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

[Behdad Esfahbod]

Fair.  I'll do some measurements and report back if I find something
interesting.

behdad
http://behdad.org/


On Tue, Dec 12, 2023 at 4:01 PM Ned Holbrook <ned at apple.com> wrote:

> My main concern with producing multiple glyphs is that it has substantial
> API and tooling implications.
>
> On Dec 12, 2023, at 10:57 AM, Behdad Esfahbod <behdad at behdad.org> wrote:
>
> On Tue, Dec 12, 2023 at 11:51 AM John Hudson <john at tiro.ca> wrote:
>
>> 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?
>>
> Thanks John. The main benefit in my opinion is not allocating a gid to
> every precomposed Unicode character, most of them Latin. The Arabic
> use-case is extra.
>
> b
>
>
> 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/
>>
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>> --
>>
>> John Hudson
>> Tiro Typeworks Ltd    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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