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[emacs.git] / lispref / frames.texi

@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001,
@c   2002, 2003, 2004, 2005, 2006, 2007, 2008  Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/frames
@node Frames, Positions, Windows, Top
@chapter Frames
@cindex frame

  In Emacs editing, A @dfn{frame} is a screen object that contains one
or more Emacs windows.  It's the kind of object that is called a
``window'' in the terminology of graphical environments; but we can't
call it a ``window'' here, because Emacs uses that word in a different
way.

  A frame initially contains a single main window and/or a minibuffer
window; you can subdivide the main window vertically or horizontally
into smaller windows.  In Emacs Lisp, a @dfn{frame object} is a Lisp
object that represents a frame on the screen.

@cindex terminal frame
  When Emacs runs on a text-only terminal, it starts with one
@dfn{terminal frame}.  If you create additional ones, Emacs displays
one and only one at any given time---on the terminal screen, of course.

@cindex window frame
  When Emacs communicates directly with a supported window system, such
as X, it does not have a terminal frame; instead, it starts with
a single @dfn{window frame}, but you can create more, and Emacs can
display several such frames at once as is usual for window systems.

@defun framep object
This predicate returns a non-@code{nil} value if @var{object} is a
frame, and @code{nil} otherwise.  For a frame, the value indicates which
kind of display the frame uses:

@table @code
@item x
The frame is displayed in an X window.
@item t
A terminal frame on a character display.
@item mac
The frame is displayed on a Macintosh.
@item w32
The frame is displayed on MS-Windows 9X/NT.
@item pc
The frame is displayed on an MS-DOS terminal.
@end table
@end defun

@menu
* Creating Frames::             Creating additional frames.
* Multiple Displays::           Creating frames on other displays.
* Frame Parameters::            Controlling frame size, position, font, etc.
* Frame Titles::                Automatic updating of frame titles.
* Deleting Frames::             Frames last until explicitly deleted.
* Finding All Frames::          How to examine all existing frames.
* Frames and Windows::          A frame contains windows;
                                  display of text always works through windows.
* Minibuffers and Frames::      How a frame finds the minibuffer to use.
* Input Focus::                 Specifying the selected frame.
* Visibility of Frames::        Frames may be visible or invisible, or icons.
* Raising and Lowering::        Raising a frame makes it hide other windows;
                                  lowering it makes the others hide it.
* Frame Configurations::        Saving the state of all frames.
* Mouse Tracking::              Getting events that say when the mouse moves.
* Mouse Position::              Asking where the mouse is, or moving it.
* Pop-Up Menus::                Displaying a menu for the user to select from.
* Dialog Boxes::                Displaying a box to ask yes or no.
* Pointer Shape::               Specifying the shape of the mouse pointer.
* Window System Selections::    Transferring text to and from other X clients.
* Drag and Drop::               Internals of Drag-and-Drop implementation.
* Color Names::                 Getting the definitions of color names.
* Text Terminal Colors::        Defining colors for text-only terminals.
* Resources::                   Getting resource values from the server.
* Display Feature Testing::     Determining the features of a terminal.
@end menu

  @xref{Display}, for information about the related topic of
controlling Emacs redisplay.

@node Creating Frames
@section Creating Frames

To create a new frame, call the function @code{make-frame}.

@defun make-frame &optional alist
This function creates and returns a new frame, displaying the current
buffer.  If you are using a supported window system, it makes a window
frame; otherwise, it makes a terminal frame.

The argument is an alist specifying frame parameters.  Any parameters
not mentioned in @var{alist} default according to the value of the
variable @code{default-frame-alist}; parameters not specified even there
default from the standard X resources or whatever is used instead on
your system.

The set of possible parameters depends in principle on what kind of
window system Emacs uses to display its frames.  @xref{Window Frame
Parameters}, for documentation of individual parameters you can specify.

This function itself does not make the new frame the selected frame.
@xref{Input Focus}.  The previously selected frame remains selected.
However, the window system may select the new frame for its own reasons,
for instance if the frame appears under the mouse pointer and your
setup is for focus to follow the pointer.
@end defun

@defvar before-make-frame-hook
A normal hook run by @code{make-frame} before it actually creates the
frame.
@end defvar

@defvar after-make-frame-functions
An abnormal hook run by @code{make-frame} after it creates the frame.
Each function in @code{after-make-frame-functions} receives one argument, the
frame just created.
@end defvar

@node Multiple Displays
@section Multiple Displays
@cindex multiple X displays
@cindex displays, multiple

  A single Emacs can talk to more than one X display.
Initially, Emacs uses just one display---the one chosen with the
@code{DISPLAY} environment variable or with the @samp{--display} option
(@pxref{Initial Options,,, emacs, The GNU Emacs Manual}).  To connect to
another display, use the command @code{make-frame-on-display} or specify
the @code{display} frame parameter when you create the frame.

  Emacs treats each X server as a separate terminal, giving each one its
own selected frame and its own minibuffer windows.  However, only one of
those frames is ``@emph{the} selected frame'' at any given moment, see
@ref{Input Focus}.

  A few Lisp variables are @dfn{terminal-local}; that is, they have a
separate binding for each terminal.  The binding in effect at any time
is the one for the terminal that the currently selected frame belongs
to.  These variables include @code{default-minibuffer-frame},
@code{defining-kbd-macro}, @code{last-kbd-macro}, and
@code{system-key-alist}.  They are always terminal-local, and can never
be buffer-local (@pxref{Buffer-Local Variables}).

  A single X server can handle more than one screen.  A display name
@samp{@var{host}:@var{server}.@var{screen}} has three parts; the last
part specifies the screen number for a given server.  When you use two
screens belonging to one server, Emacs knows by the similarity in their
names that they share a single keyboard, and it treats them as a single
terminal.

  Note that some graphical terminals can output to more than a one
monitor (or other output device) at the same time.  On these
``multi-monitor'' setups, a single @var{display} value controls the
output to all the physical monitors.  In this situation, there is
currently no platform-independent way for Emacs to distinguish between
the different physical monitors.

@deffn Command make-frame-on-display display &optional parameters
This creates and returns a new frame on display @var{display}, taking
the other frame parameters from @var{parameters}.  Aside from the
@var{display} argument, it is like @code{make-frame} (@pxref{Creating
Frames}).
@end deffn

@defun x-display-list
This returns a list that indicates which X displays Emacs has a
connection to.  The elements of the list are strings, and each one is
a display name.
@end defun

@defun x-open-connection display &optional xrm-string must-succeed
This function opens a connection to the X display @var{display}.  It
does not create a frame on that display, but it permits you to check
that communication can be established with that display.

The optional argument @var{xrm-string}, if not @code{nil}, is a
string of resource names and values, in the same format used in the
@file{.Xresources} file.  The values you specify override the resource
values recorded in the X server itself; they apply to all Emacs frames
created on this display.  Here's an example of what this string might
look like:

@example
"*BorderWidth: 3\n*InternalBorder: 2\n"
@end example

@xref{X Resources,, X Resources, emacs, The GNU Emacs Manual}.

If @var{must-succeed} is non-@code{nil}, failure to open the connection
terminates Emacs.  Otherwise, it is an ordinary Lisp error.
@end defun

@defun x-close-connection display
This function closes the connection to display @var{display}.  Before
you can do this, you must first delete all the frames that were open on
that display (@pxref{Deleting Frames}).
@end defun

@node Frame Parameters
@section Frame Parameters
@cindex frame parameters

  A frame has many parameters that control its appearance and behavior.
Just what parameters a frame has depends on what display mechanism it
uses.

  Frame parameters exist mostly for the sake of window systems.  A
terminal frame has a few parameters, mostly for compatibility's sake;
only the @code{height}, @code{width}, @code{name}, @code{title},
@code{menu-bar-lines}, @code{buffer-list} and @code{buffer-predicate}
parameters do something special.  If the terminal supports colors, the
parameters @code{foreground-color}, @code{background-color},
@code{background-mode} and @code{display-type} are also meaningful.

@menu
* Parameter Access::       How to change a frame's parameters.
* Initial Parameters::     Specifying frame parameters when you make a frame.
* Window Frame Parameters:: List of frame parameters for window systems.
* Size and Position::      Changing the size and position of a frame.
* Geometry::               Parsing geometry specifications.
@end menu

@node Parameter Access
@subsection Access to Frame Parameters

These functions let you read and change the parameter values of a
frame.

@defun frame-parameter frame parameter
This function returns the value of the parameter @var{parameter} (a
symbol) of @var{frame}.  If @var{frame} is @code{nil}, it returns the
selected frame's parameter.  If @var{frame} has no setting for
@var{parameter}, this function returns @code{nil}.
@end defun

@defun frame-parameters &optional frame
The function @code{frame-parameters} returns an alist listing all the
parameters of @var{frame} and their values.  If @var{frame} is
@code{nil} or omitted, this returns the selected frame's parameters
@end defun

@defun modify-frame-parameters frame alist
This function alters the parameters of frame @var{frame} based on the
elements of @var{alist}.  Each element of @var{alist} has the form
@code{(@var{parm} . @var{value})}, where @var{parm} is a symbol naming a
parameter.  If you don't mention a parameter in @var{alist}, its value
doesn't change.  If @var{frame} is @code{nil}, it defaults to the selected
frame.
@end defun

@defun modify-all-frames-parameters alist
This function alters the frame parameters of all existing frames
according to @var{alist}, then modifies @code{default-frame-alist}
(and, if necessary, @code{initial-frame-alist}) to apply the same
parameter values to frames that will be created henceforth.
@end defun

@node Initial Parameters
@subsection Initial Frame Parameters

You can specify the parameters for the initial startup frame
by setting @code{initial-frame-alist} in your init file (@pxref{Init File}).

