screen display.
1067 * Finding Overlays:: Searching for overlays.
1070 @node Managing Overlays
1071 @subsection Managing Overlays
1073 This section describes the functions to create, delete and move
1074 overlays, and to examine their contents. Overlay changes are not
1075 recorded in the buffer's undo list, since the overlays are not
1076 part of the buffer's contents.
1078 @defun overlayp object
1079 This function returns @code{t} if @var{object} is an overlay.
1082 @defun make-overlay start end &optional buffer front-advance rear-advance
1083 This function creates and returns an overlay that belongs to
1084 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1085 and @var{end} must specify buffer positions; they may be integers or
1086 markers. If @var{buffer} is omitted, the overlay is created in the
1089 The arguments @var{front-advance} and @var{rear-advance} specify the
1090 insertion type for the start of the overlay and for the end of the
1091 overlay, respectively. @xref{Marker Insertion Types}. If
1092 @var{front-advance} is non-@code{nil}, text inserted at the beginning
1093 of the overlay is excluded from the overlay. If @var{read-advance} is
1094 non-@code{nil}, text inserted at the beginning of the overlay is
1095 included in the overlay.
1098 @defun overlay-start overlay
1099 This function returns the position at which @var{overlay} starts,
1103 @defun overlay-end overlay
1104 This function returns the position at which @var{overlay} ends,
1108 @defun overlay-buffer overlay
1109 This function returns the buffer that @var{overlay} belongs to. It
1110 returns @code{nil} if @var{overlay} has been deleted.
1113 @defun delete-overlay overlay
1114 This function deletes @var{overlay}. The overlay continues to exist as
1115 a Lisp object, and its property list is unchanged, but it ceases to be
1116 attached to the buffer it belonged to, and ceases to have any effect on
1119 A deleted overlay is not permanently disconnected. You can give it a
1120 position in a buffer again by calling @code{move-overlay}.
1123 @defun move-overlay overlay start end &optional buffer
1124 This function moves @var{overlay} to @var{buffer}, and places its bounds
1125 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1126 must specify buffer positions; they may be integers or markers.
1128 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1129 was already associated with; if @var{overlay} was deleted, it goes into
1132 The return value is @var{overlay}.
1134 This is the only valid way to change the endpoints of an overlay. Do
1135 not try modifying the markers in the overlay by hand, as that fails to
1136 update other vital data structures and can cause some overlays to be
1140 @defun remove-overlays &optional start end name value
1141 This function removes all the overlays between @var{start} and
1142 @var{end} whose property @var{name} has the value @var{value}. It can
1143 move the endpoints of the overlays in the region, or split them.
1145 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1146 the specified region. If @var{start} and/or @var{end} are omitted or
1147 @code{nil}, that means the beginning and end of the buffer respectively.
1148 Therefore, @code{(remove-overlays)} removes all the overlays in the
1152 Here are some examples:
1155 ;; @r{Create an overlay.}
1156 (setq foo (make-overlay 1 10))
1157 @result{} #<overlay from 1 to 10 in display.texi>
1162 (overlay-buffer foo)
1163 @result{} #<buffer display.texi>
1164 ;; @r{Give it a property we can check later.}
1165 (overlay-put foo 'happy t)
1167 ;; @r{Verify the property is present.}
1168 (overlay-get foo 'happy)
1170 ;; @r{Move the overlay.}
1171 (move-overlay foo 5 20)
1172 @result{} #<overlay from 5 to 20 in display.texi>
1177 ;; @r{Delete the overlay.}
1178 (delete-overlay foo)
1180 ;; @r{Verify it is deleted.}
1182 @result{} #<overlay in no buffer>
1183 ;; @r{A deleted overlay has no position.}
1188 (overlay-buffer foo)
1190 ;; @r{Undelete the overlay.}
1191 (move-overlay foo 1 20)
1192 @result{} #<overlay from 1 to 20 in display.texi>
1193 ;; @r{Verify the results.}
1198 (overlay-buffer foo)
1199 @result{} #<buffer display.texi>
1200 ;; @r{Moving and deleting the overlay does not change its properties.}
1201 (overlay-get foo 'happy)
1205 @node Overlay Properties
1206 @subsection Overlay Properties
1208 Overlay properties are like text properties in that the properties that
1209 alter how a character is displayed can come from either source. But in
1210 most respects they are different. @xref{Text Properties}, for comparison.
1212 Text properties are considered a part of the text; overlays and
1213 their properties are specifically considered not to be part of the
1214 text. Thus, copying text between various buffers and strings
1215 preserves text properties, but does not try to preserve overlays.
1216 Changing a buffer's text properties marks the buffer as modified,
1217 while moving an overlay or changing its properties does not. Unlike
1218 text property changes, overlay property changes are not recorded in
1219 the buffer's undo list.
1221 These functions read and set the properties of an overlay:
1223 @defun overlay-get overlay prop
1224 This function returns the value of property @var{prop} recorded in
1225 @var{overlay}, if any. If @var{overlay} does not record any value for
1226 that property, but it does have a @code{category} property which is a
1227 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1231 @defun overlay-put overlay prop value
1232 This function sets the value of property @var{prop} recorded in
1233 @var{overlay} to @var{value}. It returns @var{value}.
1236 @defun overlay-properties overlay
1237 This returns a copy of the property list of @var{overlay}.
1240 See also the function @code{get-char-property} which checks both
1241 overlay properties and text properties for a given character.
1242 @xref{Examining Properties}.
1244 Many overlay properties have special meanings; here is a table
1249 @kindex priority @r{(overlay property)}
1250 This property's value (which should be a nonnegative integer number)
1251 determines the priority of the overlay. The priority matters when two
1252 or more overlays cover the same character and both specify the same
1253 property; the one whose @code{priority} value is larger takes priority
1254 over the other. For the @code{face} property, the higher priority
1255 value does not completely replace the other; instead, its face
1256 attributes override the face attributes of the lower priority
1257 @code{face} property.
1259 Currently, all overlays take priority over text properties. Please
1260 avoid using negative priority values, as we have not yet decided just
1261 what they should mean.
1264 @kindex window @r{(overlay property)}
1265 If the @code{window} property is non-@code{nil}, then the overlay
1266 applies only on that window.
1269 @kindex category @r{(overlay property)}
1270 If an overlay has a @code{category} property, we call it the
1271 @dfn{category} of the overlay. It should be a symbol. The properties
1272 of the symbol serve as defaults for the properties of the overlay.
1275 @kindex face @r{(overlay property)}
1276 This property controls the way text is displayed---for example, which
1277 font and which colors. @xref{Faces}, for more information.
1279 In the simplest case, the value is a face name. It can also be a list;
1280 then each element can be any of these possibilities:
1284 A face name (a symbol or string).
1287 A property list of face attributes. This has the form (@var{keyword}
1288 @var{value} @dots{}), where each @var{keyword} is a face attribute
1289 name and @var{value} is a meaningful value for that attribute. With
1290 this feature, you do not need to create a face each time you want to
1291 specify a particular attribute for certain text. @xref{Face
1295 A cons cell of the form @code{(foreground-color . @var{color-name})} or
1296 @code{(background-color . @var{color-name})}. These elements specify
1297 just the foreground color or just the background color.
1299 @code{(foreground-color . @var{color-name})} has the same effect as
1300 @code{(:foreground @var{color-name})}; likewise for the background.
1304 @kindex mouse-face @r{(overlay property)}
1305 This property is used instead of @code{face} when the mouse is within
1306 the range of the overlay.
1309 @kindex display @r{(overlay property)}
1310 This property activates various features that change the
1311 way text is displayed. For example, it can make text appear taller
1312 or shorter, higher or lower, wider or narrower, or replaced with an image.
1313 @xref{Display Property}.
1316 @kindex help-echo @r{(overlay property)}
1317 If an overlay has a @code{help-echo} property, then when you move the
1318 mouse onto the text in the overlay, Emacs displays a help string in the
1319 echo area, or in the tooltip window. For details see @ref{Text
1322 @item modification-hooks
1323 @kindex modification-hooks @r{(overlay property)}
1324 This property's value is a list of functions to be called if any
1325 character within the overlay is changed or if text is inserted strictly
1328 The hook functions are called both before and after each change.
1329 If the functions save the information they receive, and compare notes
1330 between calls, they can determine exactly what change has been made
1333 When called before a change, each function receives four arguments: the
1334 overlay, @code{nil}, and the beginning and end of the text range to be
1337 When called after a change, each function receives five arguments: the
1338 overlay, @code{t}, the beginning and end of the text range just
1339 modified, and the length of the pre-change text replaced by that range.
1340 (For an insertion, the pre-change length is zero; for a deletion, that
1341 length is the number of characters deleted, and the post-change
1342 beginning and end are equal.)
1344 @item insert-in-front-hooks
1345 @kindex insert-in-front-hooks @r{(overlay property)}
1346 This property's value is a list of functions to be called before and
1347 after inserting text right at the beginning of the overlay. The calling
1348 conventions are the same as for the @code{modification-hooks} functions.
1350 @item insert-behind-hooks
1351 @kindex insert-behind-hooks @r{(overlay property)}
1352 This property's value is a list of functions to be called before and
1353 after inserting text right at the end of the overlay. The calling
1354 conventions are the same as for the @code{modification-hooks} functions.
1357 @kindex invisible @r{(overlay property)}
1358 The @code{invisible} property can make the text in the overlay
1359 invisible, which means that it does not appear on the screen.
1360 @xref{Invisible Text}, for details.
1363 @kindex intangible @r{(overlay property)}
1364 The @code{intangible} property on an overlay works just like the
1365 @code{intangible} text property. @xref{Special Properties}, for details.
1367 @item isearch-open-invisible
1368 This property tells incremental search how to make an invisible overlay
1369 visible, permanently, if the final match overlaps it. @xref{Invisible
1372 @item isearch-open-invisible-temporary
1373 This property tells incremental search how to make an invisible overlay
1374 visible, temporarily, during the search. @xref{Invisible Text}.
1377 @kindex before-string @r{(overlay property)}
1378 This property's value is a string to add to the display at the beginning
1379 of the overlay. The string does not appear in the buffer in any
1380 sense---only on the screen.
1383 @kindex after-string @r{(overlay property)}
1384 This property's value is a string to add to the display at the end of
1385 the overlay. The string does not appear in the buffer in any
1386 sense---only on the screen.
1389 @kindex evaporate @r{(overlay property)}
1390 If this property is non-@code{nil}, the overlay is deleted automatically
1391 if it becomes empty (i.e., if its length becomes zero). If you give
1392 an empty overlay a non-@code{nil} @code{evaporate} property, that deletes
1396 @cindex keymap of character (and overlays)
1397 @kindex local-map @r{(overlay property)}
1398 If this property is non-@code{nil}, it specifies a keymap for a portion
1399 of the text. The property's value replaces the buffer's local map, when
1400 the character after point is within the overlay. @xref{Active Keymaps}.
1403 @kindex keymap @r{(overlay property)}
1404 The @code{keymap} property is similar to @code{local-map} but overrides the
1405 buffer's local map (and the map specified by the @code{local-map}
1406 property) rather than replacing it.
1409 @node Finding Overlays
1410 @subsection Searching for Overlays
1412 @defun overlays-at pos
1413 This function returns a list of all the overlays that cover the
1414 character at position @var{pos} in the current buffer. The list is in
1415 no particular order. An overlay contains position @var{pos} if it
1416 begins at or before @var{pos}, and ends after @var{pos}.
1418 To illustrate usage, here is a Lisp function that returns a list of the
1419 overlays that specify property @var{prop} for the character at point:
1422 (defun find-overlays-specifying (prop)
1423 (let ((overlays (overlays-at (point)))
1426 (let ((overlay (car overlays)))
1427 (if (overlay-get overlay prop)
1428 (setq found (cons overlay found))))
1429 (setq overlays (cdr overlays)))
1434 @defun overlays-in beg end
1435 This function returns a list of the overlays that overlap the region
1436 @var{beg} through @var{end}. ``Overlap'' means that at least one
1437 character is contained within the overlay and also contained within the
1438 specified region; however, empty overlays are included in the result if
1439 they are located at @var{beg}, or strictly between @var{beg} and @var{end}.
1442 @defun next-overlay-change pos
1443 This function returns the buffer position of the next beginning or end
1444 of an overlay, after @var{pos}. If there is none, it returns
1448 @defun previous-overlay-change pos
1449 This function returns the buffer position of the previous beginning or
1450 end of an overlay, before @var{pos}. If there is none, it returns
1454 Here's an easy way to use @code{next-overlay-change} to search for the
1455 next character which gets a non-@code{nil} @code{happy} property from
1456 either its overlays or its text properties (@pxref{Property Search}):
1459 (defun find-overlay-prop (prop)
1461 (while (and (not (eobp))
1462 (not (get-char-property (point) 'happy)))
1463 (goto-char (min (next-overlay-change (point))
1464 (next-single-property-change (point) 'happy))))
1471 Since not all characters have the same width, these functions let you
1472 check the width of a character. @xref{Primitive Indent}, and
1473 @ref{Screen Lines}, for related functions.
1475 @defun char-width char
1476 This function returns the width in columns of the character @var{char},
1477 if it were displayed in the current buffer and the selected window.
1480 @defun string-width string
1481 This function returns the width in columns of the string @var{string},
1482 if it were displayed in the current buffer and the selected window.
1485 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1486 This function returns the part of @var{string} that fits within
1487 @var{width} columns, as a new string.
1489 If @var{string} does not reach @var{width}, then the result ends where
1490 @var{string} ends. If one multi-column character in @var{string}
1491 extends across the column @var{width}, that character is not included in
1492 the result. Thus, the result can fall short of @var{width} but cannot
1495 The optional argument @var{start-column} specifies the starting column.
1496 If this is non-@code{nil}, then the first @var{start-column} columns of
1497 the string are omitted from the value. If one multi-column character in
1498 @var{string} extends across the column @var{start-column}, that
1499 character is not included.
1501 The optional argument @var{padding}, if non-@code{nil}, is a padding
1502 character added at the beginning and end of the result string, to extend
1503 it to exactly @var{width} columns. The padding character is used at the
1504 end of the result if it falls short of @var{width}. It is also used at
1505 the beginning of the result if one multi-column character in
1506 @var{string} extends across the column @var{start-column}.
1508 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1509 replace the end of @var{str} (including any padding) if it extends
1510 beyond @var{end-column}, unless the display width of @var{str} is
1511 equal to or less than the display width of @var{ellipsis}. If
1512 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1516 (truncate-string-to-width "\tab\t" 12 4)
1518 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1524 @section Line Height
1527 The total height of each display line consists of the height of the
1528 contents of the line, and additional vertical line spacing below the
1531 The height of the line contents is normally determined from the
1532 maximum height of any character or image on that display line,
1533 including the final newline if there is one. (A line that is
1534 continued doesn't include a final newline.) In the most common case,
1535 the line height equals the height of the default frame font.
1537 There are several ways to explicitly control or change the line
1538 height, either by specifying an absolute height for the display line,
1539 or by adding additional vertical space below one or all lines.
1541 @kindex line-height @r{(text property)}
1542 A newline can have a @code{line-height} text or overlay property
1543 that controls the total height of the display line ending in that
1546 If the property value is a list @code{(@var{height} @var{total})},
1547 then @var{height} is used as the actual property value for the
1548 @code{line-height}, and @var{total} specifies the total displayed
1549 height of the line, so the line spacing added below the line equals
1550 the @var{total} height minus the actual line height. In this case,
1551 the other ways to specify the line spacing are ignored.
1553 If the property value is @code{t}, the displayed height of the
1554 line is exactly what its contents demand; no line-spacing is added.
1555 This case is useful for tiling small images or image slices without
1556 adding blank areas between the images.
1558 If the property value is not @code{t}, it is a height spec. A height
1559 spec stands for a numeric height value; this height spec specifies the
1560 actual line height, @var{line-height}. There are several ways to
1561 write a height spec; here's how each of them translates into a numeric
1566 If the height spec is a positive integer, the height value is that integer.
1568 If the height spec is a float, @var{float}, the numeric height value
1569 is @var{float} times the frame's default line height.
1570 @item (@var{face} . @var{ratio})
1571 If the height spec is a cons of the format shown, the numeric height
1572 is @var{ratio} times the height of face @var{face}. @var{ratio} can
1573 be any type of number, or @code{nil} which means a ratio of 1.
1574 If @var{face} is @code{t}, it refers to the current face.
1575 @item (nil . @var{ratio})
1576 If the height spec is a cons of the format shown, the numeric height
1577 is @var{ratio} times the height of the contents of the line.
