bug#40845: SVG rendering issues

[Pip Cet]

On Sat, Apr 25, 2020 at 3:30 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > I've played around a while ago in an attempt to fix these issues, and
> > be able to define "character-like" SVG glyphs. My approach was to add
> > a display spec of the form (gen FN), which calls FN with the current
> > face parameters as arguments whenever redisplaying the spec, then uses
> > the return value (an image spec) as the actual spec to be displayed.
>
> I don't think I understand why we need to call a function for this.
> This is about displaying an image with a specific background color,
> isn't it?

Even if the problem were just the choice of background color, that
would require significant and non-trivial changes for some cases: for
example, an emoji might have to choose foreground colors that provide
sufficient contrast to the background color, and antialiasing and
sub-pixel rendering would also need to be taken into account.

But, at least for me, it's not: I want to be able to define something
that behaves like a character, including displaying differently in
different frames and depending on different face parameters such as
weight, slant, and RTL-ness. I don't really see a way of doing that
satisfactorily without invoking user code outside of the display
engine/image backend code.