@defvar initial-frame-alist
This variable's value is an alist of parameter values used when creating
the initial window frame.  You can set this variable to specify the
appearance of the initial frame without altering subsequent frames.
Each element has the form:

@example
(@var{parameter} . @var{value})
@end example

Emacs creates the initial frame before it reads your init
file.  After reading that file, Emacs checks @code{initial-frame-alist},
and applies the parameter settings in the altered value to the already
created initial frame.

If these settings affect the frame geometry and appearance, you'll see
the frame appear with the wrong ones and then change to the specified
ones.  If that bothers you, you can specify the same geometry and
appearance with X resources; those do take effect before the frame is
created.  @xref{X Resources,, X Resources, emacs, The GNU Emacs Manual}.

X resource settings typically apply to all frames.  If you want to
specify some X resources solely for the sake of the initial frame, and
you don't want them to apply to subsequent frames, here's how to achieve
this.  Specify parameters in @code{default-frame-alist} to override the
X resources for subsequent frames; then, to prevent these from affecting
the initial frame, specify the same parameters in
@code{initial-frame-alist} with values that match the X resources.
@end defvar

If these parameters specify a separate minibuffer-only frame with
@code{(minibuffer . nil)}, and you have not created one, Emacs creates
one for you.

@defvar minibuffer-frame-alist
This variable's value is an alist of parameter values used when creating
an initial minibuffer-only frame---if such a frame is needed, according
to the parameters for the main initial frame.
@end defvar

@defvar default-frame-alist
This is an alist specifying default values of frame parameters for all
Emacs frames---the first frame, and subsequent frames.  When using the X
Window System, you can get the same results by means of X resources
in many cases.

Setting this variable does not affect existing frames.
@end defvar

See also @code{special-display-frame-alist}.  @xref{Definition of
special-display-frame-alist}.

If you use options that specify window appearance when you invoke Emacs,
they take effect by adding elements to @code{default-frame-alist}.  One
exception is @samp{-geometry}, which adds the specified position to
@code{initial-frame-alist} instead.  @xref{Emacs Invocation,, Command
Line Arguments for Emacs Invocation, emacs, The GNU Emacs Manual}.

@node Window Frame Parameters
@subsection Window Frame Parameters

  Just what parameters a frame has depends on what display mechanism
it uses.  This section describes the parameters that have special
meanings on some or all kinds of terminals.  Of these, @code{name},
@code{title}, @code{height}, @code{width}, @code{buffer-list} and
@code{buffer-predicate} provide meaningful information in terminal
frames, and @code{tty-color-mode} is meaningful @emph{only} in
terminal frames.

@menu
* Basic Parameters::            Parameters that are fundamental.
* Position Parameters::         The position of the frame on the screen.
* Size Parameters::             Frame's size.
* Layout Parameters::           Size of parts of the frame, and
                                  enabling or disabling some parts.
* Buffer Parameters::           Which buffers have been or should be shown.
* Management Parameters::       Communicating with the window manager.
* Cursor Parameters::           Controlling the cursor appearance.
* Color Parameters::            Colors of various parts of the frame.
@end menu

@node Basic Parameters
@subsubsection Basic Parameters

  These frame parameters give the most basic information about the
frame.  @code{title} and @code{name} are meaningful on all terminals.

@table @code
@item display
The display on which to open this frame.  It should be a string of the
form @code{"@var{host}:@var{dpy}.@var{screen}"}, just like the
@code{DISPLAY} environment variable.

@item display-type
This parameter describes the range of possible colors that can be used
in this frame.  Its value is @code{color}, @code{grayscale} or
@code{mono}.

@item title
If a frame has a non-@code{nil} title, it appears in the window
system's title bar at the top of the frame, and also in the mode line
of windows in that frame if @code{mode-line-frame-identification} uses
@samp{%F} (@pxref{%-Constructs}).  This is normally the case when
Emacs is not using a window system, and can only display one frame at
a time.  @xref{Frame Titles}.

@item name
The name of the frame.  The frame name serves as a default for the frame
title, if the @code{title} parameter is unspecified or @code{nil}.  If
you don't specify a name, Emacs sets the frame name automatically
(@pxref{Frame Titles}).

If you specify the frame name explicitly when you create the frame, the
name is also used (instead of the name of the Emacs executable) when
looking up X resources for the frame.
@end table

@node Position Parameters
@subsubsection Position Parameters

  Position parameters' values are normally measured in pixels, but on
text-only terminals they count characters or lines instead.

@table @code
@item left
The screen position of the left edge, in pixels, with respect to the
left edge of the screen.  The value may be a positive number @var{pos},
or a list of the form @code{(+ @var{pos})} which permits specifying a
negative @var{pos} value.

A negative number @minus{}@var{pos}, or a list of the form @code{(-
@var{pos})}, actually specifies the position of the right edge of the
window with respect to the right edge of the screen.  A positive value
of @var{pos} counts toward the left.  @strong{Reminder:} if the
parameter is a negative integer @minus{}@var{pos}, then @var{pos} is
positive.

Some window managers ignore program-specified positions.  If you want to
be sure the position you specify is not ignored, specify a
non-@code{nil} value for the @code{user-position} parameter as well.

@item top
The screen position of the top edge, in pixels, with respect to the
top edge of the screen.  It works just like @code{left}, except vertically
instead of horizontally.

@item icon-left
The screen position of the left edge @emph{of the frame's icon}, in
pixels, counting from the left edge of the screen.  This takes effect if
and when the frame is iconified.

If you specify a value for this parameter, then you must also specify
a value for @code{icon-top} and vice versa.  The window manager may
ignore these two parameters.

@item icon-top
The screen position of the top edge @emph{of the frame's icon}, in
pixels, counting from the top edge of the screen.  This takes effect if
and when the frame is iconified.

@item user-position
When you create a frame and specify its screen position with the
@code{left} and @code{top} parameters, use this parameter to say whether
the specified position was user-specified (explicitly requested in some
way by a human user) or merely program-specified (chosen by a program).
A non-@code{nil} value says the position was user-specified.

Window managers generally heed user-specified positions, and some heed
program-specified positions too.  But many ignore program-specified
positions, placing the window in a default fashion or letting the user
place it with the mouse.  Some window managers, including @code{twm},
let the user specify whether to obey program-specified positions or
ignore them.

When you call @code{make-frame}, you should specify a non-@code{nil}
value for this parameter if the values of the @code{left} and @code{top}
parameters represent the user's stated preference; otherwise, use
@code{nil}.
@end table

@node Size Parameters
@subsubsection Size Parameters

  Size parameters' values are normally measured in pixels, but on
text-only terminals they count characters or lines instead.

@table @code
@item height
The height of the frame contents, in characters.  (To get the height in
pixels, call @code{frame-pixel-height}; see @ref{Size and Position}.)

@item width
The width of the frame contents, in characters.  (To get the width in
pixels, call @code{frame-pixel-width}; see @ref{Size and Position}.)

@item user-size
This does for the size parameters @code{height} and @code{width} what
the @code{user-position} parameter (see above) does for the position
parameters @code{top} and @code{left}.

@item fullscreen
Specify that width, height or both shall be set to the size of the screen.
The value @code{fullwidth} specifies that width shall be the size of the
screen.  The value @code{fullheight} specifies that height shall be the
size of the screen.  The value @code{fullboth} specifies that both the
width and the height shall be set to the size of the screen.
@end table

@node Layout Parameters
@subsubsection Layout Parameters

  These frame parameters enable or disable various parts of the
frame, or control their sizes.

@table @code
@item border-width
The width in pixels of the frame's border.

@item internal-border-width
The distance in pixels between text (or fringe) and the frame's border.

@item vertical-scroll-bars
Whether the frame has scroll bars for vertical scrolling, and which side
of the frame they should be on.  The possible values are @code{left},
@code{right}, and @code{nil} for no scroll bars.

@ignore
@item horizontal-scroll-bars
Whether the frame has scroll bars for horizontal scrolling
(non-@code{nil} means yes).  Horizontal scroll bars are not currently
implemented.
@end ignore

@item scroll-bar-width
The width of vertical scroll bars, in pixels, or @code{nil} meaning to
use the default width.

@item left-fringe
@itemx right-fringe
The default width of the left and right fringes of windows in this
frame (@pxref{Fringes}).  If either of these is zero, that effectively
removes the corresponding fringe.  A value of @code{nil} stands for
the standard fringe width, which is the width needed to display the
fringe bitmaps.

The combined fringe widths must add up to an integral number of
columns, so the actual default fringe widths for the frame may be
larger than the specified values.  The extra width needed to reach an
acceptable total is distributed evenly between the left and right
fringe.  However, you can force one fringe or the other to a precise
width by specifying that width as a negative integer.  If both widths are
negative, only the left fringe gets the specified width.

@item menu-bar-lines
The number of lines to allocate at the top of the frame for a menu
bar.  The default is 1.  A value of @code{nil} means don't display a
menu bar.  @xref{Menu Bar}.  (The X toolkit and GTK allow at most one
menu bar line; they treat larger values as 1.)

@item tool-bar-lines
The number of lines to use for the tool bar.  A value of @code{nil}
means don't display a tool bar.  (GTK allows at most one tool bar line;
it treats larger values as 1.)

@item line-spacing
Additional space to leave below each text line, in pixels (a positive
integer).  @xref{Line Height}, for more information.
@end table

@node Buffer Parameters
@subsubsection Buffer Parameters

  These frame parameters, meaningful on all kinds of terminals, deal
with which buffers have been, or should, be displayed in the frame.

@table @code
@item minibuffer
Whether this frame has its own minibuffer.  The value @code{t} means
yes, @code{nil} means no, @code{only} means this frame is just a
minibuffer.  If the value is a minibuffer window (in some other frame),
the new frame uses that minibuffer.