1580 Thus, any valid non-@code{t} property value specifies a height in pixels,
1581 @var{line-height}, one way or another. If the line contents' height
1582 is less than @var{line-height}, Emacs adds extra vertical space above
1583 the line to achieve the total height @var{line-height}. Otherwise,
1584 @var{line-height} has no effect.
1586 If you don't specify the @code{line-height} property, the line's
1587 height consists of the contents' height plus the line spacing.
1588 There are several ways to specify the line spacing for different
1589 parts of Emacs text.
1591 @vindex default-line-spacing
1592 You can specify the line spacing for all lines in a frame with the
1593 @code{line-spacing} frame parameter, @xref{Window Frame Parameters}.
1594 However, if the variable @code{default-line-spacing} is
1595 non-@code{nil}, it overrides the frame's @code{line-spacing}
1596 parameter. An integer value specifies the number of pixels put below
1597 lines on window systems. A floating point number specifies the
1598 spacing relative to the frame's default line height.
1600 @vindex line-spacing
1601 You can specify the line spacing for all lines in a buffer via the
1602 buffer-local @code{line-spacing} variable. An integer value specifies
1603 the number of pixels put below lines on window systems. A floating
1604 point number specifies the spacing relative to the default frame line
1605 height. This overrides line spacings specified for the frame.
1607 @kindex line-spacing @r{(text property)}
1608 Finally, a newline can have a @code{line-spacing} text or overlay
1609 property that controls the height of the display line ending with that
1610 newline. The property value overrides the default frame line spacing
1611 and the buffer local @code{line-spacing} variable.
1613 One way or another, these mechanisms specify a Lisp value for the
1614 spacing of each line. The value is a height spec, and it translates
1615 into a Lisp value as described above. However, in this case the
1616 numeric height value specifies the line spacing, rather than the line
1623 A @dfn{face} is a named collection of graphical attributes: font
1624 family, foreground color, background color, optional underlining, and
1625 many others. Faces are used in Emacs to control the style of display of
1626 particular parts of the text or the frame.
1629 Each face has its own @dfn{face number}, which distinguishes faces at
1630 low levels within Emacs. However, for most purposes, you refer to
1631 faces in Lisp programs by their names.
1634 This function returns @code{t} if @var{object} is a face name symbol (or
1635 if it is a vector of the kind used internally to record face data). It
1636 returns @code{nil} otherwise.
1639 Each face name is meaningful for all frames, and by default it has the
1640 same meaning in all frames. But you can arrange to give a particular
1641 face name a special meaning in one frame if you wish.
1644 * Standard Faces:: The faces Emacs normally comes with.
1645 * Defining Faces:: How to define a face with @code{defface}.
1646 * Face Attributes:: What is in a face?
1647 * Attribute Functions:: Functions to examine and set face attributes.
1648 * Displaying Faces:: How Emacs combines the faces specified for a character.
1649 * Font Selection:: Finding the best available font for a face.
1650 * Face Functions:: How to define and examine faces.
1651 * Auto Faces:: Hook for automatic face assignment.
1652 * Font Lookup:: Looking up the names of available fonts
1653 and information about them.
1654 * Fontsets:: A fontset is a collection of fonts
1655 that handle a range of character sets.
1658 @node Standard Faces
1659 @subsection Standard Faces
1661 This table lists all the standard faces and their uses. Most of them
1662 are used for displaying certain parts of the frames or certain kinds of
1663 text; you can control how those places look by customizing these faces.
1667 @kindex default @r{(face name)}
1668 This face is used for ordinary text.
1671 @kindex mode-line @r{(face name)}
1672 This face is used for the mode line of the selected window, and for
1673 menu bars when toolkit menus are not used---but only if
1674 @code{mode-line-inverse-video} is non-@code{nil}.
1677 @kindex modeline @r{(face name)}
1678 This is an alias for the @code{mode-line} face, for compatibility with
1681 @item mode-line-inactive
1682 @kindex mode-line-inactive @r{(face name)}
1683 This face is used for mode lines of non-selected windows.
1684 This face inherits from @code{mode-line}, so changes
1685 in that face affect all windows.
1688 @kindex header-line @r{(face name)}
1689 This face is used for the header lines of windows that have them.
1692 This face controls the display of menus, both their colors and their
1693 font. (This works only on certain systems.)
1696 @kindex fringe @r{(face name)}
1697 This face controls the default colors of window fringes, the thin
1698 areas on either side that are used to display continuation and
1699 truncation glyphs. Other faces used to display bitmaps in the fringe
1700 are implicitly merged with this face.
1702 @item minibuffer-prompt
1703 @kindex minibuffer-prompt @r{(face name)}
1704 @vindex minibuffer-prompt-properties
1705 This face is used for the text of minibuffer prompts. By default,
1706 Emacs automatically adds this face to the value of
1707 @code{minibuffer-prompt-properties}, which is a list of text
1708 properties used to display the prompt text.
1711 @kindex scroll-bar @r{(face name)}
1712 This face controls the colors for display of scroll bars.
1715 @kindex tool-bar @r{(face name)}
1716 This face is used for display of the tool bar, if any.
1719 @kindex region @r{(face name)}
1720 This face is used for highlighting the region in Transient Mark mode.
1722 @item secondary-selection
1723 @kindex secondary-selection @r{(face name)}
1724 This face is used to show any secondary selection you have made.
1727 @kindex highlight @r{(face name)}
1728 This face is meant to be used for highlighting for various purposes.
1730 @item mode-line-highlight
1731 @kindex mode-line-highlight @r{(face name)}
1732 This face is used for highlighting something on @code{mode-line} or
1733 @code{header-line} for various purposes.
1735 @item trailing-whitespace
1736 @kindex trailing-whitespace @r{(face name)}
1737 This face is used to display excess whitespace at the end of a line,
1738 if @code{show-trailing-whitespace} is non-@code{nil}.
1741 @kindex escape-glyph @r{(face name)}
1742 This face is used to display control characters and escape glyphs.
1745 In contrast, these faces are provided to change the appearance of text
1746 in specific ways. You can use them on specific text, when you want
1747 the effects they produce.
1751 @kindex bold @r{(face name)}
1752 This face uses a bold font, if possible. It uses the bold variant of
1753 the frame's font, if it has one. It's up to you to choose a default
1754 font that has a bold variant, if you want to use one.
1757 @kindex italic @r{(face name)}
1758 This face uses the italic variant of the frame's font, if it has one.
1761 @kindex bold-italic @r{(face name)}
1762 This face uses the bold italic variant of the frame's font, if it has
1766 @kindex underline @r{(face name)}
1767 This face underlines text.
1770 @kindex fixed-pitch @r{(face name)}
1771 This face forces use of a particular fixed-width font.
1773 @item variable-pitch
1774 @kindex variable-pitch @r{(face name)}
1775 This face forces use of a particular variable-width font. It's
1776 reasonable to customize this to use a different variable-width font, if
1777 you like, but you should not make it a fixed-width font.
1780 @kindex shadow @r{(face name)}
1781 This face is used for making the text less noticeable than the
1782 surrounding ordinary text.
1785 @defvar show-trailing-whitespace
1786 @tindex show-trailing-whitespace
1787 If this variable is non-@code{nil}, Emacs uses the
1788 @code{trailing-whitespace} face to display any spaces and tabs at the
1792 @node Defining Faces
1793 @subsection Defining Faces
1795 The way to define a new face is with @code{defface}. This creates a
1796 kind of customization item (@pxref{Customization}) which the user can
1797 customize using the Customization buffer (@pxref{Easy Customization,,,
1798 emacs, The GNU Emacs Manual}).
1800 @defmac defface face spec doc [keyword value]...
1801 This declares @var{face} as a customizable face that defaults
1802 according to @var{spec}. You should not quote the symbol @var{face},
1803 and it should not end in @samp{-face} (that would be redundant). The
1804 argument @var{doc} specifies the face documentation. The keywords you
1805 can use in @code{defface} are the same as in @code{defgroup} and
1806 @code{defcustom} (@pxref{Common Keywords}).
1808 When @code{defface} executes, it defines the face according to
1809 @var{spec}, then uses any customizations that were read from the
1810 init file (@pxref{Init File}) to override that specification.
1812 The purpose of @var{spec} is to specify how the face should appear on
1813 different kinds of terminals. It should be an alist whose elements
1814 have the form @code{(@var{display} @var{atts})}. Each element's
1815 @sc{car}, @var{display}, specifies a class of terminals. (The first
1816 element, if it s @sc{car} is @code{default}, is special---it specifies
1817 defaults for the remaining elements). The element's @sc{cadr},
1818 @var{atts}, is a list of face attributes and their values; it
1819 specifies what the face should look like on that kind of terminal.
1820 The possible attributes are defined in the value of
1821 @code{custom-face-attributes}.
1823 The @var{display} part of an element of @var{spec} determines which
1824 frames the element matches. If more than one element of @var{spec}
1825 matches a given frame, the first element that matches is the one used
1826 for that frame. There are three possibilities for @var{display}:
1829 @item @code{default}
1830 This element of @var{spec} doesn't match any frames; instead, it
1831 specifies defaults that apply to all frames. This kind of element, if
1832 used, must be the first element of @var{spec}. Each of the following
1833 elements can override any or all of these defaults.
1836 This element of @var{spec} matches all frames. Therefore, any
1837 subsequent elements of @var{spec} are never used. Normally
1838 @code{t} is used in the last (or only) element of @var{spec}.
1841 If @var{display} is a list, each element should have the form
1842 @code{(@var{characteristic} @var{value}@dots{})}. Here
1843 @var{characteristic} specifies a way of classifying frames, and the
1844 @var{value}s are possible classifications which @var{display} should
1845 apply to. Here are the possible values of @var{characteristic}:
1849 The kind of window system the frame uses---either @code{graphic} (any
1850 graphics-capable display), @code{x}, @code{pc} (for the MS-DOS console),
1851 @code{w32} (for MS Windows 9X/NT), or @code{tty} (a non-graphics-capable
1855 What kinds of colors the frame supports---either @code{color},
1856 @code{grayscale}, or @code{mono}.
1859 The kind of background---either @code{light} or @code{dark}.
1862 An integer that represents the minimum number of colors the frame
1863 should support. This matches a frame if its
1864 @code{display-color-cells} value is at least the specified integer.
1867 Whether or not the frame can display the face attributes given in
1868 @var{value}@dots{} (@pxref{Face Attributes}). See the documentation
1869 for the function @code{display-supports-face-attributes-p} for more
1870 information on exactly how this testing is done. @xref{Display Face
1874 If an element of @var{display} specifies more than one @var{value} for a
1875 given @var{characteristic}, any of those values is acceptable. If
1876 @var{display} has more than one element, each element should specify a
1877 different @var{characteristic}; then @emph{each} characteristic of the
1878 frame must match one of the @var{value}s specified for it in
1883 Here's how the standard face @code{region} is defined:
1887 '((((class color) (min-colors 88) (background dark))
1888 :background "blue3")
1890 (((class color) (min-colors 88) (background light))
1891 :background "lightgoldenrod2")
1892 (((class color) (min-colors 16) (background dark))
1893 :background "blue3")
1894 (((class color) (min-colors 16) (background light))
1895 :background "lightgoldenrod2")
1896 (((class color) (min-colors 8))
1897 :background "blue" :foreground "white")
1898 (((type tty) (class mono))
1900 (t :background "gray"))
1902 "Basic face for highlighting the region."
1903 :group 'basic-faces)
1907 Internally, @code{defface} uses the symbol property
1908 @code{face-defface-spec} to record the face attributes specified in
1909 @code{defface}, @code{saved-face} for the attributes saved by the user
1910 with the customization buffer, @code{customized-face} for the
1911 attributes customized by the user for the current session, but not
1912 saved, and @code{face-documentation} for the documentation string.
1914 @defopt frame-background-mode
1915 This option, if non-@code{nil}, specifies the background type to use for
1916 interpreting face definitions. If it is @code{dark}, then Emacs treats
1917 all frames as if they had a dark background, regardless of their actual
1918 background colors. If it is @code{light}, then Emacs treats all frames
1919 as if they had a light background.
1922 @node Face Attributes
1923 @subsection Face Attributes
1924 @cindex face attributes
1926 The effect of using a face is determined by a fixed set of @dfn{face
1927 attributes}. This table lists all the face attributes, and what they
1928 mean. Note that in general, more than one face can be specified for a
1929 given piece of text; when that happens, the attributes of all the faces
1930 are merged to specify how to display the text. @xref{Displaying Faces}.
1932 Any attribute in a face can have the value @code{unspecified}. This
1933 means the face doesn't specify that attribute. In face merging, when
1934 the first face fails to specify a particular attribute, that means the
1935 next face gets a chance. However, the @code{default} face must
1936 specify all attributes.
1938 Some of these font attributes are meaningful only on certain kinds of
1939 displays---if your display cannot handle a certain attribute, the
1940 attribute is ignored. (The attributes @code{:family}, @code{:width},
1941 @code{:height}, @code{:weight}, and @code{:slant} correspond to parts of
1942 an X Logical Font Descriptor.)
1946 Font family name, or fontset name (@pxref{Fontsets}). If you specify a
1947 font family name, the wild-card characters @samp{*} and @samp{?} are
1951 Relative proportionate width, also known as the character set width or
1952 set width. This should be one of the symbols @code{ultra-condensed},
1953 @code{extra-condensed}, @code{condensed}, @code{semi-condensed},
1954 @code{normal}, @code{semi-expanded}, @code{expanded},
1955 @code{extra-expanded}, or @code{ultra-expanded}.
1958 Either the font height, an integer in units of 1/10 point, a floating
1959 point number specifying the amount by which to scale the height of any
1960 underlying face, or a function, which is called with the old height
1961 (from the underlying face), and should return the new height.
1964 Font weight---a symbol from this series (from most dense to most faint):
1965 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
1966 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light},
1967 or @code{ultra-light}.
1969 On a text-only terminal, any weight greater than normal is displayed as
1970 extra bright, and any weight less than normal is displayed as
1971 half-bright (provided the terminal supports the feature).
1974 Font slant---one of the symbols @code{italic}, @code{oblique}, @code{normal},
1975 @code{reverse-italic}, or @code{reverse-oblique}.
1977 On a text-only terminal, slanted text is displayed as half-bright, if
1978 the terminal supports the feature.
1981 Foreground color, a string. The value can be a system-defined color
1982 name, or a hexadecimal color specification of the form
1983 @samp{#@var{rr}@var{gg}@var{bb}}. (@samp{#000000} is black,
1984 @samp{#ff0000} is red, @samp{#00ff00} is green, @samp{#0000ff} is
1985 blue, and @samp{#ffffff} is white.)
1988 Background color, a string, like the foreground color.
1990 @item :inverse-video
1991 Whether or not characters should be displayed in inverse video. The
1992 value should be @code{t} (yes) or @code{nil} (no).
1995 The background stipple, a bitmap.
1997 The value can be a string; that should be the name of a file containing
1998 external-format X bitmap data. The file is found in the directories
1999 listed in the variable @code{x-bitmap-file-path}.
2001 Alternatively, the value can specify the bitmap directly, with a list
2002 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2003 @var{width} and @var{height} specify the size in pixels, and
2004 @var{data} is a string containing the raw bits of the bitmap, row by
2005 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2006 in the string (which should be a unibyte string for best results).
2007 This means that each row always occupies at least one whole byte.
2009 If the value is @code{nil}, that means use no stipple pattern.
2011 Normally you do not need to set the stipple attribute, because it is
2012 used automatically to handle certain shades of gray.
2015 Whether or not characters should be underlined, and in what color. If
2016 the value is @code{t}, underlining uses the foreground color of the
2017 face. If the value is a string, underlining uses that color. The
2018 value @code{nil} means do not underline.
2021 Whether or not characters should be overlined, and in what color.
2022 The value is used like that of @code{:underline}.
2024 @item :strike-through
2025 Whether or not characters should be strike-through, and in what
2026 color. The value is used like that of @code{:underline}.
2029 The name of a face from which to inherit attributes, or a list of face
2030 names. Attributes from inherited faces are merged into the face like an
2031 underlying face would be, with higher priority than underlying faces.
2032 If a list of faces is used, attributes from faces earlier in the list
2033 override those from later faces.
2036 Whether or not a box should be drawn around characters, its color, the
2037 width of the box lines, and 3D appearance.
2040 Here are the possible values of the @code{:box} attribute, and what
2048 Draw a box with lines of width 1, in the foreground color.
2051 Draw a box with lines of width 1, in color @var{color}.
2053 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2054 This way you can explicitly specify all aspects of the box. The value
2055 @var{width} specifies the width of the lines to draw; it defaults to 1.
