Why even create OT for Arabic?

[Ahmad Osman]

This is not a rhetoric question by the way, I really have ceased to know why.

When I learnt OT about a year ago, I understood that, at least so far as Arabic is concerned, OT was useful for three purposes:
1. To substitute isolated forms for glyphs for other forms (initial, medial, final, or isolated)
2. To create ligatures
3. To distinguish high vocalisation marks from low vocalisation marks, something which necessitates that low-glyph and high-glyph classes be created.

Working on Latin typefaces, I found out (please correct me if I were mistaken) that there are only so many preset ligatures that one can find in the unicode ranges, and that OT is also necessary for alternative forms. Great.

Working on Arabic typefaces, however, I found out that the Arabic glyph compartments were programmed as to perform the basic substitution operation (from isolated to other forms) without OT.

I also found out that basically all the ligatures that I could dream of were in the 'Arabic Presentation Forms-A' unicode range. Those preset ligatures seem to work fine without need for OT. Same for the vocalisation marks, which also got substituted by their low counterparts by sheer glyph programming (I suppose).

Given all of that, why would I as an Arabic typeface designer need OT?

[Glagolitic]

You are correct. Rendering Arabic is usually the job of the OS rather than OT.

The precomposed arabic forms in Unicode are for compatibility — and are not actually used when entering text. Arabic text remains in decomposed form, while being correctly displayed by the OS with all forms.

[Luc[as]]

What application and system were you using to test? In order to make Arabic work in a standard MS Word, you need OT programming. Without OT it might look acceptable in InDesign ME, but properly designed and positioned vocalisation can only work with a lot of programming in Volt.

[Ahmad Osman]

To answer Luc(as), indeed I am designing typefaces to be used on Adobe InDesign ME, so apparently that's why I did not see the relevance.
Question to Glagolitic: What is OS? Something system-related?
Lots of thanks to both.

[Glagolitic]

To answer Luc(as), indeed I am designing typefaces to be used on Adobe InDesign ME, so apparently that's why I did not see the relevance.
Question to Glagolitic: What is OS? Something system-related?
Lots of thanks to both.

OS = Operating System.

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