[gnu-emacs] / doc / lispref / frames.texi

@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990-1995, 1998-1999, 2001-2015 Free Software
@c Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@node Frames
@chapter Frames
@cindex frame

  A @dfn{frame} is a screen object that contains one or more Emacs
windows (@pxref{Windows}).  It is the kind of object 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.  In Emacs Lisp, a @dfn{frame object} is a Lisp object that
represents a frame on the screen.  @xref{Frame Type}.

  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.  @xref{Splitting Windows}.

@cindex terminal
  A @dfn{terminal} is a display device capable of displaying one or
more Emacs frames.  In Emacs Lisp, a @dfn{terminal object} is a Lisp
object that represents a terminal.  @xref{Terminal Type}.

@cindex text terminal
@cindex graphical terminal
@cindex graphical display
  There are two classes of terminals: @dfn{text terminals} and
@dfn{graphical terminals}.  Text terminals are non-graphics-capable
displays, including @command{xterm} and other terminal emulators.  On
a text terminal, each Emacs frame occupies the terminal's entire
screen; although you can create additional frames and switch between
them, the terminal only shows one frame at a time.  Graphical
terminals, on the other hand, are managed by graphical display systems
such as the X Window System, which allow Emacs to show multiple frames
simultaneously on the same display.

  On GNU and Unix systems, you can create additional frames on any
available terminal, within a single Emacs session, regardless of
whether Emacs was started on a text or graphical terminal.  Emacs can
display on both graphical and text terminals simultaneously.  This
comes in handy, for instance, when you connect to the same session
from several remote locations.  @xref{Multiple Terminals}.

@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 t
The frame is displayed on a text terminal.
@item x
The frame is displayed on an X graphical terminal.
@item w32
The frame is displayed on a MS-Windows graphical terminal.
@item ns
The frame is displayed on a GNUstep or Macintosh Cocoa graphical
terminal.
@item pc
The frame is displayed on an MS-DOS terminal.
@end table
@end defun

@defun frame-terminal &optional frame
This function returns the terminal object that displays @var{frame}.
If @var{frame} is @code{nil} or unspecified, it defaults to the
selected frame.
@end defun

@defun terminal-live-p object
This predicate returns a non-@code{nil} value if @var{object} is a
terminal that is live (i.e., not deleted), and @code{nil} otherwise.
For live terminals, the return value indicates what kind of frames are
displayed on that terminal; the list of possible values is the same as
for @code{framep} above.
@end defun

@menu
* Creating Frames::             Creating additional frames.
* Multiple Terminals::          Displaying on several different devices.
* Frame Parameters::            Controlling frame size, position, font, etc.
* Terminal Parameters::         Parameters common for all frames on terminal.
* Frame Titles::                Automatic updating of frame titles.
* Deleting Frames::             Frames last until explicitly deleted.
* Finding All Frames::          How to examine all existing frames.
* 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 terminals.
* Resources::                   Getting resource values from the server.
* Display Feature Testing::     Determining the features of a terminal.
@end menu

@node Creating Frames
@section Creating Frames
@cindex frame creation

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

@deffn Command make-frame &optional alist
This function creates and returns a new frame, displaying the current
buffer.

The @var{alist} argument is an alist that specifies frame parameters
for the new frame.  @xref{Frame Parameters}.  If you specify the
@code{terminal} parameter in @var{alist}, the new frame is created on
that terminal.  Otherwise, if you specify the @code{window-system}
frame parameter in @var{alist}, that determines whether the frame
should be displayed on a text terminal or a graphical terminal.
@xref{Window Systems}.  If neither is specified, the new frame is
created in the same terminal as the selected frame.

Any parameters not mentioned in @var{alist} default to the values in
the alist @code{default-frame-alist} (@pxref{Initial Parameters});
parameters not specified there default from the X resources or its
equivalent on your operating system (@pxref{X Resources,, X Resources,
emacs, The GNU Emacs Manual}).  After the frame is created, Emacs
applies any parameters listed in @code{frame-inherited-parameters}
(see below) and not present in the argument, taking the values from
the frame that was selected when @code{make-frame} was called.

Note that on multi-monitor displays (@pxref{Multiple Terminals}), the
window manager might position the frame differently than specified by
the positional parameters in @var{alist} (@pxref{Position
Parameters}).  For example, some window managers have a policy of
displaying the frame on the monitor that contains the largest part of
the window (a.k.a.@: the @dfn{dominating} monitor).

This function itself does not make the new frame the selected frame.
@xref{Input Focus}.  The previously selected frame remains selected.
On graphical terminals, however, the windowing system may select the
new frame for its own reasons.
@end deffn

@defvar before-make-frame-hook
A normal hook run by @code{make-frame} before it 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

@defvar frame-inherited-parameters
This variable specifies the list of frame parameters that a newly
created frame inherits from the currently selected frame.  For each
parameter (a symbol) that is an element in the list and is not present
in the argument to @code{make-frame}, the function sets the value of
that parameter in the created frame to its value in the selected
frame.
@end defvar

@node Multiple Terminals
@section Multiple Terminals
@cindex multiple terminals
@cindex multi-tty
@cindex multiple X displays
@cindex displays, multiple

  Emacs represents each terminal as a @dfn{terminal object} data type
(@pxref{Terminal Type}).  On GNU and Unix systems, Emacs can use
multiple terminals simultaneously in each session.  On other systems,
it can only use a single terminal.  Each terminal object has the
following attributes:

@itemize @bullet
@item
The name of the device used by the terminal (e.g., @samp{:0.0} or
@file{/dev/tty}).

@item
The terminal and keyboard coding systems used on the terminal.
@xref{Terminal I/O Encoding}.

@item
The kind of display associated with the terminal.  This is the symbol
returned by the function @code{terminal-live-p} (i.e., @code{x},
@code{t}, @code{w32}, @code{ns}, or @code{pc}).  @xref{Frames}.

@item
A list of terminal parameters.  @xref{Terminal Parameters}.
@end itemize

  There is no primitive for creating terminal objects.  Emacs creates
them as needed, such as when you call @code{make-frame-on-display}
(described below).

