bug#56691: outline-minor-mode displays navigation arrow buttons as emojis

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: hello@paulwrankin.com,  56691@debbugs.gnu.org
> Date: Sat, 30 Jul 2022 13:33:44 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I think we can currently only do that by looking at the details of the
> > build.  Currently, color Emoji are supported only by builds with Cairo
> > and HarfBuzz on Unix and by macOS builds.
> 
> We don't support colour emojis on Windows?  I didn't know that.

We don't.  The APIs used on Windows to display characters don't
support that, and more sophisticated APIs which do can only be called
from C++.

> Symbola doesn't have support for LARGE ORANGE CIRCLE "🟠", so we could
> try that instead.  I know, it's brittle, but so is listing all known
> colour emoji fonts.

Maybe.  It doesn't take care of issues raised by Robert, though.

> The real fix would be to look at the actual glyph data produced, and see
> whether it's colourful or not, wouldn't it?  Is that possible?

I don't know how to do that.  I don't think these aspects of the
glyphs are exposed to Emacs, but maybe I'm wrong.

> Or alternatively -- query the font whether it has colour glyphs, but
> I don't know whether that's easy, either.  Anybody know?

Not me.