Re: Treatment of Variation Selectors in the Client

On 2024-10-17 09:28, Skef Iterum wrote:
>
> I may be reading the code wrong, but both the HarfBuzz and fontations 
> subsetters variation alternates are treated as potential substitutes 
> for "individual" Unicode regardless of the unicode values to be 
> included. That is, the implementation doesn't look to see whether the 
> variation selector itself has been requested to be included. So, in 
> effect, UVS mappings are supported by default (unless I'm misreading).
>
> It's not clear to me why this is the case. I suppose one explanation 
> would be that certain shapers might use variation selectors 
> implicitly, and therefore they aren't considered to be "real" 
> codepoints. But in that case maybe we should treat them like layout 
> features that are used by default, giving the option to a shaper, and 
> therefore a client, to skip them when they aren't needed.

Is it possible to query the format 14 cmap subtable and include only the 
U+xxxx+UVS mappings found there that correspond to the subset for a 
given initial font delivery or patch?

JH


-- 

John Hudson
Tiro Typeworks Ltdwww.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.