@defun terminal-name &optional terminal
This function returns the file name of the device used by
@var{terminal}.  If @var{terminal} is omitted or @code{nil}, it
defaults to the selected frame's terminal.  @var{terminal} can also be
a frame, meaning that frame's terminal.
@end defun

@defun terminal-list
This function returns a list of all live terminal objects.
@end defun

@defun get-device-terminal device
This function returns a terminal whose device name is given by
@var{device}.  If @var{device} is a string, it can be either the file
name of a terminal device, or the name of an X display of the form
@samp{@var{host}:@var{server}.@var{screen}}.  If @var{device} is a
frame, this function returns that frame's terminal; @code{nil} means
the selected frame.  Finally, if @var{device} is a terminal object
that represents a live terminal, that terminal is returned.  The
function signals an error if its argument is none of the above.
@end defun

@defun delete-terminal &optional terminal force
This function deletes all frames on @var{terminal} and frees the
resources used by it.  It runs the abnormal hook
@code{delete-terminal-functions}, passing @var{terminal} as the
argument to each function.

If @var{terminal} is omitted or @code{nil}, it defaults to the
selected frame's terminal.  @var{terminal} can also be a frame,
meaning that frame's terminal.

Normally, this function signals an error if you attempt to delete the
sole active terminal, but if @var{force} is non-@code{nil}, you are
allowed to do so.  Emacs automatically calls this function when the
last frame on a terminal is deleted (@pxref{Deleting Frames}).
@end defun

@defvar delete-terminal-functions
An abnormal hook run by @code{delete-terminal}.  Each function
receives one argument, the @var{terminal} argument passed to
@code{delete-terminal}.  Due to technical details, the functions may
be called either just before the terminal is deleted, or just
afterwards.
@end defvar

@cindex terminal-local variables
  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}).

  On GNU and Unix systems, each X display is a separate graphical
terminal.  When Emacs is started from within the X window system, it
uses the X display specified by the @env{DISPLAY} environment
variable, or by the @samp{--display} option (@pxref{Initial Options,,,
emacs, The GNU Emacs Manual}).  Emacs can connect to other X displays
via the command @code{make-frame-on-display}.  Each X display has its
own selected frame and its own minibuffer windows; however, only one
of those frames is ``@emph{the} selected frame'' at any given moment
(@pxref{Input Focus}).  Emacs can even connect to other text
terminals, by interacting with the @command{emacsclient} program.
@xref{Emacs Server,,, emacs, The GNU Emacs Manual}.

@cindex X display names
@cindex display name on X
  A single X server can handle more than one display.  Each X display
has a three-part name,
@samp{@var{hostname}:@var{displaynumber}.@var{screennumber}}.  The
first part, @var{hostname}, specifies the name of the machine to which
the display is physically connected.  The second part,
@var{displaynumber}, is a zero-based number that identifies one or
more monitors connected to that machine that share a common keyboard
and pointing device (mouse, tablet, etc.).  The third part,
@var{screennumber}, identifies a zero-based screen number (a separate
monitor) that is part of a single monitor collection on that X server.
When you use two or more screens belonging to one server, Emacs knows
by the similarity in their names that they share a single keyboard.

  Systems that don't use the X window system, such as MS-Windows,
don't support the notion of X displays, and have only one display on
each host.  The display name on these systems doesn't follow the above
3-part format; for example, the display name on MS-Windows systems is
a constant string @samp{w32}, and exists for compatibility, so that
you could pass it to functions that expect a display name.

@deffn Command make-frame-on-display display &optional parameters
This function creates and returns a new frame on @var{display}, taking
the other frame parameters from the alist @var{parameters}.
@var{display} should be the name of an X display (a string).

Before creating the frame, this function ensures that Emacs is ``set
up'' to display graphics.  For instance, if Emacs has not processed X
resources (e.g., if it was started on a text terminal), it does so at
this time.  In all other respects, this function behaves like
@code{make-frame} (@pxref{Creating Frames}).
@end deffn

@defun x-display-list
This function 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},
without creating a frame on that display.  Normally, Emacs Lisp
programs need not call this function, as @code{make-frame-on-display}
calls it automatically.  The only reason for calling it is to check
whether communication can be established with a given X 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.  @xref{X Resources,, X Resources, emacs, The
GNU Emacs Manual}.  These values apply to all Emacs frames created on
this display, overriding the resource values recorded in the X server.
Here's an example of what this string might look like:

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

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

@cindex multi-monitor
  On some ``multi-monitor'' setups, a single X display outputs to more
than one physical monitor.  You can use the functions
@code{display-monitor-attributes-list} and @code{frame-monitor-attributes}
to obtain information about such setups.

@defun display-monitor-attributes-list &optional display
This function returns a list of physical monitor attributes on
@var{display}, which can be a display name (a string), a terminal, or
a frame; if omitted or @code{nil}, it defaults to the selected frame's
display.  Each element of the list is an association list,
representing the attributes of a physical monitor.  The first element
corresponds to the primary monitor.  The attribute keys and values
are:

@table @samp
@item geometry
Position of the top-left corner of the monitor's screen and its size,
in pixels, as @samp{(@var{x} @var{y} @var{width} @var{height})}.  Note
that, if the monitor is not the primary monitor, some of the
coordinates might be negative.

@item workarea
Position of the top-left corner and size of the work area (``usable''
space) in pixels as @samp{(@var{x} @var{y} @var{width} @var{height})}.
This may be different from @samp{geometry} in that space occupied by
various window manager features (docks, taskbars, etc.)@: may be
excluded from the work area.  Whether or not such features actually
subtract from the work area depends on the platform and environment.
Again, if the monitor is not the primary monitor, some of the
coordinates might be negative.

@item mm-size
Width and height in millimeters as @samp{(@var{width} @var{height})}

@item frames
List of frames that this physical monitor dominates (see below).

@item name
Name of the physical monitor as @var{string}.

@item source
Source of the multi-monitor information as @var{string};
e.g., @samp{XRandr} or @samp{Xinerama}.
@end table

@var{x}, @var{y}, @var{width}, and @var{height} are integers.
@samp{name} and @samp{source} may be absent.

