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

[Alan Third <alan@idiocy.org>]

On Tue, Jun 28, 2022 at 08:38:11PM +0200, Pascal Quesseveur wrote:
> From what I understand the way to deal with background transparency of
> SVG images has changed in version 28.1 in function svg_load_image
> (comments about opacity are still there but I think they are
> irrelevant). Now the SVG image is encapsulated in another SVG image in
> which a rect element is defined with the background color of the
> image.
> 
> 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.

Apologies for leaving this so long.

Is this an issue for *all* Windows machines? The documentation for
COLORREF[1] suggests that Windows uses a byte format for *all* colours
of 0x00BBGGRR, which would explain this, but I thought it worked fine
on some machines?

Alternatively, I'm looking at the wrong documentation, however it
appears the code in w32term.c uses this COLORREF for colours as
defined in a face, so I think it's the right thing.

If this is right and Windows always uses this format, all we need to
do is format the SVG colour differently on Windows.

[1] https://learn.microsoft.com/en-gb/windows/win32/gdi/colorref?redirectedfrom=MSDN

-- 
Alan Third