bug#43889: 28.0.50; [PATCH] Add new smiley-style emoji to Gnus

[Eli Zaretskii <eliz@gnu.org>]

> From: Robert Pluim <rpluim@gmail.com>
> Cc: Eli Zaretskii <eliz@gnu.org>,  43889@debbugs.gnu.org
> Date: Mon, 12 Oct 2020 11:03:53 +0200
> 
>     >> How about adding that: the font-backend frame parameter should tell
>     >> you if HarfBuzz is available.
> 
> By looking for the substring 'hb' in it?

Not necessarily.  The set of HarfBuzz-based font backends is very
small, so we could just have a list and test against it.

> Could we add something a little less icky, along the lines of
> 'libxml-available-p'?

We could, but it wouldn't tell us whether HarfBuzz is actually being
used (as opposed to being the fallback).

But this looks like a moot point, given what you write below:

>     Adam> Do you mean removing the option if HarfBuzz isn't available?
> 
> I donʼt think this is dependent on Harfbuzz, etc/NEWS.27:
> 
>     ** Multicolor fonts such as "Noto Color Emoji" can be displayed on
>     Emacs configured with Cairo drawing and linked with cairo >= 1.16.0.
> 
> (and on macOS, if explicitly requested)
> 
>     Adam> As far as I understand it, emoji can be displayed without, they just
>     Adam> won't have color? Which might be something that users without HarfBuzz
>     Adam> would like to be able to choose.
> 
>     Adam> (Having color emoji is just my motivation to make the patch.)
> 
> They'd be displayed with whatever font Emacs found for them.
> 
>     >> Perhaps when HarfBuzz is being used, it should be the default?  I
>     >> don't use Gnus, but maybe such a new default will make sense to Gnus
>     >> users?
> 
> 
>     Adam> I think changing the default would be annoying to users, but I don't
>     Adam> have any evidence in either direction. Maybe some users would consider
>     Adam> it "modern" to change it.
> 
> As a Gnus user I wouldnʼt object to it being the default, as long as
> there was a reasonable fallback for when those characters cannot be
> displayed.