A frame is @dfn{dominated} by a physical monitor when either the
largest area of the frame resides in that monitor, or (if the frame
does not intersect any physical monitors) that monitor is the closest
to the frame.  Every (non-tooltip) frame (whether visible or not) in a
graphical display is dominated by exactly one physical monitor at a
time, though the frame can span multiple (or no) physical monitors.

Here's an example of the data produced by this function on a 2-monitor
display:

@lisp
  (display-monitor-attributes-list)
  @result{}
  (((geometry 0 0 1920 1080) ;; @r{Left-hand, primary monitor}
    (workarea 0 0 1920 1050) ;; @r{A taskbar occupies some of the height}
    (mm-size 677 381)
    (name . "DISPLAY1")
    (frames #<frame emacs@@host *Messages* 0x11578c0>
            #<frame emacs@@host *scratch* 0x114b838>))
   ((geometry 1920 0 1680 1050) ;; @r{Right-hand monitor}
    (workarea 1920 0 1680 1050) ;; @r{Whole screen can be used}
    (mm-size 593 370)
    (name . "DISPLAY2")
    (frames)))
@end lisp

@end defun

@defun frame-monitor-attributes &optional frame
This function returns the attributes of the physical monitor
dominating (see above) @var{frame}, which defaults to the selected frame.
@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 graphical displays.
Most frame parameters have no effect when applied to a frame on a text
terminal; 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.  If the terminal supports
frame transparency, the parameter @code{alpha} is 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 set-frame-parameter frame parm value
This function sets the frame parameter @var{parm} to the specified
@var{value}.  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
@cindex parameters of initial frame

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

@defopt initial-frame-alist
This variable's value is an alist of parameter values used when
creating the initial 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 defopt

@cindex minibuffer-only frame
If these parameters include @code{(minibuffer . nil)}, that indicates
that the initial frame should have no minibuffer.  In this case, Emacs
creates a separate @dfn{minibuffer-only frame} as well.

@defopt minibuffer-frame-alist
This variable's value is an alist of parameter values used when
creating an initial minibuffer-only frame (i.e., the minibuffer-only
frame that Emacs creates if @code{initial-frame-alist} specifies a
frame with no minibuffer).
@end defopt

@defopt 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.  Furthermore,
functions that display a buffer in a separate frame may override the
default parameters by supplying their own parameters.
@end defopt

If you invoke Emacs with command-line options that specify frame
appearance, those options take effect by adding elements to either
@code{initial-frame-alist} or @code{default-frame-alist}.  Options
which affect just the initial frame, such as @samp{--geometry} and
@samp{--maximized}, add to @code{initial-frame-alist}; the others add
to @code{default-frame-alist}.  @pxref{Emacs Invocation,, Command Line
Arguments for Emacs Invocation, emacs, The GNU Emacs Manual}.

@node Window Frame Parameters
@subsection Window Frame Parameters
@cindex frame parameters for windowed displays

  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 only for frames on
text terminals.

@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.
* Font and Color Parameters::   Fonts and colors for the frame text.
@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
@vindex display, a frame parameter
@item display
The display on which to open this frame.  It should be a string of the
form @samp{@var{host}:@var{dpy}.@var{screen}}, just like the
@env{DISPLAY} environment variable.  @xref{Multiple Terminals}, for
more details about display names.

@vindex display-type, a frame parameter
@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}.

@vindex title, a frame parameter
@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}.

@vindex name, a frame parameter
@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.

@item explicit-name
If the frame name was specified explicitly when the frame was created,
this parameter will be that name.  If the frame wasn't explicitly
named, this parameter will be @code{nil}.
@end table

@node Position Parameters
@subsubsection Position Parameters
@cindex window position on display
@cindex frame position

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

@table @code
@vindex left, a frame parameter
@item left
The position, in pixels, of the left (or right) edge of the frame with
respect to the left (or right) edge of the screen.  The value may be:

@table @asis
@item an integer
A positive integer relates the left edge of the frame to the left edge
of the screen.  A negative integer relates the right frame edge to the
right screen edge.

@item @code{(+ @var{pos})}
This specifies the position of the left frame edge relative to the left
screen edge.  The integer @var{pos} may be positive or negative; a
negative value specifies a position outside the screen or on a monitor
other than the primary one (for multi-monitor displays).

@item @code{(- @var{pos})}
This specifies the position of the right frame edge relative to the right
screen edge.  The integer @var{pos} may be positive or negative; a
negative value specifies a position outside the screen or on a monitor
other than the primary one (for multi-monitor displays).
@end table

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.

@vindex top, a frame parameter
@item top
The screen position of the top (or bottom) edge, in pixels, with respect
to the top (or bottom) edge of the screen.  It works just like
@code{left}, except vertically instead of horizontally.

@vindex icon-left, a frame parameter
@item icon-left
The screen position of the left edge of the frame's icon, in pixels,
counting from the left edge of the screen.  This takes effect when the
frame is iconified, if the window manager supports this feature.  If
you specify a value for this parameter, then you must also specify a
value for @code{icon-top} and vice versa.

@vindex icon-top, a frame parameter
@item icon-top
The screen position of the top edge of the frame's icon, in pixels,
counting from the top edge of the screen.  This takes effect when the
frame is iconified, if the window manager supports this feature.

@vindex user-position, a frame parameter
@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.

@cindex window positions and window managers
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
@cindex window size on display

  Frame parameters specify frame sizes in character units.  On
graphical displays, the @code{default} face determines the actual
pixel sizes of these character units (@pxref{Face Attributes}).

@table @code
@vindex height, a frame parameter
@item height
The height of the frame's text area (@pxref{Size and Position}), in
characters.

@vindex width, a frame parameter
@item width
The width of the frame's text area (@pxref{Size and Position}), in
characters.

@vindex user-size, a frame parameter
@item user-size
This does for the size parameters @code{height} and @code{width} what
the @code{user-position} parameter (@pxref{Position Parameters,
user-position}) does for the position parameters @code{top} and
@code{left}.

