HTML manual Retina resolution animated gifs

[gracjan]

Write an Emacs function that will change IMG tags in documentation from:

<img src="xxx.gif">

to

<img width="W" height="H" src="xxx.gif">

where W and H are half of gif width and height. (Half because screenshots are made on retina display).

Invocation should be:

emacs -l haskell-manual-gif-size-fixup.el -f haskell-manual-gif-size-fixup-batch-and-exit *.html

[gracjan]

To get gif dimensions:

(defun get-gif-dimensions (filename)
  (interactive "fFile name:")
  (with-temp-buffer
    (insert-file-contents-literally filename nil 0 10 nil)
    (let ((result
           (cons (+ (char-after 7) (* 256 (char-after 8)))
                 (+ (char-after 9) (* 256 (char-after 10))))))
      (if (called-interactively-p)
          (message "Dimensions: %dx%d" (car result) (cdr result)))
      result)))