[MPEG-OTSPEC] 回复: [EXTERNAL] Re: Shaping behavior standardization: multi-engine or "Super USE"?

[Peter Constable]

Well, that certainly seems like a reason why language systems and features need to remain organized by scripts.

Now, in some OT2.0 future, maybe new formats could be created in which language systems don’t use OT tags at all but use BCP-47 tags directly. Then that would address that issue. And if ‘loc’ features were organized that way but other features don’t need to be shoe-horned into that structure, we could still have features applied script boundaries triggering lookups that can act on glyphs of whatever scripts.


Peter

From: mpeg-otspec <mpeg-otspec-bounces at lists.aau.at> On Behalf Of John Hudson
Sent: Friday, August 21, 2020 3:09 PM
To: mpeg-otspec at lists.aau.at
Subject: Re: [MPEG-OTSPEC] 回复: [EXTERNAL] Re: Shaping behavior standardization: multi-engine or "Super USE"?

On 21082020 1:52 pm, Peter Constable wrote:
Thirdly, if there is one shaping engine for all scripts, would there be any need at all for LangSys and Feature tables to still be organized hierarchically under different script tags? (That’s another existing obstacle to glyph actions across script-run boundaries.) IOW, instead of a new _set_ of script tags, would just _one_ new “script” tag suffice?

That’s where my mind started going today. But I'm not sure all the issues that arise can be resolved in that model.

If itemisation and glyph run segmentation is not performed on the basis of script tag, and everything using the new USE tag gets processed as a single run, how do we handle characters with locl substitution forms specific to individual scripts? And if such characters are Unicode script=common, are we pushing the segmentation down a level rather than removing it?

J.

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John Hudson

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