@cindex full-screen frames
@vindex fullscreen, a frame parameter
@item fullscreen
Specify that width, height or both shall be maximized.  The value
@code{fullwidth} specifies that width shall be as wide as possible.  The
value @code{fullheight} specifies that height shall be as tall as
possible.  The value @code{fullboth} specifies that both the width and
the height shall be set to the size of the screen.  The value
@code{maximized} specifies that the frame shall be maximized.

The difference between @code{maximized} and @code{fullboth} is that a
maximized frame usually keeps its title bar and the buttons for resizing
and closing the frame.  Also, maximized frames typically avoid hiding
any task bar or panels displayed on the desktop.  ``Fullboth'' frames,
on the other hand, usually omit the title bar and occupy the entire
available screen space.

``Fullheight'' and ``fullwidth'' frames are more similar to maximized
frames in this regard.  However, these typically display an external
border which might be absent with maximized frames.  Hence the heights
of maximized and fullheight frames and the widths of maximized and
fullwidth frames often differ by a few pixels.

With some window managers you may have to customize the variable
@code{frame-resize-pixelwise} (@pxref{Size and Position}) in order to
make a frame truly appear ``maximized'' or ``fullscreen''.  Moreover,
some window managers might not support smooth transition between the
various fullscreen or maximization states.  Customizing the variable
@code{x-frame-normalize-before-maximize} can help to overcome that.

@vindex fullscreen-restore, a frame parameter
@item fullscreen-restore
This parameter specifies the desired ``fullscreen'' state of the frame
after invoking the @code{toggle-frame-fullscreen} command (@pxref{Frame
Commands,,, emacs, The GNU Emacs Manual}) in the ``fullboth'' state.
Normally this parameter is installed automatically by that command when
toggling the state to fullboth.  If, however, you start Emacs in the
fullboth state, you have to specify the desired behavior in your initial
file as, for example

@example
(setq default-frame-alist
    '((fullscreen . fullboth) (fullscreen-restore . fullheight)))
@end example

This will give a new frame full height after typing in it @key{F11} for
the first time.
@end table


@node Layout Parameters
@subsubsection Layout Parameters
@cindex layout parameters of frames
@cindex frame layout parameters

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

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

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

@vindex vertical-scroll-bars, a frame parameter
@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.

@vindex horizontal-scroll-bars, a frame parameter
@item horizontal-scroll-bars
Whether the frame has scroll bars for horizontal scrolling (@code{t} and
@code{bottom} mean yes, @code{nil} means no).

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

@vindex scroll-bar-height, a frame parameter
@item scroll-bar-height
The height of horizontal scroll bars, in pixels, or @code{nil} meaning
to use the default height.

@vindex left-fringe, a frame parameter
@vindex right-fringe, a frame parameter
@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.

When you use @code{frame-parameter} to query the value of either of
these two frame parameters, the return value is always an integer.
When using @code{set-frame-parameter}, passing a @code{nil} value
imposes an actual default value of 8 pixels.

@vindex right-divider-width, a frame parameter
@item right-divider-width
The width (thickness) reserved for the right divider (@pxref{Window
Dividers}) of any window on the frame, in pixels.  A value of zero means
to not draw right dividers.

@vindex bottom-divider-width, a frame parameter
@item bottom-divider-width
The width (thickness) reserved for the bottom divider (@pxref{Window
Dividers}) of any window on the frame, in pixels.  A value of zero means
to not draw bottom dividers.

@vindex menu-bar-lines frame parameter
@item menu-bar-lines
The number of lines to allocate at the top of the frame for a menu
bar.  The default is 1 if Menu Bar mode is enabled, and 0 otherwise.
@xref{Menu Bars,,,emacs, The GNU Emacs Manual}.

@vindex tool-bar-lines frame parameter
@item tool-bar-lines
The number of lines to use for the tool bar.  The default is 1 if Tool
Bar mode is enabled, and 0 otherwise.  @xref{Tool Bars,,,emacs, The
GNU Emacs Manual}.

@vindex tool-bar-position frame parameter
@item tool-bar-position
The position of the tool bar.  Currently only for the GTK tool bar.
Value can be one of @code{top}, @code{bottom} @code{left}, @code{right}.
The default is  @code{top}.

@vindex line-spacing, a frame parameter
@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
@cindex frame, which buffers to display
@cindex buffers to display on frame

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

@table @code
@vindex minibuffer, a frame parameter
@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 frame uses that minibuffer.

This frame parameter takes effect when the frame is created, and can
not be changed afterwards.

@vindex buffer-predicate, a frame parameter
@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.

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

@vindex unsplittable, a frame parameter
@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 interaction, and frame parameters

  The following frame parameters control various aspects of the
frame's interaction with the window manager.  They have no effect on
text terminals.

@table @code
@vindex visibility, a frame parameter
@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}.

@vindex auto-raise, a frame parameter
@item auto-raise
If non-@code{nil}, Emacs automatically raises the frame when it is
selected.  Some window managers do not allow this.

@vindex auto-lower, a frame parameter
@item auto-lower
If non-@code{nil}, Emacs automatically lowers the frame when it is
deselected.  Some window managers do not allow this.

@vindex icon-type, a frame parameter
@item icon-type
The type of icon to use for this frame.  If the value is a string,
that specifies a file containing a bitmap to use; @code{nil} specifies
no icon (in which case the window manager decides what to show); any
other non-@code{nil} value specifies the default Emacs icon.

@vindex icon-name, a frame parameter
@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.

@vindex window-id, a frame parameter
@item window-id
The ID number which the graphical display uses for this frame.  Emacs
assigns this parameter when the frame is created; changing the
parameter has no effect on the actual ID number.

@vindex outer-window-id, a frame parameter
@item outer-window-id
The ID number of the outermost window-system window in which the frame
exists.  As with @code{window-id}, changing this parameter has no
actual effect.

@vindex wait-for-wm, a frame parameter
@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.

@vindex sticky, a frame parameter
@item sticky
If non-@code{nil}, the frame is visible on all virtual desktops on systems
with virtual desktops.