@item buffer-predicate
The buffer-predicate function for this frame.  The function
@code{other-buffer} uses this predicate (from the selected frame) to
decide which buffers it should consider, if the predicate is not
@code{nil}.  It calls the predicate with one argument, a buffer, once for
each buffer; if the predicate returns a non-@code{nil} value, it
considers that buffer.

@item buffer-list
A list of buffers that have been selected in this frame,
ordered most-recently-selected first.

@item unsplittable
If non-@code{nil}, this frame's window is never split automatically.
@end table

@node Management Parameters
@subsubsection Window Management Parameters
@cindex window manager, and frame parameters

  These frame parameters, meaningful only on window system displays,
interact with the window manager.

@table @code
@item visibility
The state of visibility of the frame.  There are three possibilities:
@code{nil} for invisible, @code{t} for visible, and @code{icon} for
iconified.  @xref{Visibility of Frames}.

@item auto-raise
Whether selecting the frame raises it (non-@code{nil} means yes).

@item auto-lower
Whether deselecting the frame lowers it (non-@code{nil} means yes).

@item icon-type
The type of icon to use for this frame when it is iconified.  If the
value is a string, that specifies a file containing a bitmap to use.
Any other non-@code{nil} value specifies the default bitmap icon (a
picture of a gnu); @code{nil} specifies a text icon.

@item icon-name
The name to use in the icon for this frame, when and if the icon
appears.  If this is @code{nil}, the frame's title is used.

@item window-id
The number of the window-system window used by the frame
to contain the actual Emacs windows.

@item outer-window-id
The number of the outermost window-system window used for the whole frame.

@item wait-for-wm
If non-@code{nil}, tell Xt to wait for the window manager to confirm
geometry changes.  Some window managers, including versions of Fvwm2
and KDE, fail to confirm, so Xt hangs.  Set this to @code{nil} to
prevent hanging with those window managers.

@ignore
@item parent-id
@c ??? Not yet working.
The X window number of the window that should be the parent of this one.
Specifying this lets you create an Emacs window inside some other
application's window.  (It is not certain this will be implemented; try
it and see if it works.)
@end ignore
@end table

@node Cursor Parameters
@subsubsection Cursor Parameters

  This frame parameter controls the way the cursor looks.

@table @code
@item cursor-type
How to display the cursor.  Legitimate values are:

@table @code
@item box
Display a filled box.  (This is the default.)
@item hollow
Display a hollow box.
@item nil
Don't display a cursor.
@item bar
Display a vertical bar between characters.
@item (bar . @var{width})
Display a vertical bar @var{width} pixels wide between characters.
@item hbar
Display a horizontal bar.
@item (hbar . @var{height})
Display a horizontal bar @var{height} pixels high.
@end table
@end table

@vindex cursor-type
The buffer-local variable @code{cursor-type} overrides the value of
the @code{cursor-type} frame parameter, but if it is @code{t}, that
means to use the cursor specified for the frame.

@defvar blink-cursor-alist
This variable specifies how to blink the cursor.  Each element has the
form @code{(@var{on-state} . @var{off-state})}.  Whenever the cursor
type equals @var{on-state} (comparing using @code{equal}), the
corresponding @var{off-state} specifies what the cursor looks like
when it blinks ``off.''  Both @var{on-state} and @var{off-state}
should be suitable values for the @code{cursor-type} frame parameter.

There are various defaults for how to blink each type of cursor, if
the type is not mentioned as an @var{on-state} here.  Changes in this
variable do not take effect immediately, only when you specify the
@code{cursor-type} frame parameter.
@end defvar

@defvar cursor-in-non-selected-windows
This variable controls how the cursor looks in a window that is not
selected.  It supports the same values as the @code{cursor-type} frame
parameter; also, @code{nil} means don't display a cursor in
nonselected windows, and @code{t} (the default) means use a standard
modificatoin of the usual cursor type (solid box becomes hollow box,
and bar becomes a narrower bar).
@end defvar

@node Color Parameters
@subsubsection Color Parameters

  These frame parameters control the use of colors.

@table @code
@item background-mode
This parameter is either @code{dark} or @code{light}, according
to whether the background color is a light one or a dark one.

@item tty-color-mode
@cindex standard colors for character terminals
This parameter overrides the terminal's color support as given by the
system's terminal capabilities database in that this parameter's value
specifies the color mode to use in terminal frames.  The value can be
either a symbol or a number.  A number specifies the number of colors
to use (and, indirectly, what commands to issue to produce each
color).  For example, @code{(tty-color-mode . 8)} specifies use of the
ANSI escape sequences for 8 standard text colors.  A value of -1 turns
off color support.

If the parameter's value is a symbol, it specifies a number through
the value of @code{tty-color-mode-alist}, and the associated number is
used instead.

@item screen-gamma
@cindex gamma correction
If this is a number, Emacs performs ``gamma correction'' which adjusts
the brightness of all colors.  The value should be the screen gamma of
your display, a floating point number.

Usual PC monitors have a screen gamma of 2.2, so color values in
Emacs, and in X windows generally, are calibrated to display properly
on a monitor with that gamma value.  If you specify 2.2 for
@code{screen-gamma}, that means no correction is needed.  Other values
request correction, designed to make the corrected colors appear on
your screen the way they would have appeared without correction on an
ordinary monitor with a gamma value of 2.2.

If your monitor displays colors too light, you should specify a
@code{screen-gamma} value smaller than 2.2.  This requests correction
that makes colors darker.  A screen gamma value of 1.5 may give good
results for LCD color displays.
@end table

These frame parameters are semi-obsolete in that they are automatically
equivalent to particular face attributes of particular faces.
@xref{Standard Faces,,, emacs, The Emacs Manual}.

@table @code
@item font
The name of the font for displaying text in the frame.  This is a
string, either a valid font name for your system or the name of an Emacs
fontset (@pxref{Fontsets}).  It is equivalent to the @code{font}
attribute of the @code{default} face.

@item foreground-color
The color to use for the image of a character.  It is equivalent to
the @code{:foreground} attribute of the @code{default} face.

@item background-color
The color to use for the background of characters.  It is equivalent to
the @code{:background} attribute of the @code{default} face.

@item mouse-color
The color for the mouse pointer.  It is equivalent to the @code{:background}
attribute of the @code{mouse} face.

@item cursor-color
The color for the cursor that shows point.  It is equivalent to the
@code{:background} attribute of the @code{cursor} face.

@item border-color
The color for the border of the frame.  It is equivalent to the
@code{:background} attribute of the @code{border} face.

@item scroll-bar-foreground
If non-@code{nil}, the color for the foreground of scroll bars.  It is
equivalent to the @code{:foreground} attribute of the
@code{scroll-bar} face.

@item scroll-bar-background
If non-@code{nil}, the color for the background of scroll bars.  It is
equivalent to the @code{:background} attribute of the
@code{scroll-bar} face.
@end table

@node Size and Position
@subsection Frame Size And Position
@cindex size of frame
@cindex screen size
@cindex frame size
@cindex resize frame

  You can read or change the size and position of a frame using the
frame parameters @code{left}, @code{top}, @code{height}, and
@code{width}.  Whatever geometry parameters you don't specify are chosen
by the window manager in its usual fashion.

  Here are some special features for working with sizes and positions.
(For the precise meaning of ``selected frame'' used by these functions,
see @ref{Input Focus}.)

@defun set-frame-position frame left top
This function sets the position of the top left corner of @var{frame} to
@var{left} and @var{top}.  These arguments are measured in pixels, and
normally count from the top left corner of the screen.

Negative parameter values position the bottom edge of the window up from
the bottom edge of the screen, or the right window edge to the left of
the right edge of the screen.  It would probably be better if the values
were always counted from the left and top, so that negative arguments
would position the frame partly off the top or left edge of the screen,
but it seems inadvisable to change that now.
@end defun

@defun frame-height &optional frame
@defunx frame-width &optional frame
These functions return the height and width of @var{frame}, measured in
lines and columns.  If you don't supply @var{frame}, they use the
selected frame.
@end defun

@defun screen-height
@defunx screen-width
These functions are old aliases for @code{frame-height} and
@code{frame-width}.  When you are using a non-window terminal, the size
of the frame is normally the same as the size of the terminal screen.
@end defun

@defun frame-pixel-height &optional frame
@defunx frame-pixel-width &optional frame
These functions return the height and width of the main display area
of @var{frame}, measured in pixels.  If you don't supply @var{frame},
they use the selected frame.

These values include the internal borders, and windows' scroll bars
and fringes (which belong to individual windows, not to the frame
itself), but do not include menu bars or tool bars (except when using
X without an X toolkit).
@end defun

@defun frame-char-height &optional frame
@defunx frame-char-width &optional frame
These functions return the height and width of a character in
@var{frame}, measured in pixels.  The values depend on the choice of
font.  If you don't supply @var{frame}, these functions use the selected
frame.
@end defun

@defun set-frame-size frame cols rows
This function sets the size of @var{frame}, measured in characters;
@var{cols} and @var{rows} specify the new width and height.

To set the size based on values measured in pixels, use
@code{frame-char-height} and @code{frame-char-width} to convert
them to units of characters.
@end defun

@defun set-frame-height frame lines &optional pretend
This function resizes @var{frame} to a height of @var{lines} lines.  The
sizes of existing windows in @var{frame} are altered proportionally to
fit.

