bug#44020: 28.0.50; Prefer selection of colour emoji fonts?

[Stephen Berman]

On Mon, 19 Oct 2020 22:46:50 +0300 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Stephen Berman <stephen.berman@gmx.net>
>> Cc: Robert Pluim <rpluim@gmail.com>,  44020@debbugs.gnu.org,  larsi@gnus.org
>> Date: Mon, 19 Oct 2020 21:03:49 +0200
>>
>> > Didn't someone say they can see color emoji on Cairo?
>>
>> Yes, Lars noted (and I confirm) that the following two lines suffice:
>>
>> (set-fontset-font t 'symbol "Noto Color Emoji")
>> (set-fontset-font t 'symbol "Symbola" nil 'append)
>
> Are the Emoji displayed by Noto Color Emoji or by Symbola?

The majority of characters in emoji-data.txt are displayed by Noto Color
Emoji, but a number of them are displayed by Symbola and some are
displayed as tofu.

> And what version of Noto Color Emoji do you have?

v2018-04-24-pistol-update

> And finally, could you step through the code shown by Robert and tell
> whether the Noto Color Emoji's average_width you get is also zero or
> non-zero?

I started emacs -Q in gdb, evaluated the above two set-fontset-font
sexps, put a breakpoint on font_open_entity, and typed `M-x 8 RET
GRINNING FACE RET' and gdb took control, then I stepped through the
function until gdb output `if (font->average_width > 0 && font->height >
0)' and then I entered `p font->average_width' and gdb output $1 = 16.
Did I do this right and does that answer your question?  If not, please
advise.

Steve Berman