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XBM images sometimes inverted on Windows

From: Neil Roberts
Subject: XBM images sometimes inverted on Windows
Date: Fri, 30 Nov 2007 12:42:26 +0000
User-agent: Mutt/1.5.16 (2007-06-09)


I've noticed that when running Emacs under Windows, if you create an
XBM image where the :data keyword is set to a string containing the
actual bits of the bitmap then the foreground and background colours
are swapped. If you use the same image but set the :data keyword to an
XBM image string then the swapping does not occur. The swapping
doesn't occur either way under X. Is this a bug?

Please eval the following code snippet to demonstrate. Under X, both
smilies look the same, but under Windows the bottom smiley is
white-on-black, and the top smiley is black-on-white.

(defconst smiley-data '(#x00 #x00 #x24 #x00 #x00 #x24 #x18 #x00))

(defun smiley-from-xbm-data ()
  ;; Make an XBM image from the smiley data
  (list 'image :type 'xbm :ascent 100 :data
        (concat "#define smiley_width 8\n"
                "#define smiley_height 8\n"
                "static unsigned char smiley_bits[] = {\n"
                "   "
                (mapconcat (lambda (byte) (format "0x%02x" byte))
                           smiley-data ", ")
                " };")))

(defun smiley-from-xbm-bytes ()
  ;; Make an image using the bytes directly in a string
  (list 'image :type 'xbm :ascent 100 :width 8 :height 8
        :data (apply 'string smiley-data)))

  (set-buffer (get-buffer-create "*Smiley demo*"))
  (insert "Smiley created from XBM image: "
          (propertize ":)" 'display (smiley-from-xbm-data)) "\n"
          "Smiley created from the actual bytes: "
          (propertize ":)" 'display (smiley-from-xbm-bytes)) "\n")
  (pop-to-buffer (current-buffer)))

- Neil

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