[MPEG-OTSPEC] [EXTERNAL] Feature name parameters in multi-script and multi-language fonts

[Peter Constable]

Hi, John

I posted a response in the typography-issues issue.


Peter

From: mpeg-otspec <mpeg-otspec-bounces at lists.aau.at> on behalf of John Hudson <john at tiro.ca>
Date: Sunday, October 15, 2023 at 9:07 AM
To: mpeg-otspec at lists.aau.at <mpeg-otspec at lists.aau.at>
Subject: [EXTERNAL] [MPEG-OTSPEC] Feature name parameters in multi-script and multi-language fonts
I posted this query on the MS typography-issues board back in March, but
received no replies.
https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FMicrosoftDocs%2Ftypography-issues%2Fissues%2F1015&data=05%7C01%7Cpconstable%40microsoft.com%7C52b68c348a9747d1aff708dbcd98e3d8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C638329828780884437%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=lY6Fh7fxYS5PWVdqBzc3IkjJ8Pfp5DoVHup3zvbneEc%3D&reserved=0<https://github.com/MicrosoftDocs/typography-issues/issues/1015>

My understanding from reading the specification for GSUB feature
parameters for Stylistic Sets and Character Variant features is that a
single feature parameter can be applied to a feature tag, regardless of
how that tag is used in terms of lookup contents for different script or
language system tags. Is that understanding correct?

This seems to me to be contrary to the overall OTL model of script and
langsys structures that are specifically designed to enable different
writing systems to have different layout behaviours. So, for example,
when making a font supporting Latin, Cyrillic and Greek script, it is
perfectly feasible for a stylistic set feature such as ss01 to have
entirely different behaviour appropriate to each script, and given the
limited number of 20 registered stylistic set features this is a more
efficient use of the features; also, it is more intuitive for the user
of a particular script for accessible stylistic sets in the UI to begin
as ss01, ss02, etc. rather than these be reserved to some other, unused
writing system.

There are also cases where behaviour of stylistic set features might
differ within a script, at the langsys level. I am currently looking at
implementing a stylistic set within the Latin script that is specific to
traditional Irish orthography (langsys IRT). Since it is the only
stylistic set that would be meaningful within that langsys, my
inclination would be to use ss01, but that feature has different
behaviour for other Latin script languages, and different behaviour
again for other scripts.

Can anyone see a route out of this, in terms of being able to link
feature parameters to specific script/langsys combinations?

JH


--

John Hudson
Tiro Typeworks Ltd    https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.tiro.com%2F&data=05%7C01%7Cpconstable%40microsoft.com%7C52b68c348a9747d1aff708dbcd98e3d8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C638329828780892990%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=XY4aK3f1ZvdkVN61IM28Ogqcm87Vii7llLgbN5gcV0I%3D&reserved=0<http://www.tiro.com/>

Tiro Typeworks is physically located on islands
in the Salish Sea, on the traditional territory
of the Snuneymuxw and Penelakut First Nations.

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