[HarfBuzz] Better handling variation selectors

[Behdad Esfahbod]

On 13-04-22 09:16 PM, suzuki toshiya wrote:
> Dear Behdad,
> 
>> Though, we still have to assess what
>> effect it would have on fonts that implement variation-selectors via GSUB
>> instead of cmap.  Does anyone know any fonts like that?
> 
> Maybe some Mongolian fonts have VS to be handled via GSUB,
> instead of cmap format 14 (because Mongolian VS were standardized
> before cmap format 14). Please let me know what I should
> check in detail.

Thanks.  If you come across them, please send me a note.  Otherwise no need to
go looking right now.

Cheers,
behdad


> Regards,
> mpsuzuki
> 
> Behdad Esfahbod wrote:
>> On 13-04-22 08:20 PM, Khaled Hosny wrote:
>>> On Sat, Apr 20, 2013 at 10:49:26AM +0100, Jonathan Kew wrote:
>>>> On 19/4/13 22:13, Behdad Esfahbod wrote:
>>>>
>>>>>   - What should HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES do to variation
>>>>> selectors?  Right now they do not become visible no matter what.  Is it
>>>>> relevant whether the variation selector was actually used during glyph lookup
>>>>> or not?
>>>> Yes, I think it's relevant. A variation selector that was used
>>>> during glyph lookup has (in a sense) become "visible", manifested as
>>>> a particular choice of glyph. I don't think it should -also- appear
>>>> as a separate glyph, even in a "show invisibles" mode. In effect,
>>>> the <base, VS> pair has been ligated - it's just a "ligation" that's
>>>> handled by the cmap instead of GSUB.
>>> But this can be said about many other control characters, ZWJ or ZWNJ
>>> for example, they have a visual effect.
>>>
>>> IMO PRESERVE_DEFAULT_IGNORABLES should simply show any default ignorable
>>> character that is being removed from the output not as a result of
>>> OpenType glyph substitution. One use of such feature (the only use?) is
>>> to make visible all characters that has mysterious effects on the output
>>> so they can be easily checked/edited, and I can see variation selectors
>>> benefiting from this just like any other default ignorable.
>>
>>
>> Note that if the font has a lookup ligating with ZWJ / ZWNJ (or any other
>> default-ignorable) those won't be display even with
>> PRESERVE_DEFAULT_IGNORABLES either.  We have to go out of our way to make that
>> happen (may be very hard for GSUB).  It just happens that for
>> variation-selectors it may be easier.  Though, we still have to assess what
>> effect it would have on fonts that implement variation-selectors via GSUB
>> instead of cmap.  Does anyone know any fonts like that?
>>
>> behdad
>>
>>> Regards,
>>> Khaled
>>> _______________________________________________
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>>>
>>
> 
> 

-- 
behdad
http://behdad.org/