If @var{pretend} is non-@code{nil}, then Emacs displays @var{lines}
lines of output in @var{frame}, but does not change its value for the
actual height of the frame.  This is only useful for a terminal frame.
Using a smaller height than the terminal actually implements may be
useful to reproduce behavior observed on a smaller screen, or if the
terminal malfunctions when using its whole screen.  Setting the frame
height ``for real'' does not always work, because knowing the correct
actual size may be necessary for correct cursor positioning on a
terminal frame.
@end defun

@defun set-frame-width frame width &optional pretend
This function sets the width of @var{frame}, measured in characters.
The argument @var{pretend} has the same meaning as in
@code{set-frame-height}.
@end defun

@findex set-screen-height
@findex set-screen-width
  The older functions @code{set-screen-height} and
@code{set-screen-width} were used to specify the height and width of the
screen, in Emacs versions that did not support multiple frames.  They
are semi-obsolete, but still work; they apply to the selected frame.

@node Geometry
@subsection Geometry

  Here's how to examine the data in an X-style window geometry
specification:

@defun x-parse-geometry geom
@cindex geometry specification
The function @code{x-parse-geometry} converts a standard X window
geometry string to an alist that you can use as part of the argument to
@code{make-frame}.

The alist describes which parameters were specified in @var{geom}, and
gives the values specified for them.  Each element looks like
@code{(@var{parameter} . @var{value})}.  The possible @var{parameter}
values are @code{left}, @code{top}, @code{width}, and @code{height}.

For the size parameters, the value must be an integer.  The position
parameter names @code{left} and @code{top} are not totally accurate,
because some values indicate the position of the right or bottom edges
instead.  These are the @var{value} possibilities for the position
parameters:

@table @asis
@item an integer
A positive integer relates the left edge or top edge of the window to
the left or top edge of the screen.  A negative integer relates the
right or bottom edge of the window to the right or bottom edge of the
screen.

@item @code{(+ @var{position})}
This specifies the position of the left or top edge of the window
relative to the left or top edge of the screen.  The integer
@var{position} may be positive or negative; a negative value specifies a
position outside the screen.

@item @code{(- @var{position})}
This specifies the position of the right or bottom edge of the window
relative to the right or bottom edge of the screen.  The integer
@var{position} may be positive or negative; a negative value specifies a
position outside the screen.
@end table

Here is an example:

@example
(x-parse-geometry "35x70+0-0")
     @result{} ((height . 70) (width . 35)
         (top - 0) (left . 0))
@end example
@end defun

@node Frame Titles
@section Frame Titles
@cindex frame title

  Every frame has a @code{name} parameter; this serves as the default
for the frame title which window systems typically display at the top of
the frame.  You can specify a name explicitly by setting the @code{name}
frame property.

  Normally you don't specify the name explicitly, and Emacs computes the
frame name automatically based on a template stored in the variable
@code{frame-title-format}.  Emacs recomputes the name each time the
frame is redisplayed.

@defvar frame-title-format
This variable specifies how to compute a name for a frame when you have
not explicitly specified one.  The variable's value is actually a mode
line construct, just like @code{mode-line-format}, except that the
@samp{%c} and @samp{%l} constructs are ignored.  @xref{Mode Line
Data}.
@end defvar

@defvar icon-title-format
This variable specifies how to compute the name for an iconified frame,
when you have not explicitly specified the frame title.  This title
appears in the icon itself.
@end defvar

@defvar multiple-frames
This variable is set automatically by Emacs.  Its value is @code{t} when
there are two or more frames (not counting minibuffer-only frames or
invisible frames).  The default value of @code{frame-title-format} uses
@code{multiple-frames} so as to put the buffer name in the frame title
only when there is more than one frame.

The value of this variable is not guaranteed to be accurate except
while processing @code{frame-title-format} or
@code{icon-title-format}.
@end defvar

@node Deleting Frames
@section Deleting Frames
@cindex deleting frames

Frames remain potentially visible until you explicitly @dfn{delete}
them.  A deleted frame cannot appear on the screen, but continues to
exist as a Lisp object until there are no references to it.

@deffn Command delete-frame &optional frame force
@vindex delete-frame-functions
This function deletes the frame @var{frame}.  Unless @var{frame} is a
tooltip, it first runs the hook @code{delete-frame-functions} (each
function gets one argument, @var{frame}).  By default, @var{frame} is
the selected frame.

A frame cannot be deleted if its minibuffer is used by other frames.
Normally, you cannot delete a frame if all other frames are invisible,
but if the @var{force} is non-@code{nil}, then you are allowed to do so.
@end deffn

@defun frame-live-p frame
The function @code{frame-live-p} returns non-@code{nil} if the frame
@var{frame} has not been deleted.  The possible non-@code{nil} return
values are like those of @code{framep}.  @xref{Frames}.
@end defun

  Some window managers provide a command to delete a window.  These work
by sending a special message to the program that operates the window.
When Emacs gets one of these commands, it generates a
@code{delete-frame} event, whose normal definition is a command that
calls the function @code{delete-frame}.  @xref{Misc Events}.

@node Finding All Frames
@section Finding All Frames
@cindex frames, scanning all

@defun frame-list
The function @code{frame-list} returns a list of all the frames that
have not been deleted.  It is analogous to @code{buffer-list} for
buffers, and includes frames on all terminals.  The list that you get is
newly created, so modifying the list doesn't have any effect on the
internals of Emacs.
@end defun

@defun visible-frame-list
This function returns a list of just the currently visible frames.
@xref{Visibility of Frames}.  (Terminal frames always count as
``visible,'' even though only the selected one is actually displayed.)
@end defun

@defun next-frame &optional frame minibuf
The function @code{next-frame} lets you cycle conveniently through all
the frames on the current display from an arbitrary starting point.  It
returns the ``next'' frame after @var{frame} in the cycle.  If
@var{frame} is omitted or @code{nil}, it defaults to the selected frame
(@pxref{Input Focus}).

The second argument, @var{minibuf}, says which frames to consider:

@table @asis
@item @code{nil}
Exclude minibuffer-only frames.
@item @code{visible}
Consider all visible frames.
@item 0
Consider all visible or iconified frames.
@item a window
Consider only the frames using that particular window as their
minibuffer.
@item anything else
Consider all frames.
@end table
@end defun

@defun previous-frame &optional frame minibuf
Like @code{next-frame}, but cycles through all frames in the opposite
direction.
@end defun

  See also @code{next-window} and @code{previous-window}, in @ref{Cyclic
Window Ordering}.

@node Frames and Windows
@section Frames and Windows

  Each window is part of one and only one frame; you can get the frame
with @code{window-frame}.

@defun window-frame window
This function returns the frame that @var{window} is on.
@end defun

  All the non-minibuffer windows in a frame are arranged in a cyclic
order.  The order runs from the frame's top window, which is at the
upper left corner, down and to the right, until it reaches the window at
the lower right corner (always the minibuffer window, if the frame has
one), and then it moves back to the top.  @xref{Cyclic Window Ordering}.

@defun frame-first-window &optional frame
This returns the topmost, leftmost window of frame @var{frame}.
If omitted or @code{nil}, @var{frame} defaults to the selected frame.
@end defun

At any time, exactly one window on any frame is @dfn{selected within the
frame}.  The significance of this designation is that selecting the
frame also selects this window.  You can get the frame's current
selected window with @code{frame-selected-window}.

@defun frame-selected-window  &optional frame
This function returns the window on @var{frame} that is selected
within @var{frame}.  If omitted or @code{nil}, @var{frame} defaults to
the selected frame.
@end defun

@defun set-frame-selected-window frame window
This sets the selected window of frame @var{frame} to @var{window}.
If @var{frame} is @code{nil}, it operates on the selected frame.  If
@var{frame} is the selected frame, this makes @var{window} the
selected window.  This function returns @var{window}.
@end defun

  Conversely, selecting a window for Emacs with @code{select-window} also
makes that window selected within its frame.  @xref{Selecting Windows}.

  Another function that (usually) returns one of the windows in a given
frame is @code{minibuffer-window}.  @xref{Definition of minibuffer-window}.

@node Minibuffers and Frames
@section Minibuffers and Frames

Normally, each frame has its own minibuffer window at the bottom, which
is used whenever that frame is selected.  If the frame has a minibuffer,
you can get it with @code{minibuffer-window} (@pxref{Definition of
minibuffer-window}).

However, you can also create a frame with no minibuffer.  Such a frame
must use the minibuffer window of some other frame.  When you create the
frame, you can specify explicitly the minibuffer window to use (in some
other frame).  If you don't, then the minibuffer is found in the frame
which is the value of the variable @code{default-minibuffer-frame}.  Its
value should be a frame that does have a minibuffer.

If you use a minibuffer-only frame, you might want that frame to raise
when you enter the minibuffer.  If so, set the variable
@code{minibuffer-auto-raise} to @code{t}.  @xref{Raising and Lowering}.

@defvar default-minibuffer-frame
This variable specifies the frame to use for the minibuffer window, by
default.  It does not affect existing frames.  It is always local to
the current terminal and cannot be buffer-local.  @xref{Multiple
Displays}.
@end defvar

@node Input Focus
@section Input Focus
@cindex input focus
@c @cindex selected frame    Duplicates selected-frame

At any time, one frame in Emacs is the @dfn{selected frame}.  The selected
window always resides on the selected frame.

When Emacs displays its frames on several terminals (@pxref{Multiple
Displays}), each terminal has its own selected frame.  But only one of
these is ``@emph{the} selected frame'': it's the frame that belongs to
the terminal from which the most recent input came.  That is, when Emacs
runs a command that came from a certain terminal, the selected frame is
the one of that terminal.  Since Emacs runs only a single command at any
given time, it needs to consider only one selected frame at a time; this
frame is what we call @dfn{the selected frame} in this manual.  The
display on which the selected frame is displayed is the @dfn{selected
frame's display}.

