bug#6918: Colors of xbm image are swapped on Windows

[Lars Ingebrigtsen]

Kazuhiro Ito <kzhr@d1.dion.ne.jp> writes:

> When I evaluate below expression with Emacs on Windows, colors of the
> second image are swapped.  With Emacs on other environment
> (e.g. Debian), second image is identical to first image.

[...]

> Attached patch would fix problem.  But I don't know this patch is
> correct, because this swapping seems intended.
>
>> 2007-06-21  Jason Rumney  <jasonr@gnu.org>
>>      * image.c (convert_mono_to_color_image): Swap fore and background.
>
> I guess this swapping has become unnecessary anymore by later change.
>
>> 2007-12-05  Jason Rumney  <jasonr@gnu.org>
>>      * image.c (xbm_load) [WINDOWSNT]: Shuffle the bits of directly
>>      specified XBMs.

The code in question seems odd, indeed:

  /* Windows convention for mono bitmaps is black = background,
     white = foreground.  */
  SetTextColor (new_img_dc, background);
  SetBkColor (new_img_dc, foreground);

Can anybody who works on Windows say whether this is the case?

In any case, it seems very odd that the test code (included below again
for easy C-x C-e) should produce image with different colours, since
they should just be two ways of specifying the same image.  I think?

(let ((image "#define default_width 8
#define default_height 16
static char default_bits[] = {
0x81, 0x81, 0x42, 0x42, 0x24, 0x24, 0x18, 0x18, 0x18,
 0x18, 0x24, 0x24, 0x42, 0x42, 0x81, 0x81};")
      (face 'default)
      (string "_"))
  (set-text-properties 0 (length string) `(face ,face) string)
  (with-temp-buffer
    (switch-to-buffer (current-buffer))
    (insert-image
     (create-image image 'xbm t) string)
    (sit-for 1)
    (insert-image
     (create-image image 'xbm t
                   :foreground (face-foreground face)
                   :background (face-background face)
                   ) string)
    (sit-for 3)))


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