[HarfBuzz] Issue regarding chaining contextual substitution

[Behdad Esfahbod]

On 04/06/11 12:35, Behdad Esfahbod wrote:
> Hi Dohyun,,
> 
> On 03/17/11 08:32, Dohyun Kim wrote:
>> Yes, I know that harfbuzz-ng does not provide Hangul Jamo shaping
>> (ljmo, vjmo, tjmo) yet.
>> However, this font has "calt" feature which is equivalent to ljmo + vjmo + tjmo.
>> It seems that harfbuzz has invoked this calt feature for rendering;
>> and the result was good to a large extent.
> 
> I can confirm your observation.  Given that Pango renders your sample
> correctly, I'm guessing that adding compose/decompose logic to HarfBuzz will
> fix this.  That said, I'd add a Hangul jamo shaper too.

Humm, you seem to suggest that this may be a bug in chaining contextual
substitution.  That's possible but I cannot debug it immediately without
digging deep into the font to make sure the tables are correctly designed to
handle it though.  Feel free to debug it by compiling harfbuzz with
-DHB_DEBUG=100 and check the trace.

behdad

> Thanks,
> behdad