@defun selected-frame
This function returns the selected frame.
@end defun

Some window systems and window managers direct keyboard input to the
window object that the mouse is in; others require explicit clicks or
commands to @dfn{shift the focus} to various window objects.  Either
way, Emacs automatically keeps track of which frame has the focus.  To
switch to a different frame from a Lisp function, call
@code{select-frame-set-input-focus}.

Lisp programs can also switch frames ``temporarily'' by calling the
function @code{select-frame}.  This does not alter the window system's
concept of focus; rather, it escapes from the window manager's control
until that control is somehow reasserted.

When using a text-only terminal, only one frame can be displayed at a
time on the terminal, so after a call to @code{select-frame}, the next
redisplay actually displays the newly selected frame.  This frame
remains selected until a subsequent call to @code{select-frame} or
@code{select-frame-set-input-focus}.  Each terminal frame has a number
which appears in the mode line before the buffer name (@pxref{Mode
Line Variables}).

@defun select-frame-set-input-focus frame
This function makes @var{frame} the selected frame, raises it (should
it happen to be obscured by other frames) and tries to give it the X
server's focus.  On a text-only terminal, the next redisplay displays
the new frame on the entire terminal screen.  The return value of this
function is not significant.
@end defun

@c ??? This is not yet implemented properly.
@defun select-frame frame
This function selects frame @var{frame}, temporarily disregarding the
focus of the X server if any.  The selection of @var{frame} lasts until
the next time the user does something to select a different frame, or
until the next time this function is called.  (If you are using a
window system, the previously selected frame may be restored as the
selected frame after return to the command loop, because it still may
have the window system's input focus.)  The specified @var{frame}
becomes the selected frame, as explained above, and the terminal that
@var{frame} is on becomes the selected terminal.  This function
returns @var{frame}, or @code{nil} if @var{frame} has been deleted.

In general, you should never use @code{select-frame} in a way that could
switch to a different terminal without switching back when you're done.
@end defun

Emacs cooperates with the window system by arranging to select frames as
the server and window manager request.  It does so by generating a
special kind of input event, called a @dfn{focus} event, when
appropriate.  The command loop handles a focus event by calling
@code{handle-switch-frame}.  @xref{Focus Events}.

@deffn Command handle-switch-frame frame
This function handles a focus event by selecting frame @var{frame}.

Focus events normally do their job by invoking this command.
Don't call it for any other reason.
@end deffn

@defun redirect-frame-focus frame &optional focus-frame
This function redirects focus from @var{frame} to @var{focus-frame}.
This means that @var{focus-frame} will receive subsequent keystrokes and
events intended for @var{frame}.  After such an event, the value of
@code{last-event-frame} will be @var{focus-frame}.  Also, switch-frame
events specifying @var{frame} will instead select @var{focus-frame}.

If @var{focus-frame} is omitted or @code{nil}, that cancels any existing
redirection for @var{frame}, which therefore once again receives its own
events.

One use of focus redirection is for frames that don't have minibuffers.
These frames use minibuffers on other frames.  Activating a minibuffer
on another frame redirects focus to that frame.  This puts the focus on
the minibuffer's frame, where it belongs, even though the mouse remains
in the frame that activated the minibuffer.

Selecting a frame can also change focus redirections.  Selecting frame
@code{bar}, when @code{foo} had been selected, changes any redirections
pointing to @code{foo} so that they point to @code{bar} instead.  This
allows focus redirection to work properly when the user switches from
one frame to another using @code{select-window}.

This means that a frame whose focus is redirected to itself is treated
differently from a frame whose focus is not redirected.
@code{select-frame} affects the former but not the latter.

The redirection lasts until @code{redirect-frame-focus} is called to
change it.
@end defun

@defopt focus-follows-mouse
This option is how you inform Emacs whether the window manager transfers
focus when the user moves the mouse.  Non-@code{nil} says that it does.
When this is so, the command @code{other-frame} moves the mouse to a
position consistent with the new selected frame.  (This option has no
effect on MS-Windows, where the mouse pointer is always automatically
moved by the OS to the selected frame.)
@end defopt

@node Visibility of Frames
@section Visibility of Frames
@cindex visible frame
@cindex invisible frame
@cindex iconified frame
@cindex frame visibility

A window frame may be @dfn{visible}, @dfn{invisible}, or
@dfn{iconified}.  If it is visible, you can see its contents, unless
other windows cover it.  If it is iconified, the frame's contents do
not appear on the screen, but an icon does.  If the frame is
invisible, it doesn't show on the screen, not even as an icon.

Visibility is meaningless for terminal frames, since only the selected
one is actually displayed in any case.

@deffn Command make-frame-visible &optional frame
This function makes frame @var{frame} visible.  If you omit
@var{frame}, it makes the selected frame visible.  This does not raise
the frame, but you can do that with @code{raise-frame} if you wish
(@pxref{Raising and Lowering}).
@end deffn

@deffn Command make-frame-invisible &optional frame force
This function makes frame @var{frame} invisible.  If you omit
@var{frame}, it makes the selected frame invisible.

Unless @var{force} is non-@code{nil}, this function refuses to make
@var{frame} invisible if all other frames are invisible..
@end deffn

@deffn Command iconify-frame &optional frame
This function iconifies frame @var{frame}.  If you omit @var{frame}, it
iconifies the selected frame.
@end deffn

@defun frame-visible-p frame
This returns the visibility status of frame @var{frame}.  The value is
@code{t} if @var{frame} is visible, @code{nil} if it is invisible, and
@code{icon} if it is iconified.

On a text-only terminal, all frames are considered visible, whether
they are currently being displayed or not, and this function returns
@code{t} for all frames.
@end defun

  The visibility status of a frame is also available as a frame
parameter.  You can read or change it as such.  @xref{Management
Parameters}.

  The user can iconify and deiconify frames with the window manager.
This happens below the level at which Emacs can exert any control, but
Emacs does provide events that you can use to keep track of such
changes.  @xref{Misc Events}.

@node Raising and Lowering
@section Raising and Lowering Frames

  Most window systems use a desktop metaphor.  Part of this metaphor is
the idea that windows are stacked in a notional third dimension
perpendicular to the screen surface, and thus ordered from ``highest''
to ``lowest.''  Where two windows overlap, the one higher up covers
the one underneath.  Even a window at the bottom of the stack can be
seen if no other window overlaps it.

@c @cindex raising a frame  redundant with raise-frame
@cindex lowering a frame
  A window's place in this ordering is not fixed; in fact, users tend
to change the order frequently.  @dfn{Raising} a window means moving
it ``up,'' to the top of the stack.  @dfn{Lowering} a window means
moving it to the bottom of the stack.  This motion is in the notional
third dimension only, and does not change the position of the window
on the screen.

  You can raise and lower Emacs frame Windows with these functions:

@deffn Command raise-frame &optional frame
This function raises frame @var{frame} (default, the selected frame).
If @var{frame} is invisible or iconified, this makes it visible.
@end deffn

@deffn Command lower-frame &optional frame
This function lowers frame @var{frame} (default, the selected frame).
@end deffn

@defopt minibuffer-auto-raise
If this is non-@code{nil}, activation of the minibuffer raises the frame
that the minibuffer window is in.
@end defopt

You can also enable auto-raise (raising automatically when a frame is
selected) or auto-lower (lowering automatically when it is deselected)
for any frame using frame parameters.  @xref{Management Parameters}.

@node Frame Configurations
@section Frame Configurations
@cindex frame configuration

  A @dfn{frame configuration} records the current arrangement of frames,
all their properties, and the window configuration of each one.
(@xref{Window Configurations}.)

@defun current-frame-configuration
This function returns a frame configuration list that describes
the current arrangement of frames and their contents.
@end defun

@defun set-frame-configuration configuration &optional nodelete
This function restores the state of frames described in
@var{configuration}.  However, this function does not restore deleted
frames.

Ordinarily, this function deletes all existing frames not listed in
@var{configuration}.  But if @var{nodelete} is non-@code{nil}, the
unwanted frames are iconified instead.
@end defun

@node Mouse Tracking
@section Mouse Tracking
@cindex mouse tracking
@c @cindex tracking the mouse   Duplicates track-mouse

  Sometimes it is useful to @dfn{track} the mouse, which means to display
something to indicate where the mouse is and move the indicator as the
mouse moves.  For efficient mouse tracking, you need a way to wait until
the mouse actually moves.

  The convenient way to track the mouse is to ask for events to represent
mouse motion.  Then you can wait for motion by waiting for an event.  In
addition, you can easily handle any other sorts of events that may
occur.  That is useful, because normally you don't want to track the
mouse forever---only until some other event, such as the release of a
button.

@defspec track-mouse body@dots{}
This special form executes @var{body}, with generation of mouse motion
events enabled.  Typically @var{body} would use @code{read-event} to
read the motion events and modify the display accordingly.  @xref{Motion
Events}, for the format of mouse motion events.

The value of @code{track-mouse} is that of the last form in @var{body}.
You should design @var{body} to return when it sees the up-event that
indicates the release of the button, or whatever kind of event means
it is time to stop tracking.
@end defspec

The usual purpose of tracking mouse motion is to indicate on the screen
the consequences of pushing or releasing a button at the current
position.

In many cases, you can avoid the need to track the mouse by using
the @code{mouse-face} text property (@pxref{Special Properties}).
That works at a much lower level and runs more smoothly than
Lisp-level mouse tracking.

@ignore
@c These are not implemented yet.

These functions change the screen appearance instantaneously.  The
effect is transient, only until the next ordinary Emacs redisplay.  That
is OK for mouse tracking, since it doesn't make sense for mouse tracking
to change the text, and the body of @code{track-mouse} normally reads
the events itself and does not do redisplay.