2057 The value @var{color} specifies the color to draw with. The default is
2058 the foreground color of the face for simple boxes, and the background
2059 color of the face for 3D boxes.
2061 The value @var{style} specifies whether to draw a 3D box. If it is
2062 @code{released-button}, the box looks like a 3D button that is not being
2063 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2064 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2068 In older versions of Emacs, before @code{:family}, @code{:height},
2069 @code{:width}, @code{:weight}, and @code{:slant} existed, these
2070 attributes were used to specify the type face. They are now
2071 semi-obsolete, but they still work:
2075 This attribute specifies the font name.
2078 A non-@code{nil} value specifies a bold font.
2081 A non-@code{nil} value specifies an italic font.
2084 For compatibility, you can still set these ``attributes'', even
2085 though they are not real face attributes. Here is what that does:
2089 You can specify an X font name as the ``value'' of this ``attribute'';
2090 that sets the @code{:family}, @code{:width}, @code{:height},
2091 @code{:weight}, and @code{:slant} attributes according to the font name.
2093 If the value is a pattern with wildcards, the first font that matches
2094 the pattern is used to set these attributes.
2097 A non-@code{nil} makes the face bold; @code{nil} makes it normal.
2098 This actually works by setting the @code{:weight} attribute.
2101 A non-@code{nil} makes the face italic; @code{nil} makes it normal.
2102 This actually works by setting the @code{:slant} attribute.
2105 @defvar x-bitmap-file-path
2106 This variable specifies a list of directories for searching
2107 for bitmap files, for the @code{:stipple} attribute.
2110 @defun bitmap-spec-p object
2111 This returns @code{t} if @var{object} is a valid bitmap specification,
2112 suitable for use with @code{:stipple} (see above). It returns
2113 @code{nil} otherwise.
2116 @node Attribute Functions
2117 @subsection Face Attribute Functions
2119 You can modify the attributes of an existing face with the following
2120 functions. If you specify @var{frame}, they affect just that frame;
2121 otherwise, they affect all frames as well as the defaults that apply to
2124 @tindex set-face-attribute
2125 @defun set-face-attribute face frame &rest arguments
2126 This function sets one or more attributes of face @var{face}
2127 for frame @var{frame}. If @var{frame} is @code{nil}, it sets
2128 the attribute for all frames, and the defaults for new frames.
2130 The extra arguments @var{arguments} specify the attributes to set, and
2131 the values for them. They should consist of alternating attribute names
2132 (such as @code{:family} or @code{:underline}) and corresponding values.
2136 (set-face-attribute 'foo nil
2143 sets the attributes @code{:width}, @code{:weight} and @code{:underline}
2144 to the corresponding values.
2147 @tindex face-attribute
2148 @defun face-attribute face attribute &optional frame inherit
2149 This returns the value of the @var{attribute} attribute of face
2150 @var{face} on @var{frame}. If @var{frame} is @code{nil},
2151 that means the selected frame (@pxref{Input Focus}).
2153 If @var{frame} is @code{t}, the value is the default for
2154 @var{face} for new frames.
2156 If @var{inherit} is @code{nil}, only attributes directly defined by
2157 @var{face} are considered, so the return value may be
2158 @code{unspecified}, or a relative value. If @var{inherit} is
2159 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2160 with the faces specified by its @code{:inherit} attribute; however the
2161 return value may still be @code{unspecified} or relative. If
2162 @var{inherit} is a face or a list of faces, then the result is further
2163 merged with that face (or faces), until it becomes specified and
2166 To ensure that the return value is always specified and absolute, use
2167 a value of @code{default} for @var{inherit}; this will resolve any
2168 unspecified or relative values by merging with the @code{default} face
2169 (which is always completely specified).
2174 (face-attribute 'bold :weight)
2179 The functions above did not exist before Emacs 21. For compatibility
2180 with older Emacs versions, you can use the following functions to set
2181 and examine the face attributes which existed in those versions.
2183 @tindex face-attribute-relative-p
2184 @defun face-attribute-relative-p attribute value
2185 This function returns non-@code{nil} if @var{value}, when used as
2186 the value of the face attribute @var{attribute}, is relative (that is,
2187 if it modifies an underlying or inherited value of @var{attribute}).
2190 @tindex merge-face-attribute
2191 @defun merge-face-attribute attribute value1 value2
2192 If @var{value1} is a relative value for the face attribute
2193 @var{attribute}, returns it merged with the underlying value
2194 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2195 face attribute @var{attribute}, returns @var{value1} unchanged.
2198 @defun set-face-foreground face color &optional frame
2199 @defunx set-face-background face color &optional frame
2200 These functions set the foreground (or background, respectively) color
2201 of face @var{face} to @var{color}. The argument @var{color} should be a
2202 string, the name of a color.
2204 Certain shades of gray are implemented by stipple patterns on
2205 black-and-white screens.
2208 @defun set-face-stipple face pattern &optional frame
2209 This function sets the background stipple pattern of face @var{face}
2210 to @var{pattern}. The argument @var{pattern} should be the name of a
2211 stipple pattern defined by the X server, or actual bitmap data
2212 (@pxref{Face Attributes}), or @code{nil} meaning don't use stipple.
2214 Normally there is no need to pay attention to stipple patterns, because
2215 they are used automatically to handle certain shades of gray.
2218 @defun set-face-font face font &optional frame
2219 This function sets the font of face @var{face}. This actually sets
2220 the attributes @code{:family}, @code{:width}, @code{:height},
2221 @code{:weight}, and @code{:slant} according to the font name
2225 @defun set-face-bold-p face bold-p &optional frame
2226 This function specifies whether @var{face} should be bold. If
2227 @var{bold-p} is non-@code{nil}, that means yes; @code{nil} means no.
2228 This actually sets the @code{:weight} attribute.
2231 @defun set-face-italic-p face italic-p &optional frame
2232 This function specifies whether @var{face} should be italic. If
2233 @var{italic-p} is non-@code{nil}, that means yes; @code{nil} means no.
2234 This actually sets the @code{:slant} attribute.
2237 @defun set-face-underline-p face underline-p &optional frame
2238 This function sets the underline attribute of face @var{face}.
2239 Non-@code{nil} means do underline; @code{nil} means don't.
2242 @defun invert-face face &optional frame
2243 This function inverts the @code{:inverse-video} attribute of face
2244 @var{face}. If the attribute is @code{nil}, this function sets it to
2245 @code{t}, and vice versa.
2248 These functions examine the attributes of a face. If you don't
2249 specify @var{frame}, they refer to the default data for new frames.
2250 They return the symbol @code{unspecified} if the face doesn't define any
2251 value for that attribute.
2253 @defun face-foreground face &optional frame inherit
2254 @defunx face-background face &optional frame
2255 These functions return the foreground color (or background color,
2256 respectively) of face @var{face}, as a string.
2258 If @var{inherit} is @code{nil}, only a color directly defined by the face is
2259 returned. If @var{inherit} is non-@code{nil}, any faces specified by its
2260 @code{:inherit} attribute are considered as well, and if @var{inherit}
2261 is a face or a list of faces, then they are also considered, until a
2262 specified color is found. To ensure that the return value is always
2263 specified, use a value of @code{default} for @var{inherit}.
2266 @defun face-stipple face &optional frame inherit
2267 This function returns the name of the background stipple pattern of face
2268 @var{face}, or @code{nil} if it doesn't have one.
2270 If @var{inherit} is @code{nil}, only a stipple directly defined by the
2271 face is returned. If @var{inherit} is non-@code{nil}, any faces
2272 specified by its @code{:inherit} attribute are considered as well, and
2273 if @var{inherit} is a face or a list of faces, then they are also
2274 considered, until a specified stipple is found. To ensure that the
2275 return value is always specified, use a value of @code{default} for
2279 @defun face-font face &optional frame
2280 This function returns the name of the font of face @var{face}.
2283 @defun face-bold-p face &optional frame
2284 This function returns @code{t} if @var{face} is bold---that is, if it is
2285 bolder than normal. It returns @code{nil} otherwise.
2288 @defun face-italic-p face &optional frame
2289 This function returns @code{t} if @var{face} is italic or oblique,
2290 @code{nil} otherwise.
2293 @defun face-underline-p face &optional frame
2294 This function returns the @code{:underline} attribute of face @var{face}.
2297 @defun face-inverse-video-p face &optional frame
2298 This function returns the @code{:inverse-video} attribute of face @var{face}.
2301 @node Displaying Faces
2302 @subsection Displaying Faces
2304 Here are the ways to specify which faces to use for display of text:
2308 With defaults. The @code{default} face is used as the ultimate
2309 default for all text. (In Emacs 19 and 20, the @code{default}
2310 face is used only when no other face is specified.)
2313 For a mode line or header line, the face @code{mode-line} or
2314 @code{mode-line-inactive}, or @code{header-line}, is merged in just
2315 before @code{default}.
2318 With text properties. A character can have a @code{face} property; if
2319 so, the faces and face attributes specified there apply. @xref{Special
2322 If the character has a @code{mouse-face} property, that is used instead
2323 of the @code{face} property when the mouse is ``near enough'' to the
2327 With overlays. An overlay can have @code{face} and @code{mouse-face}
2328 properties too; they apply to all the text covered by the overlay.
2331 With a region that is active. In Transient Mark mode, the region is
2332 highlighted with the face @code{region} (@pxref{Standard Faces}).
2335 With special glyphs. Each glyph can specify a particular face
2336 number. @xref{Glyphs}.
2339 If these various sources together specify more than one face for a
2340 particular character, Emacs merges the attributes of the various faces
2341 specified. For each attribute, Emacs tries first the face of any
2342 special glyph; then the face for region highlighting, if appropriate;
2343 then the faces specified by overlays, followed by those specified by
2344 text properties, then the @code{mode-line} or
2345 @code{mode-line-inactive} or @code{header-line} face (if in a mode
2346 line or a header line), and last the @code{default} face.
2348 When multiple overlays cover one character, an overlay with higher
2349 priority overrides those with lower priority. @xref{Overlays}.
2351 @node Font Selection
2352 @subsection Font Selection
2354 @dfn{Selecting a font} means mapping the specified face attributes for
2355 a character to a font that is available on a particular display. The
2356 face attributes, as determined by face merging, specify most of the
2357 font choice, but not all. Part of the choice depends on what character
2360 If the face specifies a fontset name, that fontset determines a
2361 pattern for fonts of the given charset. If the face specifies a font
2362 family, a font pattern is constructed.
2364 Emacs tries to find an available font for the given face attributes
2365 and character's registry and encoding. If there is a font that matches
2366 exactly, it is used, of course. The hard case is when no available font
2367 exactly fits the specification. Then Emacs looks for one that is
2368 ``close''---one attribute at a time. You can specify the order to
2369 consider the attributes. In the case where a specified font family is
2370 not available, you can specify a set of mappings for alternatives to
2373 @defvar face-font-selection-order
2374 @tindex face-font-selection-order
2375 This variable specifies the order of importance of the face attributes
2376 @code{:width}, @code{:height}, @code{:weight}, and @code{:slant}. The
2377 value should be a list containing those four symbols, in order of
2378 decreasing importance.
2380 Font selection first finds the best available matches for the first
2381 attribute listed; then, among the fonts which are best in that way, it
2382 searches for the best matches in the second attribute, and so on.
2384 The attributes @code{:weight} and @code{:width} have symbolic values in
2385 a range centered around @code{normal}. Matches that are more extreme
2386 (farther from @code{normal}) are somewhat preferred to matches that are
2387 less extreme (closer to @code{normal}); this is designed to ensure that
2388 non-normal faces contrast with normal ones, whenever possible.
2390 The default is @code{(:width :height :weight :slant)}, which means first
2391 find the fonts closest to the specified @code{:width}, then---among the
2392 fonts with that width---find a best match for the specified font height,
2395 One example of a case where this variable makes a difference is when the
2396 default font has no italic equivalent. With the default ordering, the
2397 @code{italic} face will use a non-italic font that is similar to the
2398 default one. But if you put @code{:slant} before @code{:height}, the
2399 @code{italic} face will use an italic font, even if its height is not
2403 @defvar face-font-family-alternatives
2404 @tindex face-font-family-alternatives
2405 This variable lets you specify alternative font families to try, if a
2406 given family is specified and doesn't exist. Each element should have
2410 (@var{family} @var{alternate-families}@dots{})
2413 If @var{family} is specified but not available, Emacs will try the other
2414 families given in @var{alternate-families}, one by one, until it finds a
2415 family that does exist.
2418 @defvar face-font-registry-alternatives
2419 @tindex face-font-registry-alternatives
2420 This variable lets you specify alternative font registries to try, if a
2421 given registry is specified and doesn't exist. Each element should have
2425 (@var{registry} @var{alternate-registries}@dots{})
2428 If @var{registry} is specified but not available, Emacs will try the
2429 other registries given in @var{alternate-registries}, one by one,
2430 until it finds a registry that does exist.
2433 Emacs can make use of scalable fonts, but by default it does not use
2434 them, since the use of too many or too big scalable fonts can crash
2437 @defvar scalable-fonts-allowed
2438 @tindex scalable-fonts-allowed
2439 This variable controls which scalable fonts to use. A value of
2440 @code{nil}, the default, means do not use scalable fonts. @code{t}
2441 means to use any scalable font that seems appropriate for the text.
2443 Otherwise, the value must be a list of regular expressions. Then a
2444 scalable font is enabled for use if its name matches any regular
2445 expression in the list. For example,
2448 (setq scalable-fonts-allowed '("muleindian-2$"))
2452 allows the use of scalable fonts with registry @code{muleindian-2}.
2455 @defun clear-face-cache &optional unload-p
2456 @tindex clear-face-cache
2457 This function clears the face cache for all frames.
2458 If @var{unload-p} is non-@code{nil}, that means to unload
2459 all unused fonts as well.
2462 @defvar face-font-rescale-alist
2463 This variable specifies scaling for certain faces. Its value should
2464 be a list of elements of the form
2467 (@var{fontname-regexp} . @var{scale-factor})
2470 If @var{fontname-regexp} matches the font name that is about to be
2471 used, this says to choose a larger similar font according to the
2472 factor @var{scale-factor}. You would use this feature to normalize
2473 the font size if certain fonts are bigger or smaller than their
2474 nominal heights and widths would suggest.
2477 @node Face Functions
2478 @subsection Functions for Working with Faces
2480 Here are additional functions for creating and working with faces.
2482 @defun make-face name
2483 This function defines a new face named @var{name}, initially with all
2484 attributes @code{nil}. It does nothing if there is already a face named
2489 This function returns a list of all defined face names.
2492 @defun copy-face old-face new-name &optional frame new-frame
2493 This function defines a face named @var{new-name} as a copy of the existing
2494 face named @var{old-face}. It creates the face @var{new-name} if that
2495 doesn't already exist.
2497 If the optional argument @var{frame} is given, this function applies
2498 only to that frame. Otherwise it applies to each frame individually,
2499 copying attributes from @var{old-face} in each frame to @var{new-face}
2502 If the optional argument @var{new-frame} is given, then @code{copy-face}
2503 copies the attributes of @var{old-face} in @var{frame} to @var{new-name}
2508 This function returns the face number of face @var{face}.
2511 @defun face-documentation face
2512 This function returns the documentation string of face @var{face}, or
2513 @code{nil} if none was specified for it.
2516 @defun face-equal face1 face2 &optional frame
2517 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2518 same attributes for display.
2521 @defun face-differs-from-default-p face &optional frame
2522 This returns non-@code{nil} if the face @var{face} displays
2523 differently from the default face.
2527 A @dfn{face alias} provides an equivalent name for a face. You can
2528 define a face alias by giving the alias symbol the @code{face-alias}
2529 property, with a value of the target face name. The following example
2530 makes @code{modeline} an alias for the @code{mode-line} face.
2533 (put 'modeline 'face-alias 'mode-line)
2538 @subsection Automatic Face Assignment
2539 @cindex automatic face assignment
2540 @cindex faces, automatic choice
2542 @cindex Font-Lock mode
2543 This hook is used for automatically assigning faces to text in the
2544 buffer. It is part of the implementation of Font-Lock mode.
2546 @tindex fontification-functions
2547 @defvar fontification-functions
2548 This variable holds a list of functions that are called by Emacs
2549 redisplay as needed to assign faces automatically to text in the buffer.
2551 The functions are called in the order listed, with one argument, a
2552 buffer position @var{pos}. Each function should attempt to assign faces
2553 to the text in the current buffer starting at @var{pos}.
