Function: display-backing-store

display-backing-store is a byte-compiled function defined in frame.el.gz.

Signature

(display-backing-store &optional DISPLAY)

Documentation

Return the backing store capability of DISPLAY's screen.

The value may be always, when-mapped, not-useful, or nil if the question is inapplicable to a certain kind of display. DISPLAY can be a display name or a frame. If DISPLAY is omitted or nil, it defaults to the selected frame's display.

View in manual

Probably introduced at or before Emacs version 21.1.

Source Code

;; Defined in /usr/src/emacs/lisp/frame.el.gz
;; In NS port, the return value may be `buffered', `retained', or
;; `non-retained'.  See src/nsfns.m.
(defun display-backing-store (&optional display)
  "Return the backing store capability of DISPLAY's screen.
The value may be `always', `when-mapped', `not-useful', or nil if
the question is inapplicable to a certain kind of display.
DISPLAY can be a display name or a frame.
If DISPLAY is omitted or nil, it defaults to the selected frame's display."
  (let ((frame-type (framep-on-display display)))
    (cond
     ((memq frame-type '(x w32 ns haiku pgtk android))
      (x-display-backing-store display))
     (t
      'not-useful))))