@ignore
@vindex parent-id, a frame parameter
@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
@cindex cursor, and frame parameters

  This frame parameter controls the way the cursor looks.

@table @code
@vindex cursor-type, a frame parameter
@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 @code{cursor-type} frame parameter may be overridden by the
variables @code{cursor-type} and
@code{cursor-in-non-selected-windows}:

@defvar cursor-type
This buffer-local variable controls how the cursor looks in a selected
window showing the buffer.  If its value is @code{t}, that means to
use the cursor specified by the @code{cursor-type} frame parameter.
Otherwise, the value should be one of the cursor types listed above,
and it overrides the @code{cursor-type} frame parameter.
@end defvar

@defopt cursor-in-non-selected-windows
This buffer-local 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 modification of the usual cursor type (solid box
becomes hollow box, and bar becomes a narrower bar).
@end defopt

@defopt 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 defopt

@node Font and Color Parameters
@subsubsection Font and Color Parameters
@cindex font and color, frame parameters

  These frame parameters control the use of fonts and colors.

@table @code
@vindex font-backend, a frame parameter
@item font-backend
A list of symbols, specifying the @dfn{font backends} to use for
drawing fonts in the frame, in order of priority.  On X, there are
currently two available font backends: @code{x} (the X core font
driver) and @code{xft} (the Xft font driver).  On MS-Windows, there are
currently two available font backends: @code{gdi} and
@code{uniscribe} (@pxref{Windows Fonts,,, emacs, The GNU Emacs
Manual}).  On other systems, there is only one available font backend,
so it does not make sense to modify this frame parameter.

@vindex background-mode, a frame parameter
@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.

@vindex tty-color-mode, a frame parameter
@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 on a text terminal.  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.

@vindex screen-gamma, a frame parameter
@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.

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.

@vindex alpha, a frame parameter
@item alpha
@cindex opacity, frame
@cindex transparency, frame
@vindex frame-alpha-lower-limit
This parameter specifies the opacity of the frame, on graphical
displays that support variable opacity.  It should be an integer
between 0 and 100, where 0 means completely transparent and 100 means
completely opaque.  It can also have a @code{nil} value, which tells
Emacs not to set the frame opacity (leaving it to the window manager).

To prevent the frame from disappearing completely from view, the
variable @code{frame-alpha-lower-limit} defines a lower opacity limit.
If the value of the frame parameter is less than the value of this
variable, Emacs uses the latter.  By default,
@code{frame-alpha-lower-limit} is 20.

The @code{alpha} frame parameter can also be a cons cell
@code{(@samp{active} . @samp{inactive})}, where @samp{active} is the
opacity of the frame when it is selected, and @samp{inactive} is the
opacity when it is not selected.
@end table

The following frame parameters are semi-obsolete in that they are
automatically equivalent to particular face attributes of particular
faces (@pxref{Standard Faces,,, emacs, The Emacs Manual}):

@table @code
@vindex font, a frame parameter
@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.

@vindex foreground-color, a frame parameter
@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.

@vindex background-color, a frame parameter
@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.

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

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

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

@vindex scroll-bar-foreground, a frame parameter
@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.

@vindex scroll-bar-background, a frame parameter
@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.
Most of the functions described below use a @var{frame} argument which
has to specify a live frame.  If omitted or @code{nil}, it specifies the
selected frame, 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 to the top left
corner of the rectangle allotted to the frame by the window manager.

Negative parameter values position the bottom edge of that rectangle up
from the bottom edge of the screen, or the right rectangle 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

@cindex frame default font
@cindex default font of a frame
Each frame has a @dfn{default font} which specifies the canonical height
and width of a character on that frame.  The default font is used when
retrieving or changing the size of a frame in terms of columns or lines.
It is also used when resizing (@pxref{Window Sizes}) or splitting
(@pxref{Splitting Windows}) windows.

@defun frame-char-height &optional frame
@defunx frame-char-width &optional frame
These functions return the canonical height and width of a character in
@var{frame}, measured in pixels.  Together, these values establish the
size of the default font on @var{frame}.  The values depend on the
choice of font for @var{frame}, see @ref{Font and Color Parameters}.
@end defun

The default font can be also set directly with the following function:

@deffn Command set-frame-font font &optional keep-size frames
This sets the default font to @var{font}.  When called interactively, it
prompts for the name of a font, and uses that font on the selected
frame.  When called from Lisp, @var{font} should be a font name (a
string), a font object, font entity, or a font spec.

If the optional argument @var{keep-size} is @code{nil}, this keeps the
number of frame lines and columns fixed.  (If non-@code{nil}, the option
@code{frame-inhibit-implied-resize} described below will override this.)
If @var{keep-size} is non-@code{nil} (or with a prefix argument), it
tries to keep the size of the display area of the current frame fixed by
adjusting the number of lines and columns.

If the optional argument @var{frames} is @code{nil}, this applies the
font to the selected frame only.  If @var{frames} is non-@code{nil}, it
should be a list of frames to act upon, or @code{t} meaning all existing
graphical frames.
@end deffn

@cindex frame display area
@cindex display area of a frame
The @dfn{display area} of a frame is a rectangular area within the area
allotted to the frame by the window manager.  The display area neither
includes the title bar (@pxref{Frame Titles}) nor any other decorations
provided by the window manager (like an external border used for
resizing frames via mouse dragging).

   The actual height of the display area depends on the window-system
and toolkit in use.  With GTK+, the display area does not include any
tool bar or menu bar.  With the Motif or Lucid toolkits and with
Windows, the display area includes the tool bar but not the menu bar.
In a graphical version with no toolkit, it includes both the tool bar
and menu bar.  On a text terminal, the display area includes the menu
bar.

@defun frame-pixel-height &optional frame
@defunx frame-pixel-width &optional frame
   These functions return the height and width of the display area of
@var{frame}, measured in pixels.  For a text terminal, the results are
in characters rather than pixels.
@end defun

@cindex frame text area
@cindex text area of a frame
   The @dfn{text area} of a frame is a concept implicitly used by all
functions that change a frame's height or width.  It is a rectangle
located within the display area.  Its size is obtained from that of the
display area by subtracting the sizes of any tool or menu bars that are
part of the display area, any internal borders, one vertical and one
horizontal scroll bar, and one left and one right fringe as specified
for this frame, see @ref{Layout Parameters}.

