[HarfBuzz] Arabic Presentation Forms-A in fallback shaping

[Behdad Esfahbod]

On 13-03-12 03:10 PM, Khaled Hosny wrote:
> Hi Behdad,
> 
> While comparing the fallback shaping ICU-based XeTeX with the
> HarfBuzz-based one, I noticed that ICU uses the Arabic Presentation
> Forms-A ligatures if the font have them unlike HarfBuzz. It is not a big
> issue (I don’t even have such font, I striped OT tables from fonts to
> test), but it would be nice to have.

I'm not a huge fan of those, mostly because in Persian Naskh style they are
typically not desired.  That said, changing the code to do it is trivial.  I
already have it for all two-character ligatures.  Extending it to
three-character ones takes another twenty minutes.

But I'm not sure whether we want this.  The size increment in the binary is
about 5k, which is not a big deal, but then I wonder whether I should start
adding build options to disable fallbacks.  Or perhaps we build the best
engine first and wait till someone complains about size before we figure out
how to build smaller subsets.

I'll go ahead and fix this.

b

> Here are the two fonts I tested:
> http://khaledhosny.org/files/tmp/kacstone-noot.ttf (no forms-A)
> http://khaledhosny.org/files/tmp/amiri-regular-noot.ttf (has forms-A)
> 
> Regards,
> Khaled
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-- 
behdad
http://behdad.org/