2555 Each function should record the faces they assign by setting the
2556 @code{face} property. It should also add a non-@code{nil}
2557 @code{fontified} property for all the text it has assigned faces to.
2558 That property tells redisplay that faces have been assigned to that text
2561 It is probably a good idea for each function to do nothing if the
2562 character after @var{pos} already has a non-@code{nil} @code{fontified}
2563 property, but this is not required. If one function overrides the
2564 assignments made by a previous one, the properties as they are
2565 after the last function finishes are the ones that really matter.
2567 For efficiency, we recommend writing these functions so that they
2568 usually assign faces to around 400 to 600 characters at each call.
2572 @subsection Looking Up Fonts
2574 @defun x-list-fonts pattern &optional face frame maximum
2575 This function returns a list of available font names that match
2576 @var{pattern}. If the optional arguments @var{face} and @var{frame} are
2577 specified, then the list is limited to fonts that are the same size as
2578 @var{face} currently is on @var{frame}.
2580 The argument @var{pattern} should be a string, perhaps with wildcard
2581 characters: the @samp{*} character matches any substring, and the
2582 @samp{?} character matches any single character. Pattern matching
2583 of font names ignores case.
2585 If you specify @var{face} and @var{frame}, @var{face} should be a face name
2586 (a symbol) and @var{frame} should be a frame.
2588 The optional argument @var{maximum} sets a limit on how many fonts to
2589 return. If this is non-@code{nil}, then the return value is truncated
2590 after the first @var{maximum} matching fonts. Specifying a small value
2591 for @var{maximum} can make this function much faster, in cases where
2592 many fonts match the pattern.
2595 @defun x-family-fonts &optional family frame
2596 @tindex x-family-fonts
2597 This function returns a list describing the available fonts for family
2598 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
2599 this list applies to all families, and therefore, it contains all
2600 available fonts. Otherwise, @var{family} must be a string; it may
2601 contain the wildcards @samp{?} and @samp{*}.
2603 The list describes the display that @var{frame} is on; if @var{frame} is
2604 omitted or @code{nil}, it applies to the selected frame's display
2605 (@pxref{Input Focus}).
2607 The list contains a vector of the following form for each font:
2610 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
2611 @var{fixed-p} @var{full} @var{registry-and-encoding}]
2614 The first five elements correspond to face attributes; if you
2615 specify these attributes for a face, it will use this font.
2617 The last three elements give additional information about the font.
2618 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
2619 @var{full} is the full name of the font, and
2620 @var{registry-and-encoding} is a string giving the registry and
2621 encoding of the font.
2623 The result list is sorted according to the current face font sort order.
2626 @defun x-font-family-list &optional frame
2627 @tindex x-font-family-list
2628 This function returns a list of the font families available for
2629 @var{frame}'s display. If @var{frame} is omitted or @code{nil}, it
2630 describes the selected frame's display (@pxref{Input Focus}).
2632 The value is a list of elements of this form:
2635 (@var{family} . @var{fixed-p})
2639 Here @var{family} is a font family, and @var{fixed-p} is
2640 non-@code{nil} if fonts of that family are fixed-pitch.
2643 @defvar font-list-limit
2644 @tindex font-list-limit
2645 This variable specifies maximum number of fonts to consider in font
2646 matching. The function @code{x-family-fonts} will not return more than
2647 that many fonts, and font selection will consider only that many fonts
2648 when searching a matching font for face attributes. The default is
2653 @subsection Fontsets
2655 A @dfn{fontset} is a list of fonts, each assigned to a range of
2656 character codes. An individual font cannot display the whole range of
2657 characters that Emacs supports, but a fontset can. Fontsets have names,
2658 just as fonts do, and you can use a fontset name in place of a font name
2659 when you specify the ``font'' for a frame or a face. Here is
2660 information about defining a fontset under Lisp program control.
2662 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
2663 This function defines a new fontset according to the specification
2664 string @var{fontset-spec}. The string should have this format:
2667 @var{fontpattern}, @r{[}@var{charsetname}:@var{fontname}@r{]@dots{}}
2671 Whitespace characters before and after the commas are ignored.
2673 The first part of the string, @var{fontpattern}, should have the form of
2674 a standard X font name, except that the last two fields should be
2675 @samp{fontset-@var{alias}}.
2677 The new fontset has two names, one long and one short. The long name is
2678 @var{fontpattern} in its entirety. The short name is
2679 @samp{fontset-@var{alias}}. You can refer to the fontset by either
2680 name. If a fontset with the same name already exists, an error is
2681 signaled, unless @var{noerror} is non-@code{nil}, in which case this
2682 function does nothing.
2684 If optional argument @var{style-variant-p} is non-@code{nil}, that says
2685 to create bold, italic and bold-italic variants of the fontset as well.
2686 These variant fontsets do not have a short name, only a long one, which
2687 is made by altering @var{fontpattern} to indicate the bold or italic
2690 The specification string also says which fonts to use in the fontset.
2691 See below for the details.
2694 The construct @samp{@var{charset}:@var{font}} specifies which font to
2695 use (in this fontset) for one particular character set. Here,
2696 @var{charset} is the name of a character set, and @var{font} is the font
2697 to use for that character set. You can use this construct any number of
2698 times in the specification string.
2700 For the remaining character sets, those that you don't specify
2701 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
2702 @samp{fontset-@var{alias}} with a value that names one character set.
2703 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
2704 with @samp{ISO8859-1}.
2706 In addition, when several consecutive fields are wildcards, Emacs
2707 collapses them into a single wildcard. This is to prevent use of
2708 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
2709 for editing, and scaling a smaller font is not useful because it is
2710 better to use the smaller font in its own size, which Emacs does.
2712 Thus if @var{fontpattern} is this,
2715 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
2719 the font specification for @acronym{ASCII} characters would be this:
2722 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
2726 and the font specification for Chinese GB2312 characters would be this:
2729 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
2732 You may not have any Chinese font matching the above font
2733 specification. Most X distributions include only Chinese fonts that
2734 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
2735 such a case, @samp{Fontset-@var{n}} can be specified as below:
2738 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
2739 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
2743 Then, the font specifications for all but Chinese GB2312 characters have
2744 @samp{fixed} in the @var{family} field, and the font specification for
2745 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
2748 @defun set-fontset-font name character fontname &optional frame
2749 This function modifies the existing fontset @var{name} to
2750 use the font name @var{fontname} for the character @var{character}.
2752 If @var{name} is @code{nil}, this function modifies the default
2753 fontset, whose short name is @samp{fontset-default}.
2755 @var{character} may be a cons; @code{(@var{from} . @var{to})}, where
2756 @var{from} and @var{to} are non-generic characters. In that case, use
2757 @var{fontname} for all characters in the range @var{from} and @var{to}
2760 @var{character} may be a charset. In that case, use
2761 @var{fontname} for all character in the charsets.
2763 @var{fontname} may be a cons; @code{(@var{family} . @var{registry})},
2764 where @var{family} is a family name of a font (possibly including a
2765 foundry name at the head), @var{registry} is a registry name of a font
2766 (possibly including an encoding name at the tail).
2768 For instance, this changes the default fontset to use a font of which
2769 registry name is @samp{JISX0208.1983} for all characters belonging to
2770 the charset @code{japanese-jisx0208}.
2773 (set-fontset-font nil 'japanese-jisx0208 '(nil . "JISX0208.1983"))
2777 @defun char-displayable-p char
2778 This function returns @code{t} if Emacs ought to be able to display
2779 @var{char}. More precisely, if the selected frame's fontset has a
2780 font to display the character set that @var{char} belongs to.
2782 Fontsets can specify a font on a per-character basis; when the fontset
2783 does that, this function's value may not be accurate.
2790 The @dfn{fringes} of a window are thin vertical strips down the
2791 sides that are used for displaying bitmaps that indicate truncation,
2792 continuation, horizontal scrolling, and the overlay arrow.
2795 * Fringe Size/Pos:: Specifying where to put the window fringes.
2796 * Fringe Bitmaps:: Displaying bitmaps in the window fringes.
2797 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
2798 * Overlay Arrow:: Display of an arrow to indicate position.
2801 @node Fringe Size/Pos
2802 @subsection Fringe Size and Position
2804 Here's how to control the position and width of the window fringes.
2806 @defvar fringes-outside-margins
2807 If the value is non-@code{nil}, the frames appear outside the display
2808 margins. The fringes normally appear between the display margins and
2809 the window text. It works to set @code{fringes-outside-margins}
2810 buffer-locally. @xref{Display Margins}.
2813 @defvar left-fringe-width
2814 This variable, if non-@code{nil}, specifies the width of the left
2818 @defvar right-fringe-width
2819 This variable, if non-@code{nil}, specifies the width of the right
2823 The values of these variables take effect when you display the
2824 buffer in a window. If you change them while the buffer is visible,
2825 you can call @code{set-window-buffer} to display it once again in the
2826 same window, to make the changes take effect.
2828 @defun set-window-fringes window left &optional right outside-margins
2829 This function sets the fringe widths of window @var{window}.
2830 If @var{window} is @code{nil}, the selected window is used.
2832 The argument @var{left} specifies the width in pixels of the left
2833 fringe, and likewise @var{right} for the right fringe. A value of
2834 @code{nil} for either one stands for the default width. If
2835 @var{outside-margins} is non-@code{nil}, that specifies that fringes
2836 should appear outside of the display margins.
2839 @defun window-fringes &optional window
2840 This function returns information about the fringes of a window
2841 @var{window}. If @var{window} is omitted or @code{nil}, the selected
2842 window is used. The value has the form @code{(@var{left-width}
2843 @var{right-width} @var{outside-margins})}.
2846 @defvar overflow-newline-into-fringe
2847 If this is non-@code{nil}, lines exactly as wide as the window (not
2848 counting the final newline character) are not continued. Instead,
2849 when point is at the end of the line, the cursor appears in the right
2853 @node Fringe Bitmaps
2854 @subsection Fringe Bitmaps
2855 @cindex fringe bitmaps
2856 @cindex bitmaps, fringe
2858 The @dfn{fringe bitmaps} are tiny icons Emacs displays in the window
2859 fringe (on a graphic display) to indicate truncated or continued
2860 lines, buffer boundaries, overlay arrow, etc. The fringe bitmaps are
2861 shared by all frames and windows. You can redefine the built-in
2862 fringe bitmaps, and you can define new fringe bitmaps.
2864 The way to display a bitmap in the left or right fringes for a given
2865 line in a window is by specifying the @code{display} property for one
2866 of the characters that appears in it. Use a display specification of
2867 the form @code{(left-fringe @var{bitmap} [@var{face}])} or
2868 @code{(right-fringe @var{bitmap} [@var{face}])} (@pxref{Display
2869 Property}). Here, @var{bitmap} is a symbol identifying the bitmap you
2870 want, and @var{face} (which is optional) is the name of the face whose
2871 colors should be used for displaying the bitmap, instead of the
2872 default @code{fringe} face. @var{face} is automatically merged with
2873 the @code{fringe} face, so normally @var{face} need only specify the
2874 foreground color for the bitmap.
2876 These symbols identify the standard fringe bitmaps. Evaluate
2877 @code{(require 'fringe)} to define them. Fringe bitmap symbols have
2878 their own name space.
2881 @item Truncation and continuation line bitmaps:
2882 @code{left-truncation}, @code{right-truncation},
2883 @code{continued-line}, @code{continuation-line}.
2885 @item Buffer indication bitmaps:
2886 @code{up-arrow}, @code{down-arrow},
2887 @code{top-left-angle}, @code{top-right-angle},
2888 @code{bottom-left-angle}, @code{bottom-right-angle},
2889 @code{left-bracket}, @code{right-bracket}.
2891 @item Empty line indication bitmap:
2894 @item Overlay arrow bitmap:
2895 @code{overlay-arrow}.
2897 @item Bitmaps for displaying the cursor in right fringe:
2898 @code{filled-box-cursor}, @code{hollow-box-cursor}, @code{hollow-square},
2899 @code{bar-cursor}, @code{hbar-cursor}.
2902 @defun fringe-bitmaps-at-pos &optional pos window
2903 This function returns the fringe bitmaps of the display line
2904 containing position @var{pos} in window @var{window}. The return
2905 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
2906 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
2907 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
2908 is non-@code{nil} if there is an overlay arrow in the left fringe.
2910 The value is @code{nil} if @var{pos} is not visible in @var{window}.
2911 If @var{window} is @code{nil}, that stands for the selected window.
2912 If @var{pos} is @code{nil}, that stands for the value of point in
2916 @node Customizing Bitmaps
2917 @subsection Customizing Fringe Bitmaps
2919 @defun define-fringe-bitmap bitmap bits &optional height width align
2920 This function defines the symbol @var{bitmap} as a new fringe bitmap,
2921 or replaces an existing bitmap with that name.
2923 The argument @var{bits} specifies the image to use. It should be
2924 either a string or a vector of integers, where each element (an
2925 integer) corresponds to one row of the bitmap. Each bit of an integer
2926 corresponds to one pixel of the bitmap, where the low bit corresponds
2927 to the rightmost pixel of the bitmap.
2929 The height is normally the length of @var{bits}. However, you
2930 can specify a different height with non-@code{nil} @var{height}. The width
2931 is normally 8, but you can specify a different width with non-@code{nil}
2932 @var{width}. The width must be an integer between 1 and 16.
2934 The argument @var{align} specifies the positioning of the bitmap
2935 relative to the range of rows where it is used; the default is to
2936 center the bitmap. The allowed values are @code{top}, @code{center},
2939 The @var{align} argument may also be a list @code{(@var{align}
2940 @var{periodic})} where @var{align} is interpreted as described above.
2941 If @var{periodic} is non-@code{nil}, it specifies that the rows in
2942 @code{bits} should be repeated enough times to reach the specified
2945 The return value on success is an integer identifying the new bitmap.
2946 You should save that integer in a variable so it can be used to select
2949 This function signals an error if there are no more free bitmap slots.
2952 @defun destroy-fringe-bitmap bitmap
2953 This function destroy the fringe bitmap identified by @var{bitmap}.
2954 If @var{bitmap} identifies a standard fringe bitmap, it actually
2955 restores the standard definition of that bitmap, instead of
2956 eliminating it entirely.
2959 @defun set-fringe-bitmap-face bitmap &optional face
2960 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
2961 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
2962 bitmap's face controls the color to draw it in.
2964 @var{face} is merged with the @code{fringe} face, so normally
2965 @var{face} should specify only the foreground color.
2969 @subsection The Overlay Arrow
2970 @cindex overlay arrow
2972 The @dfn{overlay arrow} is useful for directing the user's attention
2973 to a particular line in a buffer. For example, in the modes used for
2974 interface to debuggers, the overlay arrow indicates the line of code
2975 about to be executed. This feature has nothing to do with
2976 @dfn{overlays} (@pxref{Overlays}).
2978 @defvar overlay-arrow-string
2979 This variable holds the string to display to call attention to a
2980 particular line, or @code{nil} if the arrow feature is not in use.
2981 On a graphical display the contents of the string are ignored; instead a
2982 glyph is displayed in the fringe area to the left of the display area.
2985 @defvar overlay-arrow-position
2986 This variable holds a marker that indicates where to display the overlay
2987 arrow. It should point at the beginning of a line. On a non-graphical
2988 display the arrow text
2989 appears at the beginning of that line, overlaying any text that would
2990 otherwise appear. Since the arrow is usually short, and the line
2991 usually begins with indentation, normally nothing significant is
2994 The overlay string is displayed only in the buffer that this marker
2995 points into. Thus, only one buffer can have an overlay arrow at any
2997 @c !!! overlay-arrow-position: but the overlay string may remain in the display
2998 @c of some other buffer until an update is required. This should be fixed
3002 You can do a similar job by creating an overlay with a
3003 @code{before-string} property. @xref{Overlay Properties}.
3005 You can define multiple overlay arrows via the variable
3006 @code{overlay-arrow-variable-list}.
3008 @defvar overlay-arrow-variable-list
3009 This variable's value is a list of variables, each of which specifies
3010 the position of an overlay arrow. The variable
3011 @code{overlay-arrow-position} has its normal meaning because it is on
3015 Each variable on this list can have properties
3016 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
3017 specify an overlay arrow string (for text-only terminals) or fringe
3018 bitmap (for graphical terminals) to display at the corresponding
3019 overlay arrow position. If either property is not set, the default
3020 (@code{overlay-arrow-string} or @code{overlay-arrow-fringe-bitmap}) is
3024 @section Scroll Bars
3026 Normally the frame parameter @code{vertical-scroll-bars} controls
3027 whether the windows in the frame have vertical scroll bars, and
3028 whether they are on the left or right. The frame parameter
3029 @code{scroll-bar-width} specifies how wide they are (@code{nil}
3030 meaning the default). @xref{Window Frame Parameters}.