@defun frame-text-height &optional frame
@defunx frame-text-width &optional frame
These functions return the height and width of the text area of
@var{frame}, measured in pixels.  For a text terminal, the results are
in characters rather than pixels.

The value returned by @code{frame-text-height} differs from that
returned by @code{frame-pixel-height} by not including the heights of
any tool bar or menu bar, the height of one horizontal scroll bar and
the widths of the internal border.

The value returned by @code{frame-text-width} differs from that returned
by @code{frame-pixel-width} by not including the width of one vertical
scroll bar, the widths of one left and one right fringe and the widths
of the internal border.
@end defun

@defun frame-height &optional frame
@defunx frame-width &optional frame
These functions return the height and width of the text area of
@var{frame}, measured in units of the default font height and width of
@var{frame}.  These functions are plain shorthands for writing
@code{(frame-parameter frame 'height)} and @code{(frame-parameter frame
'width)}.

If the text area of @var{frame} measured in pixles is not a multiple of
its default font size, the values returned by this functions are rounded
down to the number of characters of the default font that fully fit into
the text area.
@end defun

@defopt frame-resize-pixelwise
If this option is @code{nil}, a frame's size is usually rounded to a
multiple of the current values of that frame's @code{frame-char-height}
and @code{frame-char-width}.  If this is non-@code{nil}, no rounding
occurs, hence frame sizes can increase/decrease by one pixel.

Setting this causes the next resize operation to pass the corresponding
size hints to the window manager.  This means that this variable should
be set only in a user's initial file; applications should never bind it
temporarily.

The precise meaning of a value of @code{nil} for this option depends
on the toolkit used.  Dragging the frame border with the mouse is usually
done character-wise.  Calling @code{set-frame-size} (see below)
with arguments that do not specify the frame size as an integer multiple
of its character size, however, may: be ignored, cause a
rounding (GTK+), or be accepted (Lucid, Motif, MS-Windows).

With some window managers you may have to set this to non-@code{nil} in
order to make a frame appear truly ``maximized'' or ``fullscreen''.
@end defopt

@defun set-frame-size frame width height pixelwise
This function sets the size of the text area of @var{frame}, measured in
characters; @var{width} and @var{height} specify the new width in
columns and the new height in lines.

The optional argument @var{pixelwise} non-@code{nil} means to measure
the new width and height in units of pixels instead.  Note that if
@code{frame-resize-pixelwise} is @code{nil}, some toolkits may refuse to
fully honor the request if it does not increase/decrease the frame size
to a multiple of its character size.
@end defun

@defun set-frame-height frame height &optional pretend pixelwise
This function resizes the text area of @var{frame} to a height of
@var{height} 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{height}
lines of output in @var{frame}, but does not change its value for the
actual height of the frame.  This is only useful on text terminals.
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
text terminals.

The optional fourth argument @var{pixelwise} non-@code{nil} means that
@var{frame} should be @var{height} pixels high.  Note that if
@code{frame-resize-pixelwise} is @code{nil}, some toolkits may refuse to
fully honor the request if it does not increase/decrease the frame
height to a multiple of its character height.
@end defun

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

The optional fourth argument @var{pixelwise} non-@code{nil} means that
@var{frame} should be @var{width} pixels wide.  Note that if
@code{frame-resize-pixelwise} is @code{nil}, some toolkits may refuse to
fully honor the request if it does not increase/decrease the frame width
to a multiple of its character width.
@end defun

None of these three functions will make a frame smaller than needed to
display all of its windows together with their scroll bars, fringes,
margins, dividers, mode and header lines.  This contrasts with requests
by the window manager triggered, for example, by dragging the external
border of a frame with the mouse.  Such requests are always honored by
clipping, if necessary, portions that cannot be displayed at the right,
bottom corner of the frame.

   By default, Emacs tries to keep the number of lines and columns of a
frame's text area unaltered when, for example, adding or removing a menu
bar, changing the default font or setting the width of the frame's
scroll bars.  This means, however, that in such case Emacs must ask the
window manager to resize the display area of the frame in order to
accommodate the size change.  Note that wrapping a menu or tool bar
usually does not resize the frame's display area, hence this will alter
the number of displayed lines.

   Occasionally, such implied resizing of the display area may be
unwanted, for example, when the frame is maximized or made fullscreen
where it's turned off by default.  In other cases you can disable
implied resizing with the following option:

@defopt frame-inhibit-implied-resize
If this option is @code{nil}, changing font, menu bar, tool bar,
internal borders, fringes or scroll bars of a specific frame may
implicitly resize the frame's display area in order to preserve the
number of columns or lines the frame displays.  If this option is
non-@code{nil}, no implied resizing is done.

The value of this option can be also be a list of frame parameters.  In
that case, implied resizing is inhibited when changing a parameter that
appears in this list.  The frame parameters currently handled by this
option are: @code{font}, @code{font-backend},
@code{internal-border-width}, @code{menu-bar-lines} and
@code{tool-bar-lines}.

Changing any of the @code{scroll-bar-width}, @code{scroll-bar-height},
@code{vertical-scroll-bars}, @code{horizontal-scroll-bars},
@code{left-fringe} and @code{right-fringe} frame parameters is handled
as if the frame contained just one live window.  This means, for
example, that removing vertical scroll bars on a frame containing
several side by side windows will shrink the frame width by the width of
one scroll bar provided this option is @code{nil} and keep it unchanged
if this option is either @code{t} or a list containing
@code{vertical-scroll-bars}.

The default value is @code{'(tool-bar-lines)} for Lucid, Motif and
Windows (which means that adding/removing a tool bar there does not
change the frame height), @code{nil} on all other window systems
including GTK+ (which means that changing any of the parameters listed
above may change the size of the frame), and @code{t} otherwise (which
means the frame size never changes implicitly when there's no window
system support).

