bug#56182: 28.1; Display of SVG file with transparent background is incorrect

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 28 Jun 2022 20:45:17 +0100
> From: Alan Third <alan@idiocy.org>
> Cc: Eli Zaretskii <eliz@gnu.org>, Lars Ingebrigtsen <larsi@gnus.org>,
> 	56182@debbugs.gnu.org
> 
> > I don't know why it doesn't work on the W10 computers I work on. I
> > don't know if the problem comes from this modificatino either. It
> > seems to me that the displayed color is BGR instead of RGB and the
> > screen gamma correction is not applied. For what it's worth I managed
> > to work around the problem in lisp. With version 27.1 I had
> > implemented an advice to improve the taking into account of the
> > background color in the style of SVG file. So I extended that advice
> > to solve my problem.
> 
> *scratches head*
> 
> Eli, do we need to decode the "unsigned long" colours in a special way
> on Windows? It could be I've missed a vital step and am using them
> incorrectly. So if the colour is defined in BGR byte order, and I then
> use the unsigned long directly in a printf("#%06X", colour) style,
> that's likely to be wrong, yes?

I don't think I understand what colors you had in mind here.  Can you
walk me through the relevant code?  I'm not sure I will have an
answer, but I could at least try things.

Thanks.