On 13/3/13 01:08, Behdad Esfahbod wrote:
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.
FWIW, my vote would be to -not- "fix" this. We should not do anything
that might appear to encourage font developers to think those lists of
"ligatures" have any real meaning in terms of Arabic-script type design.
I think it was a mistake for Unicode (or indeed anyone) to attempt to
define such a repertoire of ligatures for Arabic script, as the decision
as to what's included and what is excluded - and indeed where to split
longer sequences into 3-character "ligatures" in the first place - is
often rather arbitrary, and heavily dependent on the style involved.
My preference would be for the Arabic engine to ignore them entirely.
JK
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