[HarfBuzz] HarfBuzz shaping of R2L text

[Eli Zaretskii]

> Date: Fri, 31 May 2019 08:54:50 +0300
> From: Eli Zaretskii <eliz at gnu.org>
> Cc: harfbuzz at lists.freedesktop.org
> 
> > Date: Thu, 30 May 2019 21:19:00 +0100
> > From: Richard Wordingham <richard.wordingham at ntlworld.com>
> > Cc: harfbuzz at lists.freedesktop.org
> > 
> > > I don't see any reordering here (with HarfBuzz), but maybe it's
> > > because the only font I have that covers Myanmar is Code2000.
> > 
> > That's probably the problem.  I have Version 1.171 of the font, and the
> > closest is comes to layout support for Myanmar is empty lists of
> > lookups for undefined script "myan".  The script tag should be "mymr",
> > so HarfBuzz applies no script-specific shaping.  There may be other
> > issues, as changing "myan" to "mymr" doesn't fix the problem.
> 
> That figures, as Emacs by default claims there are no fonts on this
> system that support Myanmar, and I need to force it use Code2000.
> 
> I will try with other fonts later.

With Da Lekh I do see the reordering, but only with HarfBuzz as the
font backend; Uniscribe doesn't seem to support that, at least not the
version on Windows 7.