Re: Status of multicolor fonts?

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 27 Apr 2019 17:13:24 +0900
> From: mituharu@math.s.chiba-u.ac.jp
> Cc: emacs-devel@gnu.org
> 
> >> Does it count as multicolor font support on free platforms?
> >
> > I think it does, yes.  Thanks for working on this.
> 
> I've added some NEWS entries, and re-enabled multicolor fonts
> for the mac-ct font backend driver.

Thanks.

> > As long as I have your attention: could you please help in finishing
> > the development of the harfbuzz branch and landing it on master?  For
> > Posix platforms, there are just a few finishing touches left, I think,
> > the main one being make a separate font backend that uses HarfBuzz
> > interfaces for as many backend facilities as possible (I will tell the
> > details if you can offer help).  I'd appreciate help in this area.
> > TIA.
> 
> I don't know if I'll be of any help, but could you explain the details?

I think I can, but please ask more specific questions.

The general idea is to use HarfBuzz as a font backend which supports
layout of complex scripts, as a replacement for libm17n-flt on
GNU/Linux and as a replacement for Uniscribe on MS-Windows.  The
current code on the branch uses compile-time CPP directives to select
HarfBuzz as the shaper for xftfont and other font back-ends, but I
would like to make it a separate font backend instead, so that people
could choose which one to use.  I also think not every existing font
backend needs to be able to use HarfBuzz, only those which support OTF
and TTF font features should.

> Is it OK to merge master to the harfbuzz branch as the first step
> so as to resolve some conflicts caused by my recent commits?

Yes, please.  In fact, seeing your Cairo changes was what prompted me
to ask you for help in the first place.  The HarfBuzz people wrote the
initial code of the branch, but they said some time ago they didn't
have enough time to work on this, although they will answer questions
regarding HarfBuzz functionality (there's a mailing list dedicate to
HarfBuzz development and use).

TIA