[HarfBuzz] Zero-width joiner / non-joiner

[Harshula]

On Sun, 2011-05-22 at 02:48 +0200, Sebastien Metrot wrote:
> Hi all,
> 
> I'm in the process of rewriting my lib's text rendering engine with
> harfbuz as the shaper. Most things are working fine but I got some
> strange results with the rendering of some test strings. It seems that
> while the zero-width joiner and zero-width non-joiner codepoints (U
> +200C and U+200D) are interpreted correctly (they change the join
> behaviour), they are still added as glyphs to render in the output.
> The problem is that some fonts ignore these glyphs but I have come
> across fonts that actually display a sign for these codepoints. I
> would like to know if this is something that I have to handle by
> myself or if there is something else I'm missing.

Which scripts are you testing? Some scripts, e.g. Sinhala, needs the ZWJ
to be passed on to the font's GSUB lookup in order to display conjuncts.
Other scripts don't. Pango & ICU have a flag to denote that a particular
Indic script needs ZWJ passed on to the GSUB lookup.

cya,
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