[HarfBuzz] glyph advance difference between coretext and ot backend

[Behdad Esfahbod]

For what it's worth Jonathan and I looked into this in Vancouver and tracked
it down to hb-ft's abuse of FreeType API with disregard to hinting issues.
I'll try to address it soonish...

behdad

On 12-07-31 03:22 PM, Jonathan Kew wrote:
> On 31/7/12 19:29, Behdad Esfahbod wrote:
>> Interesting.  I'll take a look.
> 
> It might be worth calling CTFontGetUnitsPerEm to see what Core Text considers
> the em-square of the font to be. ISTR that I've seen cases where Core
> Graphics, at least, "normalizes" the em-units of certain fonts that aren't
> using a "typical" size; I'm not sure if that carries through to Core Text
> metrics as well, but it might be a factor here...
> 
> JK
> 
>>
>> On 07/31/2012 01:49 PM, Rolf Langenhuijzen wrote:
>>> I did a similar test with 2 fonts and it was different between the two..
>>> could it be some internal font thing that is causing this?
>>>
>>> OSX:
>>> hb-shape --shapers=coretext "/dev/fonts/MaiolaPro-Regular.otf" ABC
>>> [A=0+670|B=1+565|C=2+640]
>>>
>>> hb-shape --shapers=ot "/dev/fonts/MaiolaPro-Regular.otf" ABC
>>> [A=0+660|B=1+555|C=2+630]
>>>
>>> hb-shape --shapers=ot "/dev/Whitney-Book-Pro.otf" ABC
>>> [A=0+691|B=1+547|C=2+638]
>>>
>>> hb-shape --shapers=coretext "/dev/Whitney-Book-Pro.otf" ABC
>>> [A=0+691|B=1+547|C=2+638]
>>>
>>> I tried on Ubuntu:
>>> hb-shape --shapers=ot "MaiolaPro-Regular.otf" ABC
>>> [A=0+660|B=1+555|C=2+630]
>>>
>>> So the same as on OSX, not the same as with coretext as you are getting…
>>>
>>> Regards,
>>> Rolf
>>>
>>> On Jul 31, 2012, at 12:42 PM, Dohyun Kim wrote:
>>>
>>>> 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
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-- 
behdad
http://behdad.org/