@defun x-contour-region window beg end
This function draws lines to make a box around the text from @var{beg}
to @var{end}, in window @var{window}.
@end defun

@defun x-uncontour-region window beg end
This function erases the lines that would make a box around the text
from @var{beg} to @var{end}, in window @var{window}.  Use it to remove
a contour that you previously made by calling @code{x-contour-region}.
@end defun

@defun x-draw-rectangle frame left top right bottom
This function draws a hollow rectangle on frame @var{frame} with the
specified edge coordinates, all measured in pixels from the inside top
left corner.  It uses the cursor color, the one used for indicating the
location of point.
@end defun

@defun x-erase-rectangle frame left top right bottom
This function erases a hollow rectangle on frame @var{frame} with the
specified edge coordinates, all measured in pixels from the inside top
left corner.  Erasure means redrawing the text and background that
normally belong in the specified rectangle.
@end defun
@end ignore

@node Mouse Position
@section Mouse Position
@cindex mouse position
@cindex position of mouse

  The functions @code{mouse-position} and @code{set-mouse-position}
give access to the current position of the mouse.

@defun mouse-position
This function returns a description of the position of the mouse.  The
value looks like @code{(@var{frame} @var{x} . @var{y})}, where @var{x}
and @var{y} are integers giving the position in characters relative to
the top left corner of the inside of @var{frame}.
@end defun

@defvar mouse-position-function
If non-@code{nil}, the value of this variable is a function for
@code{mouse-position} to call.  @code{mouse-position} calls this
function just before returning, with its normal return value as the
sole argument, and it returns whatever this function returns to it.

This abnormal hook exists for the benefit of packages like
@file{xt-mouse.el} that need to do mouse handling at the Lisp level.
@end defvar

@defun set-mouse-position frame x y
This function @dfn{warps the mouse} to position @var{x}, @var{y} in
frame @var{frame}.  The arguments @var{x} and @var{y} are integers,
giving the position in characters relative to the top left corner of the
inside of @var{frame}.  If @var{frame} is not visible, this function
does nothing.  The return value is not significant.
@end defun

@defun mouse-pixel-position
This function is like @code{mouse-position} except that it returns
coordinates in units of pixels rather than units of characters.
@end defun

@defun set-mouse-pixel-position frame x y
This function warps the mouse like @code{set-mouse-position} except that
@var{x} and @var{y} are in units of pixels rather than units of
characters.  These coordinates are not required to be within the frame.

If @var{frame} is not visible, this function does nothing.  The return
value is not significant.
@end defun

@need 3000

@node Pop-Up Menus
@section Pop-Up Menus

  When using a window system, a Lisp program can pop up a menu so that
the user can choose an alternative with the mouse.

@defun x-popup-menu position menu
This function displays a pop-up menu and returns an indication of
what selection the user makes.

The argument @var{position} specifies where on the screen to put the
top left corner of the menu.  It can be either a mouse button event
(which says to put the menu where the user actuated the button) or a
list of this form:

@example
((@var{xoffset} @var{yoffset}) @var{window})
@end example

@noindent
where @var{xoffset} and @var{yoffset} are coordinates, measured in
pixels, counting from the top left corner of @var{window}.  @var{window}
may be a window or a frame.

If @var{position} is @code{t}, it means to use the current mouse
position.  If @var{position} is @code{nil}, it means to precompute the
key binding equivalents for the keymaps specified in @var{menu},
without actually displaying or popping up the menu.

The argument @var{menu} says what to display in the menu.  It can be a
keymap or a list of keymaps (@pxref{Menu Keymaps}).  In this case, the
return value is the list of events corresponding to the user's choice.
(This list has more than one element if the choice occurred in a
submenu.)  Note that @code{x-popup-menu} does not actually execute the
command bound to that sequence of events.

Alternatively, @var{menu} can have the following form:

@example
(@var{title} @var{pane1} @var{pane2}...)
@end example

@noindent
where each pane is a list of form

@example
(@var{title} @var{item1} @var{item2}...)
@end example

Each item should normally be a cons cell @code{(@var{line} . @var{value})},
where @var{line} is a string, and @var{value} is the value to return if
that @var{line} is chosen.  An item can also be a string; this makes a
non-selectable line in the menu.

If the user gets rid of the menu without making a valid choice, for
instance by clicking the mouse away from a valid choice or by typing
keyboard input, then this normally results in a quit and
@code{x-popup-menu} does not return.  But if @var{position} is a mouse
button event (indicating that the user invoked the menu with the
mouse) then no quit occurs and @code{x-popup-menu} returns @code{nil}.
@end defun

  @strong{Usage note:} Don't use @code{x-popup-menu} to display a menu
if you could do the job with a prefix key defined with a menu keymap.
If you use a menu keymap to implement a menu, @kbd{C-h c} and @kbd{C-h
a} can see the individual items in that menu and provide help for them.
If instead you implement the menu by defining a command that calls
@code{x-popup-menu}, the help facilities cannot know what happens inside
that command, so they cannot give any help for the menu's items.

  The menu bar mechanism, which lets you switch between submenus by
moving the mouse, cannot look within the definition of a command to see
that it calls @code{x-popup-menu}.  Therefore, if you try to implement a
submenu using @code{x-popup-menu}, it cannot work with the menu bar in
an integrated fashion.  This is why all menu bar submenus are
implemented with menu keymaps within the parent menu, and never with
@code{x-popup-menu}.  @xref{Menu Bar}.

  If you want a menu bar submenu to have contents that vary, you should
still use a menu keymap to implement it.  To make the contents vary, add
a hook function to @code{menu-bar-update-hook} to update the contents of
the menu keymap as necessary.

@node Dialog Boxes
@section Dialog Boxes
@cindex dialog boxes

  A dialog box is a variant of a pop-up menu---it looks a little
different, it always appears in the center of a frame, and it has just
one level and one or more buttons.  The main use of dialog boxes is
for asking questions that the user can answer with ``yes,'' ``no,''
and a few other alternatives.  With a single button, they can also
force the user to acknowledge important information.  The functions
@code{y-or-n-p} and @code{yes-or-no-p} use dialog boxes instead of the
keyboard, when called from commands invoked by mouse clicks.

@defun x-popup-dialog position contents &optional header
This function displays a pop-up dialog box and returns an indication of
what selection the user makes.  The argument @var{contents} specifies
the alternatives to offer; it has this format:

@example
(@var{title} (@var{string} . @var{value})@dots{})
@end example

@noindent
which looks like the list that specifies a single pane for
@code{x-popup-menu}.

The return value is @var{value} from the chosen alternative.

As for @code{x-popup-menu}, an element of the list may be just a
string instead of a cons cell @code{(@var{string} . @var{value})}.
That makes a box that cannot be selected.

If @code{nil} appears in the list, it separates the left-hand items from
the right-hand items; items that precede the @code{nil} appear on the
left, and items that follow the @code{nil} appear on the right.  If you
don't include a @code{nil} in the list, then approximately half the
items appear on each side.

Dialog boxes always appear in the center of a frame; the argument
@var{position} specifies which frame.  The possible values are as in
@code{x-popup-menu}, but the precise coordinates or the individual
window don't matter; only the frame matters.

If @var{header} is non-@code{nil}, the frame title for the box is
@samp{Information}, otherwise it is @samp{Question}.  The former is used
for @code{message-box} (@pxref{message-box}).

In some configurations, Emacs cannot display a real dialog box; so
instead it displays the same items in a pop-up menu in the center of the
frame.

If the user gets rid of the dialog box without making a valid choice,
for instance using the window manager, then this produces a quit and
@code{x-popup-dialog} does not return.
@end defun

@node Pointer Shape
@section Pointer Shape
@cindex pointer shape
@cindex mouse pointer shape

  You can specify the mouse pointer style for particular text or
images using the @code{pointer} text property, and for images with the
@code{:pointer} and @code{:map} image properties.  The values you can
use in these properties are @code{text} (or @code{nil}), @code{arrow},
@code{hand}, @code{vdrag}, @code{hdrag}, @code{modeline}, and
@code{hourglass}.  @code{text} stands for the usual mouse pointer
style used over text.

  Over void parts of the window (parts that do not correspond to any
of the buffer contents), the mouse pointer usually uses the
@code{arrow} style, but you can specify a different style (one of
those above) by setting @code{void-text-area-pointer}.

@defvar void-text-area-pointer
This variable specifies the mouse pointer style for void text areas.
These include the areas after the end of a line or below the last line
in the buffer.  The default is to use the @code{arrow} (non-text)
pointer style.
@end defvar

  You can specify what the @code{text} pointer style really looks like
by setting the variable @code{x-pointer-shape}.

@defvar x-pointer-shape
This variable specifies the pointer shape to use ordinarily in the
Emacs frame, for the @code{text} pointer style.
@end defvar

@defvar x-sensitive-text-pointer-shape
This variable specifies the pointer shape to use when the mouse
is over mouse-sensitive text.
@end defvar

  These variables affect newly created frames.  They do not normally
affect existing frames; however, if you set the mouse color of a
frame, that also installs the current value of those two variables.
@xref{Color Parameters}.

  The values you can use, to specify either of these pointer shapes, are
defined in the file @file{lisp/term/x-win.el}.  Use @kbd{M-x apropos
@key{RET} x-pointer @key{RET}} to see a list of them.

@node Window System Selections
@section Window System Selections
@cindex selection (for window systems)

The X server records a set of @dfn{selections} which permit transfer of
data between application programs.  The various selections are
distinguished by @dfn{selection types}, represented in Emacs by
symbols.  X clients including Emacs can read or set the selection for
any given type.

