[HarfBuzz] Selecting fonts for HarfBuzz

[Eli Zaretskii]

> From: Behdad Esfahbod <behdad at behdad.org>
> Date: Wed, 5 Jun 2019 12:07:36 -0700
> Cc: "harfbuzz at lists.freedesktop.org" <harfbuzz at lists.freedesktop.org>
> 
> In other words, I don't know of a legitimate way to filter out broken fonts like code2000.  If that's what you are
> asking for.

No, I wasn't asking about Code2000, I was asking a more general
question.

> Let me ask it differently: why do you think you need to filter anything out?

I assumed that some fonts will not benefit from HarfBuzz, i.e. will
not support complex script shaping, because they lack some fundamental
features HarfBuzz needs.

When Emacs needs to find a font for displaying a character which is
not supported by the default font, it scans the available fonts on the
system, looking for matching fonts.  On Windows, we currently have 2
matching criteria: one for fonts suitable for shaping with Uniscribe,
the other for all the rest (the latter generally don't support complex
script shaping).  For HarfBuzz, the code currently employs the same
matching criteria as for Uniscribe (I described them roughly in a
previous message).  I was asking whether HarfBuzz has additional
requirements from fonts, or would any font that's good for Uniscribe
will be good for HarfBuzz.