3032 @defun frame-current-scroll-bars &optional frame
3033 This function reports the scroll bar type settings for frame
3034 @var{frame}. The value is a cons cell
3035 @code{(@var{vertical-type} .@: @var{horizontal-type})}, where
3036 @var{vertical-type} is either @code{left}, @code{right}, or @code{nil}
3037 (which means no scroll bar.) @var{horizontal-type} is meant to
3038 specify the horizontal scroll bar type, but since they are not
3039 implemented, it is always @code{nil}.
3042 @vindex vertical-scroll-bar
3043 You can enable or disable scroll bars for a particular buffer,
3044 by setting the variable @code{vertical-scroll-bar}. This variable
3045 automatically becomes buffer-local when set. The possible values are
3046 @code{left}, @code{right}, @code{t}, which means to use the
3047 frame's default, and @code{nil} for no scroll bar.
3049 You can also control this for individual windows. Call the function
3050 @code{set-window-scroll-bars} to specify what to do for a specific window:
3052 @defun set-window-scroll-bars window width &optional vertical-type horizontal-type
3053 This function sets the width and type of scroll bars for window
3056 @var{width} specifies the scroll bar width in pixels (@code{nil} means
3057 use the width specified for the frame). @var{vertical-type} specifies
3058 whether to have a vertical scroll bar and, if so, where. The possible
3059 values are @code{left}, @code{right} and @code{nil}, just like the
3060 values of the @code{vertical-scroll-bars} frame parameter.
3062 The argument @var{horizontal-type} is meant to specify whether and
3063 where to have horizontal scroll bars, but since they are not
3064 implemented, it has no effect. If @var{window} is @code{nil}, the
3065 selected window is used.
3068 @defun window-scroll-bars &optional window
3069 Report the width and type of scroll bars specified for @var{window}.
3070 If @var{window} is omitted or @code{nil}, the selected window is used.
3071 The value is a list of the form @code{(@var{width}
3072 @var{cols} @var{vertical-type} @var{horizontal-type})}. The value
3073 @var{width} is the value that was specified for the width (which may
3074 be @code{nil}); @var{cols} is the number of columns that the scroll
3075 bar actually occupies.
3077 @var{horizontal-type} is not actually meaningful.
3080 If you don't specify these values for a window with
3081 @code{set-window-scroll-bars}, the buffer-local variables
3082 @code{scroll-bar-mode} and @code{scroll-bar-width} in the buffer being
3083 displayed control the window's vertical scroll bars. The function
3084 @code{set-window-buffer} examines these variables. If you change them
3085 in a buffer that is already visible in a window, you can make the
3086 window take note of the new values by calling @code{set-window-buffer}
3087 specifying the same buffer that is already displayed.
3089 @defvar scroll-bar-mode
3090 This variable, always local in all buffers, controls whether and where
3091 to put scroll bars in windows displaying the buffer. The possible values
3092 are @code{nil} for no scroll bar, @code{left} to put a scroll bar on
3093 the left, and @code{right} to put a scroll bar on the right.
3096 @defun window-current-scroll-bars &optional window
3097 This function reports the scroll bar type for window @var{window}.
3098 If @var{window} is omitted or @code{nil}, the selected window is used.
3099 The value is a cons cell
3100 @code{(@var{vertical-type} .@: @var{horizontal-type})}. Unlike
3101 @code{window-scroll-bars}, this reports the scroll bar type actually
3102 used, once frame defaults and @code{scroll-bar-mode} are taken into
3106 @defvar scroll-bar-width
3107 This variable, always local in all buffers, specifies the width of the
3108 buffer's scroll bars, measured in pixels. A value of @code{nil} means
3109 to use the value specified by the frame.
3113 @section Pointer Shape
3115 Normally, the mouse pointer has the @code{text} shape over text and
3116 the @code{arrow} shape over window areas which do not correspond to
3117 any buffer text. You can specify the mouse pointer shape over text or
3118 images via the @code{pointer} text property, and for images with the
3119 @code{:pointer} and @code{:map} image properties.
3121 The available pointer shapes are: @code{text} (or @code{nil}),
3122 @code{arrow}, @code{hand}, @code{vdrag}, @code{hdrag},
3123 @code{modeline}, and @code{hourglass}.
3125 @defvar void-text-area-pointer
3126 @tindex void-text-area-pointer
3127 This variable specifies the mouse pointer shape in void text areas,
3128 i.e. the areas after the end of a line or below the last line in the
3129 buffer. The default is to use the @code{arrow} (non-text) pointer.
3132 @node Display Property
3133 @section The @code{display} Property
3134 @cindex display specification
3135 @kindex display @r{(text property)}
3137 The @code{display} text property (or overlay property) is used to
3138 insert images into text, and also control other aspects of how text
3139 displays. The value of the @code{display} property should be a
3140 display specification, or a list or vector containing several display
3143 Some kinds of @code{display} properties specify something to display
3144 instead of the text that has the property. In this case, ``the text''
3145 means all the consecutive characters that have the same Lisp object as
3146 their @code{display} property; these characters are replaced as a
3147 single unit. By contrast, characters that have similar but distinct
3148 Lisp objects as their @code{display} properties are handled
3149 separately. Here's a function that illustrates this point:
3153 (goto-char (point-min))
3155 (let ((string (concat "A")))
3156 (put-text-property (point) (1+ (point)) 'display string)
3158 (put-text-property (point) (1+ (point)) 'display string)
3163 It gives each of the first ten characters in the buffer string
3164 @code{"A"} as the @code{display} property, but they don't all get the
3165 same string. The first two characters get the same string, so they
3166 together are replaced with one @samp{A}. The next two characters get
3167 a second string, so they together are replaced with one @samp{A}.
3168 Likewise for each following pair of characters. Thus, the ten
3169 characters appear as five A's. This function would have the same
3174 (goto-char (point-min))
3176 (let ((string (concat "A")))
3177 (put-text-property (point) (2+ (point)) 'display string)
3178 (put-text-property (point) (1+ (point)) 'display string)
3183 This illustrates that what matters is the property value for
3184 each character. If two consecutive characters have the same
3185 object as the @code{display} property value, it's irrelevant
3186 whether they got this property from a single call to
3187 @code{put-text-property} or from two different calls.
3189 The rest of this section describes several kinds of
3190 display specifications and what they mean.
3193 * Specified Space:: Displaying one space with a specified width.
3194 * Pixel Specification:: Specifying space width or height in pixels.
3195 * Other Display Specs:: Displaying an image; magnifying text; moving it
3196 up or down on the page; adjusting the width
3197 of spaces within text.
3198 * Display Margins:: Displaying text or images to the side of the main text.
3201 @node Specified Space
3202 @subsection Specified Spaces
3203 @cindex spaces, specified height or width
3204 @cindex specified spaces
3205 @cindex variable-width spaces
3207 To display a space of specified width and/or height, use a display
3208 specification of the form @code{(space . @var{props})}, where
3209 @var{props} is a property list (a list of alternating properties and
3210 values). You can put this property on one or more consecutive
3211 characters; a space of the specified height and width is displayed in
3212 place of @emph{all} of those characters. These are the properties you
3213 can use in @var{props} to specify the weight of the space:
3216 @item :width @var{width}
3217 If @var{width} is an integer or floating point number, it specifies
3218 that the space width should be @var{width} times the normal character
3219 width. @var{width} can also be a @dfn{pixel width} specification
3220 (@pxref{Pixel Specification}).
3222 @item :relative-width @var{factor}
3223 Specifies that the width of the stretch should be computed from the
3224 first character in the group of consecutive characters that have the
3225 same @code{display} property. The space width is the width of that
3226 character, multiplied by @var{factor}.
3228 @item :align-to @var{hpos}
3229 Specifies that the space should be wide enough to reach @var{hpos}.
3230 If @var{hpos} is a number, it is measured in units of the normal
3231 character width. @var{hpos} can also be a @dfn{pixel width}
3232 specification (@pxref{Pixel Specification}).
3235 You should use one and only one of the above properties. You can
3236 also specify the height of the space, with these properties:
3239 @item :height @var{height}
3240 Specifies the height of the space.
3241 If @var{height} is an integer or floating point number, it specifies
3242 that the space height should be @var{height} times the normal character
3243 height. The @var{height} may also be a @dfn{pixel height} specification
3244 (@pxref{Pixel Specification}).
3246 @item :relative-height @var{factor}
3247 Specifies the height of the space, multiplying the ordinary height
3248 of the text having this display specification by @var{factor}.
3250 @item :ascent @var{ascent}
3251 If the value of @var{ascent} is a non-negative number no greater than
3252 100, it specifies that @var{ascent} percent of the height of the space
3253 should be considered as the ascent of the space---that is, the part
3254 above the baseline. The ascent may also be specified in pixel units
3255 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
3259 Don't use both @code{:height} and @code{:relative-height} together.
3261 The @code{:width} and @code{:align-to} properties are supported on
3262 non-graphic terminals, but the other space properties in this section
3265 @node Pixel Specification
3266 @subsection Pixel Specification for Spaces
3267 @cindex spaces, pixel specification
3269 The value of the @code{:width}, @code{:align-to}, @code{:height},
3270 and @code{:ascent} properties can be a special kind of expression that
3271 is evaluated during redisplay. The result of the evaluation is used
3272 as an absolute number of pixels.
3274 The following expressions are supported:
3278 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
3279 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
3280 @var{unit} ::= in | mm | cm | width | height
3283 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
3285 @var{pos} ::= left | center | right
3286 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
3291 The form @var{num} specifies a fraction of the default frame font
3292 height or width. The form @code{(@var{num})} specifies an absolute
3293 number of pixels. If @var{num} is a symbol, @var{symbol}, its
3294 buffer-local variable binding is used.
3296 The @code{in}, @code{mm}, and @code{cm} units specify the number of
3297 pixels per inch, millimeter, and centimeter, respectively. The
3298 @code{width} and @code{height} units correspond to the default width
3299 and height of the current face. An image specification @code{image}
3300 corresponds to the width or height of the image.
3302 The @code{left-fringe}, @code{right-fringe}, @code{left-margin},
3303 @code{right-margin}, @code{scroll-bar}, and @code{text} elements
3304 specify to the width of the corresponding area of the window.
3306 The @code{left}, @code{center}, and @code{right} positions can be
3307 used with @code{:align-to} to specify a position relative to the left
3308 edge, center, or right edge of the text area.
3310 Any of the above window elements (except @code{text}) can also be
3311 used with @code{:align-to} to specify that the position is relative to
3312 the left edge of the given area. Once the base offset for a relative
3313 position has been set (by the first occurrence of one of these
3314 symbols), further occurrences of these symbols are interpreted as the
3315 width of the specified area. For example, to align to the center of
3316 the left-margin, use
3319 :align-to (+ left-margin (0.5 . left-margin))
3322 If no specific base offset is set for alignment, it is always relative
3323 to the left edge of the text area. For example, @samp{:align-to 0} in a
3324 header-line aligns with the first text column in the text area.
3326 A value of the form @code{(@var{num} . @var{expr})} stands for the
3327 product of the values of @var{num} and @var{expr}. For example,
3328 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
3329 @var{image})} specifies half the width (or height) of the specified
3332 The form @code{(+ @var{expr} ...)} adds up the value of the
3333 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
3334 the value of the expressions.
3336 @node Other Display Specs
3337 @subsection Other Display Specifications
3339 Here are the other sorts of display specifications that you can use
3340 in the @code{display} text property.
3344 Display @var{string} instead of the text that has this property.
3346 @item (image . @var{image-props})
3347 This kind of display specification is an image descriptor (@pxref{Images}).
3348 When used as a display specification, it means to display the image
3349 instead of the text that has the display specification.
3351 @item (slice @var{x} @var{y} @var{width} @var{height})
3352 This specification together with @code{image} specifies a @dfn{slice}
3353 (a partial area) of the image to display. The elements @var{y} and
3354 @var{x} specify the top left corner of the slice, within the image;
3355 @var{width} and @var{height} specify the width and height of the
3356 slice. Integer values are numbers of pixels. A floating point number
3357 in the range 0.0--1.0 stands for that fraction of the width or height
3358 of the entire image.
3360 @item ((margin nil) @var{string})
3362 A display specification of this form means to display @var{string}
3363 instead of the text that has the display specification, at the same
3364 position as that text. This is a special case of marginal display
3365 (@pxref{Display Margins}).
3367 Recursive display specifications are not supported---string display
3368 specifications must not have @code{display} properties themselves.
3370 @item (space-width @var{factor})
3371 This display specification affects all the space characters within the
3372 text that has the specification. It displays all of these spaces
3373 @var{factor} times as wide as normal. The element @var{factor} should
3374 be an integer or float. Characters other than spaces are not affected
3375 at all; in particular, this has no effect on tab characters.
3377 @item (height @var{height})
3378 This display specification makes the text taller or shorter.
3379 Here are the possibilities for @var{height}:
3382 @item @code{(+ @var{n})}
3383 This means to use a font that is @var{n} steps larger. A ``step'' is
3384 defined by the set of available fonts---specifically, those that match
3385 what was otherwise specified for this text, in all attributes except
3386 height. Each size for which a suitable font is available counts as
3387 another step. @var{n} should be an integer.
3389 @item @code{(- @var{n})}
3390 This means to use a font that is @var{n} steps smaller.
3392 @item a number, @var{factor}
3393 A number, @var{factor}, means to use a font that is @var{factor} times
3394 as tall as the default font.
3396 @item a symbol, @var{function}
3397 A symbol is a function to compute the height. It is called with the
3398 current height as argument, and should return the new height to use.
3400 @item anything else, @var{form}
3401 If the @var{height} value doesn't fit the previous possibilities, it is
3402 a form. Emacs evaluates it to get the new height, with the symbol
3403 @code{height} bound to the current specified font height.
3406 @item (raise @var{factor})
3407 This kind of display specification raises or lowers the text
3408 it applies to, relative to the baseline of the line.
3410 @var{factor} must be a number, which is interpreted as a multiple of the
3411 height of the affected text. If it is positive, that means to display
3412 the characters raised. If it is negative, that means to display them
3415 If the text also has a @code{height} display specification, that does
3416 not affect the amount of raising or lowering, which is based on the
3417 faces used for the text.
3420 You can make any display specification conditional. To do that,
3421 package it in another list of the form @code{(when @var{condition} .
3422 @var{spec})}. Then the specification @var{spec} applies only when
3423 @var{condition} evaluates to a non-@code{nil} value. During the
3424 evaluation, @code{object} is bound to the string or buffer having the
3425 conditional @code{display} property. @code{position} and
3426 @code{buffer-position} are bound to the position within @code{object}
3427 and the buffer position where the @code{display} property was found,
3428 respectively. Both positions can be different when @code{object} is a
3431 @node Display Margins
3432 @subsection Displaying in the Margins
3433 @cindex display margins
3434 @cindex margins, display
3436 A buffer can have blank areas called @dfn{display margins} on the left
3437 and on the right. Ordinary text never appears in these areas, but you
3438 can put things into the display margins using the @code{display}
3441 To put text in the left or right display margin of the window, use a
3442 display specification of the form @code{(margin right-margin)} or
3443 @code{(margin left-margin)} on it. To put an image in a display margin,
3444 use that display specification along with the display specification for
3445 the image. Unfortunately, there is currently no way to make
3446 text or images in the margin mouse-sensitive.
3448 If you put such a display specification directly on text in the
3449 buffer, the specified margin display appears @emph{instead of} that
3450 buffer text itself. To put something in the margin @emph{in
3451 association with} certain buffer text without preventing or altering
3452 the display of that text, put a @code{before-string} property on the
3453 text and put the display specification on the contents of the
3456 Before the display margins can display anything, you must give
3457 them a nonzero width. The usual way to do that is to set these
3460 @defvar left-margin-width
3461 @tindex left-margin-width
3462 This variable specifies the width of the left margin.
3463 It is buffer-local in all buffers.
3466 @defvar right-margin-width
3467 @tindex right-margin-width
3468 This variable specifies the width of the right margin.
3469 It is buffer-local in all buffers.
3472 Setting these variables does not immediately affect the window. These
3473 variables are checked when a new buffer is displayed in the window.
3474 Thus, you can make changes take effect by calling
3475 @code{set-window-buffer}.