@deffn Command x-set-selection type data
This function sets a ``selection'' in the X server.  It takes two
arguments: a selection type @var{type}, and the value to assign to it,
@var{data}.  If @var{data} is @code{nil}, it means to clear out the
selection.  Otherwise, @var{data} may be a string, a symbol, an integer
(or a cons of two integers or list of two integers), an overlay, or a
cons of two markers pointing to the same buffer.  An overlay or a pair
of markers stands for text in the overlay or between the markers.

The argument @var{data} may also be a vector of valid non-vector
selection values.

Each possible @var{type} has its own selection value, which changes
independently.  The usual values of @var{type} are @code{PRIMARY},
@code{SECONDARY} and @code{CLIPBOARD}; these are symbols with upper-case
names, in accord with X Window System conventions.  If @var{type} is
@code{nil}, that stands for @code{PRIMARY}.

This function returns @var{data}.
@end deffn

@defun x-get-selection &optional type data-type
This function accesses selections set up by Emacs or by other X
clients.  It takes two optional arguments, @var{type} and
@var{data-type}.  The default for @var{type}, the selection type, is
@code{PRIMARY}.

The @var{data-type} argument specifies the form of data conversion to
use, to convert the raw data obtained from another X client into Lisp
data.  Meaningful values include @code{TEXT}, @code{STRING},
@code{UTF8_STRING}, @code{TARGETS}, @code{LENGTH}, @code{DELETE},
@code{FILE_NAME}, @code{CHARACTER_POSITION}, @code{NAME},
@code{LINE_NUMBER}, @code{COLUMN_NUMBER}, @code{OWNER_OS},
@code{HOST_NAME}, @code{USER}, @code{CLASS}, @code{ATOM}, and
@code{INTEGER}.  (These are symbols with upper-case names in accord
with X conventions.)  The default for @var{data-type} is
@code{STRING}.
@end defun

@cindex cut buffer
The X server also has a set of eight numbered @dfn{cut buffers} which can
store text or other data being moved between applications.  Cut buffers
are considered obsolete, but Emacs supports them for the sake of X
clients that still use them.  Cut buffers are numbered from 0 to 7.

@defun x-get-cut-buffer &optional n
This function returns the contents of cut buffer number @var{n}.
If omitted @var{n} defaults to 0.
@end defun

@defun x-set-cut-buffer string &optional push
@anchor{Definition of x-set-cut-buffer}
This function stores @var{string} into the first cut buffer (cut buffer
0).  If @var{push} is @code{nil}, only the first cut buffer is changed.
If @var{push} is non-@code{nil}, that says to move the values down
through the series of cut buffers, much like the way successive kills in
Emacs move down the kill ring.  In other words, the previous value of
the first cut buffer moves into the second cut buffer, and the second to
the third, and so on through all eight cut buffers.
@end defun

@defvar selection-coding-system
This variable specifies the coding system to use when reading and
writing selections or the clipboard.  @xref{Coding
Systems}.  The default is @code{compound-text-with-extensions}, which
converts to the text representation that X11 normally uses.
@end defvar

@cindex clipboard support (for MS-Windows)
When Emacs runs on MS-Windows, it does not implement X selections in
general, but it does support the clipboard.  @code{x-get-selection}
and @code{x-set-selection} on MS-Windows support the text data type
only; if the clipboard holds other types of data, Emacs treats the
clipboard as empty.

@cindex scrap support (for Mac OS)
On Mac OS, selection-like data transfer between applications is
performed through a mechanism called @dfn{scraps}.  The clipboard is a
particular scrap named @code{com.apple.scrap.clipboard}.  Types of scrap
data are called @dfn{scrap flavor types}, which are identified by
four-char codes such as @code{TEXT}.  Emacs associates a selection with
a scrap, and a selection type with a scrap flavor type via
@code{mac-scrap-name} and @code{mac-ostype} properties, respectively.

@example
(get 'CLIPBOARD 'mac-scrap-name)
     @result{} "com.apple.scrap.clipboard"
(get 'com.apple.traditional-mac-plain-text 'mac-ostype)
     @result{} "TEXT"
@end example

Conventionally, selection types for scrap flavor types on Mac OS have
the form of @acronym{UTI, Uniform Type Identifier} such as
@code{com.apple.traditional-mac-plain-text},
@code{public.utf16-plain-text}, and @code{public.file-url}.

@defopt x-select-enable-clipboard
If this is non-@code{nil}, the Emacs yank functions consult the
clipboard before the primary selection, and the kill functions store in
the clipboard as well as the primary selection.  Otherwise they do not
access the clipboard at all.  The default is @code{nil} on most systems,
but @code{t} on MS-Windows and Mac.
@end defopt

@node Drag and Drop
@section Drag and Drop

@vindex x-dnd-test-function
@vindex x-dnd-known-types
  When a user drags something from another application over Emacs, that other
application expects Emacs to tell it if Emacs can handle the data that is
dragged.  The variable @code{x-dnd-test-function} is used by Emacs to determine
what to reply.  The default value is @code{x-dnd-default-test-function}
which accepts drops if the type of the data to be dropped is present in
@code{x-dnd-known-types}.  You can customize @code{x-dnd-test-function} and/or
@code{x-dnd-known-types} if you want Emacs to accept or reject drops based
on some other criteria.

@vindex x-dnd-types-alist
  If you want to change the way Emacs handles drop of different types
or add a new type, customize @code{x-dnd-types-alist}.  This requires
detailed knowledge of what types other applications use for drag and
drop.

@vindex dnd-protocol-alist
  When an URL is dropped on Emacs it may be a file, but it may also be
another URL type (ftp, http, etc.).  Emacs first checks
@code{dnd-protocol-alist} to determine what to do with the URL.  If
there is no match there and if @code{browse-url-browser-function} is
an alist, Emacs looks for a match there.  If no match is found the
text for the URL is inserted.  If you want to alter Emacs behavior,
you can customize these variables.

@node Color Names
@section Color Names

@cindex color names
@cindex specify color
@cindex numerical RGB color specification
  A color name is text (usually in a string) that specifies a color.
Symbolic names such as @samp{black}, @samp{white}, @samp{red}, etc.,
are allowed; use @kbd{M-x list-colors-display} to see a list of
defined names.  You can also specify colors numerically in forms such
as @samp{#@var{rgb}} and @samp{RGB:@var{r}/@var{g}/@var{b}}, where
@var{r} specifies the red level, @var{g} specifies the green level,
and @var{b} specifies the blue level.  You can use either one, two,
three, or four hex digits for @var{r}; then you must use the same
number of hex digits for all @var{g} and @var{b} as well, making
either 3, 6, 9 or 12 hex digits in all.  (See the documentation of the
X Window System for more details about numerical RGB specification of
colors.)

  These functions provide a way to determine which color names are
valid, and what they look like.  In some cases, the value depends on the
@dfn{selected frame}, as described below; see @ref{Input Focus}, for the
meaning of the term ``selected frame.''

@defun color-defined-p color &optional frame
This function reports whether a color name is meaningful.  It returns
@code{t} if so; otherwise, @code{nil}.  The argument @var{frame} says
which frame's display to ask about; if @var{frame} is omitted or
@code{nil}, the selected frame is used.

Note that this does not tell you whether the display you are using
really supports that color.  When using X, you can ask for any defined
color on any kind of display, and you will get some result---typically,
the closest it can do.  To determine whether a frame can really display
a certain color, use @code{color-supported-p} (see below).

@findex x-color-defined-p
This function used to be called @code{x-color-defined-p},
and that name is still supported as an alias.
@end defun

@defun defined-colors &optional frame
This function returns a list of the color names that are defined
and supported on frame @var{frame} (default, the selected frame).
If @var{frame} does not support colors, the value is @code{nil}.

@findex x-defined-colors
This function used to be called @code{x-defined-colors},
and that name is still supported as an alias.
@end defun

@defun color-supported-p color &optional frame background-p
This returns @code{t} if @var{frame} can really display the color
@var{color} (or at least something close to it).  If @var{frame} is
omitted or @code{nil}, the question applies to the selected frame.

Some terminals support a different set of colors for foreground and
background.  If @var{background-p} is non-@code{nil}, that means you are
asking whether @var{color} can be used as a background; otherwise you
are asking whether it can be used as a foreground.

The argument @var{color} must be a valid color name.
@end defun

@defun color-gray-p color &optional frame
This returns @code{t} if @var{color} is a shade of gray, as defined on
@var{frame}'s display.  If @var{frame} is omitted or @code{nil}, the
question applies to the selected frame.  If @var{color} is not a valid
color name, this function returns @code{nil}.
@end defun

@defun color-values color &optional frame
@cindex rgb value
This function returns a value that describes what @var{color} should
ideally look like on @var{frame}.  If @var{color} is defined, the
value is a list of three integers, which give the amount of red, the
amount of green, and the amount of blue.  Each integer ranges in
principle from 0 to 65535, but some displays may not use the full
range.  This three-element list is called the @dfn{rgb values} of the
color.

If @var{color} is not defined, the value is @code{nil}.

@example
(color-values "black")
     @result{} (0 0 0)
(color-values "white")
     @result{} (65280 65280 65280)
(color-values "red")
     @result{} (65280 0 0)
(color-values "pink")
     @result{} (65280 49152 51968)
(color-values "hungry")
     @result{} nil
@end example

The color values are returned for @var{frame}'s display.  If
@var{frame} is omitted or @code{nil}, the information is returned for
the selected frame's display.  If the frame cannot display colors, the
value is @code{nil}.

@findex x-color-values
This function used to be called @code{x-color-values},
and that name is still supported as an alias.
@end defun

@node Text Terminal Colors
@section Text Terminal Colors
@cindex colors on text-only terminals

  Text-only terminals usually support only a small number of colors,
and the computer uses small integers to select colors on the terminal.
This means that the computer cannot reliably tell what the selected
color looks like; instead, you have to inform your application which
small integers correspond to which colors.  However, Emacs does know
the standard set of colors and will try to use them automatically.

