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elisp: Multi-Frame Images

 
 37.17.10 Multi-Frame Images
 ---------------------------
 
 Some image files can contain more than one image.  We say that there are
 multiple “frames” in the image.  At present, Emacs supports multiple
 frames for GIF, TIFF, and certain ImageMagick formats such as DJVM.
 
    The frames can be used either to represent multiple pages (this is
 usually the case with multi-frame TIFF files, for example), or to create
 animation (usually the case with multi-frame GIF files).
 
    A multi-frame image has a property ‘:index’, whose value is an
 integer (counting from 0) that specifies which frame is being displayed.
 
  -- Function: image-multi-frame-p image
      This function returns non-‘nil’ if IMAGE contains more than one
      frame.  The actual return value is a cons ‘(NIMAGES . DELAY)’,
      where NIMAGES is the number of frames and DELAY is the delay in
      seconds between them, or ‘nil’ if the image does not specify a
      delay.  Images that are intended to be animated usually specify a
      frame delay, whereas ones that are intended to be treated as
      multiple pages do not.
 
  -- Function: image-current-frame image
      This function returns the index of the current frame number for
      IMAGE, counting from 0.
 
  -- Function: image-show-frame image n &optional nocheck
      This function switches IMAGE to frame number N.  It replaces a
      frame number outside the valid range with that of the end of the
      range, unless NOCHECK is non-‘nil’.  If IMAGE does not contain a
      frame with the specified number, the image displays as a hollow
      box.
 
  -- Function: image-animate image &optional index limit
      This function animates IMAGE.  The optional integer INDEX specifies
      the frame from which to start (default 0).  The optional argument
      LIMIT controls the length of the animation.  If omitted or ‘nil’,
      the image animates once only; if ‘t’ it loops forever; if a number
      animation stops after that many seconds.
 
 Animation operates by means of a timer.  Note that Emacs imposes a
 minimum frame delay of 0.01 (‘image-minimum-frame-delay’) seconds.  If
 the image itself does not specify a delay, Emacs uses
 ‘image-default-frame-delay’.
 
  -- Function: image-animate-timer image
      This function returns the timer responsible for animating IMAGE, if
      there is one.
 

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