3477 You can also set the margin widths immediately.
3479 @defun set-window-margins window left &optional right
3480 @tindex set-window-margins
3481 This function specifies the margin widths for window @var{window}.
3482 The argument @var{left} controls the left margin and
3483 @var{right} controls the right margin (default @code{0}).
3486 @defun window-margins &optional window
3487 @tindex window-margins
3488 This function returns the left and right margins of @var{window}
3489 as a cons cell of the form @code{(@var{left} . @var{right})}.
3490 If @var{window} is @code{nil}, the selected window is used.
3495 @cindex images in buffers
3497 To display an image in an Emacs buffer, you must first create an image
3498 descriptor, then use it as a display specifier in the @code{display}
3499 property of text that is displayed (@pxref{Display Property}).
3501 Emacs can display a number of different image formats; some of them
3502 are supported only if particular support libraries are installed on
3503 your machine. In some environments, Emacs can load image
3504 libraries on demand; if so, the variable @code{image-library-alist}
3505 can be used to modify the set of known names for these dynamic
3506 libraries (though it is not possible to add new image formats).
3508 The supported image formats include XBM, XPM (this requires the
3509 libraries @code{libXpm} version 3.4k and @code{libz}), GIF (requiring
3510 @code{libungif} 4.1.0), Postscript, PBM, JPEG (requiring the
3511 @code{libjpeg} library version v6a), TIFF (requiring @code{libtiff}
3512 v3.4), and PNG (requiring @code{libpng} 1.0.2).
3514 You specify one of these formats with an image type symbol. The image
3515 type symbols are @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
3516 @code{pbm}, @code{jpeg}, @code{tiff}, and @code{png}.
3519 This variable contains a list of those image type symbols that are
3520 potentially supported in the current configuration.
3521 @emph{Potentially} here means that Emacs knows about the image types,
3522 not necessarily that they can be loaded (they could depend on
3523 unavailable dynamic libraries, for example).
3525 To know which image types are really available, use
3526 @code{image-type-available-p}.
3529 @defvar image-library-alist
3530 This in an alist of image types vs external libraries needed to
3533 Each element is a list @code{(@var{image-type} @var{library}...)},
3534 where the car is a supported image format from @code{image-types}, and
3535 the rest are strings giving alternate filenames for the corresponding
3536 external libraries to load.
3538 Emacs tries to load the libraries in the order they appear on the
3539 list; if none is loaded, the running session of Emacs won't support
3540 the image type. @code{pbm} and @code{xbm} don't need to be listed;
3541 they're always supported.
3543 This variable is ignored if the image libraries are statically linked
3547 @defun image-type-available-p type
3548 @findex image-type-available-p
3550 This function returns non-@code{nil} if image type @var{type} is
3551 available, i.e., if images of this type can be loaded and displayed in
3552 Emacs. @var{type} should be one of the types contained in
3555 For image types whose support libraries are statically linked, this
3556 function always returns @code{t}; for other image types, it returns
3557 @code{t} if the dynamic library could be loaded, @code{nil} otherwise.
3561 * Image Descriptors:: How to specify an image for use in @code{:display}.
3562 * XBM Images:: Special features for XBM format.
3563 * XPM Images:: Special features for XPM format.
3564 * GIF Images:: Special features for GIF format.
3565 * Postscript Images:: Special features for Postscript format.
3566 * Other Image Types:: Various other formats are supported.
3567 * Defining Images:: Convenient ways to define an image for later use.
3568 * Showing Images:: Convenient ways to display an image once it is defined.
3569 * Image Cache:: Internal mechanisms of image display.
3572 @node Image Descriptors
3573 @subsection Image Descriptors
3574 @cindex image descriptor
3576 An image description is a list of the form @code{(image
3577 . @var{props})}, where @var{props} is a property list containing
3578 alternating keyword symbols (symbols whose names start with a colon) and
3579 their values. You can use any Lisp object as a property, but the only
3580 properties that have any special meaning are certain symbols, all of
3583 Every image descriptor must contain the property @code{:type
3584 @var{type}} to specify the format of the image. The value of @var{type}
3585 should be an image type symbol; for example, @code{xpm} for an image in
3588 Here is a list of other properties that are meaningful for all image
3592 @item :file @var{file}
3593 The @code{:file} property says to load the image from file
3594 @var{file}. If @var{file} is not an absolute file name, it is expanded
3595 in @code{data-directory}.
3597 @item :data @var{data}
3598 The @code{:data} property says the actual contents of the image.
3599 Each image must use either @code{:data} or @code{:file}, but not both.
3600 For most image types, the value of the @code{:data} property should be a
3601 string containing the image data; we recommend using a unibyte string.
3603 Before using @code{:data}, look for further information in the section
3604 below describing the specific image format. For some image types,
3605 @code{:data} may not be supported; for some, it allows other data types;
3606 for some, @code{:data} alone is not enough, so you need to use other
3607 image properties along with @code{:data}.
3609 @item :margin @var{margin}
3610 The @code{:margin} property specifies how many pixels to add as an
3611 extra margin around the image. The value, @var{margin}, must be a
3612 non-negative number, or a pair @code{(@var{x} . @var{y})} of such
3613 numbers. If it is a pair, @var{x} specifies how many pixels to add
3614 horizontally, and @var{y} specifies how many pixels to add vertically.
3615 If @code{:margin} is not specified, the default is zero.
3617 @item :ascent @var{ascent}
3618 The @code{:ascent} property specifies the amount of the image's
3619 height to use for its ascent---that is, the part above the baseline.
3620 The value, @var{ascent}, must be a number in the range 0 to 100, or
3621 the symbol @code{center}.
3623 If @var{ascent} is a number, that percentage of the image's height is
3624 used for its ascent.
3626 If @var{ascent} is @code{center}, the image is vertically centered
3627 around a centerline which would be the vertical centerline of text drawn
3628 at the position of the image, in the manner specified by the text
3629 properties and overlays that apply to the image.
3631 If this property is omitted, it defaults to 50.
3633 @item :relief @var{relief}
3634 The @code{:relief} property, if non-@code{nil}, adds a shadow rectangle
3635 around the image. The value, @var{relief}, specifies the width of the
3636 shadow lines, in pixels. If @var{relief} is negative, shadows are drawn
3637 so that the image appears as a pressed button; otherwise, it appears as
3638 an unpressed button.
3640 @item :conversion @var{algorithm}
3641 The @code{:conversion} property, if non-@code{nil}, specifies a
3642 conversion algorithm that should be applied to the image before it is
3643 displayed; the value, @var{algorithm}, specifies which algorithm.
3648 Specifies the Laplace edge detection algorithm, which blurs out small
3649 differences in color while highlighting larger differences. People
3650 sometimes consider this useful for displaying the image for a
3651 ``disabled'' button.
3653 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
3654 Specifies a general edge-detection algorithm. @var{matrix} must be
3655 either a nine-element list or a nine-element vector of numbers. A pixel
3656 at position @math{x/y} in the transformed image is computed from
3657 original pixels around that position. @var{matrix} specifies, for each
3658 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
3659 will influence the transformed pixel; element @math{0} specifies the
3660 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
3661 the pixel at @math{x/y-1} etc., as shown below:
3664 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
3665 x-1/y & x/y & x+1/y \cr
3666 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
3671 (x-1/y-1 x/y-1 x+1/y-1
3673 x-1/y+1 x/y+1 x+1/y+1)
3677 The resulting pixel is computed from the color intensity of the color
3678 resulting from summing up the RGB values of surrounding pixels,
3679 multiplied by the specified factors, and dividing that sum by the sum
3680 of the factors' absolute values.
3682 Laplace edge-detection currently uses a matrix of
3685 $$\pmatrix{1 & 0 & 0 \cr
3698 Emboss edge-detection uses a matrix of
3701 $$\pmatrix{ 2 & -1 & 0 \cr
3715 Specifies transforming the image so that it looks ``disabled''.
3718 @item :mask @var{mask}
3719 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
3720 a clipping mask for the image, so that the background of a frame is
3721 visible behind the image. If @var{bg} is not specified, or if @var{bg}
3722 is @code{t}, determine the background color of the image by looking at
3723 the four corners of the image, assuming the most frequently occurring
3724 color from the corners is the background color of the image. Otherwise,
3725 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
3726 specifying the color to assume for the background of the image.
3728 If @var{mask} is @code{nil}, remove a mask from the image, if it has
3729 one. Images in some formats include a mask which can be removed by
3730 specifying @code{:mask nil}.
3732 @item :pointer @var{shape}
3733 This specifies the pointer shape when the mouse pointer is over this
3734 image. @xref{Pointer Shape}, for available pointer shapes.
3736 @item :map @var{map}
3737 This associates an image map of @dfn{hot spots} with this image.
3739 An image map is an alist where each element has the format
3740 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
3741 as either a rectangle, a circle, or a polygon.
3743 A rectangle is a cons
3744 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
3745 which specifies the pixel coordinates of the upper left and bottom right
3746 corners of the rectangle area.
3749 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
3750 which specifies the center and the radius of the circle; @var{r} may
3751 be a float or integer.
3754 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
3755 where each pair in the vector describes one corner in the polygon.
3757 When the mouse pointer is above a hot-spot area of an image, the
3758 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
3759 property it defines a tool-tip for the hot-spot, and if it contains
3760 a @code{pointer} property, it defines the shape of the mouse cursor when
3761 it is over the hot-spot.
3762 @xref{Pointer Shape}, for available pointer shapes.
3764 When you click the mouse when the mouse pointer is over a hot-spot, an
3765 event is composed by combining the @var{id} of the hot-spot with the
3766 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
3767 @var{id} is @code{area4}.
3770 @defun image-mask-p spec &optional frame
3771 @tindex image-mask-p
3772 This function returns @code{t} if image @var{spec} has a mask bitmap.
3773 @var{frame} is the frame on which the image will be displayed.
3774 @var{frame} @code{nil} or omitted means to use the selected frame
3775 (@pxref{Input Focus}).
3779 @subsection XBM Images
3782 To use XBM format, specify @code{xbm} as the image type. This image
3783 format doesn't require an external library, so images of this type are
3786 Additional image properties supported for the @code{xbm} image type are:
3789 @item :foreground @var{foreground}
3790 The value, @var{foreground}, should be a string specifying the image
3791 foreground color, or @code{nil} for the default color. This color is
3792 used for each pixel in the XBM that is 1. The default is the frame's
3795 @item :background @var{background}
3796 The value, @var{background}, should be a string specifying the image
3797 background color, or @code{nil} for the default color. This color is
3798 used for each pixel in the XBM that is 0. The default is the frame's
3802 If you specify an XBM image using data within Emacs instead of an
3803 external file, use the following three properties:
3806 @item :data @var{data}
3807 The value, @var{data}, specifies the contents of the image.
3808 There are three formats you can use for @var{data}:
3812 A vector of strings or bool-vectors, each specifying one line of the
3813 image. Do specify @code{:height} and @code{:width}.
3816 A string containing the same byte sequence as an XBM file would contain.
3817 You must not specify @code{:height} and @code{:width} in this case,
3818 because omitting them is what indicates the data has the format of an
3819 XBM file. The file contents specify the height and width of the image.
3822 A string or a bool-vector containing the bits of the image (plus perhaps
3823 some extra bits at the end that will not be used). It should contain at
3824 least @var{width} * @code{height} bits. In this case, you must specify
3825 @code{:height} and @code{:width}, both to indicate that the string
3826 contains just the bits rather than a whole XBM file, and to specify the
3830 @item :width @var{width}
3831 The value, @var{width}, specifies the width of the image, in pixels.
3833 @item :height @var{height}
3834 The value, @var{height}, specifies the height of the image, in pixels.
3838 @subsection XPM Images
3841 To use XPM format, specify @code{xpm} as the image type. The
3842 additional image property @code{:color-symbols} is also meaningful with
3843 the @code{xpm} image type:
3846 @item :color-symbols @var{symbols}
3847 The value, @var{symbols}, should be an alist whose elements have the
3848 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
3849 the name of a color as it appears in the image file, and @var{color}
3850 specifies the actual color to use for displaying that name.
3854 @subsection GIF Images
3857 For GIF images, specify image type @code{gif}.
3860 @item :index @var{index}
3861 You can use @code{:index} to specify one image from a GIF file that
3862 contains more than one image. This property specifies use of image
3863 number @var{index} from the file. If the GIF file doesn't contain an
3864 image with index @var{index}, the image displays as a hollow box.
3868 This could be used to implement limited support for animated GIFs.
3869 For example, the following function displays a multi-image GIF file
3870 at point-min in the current buffer, switching between sub-images
3873 (defun show-anim (file max)
3874 "Display multi-image GIF file FILE which contains MAX subimages."
3875 (display-anim (current-buffer) file 0 max t))
3877 (defun display-anim (buffer file idx max first-time)
3880 (let ((img (create-image file nil :image idx)))
3883 (goto-char (point-min))
3884 (unless first-time (delete-char 1))
3886 (run-with-timer 0.1 nil 'display-anim buffer file (1+ idx) max nil)))
3889 @node Postscript Images
3890 @subsection Postscript Images
3891 @cindex Postscript images
3893 To use Postscript for an image, specify image type @code{postscript}.
3894 This works only if you have Ghostscript installed. You must always use
3895 these three properties:
3898 @item :pt-width @var{width}
3899 The value, @var{width}, specifies the width of the image measured in
3900 points (1/72 inch). @var{width} must be an integer.
3902 @item :pt-height @var{height}
3903 The value, @var{height}, specifies the height of the image in points
3904 (1/72 inch). @var{height} must be an integer.
3906 @item :bounding-box @var{box}
3907 The value, @var{box}, must be a list or vector of four integers, which
3908 specifying the bounding box of the Postscript image, analogous to the
3909 @samp{BoundingBox} comment found in Postscript files.
3912 %%BoundingBox: 22 171 567 738
3916 Displaying Postscript images from Lisp data is not currently
3917 implemented, but it may be implemented by the time you read this.
3918 See the @file{etc/NEWS} file to make sure.
3920 @node Other Image Types
3921 @subsection Other Image Types
3924 For PBM images, specify image type @code{pbm}. Color, gray-scale and
3925 monochromatic images are supported. For mono PBM images, two additional
3926 image properties are supported.
3929 @item :foreground @var{foreground}
3930 The value, @var{foreground}, should be a string specifying the image
3931 foreground color, or @code{nil} for the default color. This color is
3932 used for each pixel in the XBM that is 1. The default is the frame's
3935 @item :background @var{background}
3936 The value, @var{background}, should be a string specifying the image
3937 background color, or @code{nil} for the default color. This color is
3938 used for each pixel in the XBM that is 0. The default is the frame's
3942 For JPEG images, specify image type @code{jpeg}.
3944 For TIFF images, specify image type @code{tiff}.
3946 For PNG images, specify image type @code{png}.
3948 @node Defining Images
3949 @subsection Defining Images
3951 The functions @code{create-image}, @code{defimage} and
3952 @code{find-image} provide convenient ways to create image descriptors.
3954 @defun create-image file-or-data &optional type data-p &rest props
3955 @tindex create-image
3956 This function creates and returns an image descriptor which uses the
3957 data in @var{file-or-data}. @var{file-or-data} can be a file name or
3958 a string containing the image data; @var{data-p} should be @code{nil}
3959 for the former case, non-@code{nil} for the latter case.
3961 The optional argument @var{type} is a symbol specifying the image type.
3962 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
3963 determine the image type from the file's first few bytes, or else
3964 from the file's name.
3966 The remaining arguments, @var{props}, specify additional image
3967 properties---for example,
3970 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
3973 The function returns @code{nil} if images of this type are not
3974 supported. Otherwise it returns an image descriptor.
3977 @defmac defimage symbol specs &optional doc
3979 This macro defines @var{symbol} as an image name. The arguments
3980 @var{specs} is a list which specifies how to display the image.
3981 The third argument, @var{doc}, is an optional documentation string.
3983 Each argument in @var{specs} has the form of a property list, and each
3984 one should specify at least the @code{:type} property and either the
3985 @code{:file} or the @code{:data} property. The value of @code{:type}
3986 should be a symbol specifying the image type, the value of
3987 @code{:file} is the file to load the image from, and the value of
3988 @code{:data} is a string containing the actual image data. Here is an
3992 (defimage test-image
3993 ((:type xpm :file "~/test1.xpm")
3994 (:type xbm :file "~/test1.xbm")))
3997 @code{defimage} tests each argument, one by one, to see if it is
3998 usable---that is, if the type is supported and the file exists. The
3999 first usable argument is used to make an image descriptor which is
4000 stored in @var{symbol}.