Note that when a frame is not large enough to accommodate a change of
any of the parameters listed above, Emacs may try to enlarge the frame
even if this option is non-@code{nil}.
@end defopt

@c FIXME?  Belongs more in Emacs manual than here?
@c But, e.g., fit-window-to-buffer is in this manual.
If you have a frame that displays only one window, you can fit that
frame to its buffer using the command @code{fit-frame-to-buffer}.

@deffn Command fit-frame-to-buffer &optional frame max-height min-height max-width min-width only
This command adjusts the size of @var{frame} to display the contents of
its buffer exactly.  @var{frame} can be any live frame and defaults to
the selected one.  Fitting is done only if @var{frame}'s root window is
live.  The arguments @var{max-height}, @var{min-height}, @var{max-width}
and @var{min-width} specify bounds on the new total size of
@var{frame}'s root window.  @var{min-height} and @var{min-width} default
to the values of @code{window-min-height} and @code{window-min-width}
respectively.

If the optional argument @var{only} is @code{vertically}, this function
may resize the frame vertically only.  If @var{only} is
@code{horizontally}, it may resize the frame horizontally only.
@end deffn

The behavior of @code{fit-frame-to-buffer} can be controlled with the
help of the two options listed next.

@defopt fit-frame-to-buffer-margins
This option can be used to specify margins around frames to be fit by
@code{fit-frame-to-buffer}.  Such margins can be useful to avoid, for
example, that such frames overlap the taskbar.

It specifies the numbers of pixels to be left free on the left, above,
the right, and below a frame that shall be fit.  The default specifies
@code{nil} for each which means to use no margins.  The value specified
here can be overridden for a specific frame by that frame's
@code{fit-frame-to-buffer-margins} parameter, if present.
@end defopt

@defopt fit-frame-to-buffer-sizes
This option specifies size boundaries for @code{fit-frame-to-buffer}.
It specifies the total maximum and minimum lines and maximum and minimum
columns of the root window of any frame that shall be fit to its buffer.
If any of these values is non-@code{nil}, it overrides the corresponding
argument of @code{fit-frame-to-buffer}.
@end defopt


@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.  The @var{value} possibilities for the position parameters are:
an integer, a list @code{(+ @var{pos})}, or a list @code{(- @var{pos})};
as previously described (@pxref{Position Parameters}).

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 Terminal Parameters
@section Terminal Parameters
@cindex terminal parameters

  Each terminal has a list of associated parameters.  These
@dfn{terminal parameters} are mostly a convenient way of storage for
terminal-local variables, but some terminal parameters have a special
meaning.

  This section describes functions to read and change the parameter values
of a terminal.  They all accept as their argument either a terminal or
a frame; the latter means use that frame's terminal.  An argument of
@code{nil} means the selected frame's terminal.

@defun terminal-parameters &optional terminal
This function returns an alist listing all the parameters of
@var{terminal} and their values.
@end defun

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

@defun set-terminal-parameter terminal parameter value
This function sets the parameter @var{parm} of @var{terminal} to the
specified @var{value}, and returns the previous value of that
parameter.
@end defun

Here's a list of a few terminal parameters that have a special
meaning:

@table @code
@item background-mode
The classification of the terminal's background color, either
@code{light} or @code{dark}.
@item normal-erase-is-backspace
Value is either 1 or 0, depending on whether
@code{normal-erase-is-backspace-mode} is turned on or off on this
terminal.  @xref{DEL Does Not Delete,,, emacs, The Emacs Manual}.
@item terminal-initted
After the terminal is initialized, this is set to the
terminal-specific initialization function.
@item tty-mode-set-strings
When present, a list of strings containing escape sequences that Emacs
will output while configuring a tty for rendering.  Emacs emits these
strings only when configuring a terminal: if you want to enable a mode
on a terminal that is already active (for example, while in
@code{tty-setup-hook}), explicitly output the necessary escape
sequence using @code{send-string-to-terminal} in addition to adding
the sequence to @code{tty-mode-set-strings}.
@item tty-mode-reset-strings
When present, a list of strings that undo the effects of the strings
in @code{tty-mode-set-strings}.  Emacs emits these strings when
exiting, deleting a terminal, or suspending itself.
@end table

@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

  A @dfn{live frame} is one that has not been deleted.  When a frame
is deleted, it is removed from its terminal display, although it may
continue to exist as a Lisp object until there are no more 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 @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
This function returns a list of all the live frames, i.e., those 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}.  Frames on text terminals always count as
``visible'', even though only the selected one is actually displayed.
@end defun

@defun next-frame &optional frame minibuf
This function 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 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}).

@cindex frame without a minibuffer
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 explicitly specify 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
Terminals}.
@end defvar

@node Input Focus
@section Input Focus
@cindex input focus
@c @cindex selected frame    Duplicates selected-frame, same for selected-window.

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
Terminals}), 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 shown 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
explicitly 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 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}.  Each
frame on a text terminal has a number which appears in the mode line
before the buffer name (@pxref{Mode Line Variables}).

@defun select-frame-set-input-focus frame &optional norecord
This function selects @var{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 terminal, the next redisplay displays the new frame on the
entire terminal screen.  The optional argument @var{norecord} has the
same meaning as for @code{select-frame} (see below).  The return value
of this function is not significant.
@end defun

@deffn Command select-frame frame &optional norecord
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, and its terminal
becomes the selected terminal.  This function then calls
@code{select-window} as a subroutine, passing the window selected
within @var{frame} as its first argument and @var{norecord} as its
second argument (hence, if @var{norecord} is non-@code{nil}, this
avoids changing the order of recently selected windows nor the buffer
list).  @xref{Selecting Windows}.

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 deffn

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

@defvar focus-in-hook
This is a normal hook run when an Emacs frame gains input focus.
@end defvar

@defvar focus-out-hook
This is a normal hook run when an Emacs frame loses input focus.
@end defvar

@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.
@end defopt

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

A frame on a graphical display may be @dfn{visible}, @dfn{invisible},
or @dfn{iconified}.  If it is visible, its contents are displayed in
the usual manner.  If it is iconified, its contents are not displayed,
but there is a little icon somewhere to bring the frame back into view
(some window managers refer to this state as @dfn{minimized} rather
than @dfn{iconified}, but from Emacs' point of view they are the same
thing).  If a frame is invisible, it is not displayed at all.

