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

[Po Lu]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> 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?

Only if the font is already opened, and it's a fairly slow operation
that involves a roundtrip to the X server outside of Cairo.  One of the
Java X servers also supports color fonts, but they seem to be
implemented as an overlay, because if I draw some color glyphs to a
window and then use XGetImage, those glyphs do not show up in the
resulting image, even though they do show up on display.

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

I think FC_COLOR gets you halfway there, but it says nothing about Emoji
specifically.

There is no equivalent on Haiku or NS AFAICT, and on MS Windows we
simply don't support color fonts.