[HarfBuzz] uniscribe confusion

[Behdad Esfahbod]

Dear Martin,

I didn't spend much time to study your test case, but yes, it is a know
different between HB and Uniscribe that we apply attachment late, which
means we still attach to the "correct" location even if you change advance
of the base glyph after the attachment happens, where MS does it other way.

I changed HB to do it other way around, but it broke other things, so I
reverted.  See discussion in:

  https://github.com/behdad/harfbuzz/issues/211

Is that the same issue as the one you are seeing?

behdad



On Tue, Mar 15, 2016 at 2:07 AM, Martin Hosken <mhosken at gmail.com> wrote:

> Dear Behdad,
>
> This is default shaping. The u1037 is attached to the u102F and we get the
> following results:
>
> * uniscribe: [u1000=0+1002|u103D=1 at -55,0+0|u102F=2+147|u1037=3 at 217,0+0]
> * harfbuzz: [u1000=0+1002|u103D=0 at -55,0+0|u102F=0+147|u1037=0 at 217,0+0]
>
> which makes sense. Now if we introduce an increase of the advance on the
> u102F via a feature rule: u102F' 272 u1037 we get:
>
> * uniscribe: [u1000=0+1002|u103D=1 at -55,0+0|u102F=2+419|u1037=3 at 217,0+0]
> * harfbuzz: [u1000=0+1002|u103D=0 at -55,0+0|u102F=0+419|u1037=0 at -55,0+0]
>
> I'm wondering if harfbuzz is over compensating differently to how
> uniscribe does it. It looks like uniscribe just slaps on the extra advance
> and doesn't compensate its attached components. I don't really mind what
> results I get so long as they are consistent.
>
> Any thoughts?
>
> Yours,
> Martin
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-- 
behdad
http://behdad.org/
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