[HarfBuzz] Selecting fonts for HarfBuzz

[Eli Zaretskii]

> Date: Wed, 05 Jun 2019 05:36:11 +0300
> From: Eli Zaretskii <eliz at gnu.org>
> Cc: harfbuzz at lists.freedesktop.org
> 
> > We assume fonts support shaping.  Ie. we don't have a way to check for font suitability for correct shaping.
> 
> I understand, thanks.  I wasn't asking how to do that with HarfBuzz, I
> was asking what font features should my font matching function examine
> to make sure the font will "support shaping" in the HarfBuzz sense.
> Features that can be tested without actually shaping some text, of
> course, i.e. without actually opening the font and using it.

To make the question perhaps more concrete: the current code considers
a font to be a match for shaping with HarfBuzz if it's either OTF or
TTF, and covers at least one Unicode sub-range above u+00FF
codepoint.  Is this a reasonable test, or should the code consider
additional font features?

TIA