bug#36315: 27.0.50; SVG transparency handling is inaccurate

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 26 Jun 2019 08:48:25 +0900
> From: YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>
> Cc: 	pipcet@gmail.com,
> 	36315@debbugs.gnu.org
> 
> > Maybe it's just me, but I'm uneasy to bypass librsvg and call Cairo
> > directly for manipulating SVG images.  Why doesn't librsvg provide a
> > way to do this via its own APIs?
> >
> > Does anyone else think it's unusual to make such direct calls to what
> > is essentially a lower-level library?
> 
> What kind of operations do you think librsvg should provide us with,
> instead of letting us use cairo?

Those for which you called the Cairo functions directly.

> > > > I've built the patch on Windows (you forgot cairo_surface_destroy, so
> > > > I needed to add it), but the result is strange, or maybe I don't
> > > > understand what is expected.  I don't see any rectangle of color
> > > > #f00000, I see the entire frame with black background, and a few
> > > > characters in other colors.
> > > 
> > > When I tested Pip's test case, I started with emacs -Q -rv to avoid
> > > text becomes invisible.  I could see a red rectangle on X11.  Do you
> > > see such a rectangle without my patch?
> > 
> > Yes, I see an orange rectangle (a square, actually, I think).
> 
> If the square is not displayed with my patch, then there is a bug in
> it.  I've sent 3 versions and the first one was wrong.  Please try
> again with the latest one in my previous mail:
> 
>   https://debbugs.gnu.org/cgi/bugreport.cgi?att=1;msg=26;bug=36315;filename=svg-cairo.diff

I tried with the second patch.  I tried now again with the above one:
still no rectangle.

Thanks.