[MPEG-OTSPEC] Cmap format to map 1 char to multiple glyphs?

[John Hudson]

I proposed that to the OT developer list a long while ago, and recall 
that Kamal had a similar idea, initially in terms of handling Unicode 
decompositions such that fonts would not need precomposed diacritics. At 
the time, Microsoft thought it unlikely to get traction, as it implied 
significant engineering for unclear benefit, but perhaps the benefit is 
clearer now? As you say, being able to decompose a Unicode character to 
an arbitrary sequence of glyphs is very useful for Arabic, and by-passes 
the need to handle such decompositions in GSUB prior to other shaping.

I suppose the question is whether there is a significant benefit to 
doing this outside of GSUB? — or, indeed, if there might be a reason it 
would be preferable in GSUB?

The inconsistency in dot handling in different joining forms of some 
Arabic characters means that one doesn’t always want to up-front 
decompose some characters to base grapheme and combining dots, but those 
could be excluded from the cmap and passed to GSUB form decomposition in 
the joining form features. But that being the case, why not do it all in 
GSUB?

JH


On 2023-12-12 9:04 am, Behdad Esfahbod wrote:
> Thank you everyone for the very productive meeting.
>
> I like to also bring this issue up. If there is interest, I can work 
> on it. I wrote in my reply to Peter earlier:
>
> /This reminds me of another idea we discussed in, I think, 2019, from 
> Monotype to introduce a `cmap` subtable that would map individual 
> characters to sequences of glyphs. Then the pre-composed Unicode 
> characters wouldn't need to have their own glyphs. Back then we 
> dropped the idea for backwards-compat reasons. But maybe we can pick 
> it up now?/
>
> This is very useful for Arabic as well...
>
> behdad
> http://behdad.org/
>
> _______________________________________________
> mpeg-otspec mailing list
> mpeg-otspec at lists.aau.at
> https://lists.aau.at/mailman/listinfo/mpeg-otspec

-- 

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.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.aau.at/pipermail/mpeg-otspec/attachments/20231212/0971719a/attachment.html>