  Visibility is meaningless on text terminals, since only the selected
one is actually displayed in any case.

@defun frame-visible-p frame
This function 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 terminal, all frames are considered ``visible'' for the
purposes of this function, even though only one frame is displayed.
@xref{Raising and Lowering}.
@end defun

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

@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

  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 also 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

@cindex raising a frame
@cindex lowering a frame
  Most window systems use a desktop metaphor.  Part of this metaphor
is the idea that system-level windows (e.g., Emacs frames) are
stacked in a notional third dimension perpendicular to the screen
surface.  Where two overlap, the one higher up covers the one
underneath.  You can @dfn{raise} or @dfn{lower} a frame using the
functions @code{raise-frame} and @code{lower-frame}.

@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

  On window systems, you can also enable auto-raising (on frame
selection) or auto-lowering (on frame deselection) using frame
parameters.  @xref{Management Parameters}.

@cindex top frame
  The concept of raising and lowering frames also applies to text
terminal frames.  On each text terminal, only the top frame is
displayed at any one time.

@defun tty-top-frame terminal
This function returns the top frame on @var{terminal}.  @var{terminal}
should be a terminal object, a frame (meaning that frame's terminal),
or @code{nil} (meaning the selected frame's terminal).  If it does not
refer to a text terminal, the return value is @code{nil}.
@end defun

@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

@defun frame-pointer-visible-p &optional frame
This predicate function returns non-@code{nil} if the mouse pointer
displayed on @var{frame} is visible; otherwise it returns @code{nil}.
@var{frame} omitted or @code{nil} means the selected frame.  This is
useful when @code{make-pointer-invisible} is set to @code{t}: it
allows to know if the pointer has been hidden.
@xref{Mouse Avoidance,,,emacs, The Emacs Manual}.
@end defun

@need 3000

@node Pop-Up Menus
@section Pop-Up Menus
@cindex menus, popup

  A Lisp program can pop up a menu so that the user can choose an
alternative with the mouse.  On a text terminal, if the mouse is not
available, the user can choose an alternative using the keyboard
motion keys---@kbd{C-n}, @kbd{C-p}, or up- and down-arrow keys.

@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 (or the top-left corner of the frame if the mouse is not
available on a text terminal).  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.)  On text terminals and
toolkits that support menu titles, the title is taken from the prompt
string of @var{menu} if @var{menu} is a keymap, or from the prompt
string of the first keymap in @var{menu} if it is a list of keymaps
(@pxref{Defining Menus}).

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 @var{item} should 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.  Unlike in a menu keymap, a @code{nil}
@var{value} does not make the menu item non-selectable.
Alternatively, each @var{item} can be a string rather than a cons
cell; this makes a non-selectable menu item.

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
@kbd{C-g}, 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}).  (On text terminals, the
box title is not displayed.)

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}.

@defopt 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 defopt

  When using X, 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{Font and 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)
@cindex clipboard
@cindex primary selection
@cindex secondary selection

  In the X window system, data can be transferred between different
applications by means of @dfn{selections}.  X defines an arbitrary
number of @dfn{selection types}, each of which can store its own data;
however, only three are commonly used: the @dfn{clipboard},
@dfn{primary selection}, and @dfn{secondary selection}.  @xref{Cut and
Paste,, Cut and Paste, emacs, The GNU Emacs Manual}, for Emacs
commands that make use of these selections.  This section documents
the low-level functions for reading and setting X selections.

@deffn Command x-set-selection type data
This function sets an X selection.  It takes two arguments: a
selection type @var{type}, and the value to assign to it, @var{data}.

@var{type} should be a symbol; it is usually one of @code{PRIMARY},
@code{SECONDARY} or @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}.

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.

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

@defopt 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 defopt

@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.

@node Drag and Drop
@section Drag and Drop
@cindex 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''.

  To read user input of color names with completion, use
@code{read-color} (@pxref{High-Level Completion, read-color}).

@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 terminals

  Text 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 different colors on different text terminals; 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 terminal.
@end defun

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

This section describes some of the functions and variables for
querying and using X resources, or their equivalent on your operating
system.  @xref{X Resources,, X Resources, emacs, The GNU Emacs
Manual}, for more information about 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

@defvar inhibit-x-resources
If this variable is non-@code{nil}, Emacs does not look up X
resources, and X resources do not have any effect when creating new
frames.
@end defvar

@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 menu is popped up by clicking
the mouse on some portion of the Emacs display.
@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 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 height for all physical monitors associated with
@var{display}.  @xref{Multiple Terminals}.
@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 Terminals}.
@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.

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

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

@defopt 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 defopt

@cindex backing store
@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

@cindex SaveUnder feature
@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} (a limited, unchangeable number
of grays), @code{gray-scale} (a full range of grays),
@code{static-color} (a limited, unchangeable number of colors),
@code{pseudo-color} (a limited number of colors), @code{true-color} (a
full range of colors), and @code{direct-color} (a full range of
colors).
@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 about the window
system in use where Emacs shows the specified @var{display}.  (Their
names begin with @code{x-} for historical reasons.)

@defun x-server-version &optional display
This function returns the list of version numbers of the GUI window
system running on @var{display}, such as the X server on GNU and Unix
systems.  The value is a list of three integers: the major and minor
version numbers of the protocol, and the distributor-specific release
number of the window system software itself.  On GNU and Unix systems,
these are normally the version of the X protocol and the
distributor-specific release number of the X server software.  On
MS-Windows, this is the version of the Windows OS.
@end defun

@defun x-server-vendor &optional display
This function returns the ``vendor'' that provided the window system
software (as a string).  On GNU and Unix systems this really means
whoever distributes the X server.  On MS-Windows this is the vendor ID
string of the Windows OS (Microsoft).

When the developers of X labeled 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