[MPEG-OTSPEC] Shared GSUB/GPOS notes, was Re: dmap proposal

[Skef Iterum]

I would characterize it as almost entirely a data efficiency measure; it 
just reduces file size. Similarly with dmap. dmap probably slightly 
increases the amount of processing involved. Multiple overlapping GSUBs 
won't change the processing time but the design assumes one is already 
starting with a single cmap and substituting in GSUB, which will take 
slightly more time than starting with per-language/region cmaps.

I think the assumption here is that all such processing is dwarfed by, 
e.g., glyph rendering costs, so reducing file size relative to it is a 
virtue.

Skef

On 12/27/23 08:55, John Hudson wrote:

> We already make some TTCs with distinct cmap tables, and some with 
> distinct GSUB tables, so if I understand your proposal correctly it 
> is, like Peter’s DMAP proposal,*a data and processing efficiency 
> measure, correct*? A mechanism that does this at the initial 
> character-to-glyph mapping would seem to provide more robust 
> language-specific support.
>
> JH
>
>
> -- 
>
> John Hudson
> Tiro Typeworks Ltdwww.tiro.com
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