GNU Info

(elisp)Display Feature Testing

---

Prev: Resources Up: Frames

---

Enter node , (file) or (file)node

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 ordinarly uses
a popup menu could use the minibuffer if popup menus are not supported.

   The optional argument 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 `nil' (which refers
to the selected frame's display, Note: Input Focus).

   Note: Color Names, Note: Text Terminal Colors, for other
functions to obtain information about displays.

 - Function: display-popup-menus-p &optional display
     This function returns `t' if popup menus are supported on DISPLAY,
     `nil' if not.  Support for popup menus requires that the mouse be
     available, since the user cannot choose menu items without a mouse.

 - Function: display-graphic-p &optional display
     This function returns `t' if DISPLAY is a graphic display capable
     of displaying several frames and several different fonts at once.
     This is true for displays that use a window system such as X, and
     false for text-only terminals.

 - Function: display-mouse-p &optional display
     This function returns `t' if DISPLAY has a mouse available, `nil'
     if not.

 - Function: display-color-p &optional display
     This function returns `t' if the screen is a color screen.  It
     used to be called `x-display-color-p', and that name is still
     supported as an alias.

 - Function: display-grayscale-p &optional display
     This function returns `t' if the screen can display shades of gray.
     (All color displays can do this.)

 - Function: display-selections-p &optional display
     This function returns `t' if DISPLAY supports selections.
     Windowed displays normally support selections, but they may also be
     supported in some other cases.

 - Function: display-images-p &optional display
     This function returns `t' if 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.

 - Function: display-screens &optional display
     This function returns the number of screens associated with the
     display.

 - Function: display-pixel-height &optional display
     This function returns the height of the screen in pixels.

 - Function: display-mm-height &optional display
     This function returns the height of the screen in millimeters, or
     `nil' if Emacs cannot get that information.

 - Function: display-pixel-width &optional display
     This function returns the width of the screen in pixels.

 - Function: display-mm-width &optional display
     This function returns the width of the screen in millimeters, or
     `nil' if Emacs cannot get that information.

 - Function: 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 `always', `when-mapped', or
     `not-useful'.  The function can also return `nil' when the
     question is inapplicable to a certain kind of display.

 - Function: display-save-under &optional display
     This function returns non-`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.

 - Function: 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 colours supported.

 - Function: display-visual-class &optional display
     This function returns the visual class for the screen.  The value
     is one of the symbols `static-gray', `gray-scale', `static-color',
     `pseudo-color', `true-color', and `direct-color'.

 - Function: display-color-cells &optional display
     This function returns the number of color cells the screen
     supports.

   These functions obtain additional information specifically about X
displays.

 - Function: x-server-version &optional display
     This function returns the list of version numbers of the X server
     running the display.

 - Function: x-server-vendor &optional display
     This function returns the vendor that provided the X server
     software.