[HarfBuzz] Units of members of hb_glyph_position_t

Behdad Esfahbod behdad at behdad.org
Tue May 28 01:21:10 UTC 2019

On Mon, May 27, 2019 at 2:21 PM Eli Zaretskii <eliz at gnu.org> wrote:

> I cannot figure out in what units are these values reported, or how to

The meaning is left to the client.

> control those units (if they are under the client program's control).

They are controlled mainly using hb_font_set_scale().

> 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,

FreeType works in 26.6 fixed-point, ie. 64 units per 1.0.  That's where the
64 value comes from.  And you don't see it in your code because
hb_ft_font_create* sets that on hb_font for you.

In your Windows code, you should call hb_font_set_scale().  I believe right
now you are *not* calling, and you get values in the face's UPEM.  That's
the default scale for fonts.  You can get the face UPEM using

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