Re: Treatment of Variation Selectors in the Client

Perhaps the thinking is that USVs could be applied downstream?
It's probably something like this, but there's still a missing underlying explanation. After all, you might need any given codepoint downstream and the premise of subsetting is that you know what you will and won't need. One could instead treat the SVs like default-active layout features, putting them in a list that's added to the unicodes by default but allowing you to override that. But that's not what seems to have happened.

If I had to guess I would say that the rationale for how HarfBuzz works is probably "this functionality isn't widely understood and maybe even not known, so we shouldn't rely on users specifically adding the variation selectors they might need." And if that's more or less what happened I'm not sure the same answer should apply to IFT, because the spec strongly encourages providing everything in the font, and we plan to do that, it's just a question of where. So as long as "the client" (or some clients) can know whether it's about to use an SV, it might make sense to patch more cleverly on that basis. (And if some clients don't know, they can always add the SVs into the codepoint list, at the cost of loading extra patches.)

Skef
________________________________
From: John Hudson <john@tiro.ca>
Sent: Thursday, October 17, 2024 4:57 PM
To: public-webfonts-wg@w3.org <public-webfonts-wg@w3.org>
Subject: Re: Treatment of Variation Selectors in the Client

EXTERNAL: Use caution when clicking on links or opening attachments.


On 2024-10-17 15:52, Skef Iterum wrote:
> Beyond that, though, the question is how flexible we can be in
> satisfying the glyph closure requirement. It seems like the strategy
> used for static subsets (again, if I'm reading the code right) is to
> treat the variation selectors as "extra", not considering them as part
> of the list of unicodes to be preserved (or not). So, for example,
> even if VS 1 isn't in the list of codepoints to be preserved, you can
> still get glyphs only accessible using VS 1. It's not clear to me why
> that's the case.

Perhaps the thinking is that USVs could be applied downstream?

I’m giving a talk at UTW next week that touches on applying formatting
control characters in buffered states to affect text modes for readers.
My focus is ZWNJ and ZWJ in Indic scripts, but the same concept can be
applied to USVs.

J.


--

John Hudson
Tiro Typeworks Ltd    https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.tiro.com%2F&data=05%7C02%7Csiterum%40adobe.com%7C72149c4578454eba1aa508dcef077941%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C638648062620036820%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=NvVh1RqiZkGXoxrqWponvpbW3hSMq45PB7IdaZGRYbY%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.

__________

EMAIL HOUR
In the interests of productivity, I am only dealing
with email towards the end of the day, typically
between 4PM and 5PM. If you need to contact me more
urgently, please use other means.