4002 If none of the alternatives will work, then @var{symbol} is defined
4006 @defun find-image specs
4008 This function provides a convenient way to find an image satisfying one
4009 of a list of image specifications @var{specs}.
4011 Each specification in @var{specs} is a property list with contents
4012 depending on image type. All specifications must at least contain the
4013 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
4014 or @w{@code{:data @var{DATA}}}, where @var{type} is a symbol specifying
4015 the image type, e.g.@: @code{xbm}, @var{file} is the file to load the
4016 image from, and @var{data} is a string containing the actual image data.
4017 The first specification in the list whose @var{type} is supported, and
4018 @var{file} exists, is used to construct the image specification to be
4019 returned. If no specification is satisfied, @code{nil} is returned.
4021 The image is looked for first on @code{load-path} and then in
4022 @code{data-directory}.
4025 @node Showing Images
4026 @subsection Showing Images
4028 You can use an image descriptor by setting up the @code{display}
4029 property yourself, but it is easier to use the functions in this
4032 @defun insert-image image &optional string area slice
4033 This function inserts @var{image} in the current buffer at point. The
4034 value @var{image} should be an image descriptor; it could be a value
4035 returned by @code{create-image}, or the value of a symbol defined with
4036 @code{defimage}. The argument @var{string} specifies the text to put
4037 in the buffer to hold the image. If it is omitted or @code{nil},
4038 @code{insert-image} uses @code{" "} by default.
4040 The argument @var{area} specifies whether to put the image in a margin.
4041 If it is @code{left-margin}, the image appears in the left margin;
4042 @code{right-margin} specifies the right margin. If @var{area} is
4043 @code{nil} or omitted, the image is displayed at point within the
4046 The argument @var{slice} specifies a slice of the image to insert. If
4047 @var{slice} is @code{nil} or omitted the whole image is inserted.
4048 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
4049 @var{height})} which specifies the @var{x} and @var{y} positions and
4050 @var{width} and @var{height} of the image area to insert. Integer
4051 values are in units of pixels. A floating point number in the range
4052 0.0--1.0 stands for that fraction of the width or height of the entire
4055 Internally, this function inserts @var{string} in the buffer, and gives
4056 it a @code{display} property which specifies @var{image}. @xref{Display
4060 @defun insert-sliced-image image &optional string area rows cols
4061 This function inserts @var{image} in the current buffer at point, like
4062 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
4063 equally sized slices.
4066 @defun put-image image pos &optional string area
4067 This function puts image @var{image} in front of @var{pos} in the
4068 current buffer. The argument @var{pos} should be an integer or a
4069 marker. It specifies the buffer position where the image should appear.
4070 The argument @var{string} specifies the text that should hold the image
4071 as an alternative to the default.
4073 The argument @var{image} must be an image descriptor, perhaps returned
4074 by @code{create-image} or stored by @code{defimage}.
4076 The argument @var{area} specifies whether to put the image in a margin.
4077 If it is @code{left-margin}, the image appears in the left margin;
4078 @code{right-margin} specifies the right margin. If @var{area} is
4079 @code{nil} or omitted, the image is displayed at point within the
4082 Internally, this function creates an overlay, and gives it a
4083 @code{before-string} property containing text that has a @code{display}
4084 property whose value is the image. (Whew!)
4087 @defun remove-images start end &optional buffer
4088 This function removes images in @var{buffer} between positions
4089 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
4090 images are removed from the current buffer.
4092 This removes only images that were put into @var{buffer} the way
4093 @code{put-image} does it, not images that were inserted with
4094 @code{insert-image} or in other ways.
4097 @defun image-size spec &optional pixels frame
4099 This function returns the size of an image as a pair
4100 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
4101 specification. @var{pixels} non-@code{nil} means return sizes
4102 measured in pixels, otherwise return sizes measured in canonical
4103 character units (fractions of the width/height of the frame's default
4104 font). @var{frame} is the frame on which the image will be displayed.
4105 @var{frame} null or omitted means use the selected frame (@pxref{Input
4110 @subsection Image Cache
4112 Emacs stores images in an image cache when it displays them, so it can
4113 display them again more efficiently. It removes an image from the cache
4114 when it hasn't been displayed for a specified period of time.
4116 When an image is looked up in the cache, its specification is compared
4117 with cached image specifications using @code{equal}. This means that
4118 all images with equal specifications share the same image in the cache.
4120 @defvar image-cache-eviction-delay
4121 @tindex image-cache-eviction-delay
4122 This variable specifies the number of seconds an image can remain in the
4123 cache without being displayed. When an image is not displayed for this
4124 length of time, Emacs removes it from the image cache.
4126 If the value is @code{nil}, Emacs does not remove images from the cache
4127 except when you explicitly clear it. This mode can be useful for
4131 @defun clear-image-cache &optional frame
4132 @tindex clear-image-cache
4133 This function clears the image cache. If @var{frame} is non-@code{nil},
4134 only the cache for that frame is cleared. Otherwise all frames' caches
4141 @cindex buttons in buffers
4142 @cindex clickable buttons in buffers
4144 The @emph{button} package defines functions for inserting and
4145 manipulating clickable (with the mouse, or via keyboard commands)
4146 buttons in Emacs buffers, such as might be used for help hyper-links,
4147 etc. Emacs uses buttons for the hyper-links in help text and the like.
4149 A button is essentially a set of properties attached (via text
4150 properties or overlays) to a region of text in an Emacs buffer. These
4151 properties are called @dfn{button properties}.
4153 One of the these properties (@code{action}) is a function, which will
4154 be called when the user invokes it using the keyboard or the mouse.
4155 The invoked function may then examine the button and use its other
4156 properties as desired.
4158 In some ways the Emacs button package duplicates functionality offered
4159 by the widget package (@pxref{Top, , Introduction, widget, The Emacs
4160 Widget Library}), but the button package has the advantage that it is
4161 much faster, much smaller, and much simpler to use (for elisp
4162 programmers---for users, the result is about the same). The extra
4163 speed and space savings are useful mainly if you need to create many
4164 buttons in a buffer (for instance an @code{*Apropos*} buffer uses
4165 buttons to make entries clickable, and may contain many thousands of
4169 * Button Properties:: Button properties with special meanings.
4170 * Button Types:: Defining common properties for classes of buttons.
4171 * Making Buttons:: Adding buttons to Emacs buffers.
4172 * Manipulating Buttons:: Getting and setting properties of buttons.
4173 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
4176 @node Button Properties
4177 @subsection Button Properties
4178 @cindex button properties
4180 Buttons have an associated list of properties defining their
4181 appearance and behavior, and other arbitrary properties may be used
4182 for application specific purposes. Some properties that have special
4183 meaning to the button package include:
4187 @kindex action @r{(button property)}
4188 The function to call when the user invokes the button, which is passed
4189 the single argument @var{button}. By default this is @code{ignore},
4193 @kindex mouse-action @r{(button property)}
4194 This is similar to @code{action}, and when present, will be used
4195 instead of @code{action} for button invocations resulting from
4196 mouse-clicks (instead of the user hitting @key{RET}). If not
4197 present, mouse-clicks use @code{action} instead.
4200 @kindex face @r{(button property)}
4201 This is an Emacs face controlling how buttons of this type are
4202 displayed; by default this is the @code{button} face.
4205 @kindex mouse-face @r{(button property)}
4206 This is an additional face which controls appearance during
4207 mouse-overs (merged with the usual button face); by default this is
4208 the usual Emacs @code{highlight} face.
4211 @kindex keymap @r{(button property)}
4212 The button's keymap, defining bindings active within the button
4213 region. By default this is the usual button region keymap, stored
4214 in the variable @code{button-map}, which defines @key{RET} and
4215 @key{mouse-2} to invoke the button.
4218 @kindex type @r{(button property)}
4219 The button-type of the button. When creating a button, this is
4220 usually specified using the @code{:type} keyword argument.
4221 @xref{Button Types}.
4224 @kindex help-index @r{(button property)}
4225 A string displayed by the Emacs tool-tip help system; by default,
4226 @code{"mouse-2, RET: Push this button"}.
4229 @kindex follow-link @r{(button property)}
4230 The follow-link property, defining how a @key{Mouse-1} click behaves
4231 on this button, @xref{Links and Mouse-1}.
4234 @kindex button @r{(button property)}
4235 All buttons have a non-@code{nil} @code{button} property, which may be useful
4236 in finding regions of text that comprise buttons (which is what the
4237 standard button functions do).
4240 There are other properties defined for the regions of text in a
4241 button, but these are not generally interesting for typical uses.
4244 @subsection Button Types
4245 @cindex button types
4247 Every button has a button @emph{type}, which defines default values
4248 for the button's properties. Button types are arranged in a
4249 hierarchy, with specialized types inheriting from more general types,
4250 so that it's easy to define special-purpose types of buttons for
4253 @defun define-button-type name &rest properties
4254 @tindex define-button-type
4255 Define a `button type' called @var{name}. The remaining arguments
4256 form a sequence of @var{property value} pairs, specifying default
4257 property values for buttons with this type (a button's type may be set
4258 by giving it a @code{type} property when creating the button, using
4259 the @code{:type} keyword argument).
4261 In addition, the keyword argument @code{:supertype} may be used to
4262 specify a button-type from which @var{name} inherits its default
4263 property values. Note that this inheritance happens only when
4264 @var{name} is defined; subsequent changes to a supertype are not
4265 reflected in its subtypes.
4268 Using @code{define-button-type} to define default properties for
4269 buttons is not necessary---buttons without any specified type use the
4270 built-in button-type @code{button}---but it is encouraged, since
4271 doing so usually makes the resulting code clearer and more efficient.
4273 @node Making Buttons
4274 @subsection Making Buttons
4275 @cindex making buttons
4277 Buttons are associated with a region of text, using an overlay or
4278 text properties to hold button-specific information, all of which are
4279 initialized from the button's type (which defaults to the built-in
4280 button type @code{button}). Like all Emacs text, the appearance of
4281 the button is governed by the @code{face} property; by default (via
4282 the @code{face} property inherited from the @code{button} button-type)
4283 this is a simple underline, like a typical web-page link.
4285 For convenience, there are two sorts of button-creation functions,
4286 those that add button properties to an existing region of a buffer,
4287 called @code{make-...button}, and those also insert the button text,
4288 called @code{insert-...button}.
4290 The button-creation functions all take the @code{&rest} argument
4291 @var{properties}, which should be a sequence of @var{property value}
4292 pairs, specifying properties to add to the button; see @ref{Button
4293 Properties}. In addition, the keyword argument @code{:type} may be
4294 used to specify a button-type from which to inherit other properties;
4295 see @ref{Button Types}. Any properties not explicitly specified
4296 during creation will be inherited from the button's type (if the type
4297 defines such a property).
4299 The following functions add a button using an overlay
4300 (@pxref{Overlays}) to hold the button properties:
4302 @defun make-button beg end &rest properties
4304 This makes a button from @var{beg} to @var{end} in the
4305 current buffer, and returns it.
4308 @defun insert-button label &rest properties
4309 @tindex insert-button
4310 This insert a button with the label @var{label} at point,
4314 The following functions are similar, but use Emacs text properties
4315 (@pxref{Text Properties}) to hold the button properties, making the
4316 button actually part of the text instead of being a property of the
4317 buffer. Buttons using text properties do not create markers into the
4318 buffer, which is important for speed when you use extremely large
4319 numbers of buttons. Both functions return the position of the start
4322 @defun make-text-button beg end &rest properties
4323 @tindex make-text-button
4324 This makes a button from @var{beg} to @var{end} in the current buffer, using
4328 @defun insert-text-button label &rest properties
4329 @tindex insert-text-button
4330 This inserts a button with the label @var{label} at point, using text
4334 @node Manipulating Buttons
4335 @subsection Manipulating Buttons
4336 @cindex manipulating buttons
4338 These are functions for getting and setting properties of buttons.
4339 Often these are used by a button's invocation function to determine
4342 Where a @var{button} parameter is specified, it means an object
4343 referring to a specific button, either an overlay (for overlay
4344 buttons), or a buffer-position or marker (for text property buttons).
4345 Such an object is passed as the first argument to a button's
4346 invocation function when it is invoked.
4348 @defun button-start button
4349 @tindex button-start
4350 Return the position at which @var{button} starts.
4353 @defun button-end button
4355 Return the position at which @var{button} ends.
4358 @defun button-get button prop
4360 Get the property of button @var{button} named @var{prop}.
4363 @defun button-put button prop val
4365 Set @var{button}'s @var{prop} property to @var{val}.
4368 @defun button-activate button &optional use-mouse-action
4369 @tindex button-activate
4370 Call @var{button}'s @code{action} property (i.e., invoke it). If
4371 @var{use-mouse-action} is non-@code{nil}, try to invoke the button's
4372 @code{mouse-action} property instead of @code{action}; if the button
4373 has no @code{mouse-action} property, use @code{action} as normal.
4376 @defun button-label button
4377 @tindex button-label
4378 Return @var{button}'s text label.
4381 @defun button-type button
4383 Return @var{button}'s button-type.
4386 @defun button-has-type-p button type
4387 @tindex button-has-type-p
4388 Return @code{t} if @var{button} has button-type @var{type}, or one of
4389 @var{type}'s subtypes.
4392 @defun button-at pos
4394 Return the button at position @var{pos} in the current buffer, or @code{nil}.
4397 @defun button-type-put type prop val
4398 @tindex button-type-put
4399 Set the button-type @var{type}'s @var{prop} property to @var{val}.
4402 @defun button-type-get type prop
4403 @tindex button-type-get
4404 Get the property of button-type @var{type} named @var{prop}.
4407 @defun button-type-subtype-p type supertype
4408 @tindex button-type-subtype-p
4409 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
4412 @node Button Buffer Commands
4413 @subsection Button Buffer Commands
4414 @cindex button buffer commands
4416 These are commands and functions for locating and operating on
4417 buttons in an Emacs buffer.
4419 @code{push-button} is the command that a user uses to actually `push'
4420 a button, and is bound by default in the button itself to @key{RET}
4421 and to @key{mouse-2} using a region-specific keymap. Commands
4422 that are useful outside the buttons itself, such as
4423 @code{forward-button} and @code{backward-button} are additionally
4424 available in the keymap stored in @code{button-buffer-map}; a mode
4425 which uses buttons may want to use @code{button-buffer-map} as a
4426 parent keymap for its keymap.
4428 If the button has a non-@code{nil} @code{follow-link} property, and
4429 @var{mouse-1-click-follows-link} is set, a quick @key{Mouse-1} click
4430 will also activate the @code{push-button} command.
4431 @xref{Links and Mouse-1}.
4433 @deffn Command push-button &optional pos use-mouse-action
4435 Perform the action specified by a button at location @var{pos}.
4436 @var{pos} may be either a buffer position or a mouse-event. If
4437 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
4438 mouse-event (@pxref{Mouse Events}), try to invoke the button's
4439 @code{mouse-action} property instead of @code{action}; if the button
4440 has no @code{mouse-action} property, use @code{action} as normal.
4441 @var{pos} defaults to point, except when @code{push-button} is invoked
4442 interactively as the result of a mouse-event, in which case, the mouse
4443 event's position is used. If there's no button at @var{pos}, do
4444 nothing and return @code{nil}, otherwise return @code{t}.
4447 @deffn Command forward-button n &optional wrap display-message
4448 @tindex forward-button
4449 Move to the @var{n}th next button, or @var{n}th previous button if
4450 @var{n} is negative. If @var{n} is zero, move to the start of any
4451 button at point. If @var{wrap} is non-@code{nil}, moving past either
4452 end of the buffer continues from the other end. If
4453 @var{display-message} is non-@code{nil}, the button's help-echo string
4454 is displayed. Any button with a non-@code{nil} @code{skip} property
4455 is skipped over. Returns the button found.
4458 @deffn Command backward-button n &optional wrap display-message
4459 @tindex backward-button
4460 Move to the @var{n}th previous button, or @var{n}th next button if
4461 @var{n} is negative. If @var{n} is zero, move to the start of any
4462 button at point. If @var{wrap} is non-@code{nil}, moving past either
4463 end of the buffer continues from the other end. If
4464 @var{display-message} is non-@code{nil}, the button's help-echo string
4465 is displayed. Any button with a non-@code{nil} @code{skip} property
4466 is skipped over. Returns the button found.
4469 @defun next-button pos &optional count-current
4471 Return the next button after position @var{pos} in the current buffer.
4472 If @var{count-current} is non-@code{nil}, count any button at
4473 @var{pos} in the search, instead of starting at the next button.
