[XeTeX] Arabic ligatures

[Musa Furber]

On 6 Jul 2004, at 00:02, Jonathan Kew wrote:

>
> On 5 Jul 2004, at 9:12 pm, Musa Furber wrote:
>
>> I started playing around with Arabic in XeLaTeX.
>>
>> Geeza Pro works well, though it is not close enough to nuskhi (the 
>> model for printed books) or thuluth (the model for Qur'an) for my 
>> tastes.
>>
>> Al Bayan Plain is closer. Unfortunately, something odd is happening 
>> with the ligatures.
>>
>>
>> Compare this sample using Geeza Pro:
>> <pastedGraphic4.tiff>
>> with the same using Al Bayan Plain:
>> <pastedGraphic5.tiff>
>> Notice that in the Geeza sample, there is an alif. It's the vertical 
>> line to the left of the blank space between the two words. That alif 
>> is missing in the Al Bayan sample.
>>
>> I checked the sample in TextEdit, which takes advantage of typography 
>> gobbledygook. The same thing happened here as with XeLaTeX.
>>
>> I then checked the sample in Mellel, which does not seem to use 
>> typography gobbledygook. There, Al Bayan did not lose its alif.
>>
>> So, the problem is not XeLaTeX.
>>
>> Can anyone suggest a solution around this?
>>
>
> Well, it's clearly a bug in the AAT tables in Al Bayan. It's got a 
> ligature rule to access a special glyph for "Allah", but the ligature 
> glyph doesn't actually include the initial alef. I guess maybe Mellel 
> is using some other way of rendering Arabic, not through ATSUI; 
> perhaps it's using the Presentation Forms codepoints. (If so, I'll be 
> very disappointed. But that's off-topic here.) Or perhaps it's just 
> disabling optional ligatures.

In this bug, that font is not alone....

> I'll file a bug report with Apple re Al Bayan, but obviously it'll 
> take some time before a fixed version appears.

...and perhaps Apple will take more note since other fonts share the 
problem...

> Meanwhile, I suppose you could insert a zero-width non-joiner between 
> the alef and lam, to prevent the ligature formation; but it will 
> prevent getting the special ligature for "Allah". And you don't really 
> want to clutter your text like that. Better to use a different font. 
> Does Baghdad look any better than Geeza to you? Or how about DecoType 
> Naskh, if you have it; I'm not sure which systems that shipped with.

...like Badghdad and DecoType Naskh.

Too bad, too, since the Baghdad and Naskh fonts looks better. Or should 
I say "font"? I have them both and they look identical.

I would rather clutter up my TeX file than cripple my output file.

Thanks for the suggestions.

Musa