[HarfBuzz] glyph advance difference between coretext and ot backend

[Dohyun Kim]

Hi,

I have compiled harfbuzz-ng on Mac OS X Lion.
While testing some fonts, I encounterd a strange mismatch between
coretext and ot backends:

$ ./hb-shape --shapers=coretext /System/Library/Fonts/AppleGothic.ttf ABC
[gid41=0+726|gid42=1+644|gid43=2+685]

$ ./hb-shape --shapers=ot /System/Library/Fonts/AppleGothic.ttf ABC
[gid41=0+743|gid42=1+659|gid43=2+701]

The Units Per Em of AppleGothic is 1000.
However, ot backend under Mac seems to consider upem as 1024 and
increase glyph widths in proportion, resulting in incorrect glyph positions.

BTW, ot backend on ubuntu machine gives the same result as coretext under Mac.

Best,
-- 
Dohyun Kim
College of Law, Dongguk University
Seoul, Republic of Korea