[HarfBuzz] Units of members of hb_glyph_position_t

[Eli Zaretskii]

> Date: Mon, 27 May 2019 21:21:47 +0300
> From: Eli Zaretskii <eliz at gnu.org>
> 
> I cannot figure out in what units are these values reported, or how to
> control those units (if they are under the client program's control).
> In particular, I get a huge value of x_advance for the letter U+05EA
> HEBREW LETTER TAV when it is followed by U+05BB HEBREW POINT QUBUTS.
> The value of x_advance I get is 1229, which is too large even after
> dividing by 64 (which, btw, I still am not sure is TRT in my case,
> because I don't understand the source of the 64 value).

Btw, if someone wants to look at the code I'm using to call the
shaper, it's here:

  http://git.savannah.gnu.org/cgit/emacs.git/tree/src/ftfont.c?h=harfbuzz

The function that calls the HarfBuzz shaper starts at line 2978 on
that file.  This code is for GNU/Linux, but the code I'm using on
Windows (which is not yet in the repository) is an exact copy of that
function.

Thanks.