[HarfBuzz] Zero-width joiner / non-joiner

[Sebastien Metrot]

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.

Thanks in advance,

S.