bug#69782: [PATCH] Fringe bitmaps should respect alpha-background

[Nate Sandy]

Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text
editors" <bug-gnu-emacs@gnu.org> writes:

> PGTK and GTK 3 or no-toolkit X builds, with either Cairo or XRender.

Thanks, I will test with those in the next iteration of this patch and
add a ChangeLog entry.

>> The change is altering the parameter 'respect_alpha_background' in
>> {pgtk,x}_cr_draw_image - while this name sounds quite generic, I didn't
>> find any other usages of this function than drawing fringe bitmaps. I
>> hope I didn't miss any.
>
> What about x_draw_image_foreground?

Right. That in turn only gets called by
{pgtk,x}_draw_image_glyph_string. I was unable to determine what those
image glyphs are and how to create one, in order to observe whether this
patch would be detrimental to them. However it does seem sensible for
backgrounds to respect alpha-background here as well.

Where do these image glyphs get used? I didn't notice any difference
with the images I tested (having applied this patch).