[MPEG-OTSPEC] 'curs' feature: required?

[Peter Constable]

Thanks, John. That's consistent with what I was expecting. And so I think that feature description really needs to be revised.

Issue 622: 'curs' should be required for some scripts<https://github.com/MicrosoftDocs/typography-issues/issues/622>


Peter

From: mpeg-otspec <mpeg-otspec-bounces at lists.aau.at> On Behalf Of John Hudson
Sent: Monday, September 14, 2020 11:40 AM
To: mpeg-otspec at lists.aau.at
Subject: Re: [MPEG-OTSPEC] 'curs' feature: required?

On 14092020 11:29 am, Peter Constable wrote:
Is the 'curs' feature considered a required feature for Arabic or other cursively-connecting scripts?
 I would have expected it's required. It's clear the intent is for triggering cursive attachment positioning (GPOS type 3), and Microsoft's Arabic implementation spec<https://eur04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.microsoft.com%2Fen-us%2Ftypography%2Fscript-development%2Farabic&data=02%7C01%7C%7Cb4dfdb44486d4751fcae08d858dd8e0f%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637357055874456434&sdata=rGbpCQGuYZaBJA6RORiqWe4f3r%2Fhetmd91mx5jnrExA%3D&reserved=0> lists it among features to be applied in GPOS processing. But the description in the OTL feature registry<https://eur04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.microsoft.com%2Fen-us%2Ftypography%2Fopentype%2Fspec%2Ffeatures_ae%23tag-curs&data=02%7C01%7C%7Cb4dfdb44486d4751fcae08d858dd8e0f%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637357055874466422&sdata=8Yar57Rrb8cXmQ5uQ3tv4K66DYk4VWxhVvzBgYdUJA8%3D&reserved=0> is worded in a way that makes it sound optional, at the user's discretion:
 "UI suggestion: This feature could be made active or inactive by default, at the user's preference."

Based on Arabic fonts I have worked on or examined, I would say this definitely should not be optionally active, and if present the curs feature is expected to be applied by default. Indeed, a lot of fonts simply break if curs is not applied.

If a font contains support for different kinds of Arabic layout, e.g. a simplified layout with only horizontal connections and a more sophisticated display with some amount of vertical connections or cascading connections, then the curs support required for the latter still needs to be applied by default, and the differentiation of the layout styles would be implemented, somehow, in GSUB, setting up the glyphs that either will or will not require curs attachment in GPOS.

JH

--



John Hudson

Tiro Typeworks Ltd    www.tiro.com<https://eur04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.tiro.com%2F&data=02%7C01%7C%7Cb4dfdb44486d4751fcae08d858dd8e0f%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637357055874466422&sdata=8ouyKx5fsW93YCT3HlVgJ1HP7Yp%2FdqAfzl6O6x2Olfo%3D&reserved=0>

Salish Sea, BC        tiro at tiro.com<mailto:tiro at tiro.com>



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