  The functions described in this section control how terminal colors
are used by Emacs.

  Several of these functions use or return @dfn{rgb values}, described
in @ref{Color Names}.

  These functions accept a display (either a frame or the name of a
terminal) as an optional argument.  We hope in the future to make Emacs
support more than one text-only terminal at one time; then this argument
will specify which terminal to operate on (the default being the
selected frame's terminal; @pxref{Input Focus}).  At present, though,
the @var{frame} argument has no effect.

@defun tty-color-define name number &optional rgb frame
This function associates the color name @var{name} with
color number @var{number} on the terminal.

The optional argument @var{rgb}, if specified, is an rgb value, a list
of three numbers that specify what the color actually looks like.
If you do not specify @var{rgb}, then this color cannot be used by
@code{tty-color-approximate} to approximate other colors, because
Emacs will not know what it looks like.
@end defun

@defun tty-color-clear &optional frame
This function clears the table of defined colors for a text-only terminal.
@end defun

@defun tty-color-alist &optional frame
This function returns an alist recording the known colors supported by a
text-only terminal.

Each element has the form @code{(@var{name} @var{number} . @var{rgb})}
or @code{(@var{name} @var{number})}.  Here, @var{name} is the color
name, @var{number} is the number used to specify it to the terminal.
If present, @var{rgb} is a list of three color values (for red, green,
and blue) that says what the color actually looks like.
@end defun

@defun tty-color-approximate rgb &optional frame
This function finds the closest color, among the known colors
supported for @var{display}, to that described by the rgb value
@var{rgb} (a list of color values).  The return value is an element of
@code{tty-color-alist}.
@end defun

@defun tty-color-translate color &optional frame
This function finds the closest color to @var{color} among the known
colors supported for @var{display} and returns its index (an integer).
If the name @var{color} is not defined, the value is @code{nil}.
@end defun

@node Resources
@section X Resources

@defun x-get-resource attribute class &optional component subclass
The function @code{x-get-resource} retrieves a resource value from the X
Window defaults database.

Resources are indexed by a combination of a @dfn{key} and a @dfn{class}.
This function searches using a key of the form
@samp{@var{instance}.@var{attribute}} (where @var{instance} is the name
under which Emacs was invoked), and using @samp{Emacs.@var{class}} as
the class.

The optional arguments @var{component} and @var{subclass} add to the key
and the class, respectively.  You must specify both of them or neither.
If you specify them, the key is
@samp{@var{instance}.@var{component}.@var{attribute}}, and the class is
@samp{Emacs.@var{class}.@var{subclass}}.
@end defun

@defvar x-resource-class
This variable specifies the application name that @code{x-get-resource}
should look up.  The default value is @code{"Emacs"}.  You can examine X
resources for application names other than ``Emacs'' by binding this
variable to some other string, around a call to @code{x-get-resource}.
@end defvar

@defvar x-resource-name
This variable specifies the instance name that @code{x-get-resource}
should look up.  The default value is the name Emacs was invoked with,
or the value specified with the @samp{-name} or @samp{-rn} switches.
@end defvar

To illustrate some of the above, suppose that you have the line:

@example
xterm.vt100.background: yellow
@end example

@noindent
in your X resources file (whose name is usually @file{~/.Xdefaults}
or @file{~/.Xresources}).  Then:

@example
@group
(let ((x-resource-class "XTerm") (x-resource-name "xterm"))
  (x-get-resource "vt100.background" "VT100.Background"))
     @result{} "yellow"
@end group
@group
(let ((x-resource-class "XTerm") (x-resource-name "xterm"))
  (x-get-resource "background" "VT100" "vt100" "Background"))
     @result{} "yellow"
@end group
@end example

  @xref{X Resources,, X Resources, emacs, The GNU Emacs Manual}.

@node Display Feature Testing
@section Display Feature Testing
@cindex display feature testing

  The functions in this section describe the basic capabilities of a
particular display.  Lisp programs can use them to adapt their behavior
to what the display can do.  For example, a program that ordinarily uses
a popup menu could use the minibuffer if popup menus are not supported.

  The optional argument @var{display} in these functions specifies which
display to ask the question about.  It can be a display name, a frame
(which designates the display that frame is on), or @code{nil} (which
refers to the selected frame's display, @pxref{Input Focus}).

  @xref{Color Names}, @ref{Text Terminal Colors}, for other functions to
obtain information about displays.

@defun display-popup-menus-p &optional display
This function returns @code{t} if popup menus are supported on
@var{display}, @code{nil} if not.  Support for popup menus requires that
the mouse be available, since the user cannot choose menu items without
a mouse.
@end defun

@defun display-graphic-p &optional display
This function returns @code{t} if @var{display} is a graphic display
capable of displaying several frames and several different fonts at
once.  This is true for displays that use a window system such as X, and
false for text-only terminals.
@end defun

@defun display-mouse-p &optional display
@cindex mouse, availability
This function returns @code{t} if @var{display} has a mouse available,
@code{nil} if not.
@end defun

@defun display-color-p &optional display
@findex x-display-color-p
This function returns @code{t} if the screen is a color screen.
It used to be called @code{x-display-color-p}, and that name
is still supported as an alias.
@end defun

@defun display-grayscale-p &optional display
This function returns @code{t} if the screen can display shades of gray.
(All color displays can do this.)
@end defun

@defun display-supports-face-attributes-p attributes &optional display
@anchor{Display Face Attribute Testing}
This function returns non-@code{nil} if all the face attributes in
@var{attributes} are supported (@pxref{Face Attributes}).

The definition of `supported' is somewhat heuristic, but basically
means that a face containing all the attributes in @var{attributes},
when merged with the default face for display, can be represented in a
way that's

@enumerate
@item
different in appearance than the default face, and

@item
`close in spirit' to what the attributes specify, if not exact.
@end enumerate

Point (2) implies that a @code{:weight black} attribute will be
satisfied by any display that can display bold, as will
@code{:foreground "yellow"} as long as some yellowish color can be
displayed, but @code{:slant italic} will @emph{not} be satisfied by
the tty display code's automatic substitution of a `dim' face for
italic.
@end defun

@defun display-selections-p &optional display
This function returns @code{t} if @var{display} supports selections.
Windowed displays normally support selections, but they may also be
supported in some other cases.
@end defun

@defun display-images-p &optional display
This function returns @code{t} if @var{display} can display images.
Windowed displays ought in principle to handle images, but some
systems lack the support for that.  On a display that does not support
images, Emacs cannot display a tool bar.
@end defun

@defun display-screens &optional display
This function returns the number of screens associated with the display.
@end defun

@defun display-pixel-height &optional display
This function returns the height of the screen in pixels.
On a character terminal, it gives the height in characters.

For graphical terminals, note that on ``multi-monitor'' setups this
refers to the pixel width for all physical monitors associated with
@var{display}.  @xref{Multiple Displays}.
@end defun

@defun display-pixel-width &optional display
This function returns the width of the screen in pixels.
On a character terminal, it gives the width in characters.

For graphical terminals, note that on ``multi-monitor'' setups this
refers to the pixel width for all physical monitors associated with
@var{display}.  @xref{Multiple Displays}.
@end defun

@defun display-mm-height &optional display
This function returns the height of the screen in millimeters,
or @code{nil} if Emacs cannot get that information.
@end defun

@defun display-mm-width &optional display
This function returns the width of the screen in millimeters,
or @code{nil} if Emacs cannot get that information.
@end defun

@defvar display-mm-dimensions-alist
This variable allows the user to specify the dimensions of graphical
displays returned by @code{display-mm-height} and
@code{display-mm-width} in case the system provides incorrect values.
@end defvar

@defun display-backing-store &optional display
This function returns the backing store capability of the display.
Backing store means recording the pixels of windows (and parts of
windows) that are not exposed, so that when exposed they can be
displayed very quickly.

Values can be the symbols @code{always}, @code{when-mapped}, or
@code{not-useful}.  The function can also return @code{nil}
when the question is inapplicable to a certain kind of display.
@end defun

@defun display-save-under &optional display
This function returns non-@code{nil} if the display supports the
SaveUnder feature.  That feature is used by pop-up windows
to save the pixels they obscure, so that they can pop down
quickly.
@end defun

@defun display-planes &optional display
This function returns the number of planes the display supports.
This is typically the number of bits per pixel.
For a tty display, it is log to base two of the number of colors supported.
@end defun

@defun display-visual-class &optional display
This function returns the visual class for the screen.  The value is one
of the symbols @code{static-gray}, @code{gray-scale},
@code{static-color}, @code{pseudo-color}, @code{true-color}, and
@code{direct-color}.
@end defun

@defun display-color-cells &optional display
This function returns the number of color cells the screen supports.
@end defun

  These functions obtain additional information specifically
about X displays.

@defun x-server-version &optional display
This function returns the list of version numbers of the X server
running the display.  The value is a list of three integers: the major
and minor version numbers of the X protocol, and the
distributor-specific release number of the X server software itself.
@end defun

@defun x-server-vendor &optional display
This function returns the ``vendor'' that provided the X server
software (as a string).  Really this means whoever distributes the X
server.

When the developers of X labelled software distributors as
``vendors,'' they showed their false assumption that no system could
ever be developed and distributed noncommercially.
@end defun

@ignore
@defvar x-no-window-manager
This variable's value is @code{t} if no X window manager is in use.
@end defvar
@end ignore

@ignore
@item
The functions @code{x-pixel-width} and @code{x-pixel-height} return the
width and height of an X Window frame, measured in pixels.
@end ignore

@ignore
   arch-tag: 94977df6-3dca-4730-b57b-c6329e9282ba
@end ignore