[HarfBuzz] Possible bug in chain_context_lookup with Gpos

Behdad Esfahbod behdad at behdad.org
Thu Jan 6 11:59:45 PST 2011

Thanks Keith, I pushed a cleaner fix out.


On 01/06/11 12:36, Keith Stribley wrote:
> Hi Behdad,
> I think there maybe a bug in the handling of kerns using format 3 Chaining
> Context lookups. When GPOS lookups are used, then the output part of the
> buffer does not seem to be used. In this case if there is a backtrack context,
> then the check (c->buffer->out_len<  backtrackCount) at the start of
> chain_context_lookup will always fail. For GPOS I think it should use the main
> buffer not the output buffer. Presumably the current code works fine for
> Chaining Contexts for GSUB lookups, but the attached patch may be necessary
> for GPOS.
> This patch fixes the positioning of ့ in sequences like ကဲ့ for the Padauk font
> for example, so that HBNG then behaves the same as other renderers like ICU
> and Uniscribe.
> thanks,
> Keith
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