4476 @defun previous-button pos &optional count-current
4477 @tindex previous-button
4478 Return the @var{n}th button before position @var{pos} in the current
4479 buffer. If @var{count-current} is non-@code{nil}, count any button at
4480 @var{pos} in the search, instead of starting at the next button.
4484 @section Blinking Parentheses
4485 @cindex parenthesis matching
4487 @cindex balancing parentheses
4488 @cindex close parenthesis
4490 This section describes the mechanism by which Emacs shows a matching
4491 open parenthesis when the user inserts a close parenthesis.
4493 @defvar blink-paren-function
4494 The value of this variable should be a function (of no arguments) to
4495 be called whenever a character with close parenthesis syntax is inserted.
4496 The value of @code{blink-paren-function} may be @code{nil}, in which
4497 case nothing is done.
4500 @defopt blink-matching-paren
4501 If this variable is @code{nil}, then @code{blink-matching-open} does
4505 @defopt blink-matching-paren-distance
4506 This variable specifies the maximum distance to scan for a matching
4507 parenthesis before giving up.
4510 @defopt blink-matching-delay
4511 This variable specifies the number of seconds for the cursor to remain
4512 at the matching parenthesis. A fraction of a second often gives
4513 good results, but the default is 1, which works on all systems.
4516 @deffn Command blink-matching-open
4517 This function is the default value of @code{blink-paren-function}. It
4518 assumes that point follows a character with close parenthesis syntax and
4519 moves the cursor momentarily to the matching opening character. If that
4520 character is not already on the screen, it displays the character's
4521 context in the echo area. To avoid long delays, this function does not
4522 search farther than @code{blink-matching-paren-distance} characters.
4524 Here is an example of calling this function explicitly.
4528 (defun interactive-blink-matching-open ()
4529 @c Do not break this line! -- rms.
4530 @c The first line of a doc string
4531 @c must stand alone.
4532 "Indicate momentarily the start of sexp before point."
4536 (let ((blink-matching-paren-distance
4538 (blink-matching-paren t))
4539 (blink-matching-open)))
4545 @section Inverse Video
4546 @cindex Inverse Video
4548 @defopt inverse-video
4549 @cindex highlighting
4550 This variable controls whether Emacs uses inverse video for all text
4551 on the screen. Non-@code{nil} means yes, @code{nil} means no. The
4552 default is @code{nil}.
4555 @defopt mode-line-inverse-video
4556 This variable controls the use of inverse video for mode lines and
4557 menu bars. If it is non-@code{nil}, then these lines are displayed in
4558 the face @code{mode-line}. Otherwise, these lines are displayed
4559 normally, just like other text. The default is @code{t}.
4563 @section Usual Display Conventions
4565 The usual display conventions define how to display each character
4566 code. You can override these conventions by setting up a display table
4567 (@pxref{Display Tables}). Here are the usual display conventions:
4571 Character codes 32 through 126 map to glyph codes 32 through 126.
4572 Normally this means they display as themselves.
4575 Character code 9 is a horizontal tab. It displays as whitespace
4576 up to a position determined by @code{tab-width}.
4579 Character code 10 is a newline.
4582 All other codes in the range 0 through 31, and code 127, display in one
4583 of two ways according to the value of @code{ctl-arrow}. If it is
4584 non-@code{nil}, these codes map to sequences of two glyphs, where the
4585 first glyph is the @acronym{ASCII} code for @samp{^}. (A display table can
4586 specify a glyph to use instead of @samp{^}.) Otherwise, these codes map
4587 just like the codes in the range 128 to 255.
4589 On MS-DOS terminals, Emacs arranges by default for the character code
4590 127 to be mapped to the glyph code 127, which normally displays as an
4591 empty polygon. This glyph is used to display non-@acronym{ASCII} characters
4592 that the MS-DOS terminal doesn't support. @xref{MS-DOS and MULE,,,
4593 emacs, The GNU Emacs Manual}.
4596 Character codes 128 through 255 map to sequences of four glyphs, where
4597 the first glyph is the @acronym{ASCII} code for @samp{\}, and the others are
4598 digit characters representing the character code in octal. (A display
4599 table can specify a glyph to use instead of @samp{\}.)
4602 Multibyte character codes above 256 are displayed as themselves, or as a
4603 question mark or empty box if the terminal cannot display that
4607 The usual display conventions apply even when there is a display
4608 table, for any character whose entry in the active display table is
4609 @code{nil}. Thus, when you set up a display table, you need only
4610 specify the characters for which you want special behavior.
4612 These display rules apply to carriage return (character code 13), when
4613 it appears in the buffer. But that character may not appear in the
4614 buffer where you expect it, if it was eliminated as part of end-of-line
4615 conversion (@pxref{Coding System Basics}).
4617 These variables affect the way certain characters are displayed on the
4618 screen. Since they change the number of columns the characters occupy,
4619 they also affect the indentation functions. These variables also affect
4620 how the mode line is displayed; if you want to force redisplay of the
4621 mode line using the new values, call the function
4622 @code{force-mode-line-update} (@pxref{Mode Line Format}).
4625 @cindex control characters in display
4626 This buffer-local variable controls how control characters are
4627 displayed. If it is non-@code{nil}, they are displayed as a caret
4628 followed by the character: @samp{^A}. If it is @code{nil}, they are
4629 displayed as a backslash followed by three octal digits: @samp{\001}.
4632 @c Following may have overfull hbox.
4633 @defvar default-ctl-arrow
4634 The value of this variable is the default value for @code{ctl-arrow} in
4635 buffers that do not override it. @xref{Default Value}.
4639 The value of this variable is the spacing between tab stops used for
4640 displaying tab characters in Emacs buffers. The value is in units of
4641 columns, and the default is 8. Note that this feature is completely
4642 independent of the user-settable tab stops used by the command
4643 @code{tab-to-tab-stop}. @xref{Indent Tabs}.
4646 @defopt indicate-empty-lines
4647 @tindex indicate-empty-lines
4648 @cindex fringes, and empty line indication
4649 When this is non-@code{nil}, Emacs displays a special glyph in the
4650 fringe of each empty line at the end of the buffer, on terminals that
4651 support it (window systems). @xref{Fringes}.
4654 @defvar indicate-buffer-boundaries
4655 This buffer-local variable controls how the buffer boundaries and
4656 window scrolling are indicated in the window fringes.
4658 Emacs can indicate the buffer boundaries---that is, the first and last
4659 line in the buffer---with angle icons when they appear on the screen.
4660 In addition, Emacs can display an up-arrow in the fringe to show
4661 that there is text above the screen, and a down-arrow to show
4662 there is text below the screen.
4664 There are four kinds of basic values:
4668 Don't display the icons.
4670 Display them in the left fringe.
4672 Display them in the right fringe.
4673 @item @var{anything-else}
4674 Display the icon at the top of the window top in the left fringe, and other
4675 in the right fringe.
4678 If value is a cons @code{(@var{angles} . @var{arrows})}, @var{angles}
4679 controls the angle icons, and @var{arrows} controls the arrows. Both
4680 @var{angles} and @var{arrows} work according to the table above.
4681 Thus, @code{(t . right)} places the top angle icon in the left
4682 fringe, the bottom angle icon in the right fringe, and both arrows in
4686 @defvar default-indicate-buffer-boundaries
4687 The value of this variable is the default value for
4688 @code{indicate-buffer-boundaries} in buffers that do not override it.
4691 @node Display Tables
4692 @section Display Tables
4694 @cindex display table
4695 You can use the @dfn{display table} feature to control how all possible
4696 character codes display on the screen. This is useful for displaying
4697 European languages that have letters not in the @acronym{ASCII} character
4700 The display table maps each character code into a sequence of
4701 @dfn{glyphs}, each glyph being a graphic that takes up one character
4702 position on the screen. You can also define how to display each glyph
4703 on your terminal, using the @dfn{glyph table}.
4705 Display tables affect how the mode line is displayed; if you want to
4706 force redisplay of the mode line using a new display table, call
4707 @code{force-mode-line-update} (@pxref{Mode Line Format}).
4710 * Display Table Format:: What a display table consists of.
4711 * Active Display Table:: How Emacs selects a display table to use.
4712 * Glyphs:: How to define a glyph, and what glyphs mean.
4715 @node Display Table Format
4716 @subsection Display Table Format
4718 A display table is actually a char-table (@pxref{Char-Tables}) with
4719 @code{display-table} as its subtype.
4721 @defun make-display-table
4722 This creates and returns a display table. The table initially has
4723 @code{nil} in all elements.
4726 The ordinary elements of the display table are indexed by character
4727 codes; the element at index @var{c} says how to display the character
4728 code @var{c}. The value should be @code{nil} or a vector of glyph
4729 values (@pxref{Glyphs}). If an element is @code{nil}, it says to
4730 display that character according to the usual display conventions
4731 (@pxref{Usual Display}).
4733 If you use the display table to change the display of newline
4734 characters, the whole buffer will be displayed as one long ``line.''
4736 The display table also has six ``extra slots'' which serve special
4737 purposes. Here is a table of their meanings; @code{nil} in any slot
4738 means to use the default for that slot, as stated below.
4742 The glyph for the end of a truncated screen line (the default for this
4743 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
4744 arrows in the fringes to indicate truncation, so the display table has
4748 The glyph for the end of a continued line (the default is @samp{\}).
4749 On graphical terminals, Emacs uses curved arrows in the fringes to
4750 indicate continuation, so the display table has no effect.
4753 The glyph for indicating a character displayed as an octal character
4754 code (the default is @samp{\}).
4757 The glyph for indicating a control character (the default is @samp{^}).
4760 A vector of glyphs for indicating the presence of invisible lines (the
4761 default is @samp{...}). @xref{Selective Display}.
4764 The glyph used to draw the border between side-by-side windows (the
4765 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
4766 when there are no scroll bars; if scroll bars are supported and in use,
4767 a scroll bar separates the two windows.
4770 For example, here is how to construct a display table that mimics the
4771 effect of setting @code{ctl-arrow} to a non-@code{nil} value:
4774 (setq disptab (make-display-table))
4777 (or (= i ?\t) (= i ?\n)
4778 (aset disptab i (vector ?^ (+ i 64))))
4780 (aset disptab 127 (vector ?^ ??)))
4783 @defun display-table-slot display-table slot
4784 This function returns the value of the extra slot @var{slot} of
4785 @var{display-table}. The argument @var{slot} may be a number from 0 to
4786 5 inclusive, or a slot name (symbol). Valid symbols are
4787 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
4788 @code{selective-display}, and @code{vertical-border}.
4791 @defun set-display-table-slot display-table slot value
4792 This function stores @var{value} in the extra slot @var{slot} of
4793 @var{display-table}. The argument @var{slot} may be a number from 0 to
4794 5 inclusive, or a slot name (symbol). Valid symbols are
4795 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
4796 @code{selective-display}, and @code{vertical-border}.
4799 @defun describe-display-table display-table
4800 @tindex describe-display-table
4801 This function displays a description of the display table
4802 @var{display-table} in a help buffer.
4805 @deffn Command describe-current-display-table
4806 @tindex describe-current-display-table
4807 This command displays a description of the current display table in a
4811 @node Active Display Table
4812 @subsection Active Display Table
4813 @cindex active display table
4815 Each window can specify a display table, and so can each buffer. When
4816 a buffer @var{b} is displayed in window @var{w}, display uses the
4817 display table for window @var{w} if it has one; otherwise, the display
4818 table for buffer @var{b} if it has one; otherwise, the standard display
4819 table if any. The display table chosen is called the @dfn{active}
4822 @defun window-display-table &optional window
4823 This function returns @var{window}'s display table, or @code{nil}
4824 if @var{window} does not have an assigned display table. The default
4825 for @var{window} is the selected window.
4828 @defun set-window-display-table window table
4829 This function sets the display table of @var{window} to @var{table}.
4830 The argument @var{table} should be either a display table or
4834 @defvar buffer-display-table
4835 This variable is automatically buffer-local in all buffers; its value in
4836 a particular buffer specifies the display table for that buffer. If it
4837 is @code{nil}, that means the buffer does not have an assigned display
4841 @defvar standard-display-table
4842 This variable's value is the default display table, used whenever a
4843 window has no display table and neither does the buffer displayed in
4844 that window. This variable is @code{nil} by default.
4847 If there is no display table to use for a particular window---that is,
4848 if the window specifies none, its buffer specifies none, and
4849 @code{standard-display-table} is @code{nil}---then Emacs uses the usual
4850 display conventions for all character codes in that window. @xref{Usual
4853 A number of functions for changing the standard display table
4854 are defined in the library @file{disp-table}.
4860 A @dfn{glyph} is a generalization of a character; it stands for an
4861 image that takes up a single character position on the screen. Glyphs
4862 are represented in Lisp as integers, just as characters are. Normally
4863 Emacs finds glyphs in the display table (@pxref{Display Tables}).
4865 A glyph can be @dfn{simple} or it can be defined by the @dfn{glyph
4866 table}. A simple glyph is just a way of specifying a character and a
4867 face to output it in. The glyph code for a simple glyph, mod 524288,
4868 is the character to output, and the glyph code divided by 524288
4869 specifies the face number (@pxref{Face Functions}) to use while
4870 outputting it. (524288 is
4879 On character terminals, you can set up a @dfn{glyph table} to define
4880 the meaning of glyph codes. The glyph codes is the value of the
4881 variable @code{glyph-table}.
4884 The value of this variable is the current glyph table. It should be a
4885 vector; the @var{g}th element defines glyph code @var{g}.
4887 If a glyph code is greater than or equal to the length of the glyph
4888 table, that code is automatically simple. If the value of
4889 @code{glyph-table} is @code{nil} instead of a vector, then all glyphs
4890 are simple. The glyph table is not used on graphical displays, only
4891 on character terminals. On graphical displays, all glyphs are simple.
4894 Here are the possible types of elements in the glyph table:
4898 Send the characters in @var{string} to the terminal to output
4899 this glyph. This alternative is available on character terminals,
4900 but not under a window system.
4903 Define this glyph code as an alias for glyph code @var{integer}. You
4904 can use an alias to specify a face code for the glyph and use a small
4908 This glyph is simple.
4911 @defun create-glyph string
4912 @tindex create-glyph
4913 This function returns a newly-allocated glyph code which is set up to
4914 display by sending @var{string} to the terminal.
4922 This section describes how to make Emacs ring the bell (or blink the
4923 screen) to attract the user's attention. Be conservative about how
4924 often you do this; frequent bells can become irritating. Also be
4925 careful not to use just beeping when signaling an error is more
4926 appropriate. (@xref{Errors}.)
4928 @defun ding &optional do-not-terminate
4929 @cindex keyboard macro termination
4930 This function beeps, or flashes the screen (see @code{visible-bell} below).
4931 It also terminates any keyboard macro currently executing unless
4932 @var{do-not-terminate} is non-@code{nil}.
4935 @defun beep &optional do-not-terminate
4936 This is a synonym for @code{ding}.
4939 @defopt visible-bell
4940 This variable determines whether Emacs should flash the screen to
4941 represent a bell. Non-@code{nil} means yes, @code{nil} means no. This
4942 is effective on a window system, and on a character-only terminal
4943 provided the terminal's Termcap entry defines the visible bell
4944 capability (@samp{vb}).
4947 @defvar ring-bell-function
4948 If this is non-@code{nil}, it specifies how Emacs should ``ring the
4949 bell.'' Its value should be a function of no arguments. If this is
4950 non-@code{nil}, it takes precedence over the @code{visible-bell}
4954 @node Window Systems
4955 @section Window Systems
4957 Emacs works with several window systems, most notably the X Window
4958 System. Both Emacs and X use the term ``window'', but use it
4959 differently. An Emacs frame is a single window as far as X is
4960 concerned; the individual Emacs windows are not known to X at all.
4962 @defvar window-system
4963 This variable tells Lisp programs what window system Emacs is running
4964 under. The possible values are
4968 @cindex X Window System
4969 Emacs is displaying using X.
4971 Emacs is displaying using MS-DOS.
4973 Emacs is displaying using Windows.
4975 Emacs is displaying using a Macintosh.
4977 Emacs is using a character-based terminal.
4981 @defvar window-setup-hook
4982 This variable is a normal hook which Emacs runs after handling the
4983 initialization files. Emacs runs this hook after it has completed
4984 loading your init file, the default initialization file (if
4985 any), and the terminal-specific Lisp code, and running the hook
4986 @code{term-setup-hook}.
4988 This hook is used for internal purposes: setting up communication with
4989 the window system, and creating the initial window. Users should not
4994 arch-tag: ffdf5714-7ecf-415b-9023-fbc6b409c2c6