On Sun, Feb 02, 2014 at 09:45:16AM +0000, Jonathan Kew wrote: > On 2/2/14 01:13, Khaled Hosny wrote: > >Hi, > > > >Someone reported an issue with the hireq placement under the yodh with > >Ezra SIL font[1]. When I checked this, it seemed to be because HarfBuzz > >is composing U+05D9 + U+05B4 to U+FB1D and the font has a glyph for > >U+FB1D that has a not so good placement for hireq. > > > >I thought this composition is result of Unicode normalisation, so > >HarfBuzz is doing the right thing, but the comment in > >hb-ot-shape-complex-hebrew.cc:75 indicates otherwise. I’m no very sure, > >but I feel this kind of composition should fits more into fallback > >shaping like done with Arabic and not something to be done > >unconditionally, WDYT? > > This is a difficult call. Note that U+FB1D does have a canonical > decomposition to <U+05D9, U+05B4>; the comment in > hb-ot-shape-complex-hebrew.cc relates only to the fact that these Hebrew > presentation forms are excluded from the composition rules for NFC; thus, > both NFC and NFD representations use the decomposed sequence. > > Nevertheless, the two representations *are* canonically equivalent, and > therefore it's appropriate that they should be rendered the same.
I was not sure about this, given that it is decomposition only, but I’ll take your word on this. > IMO, this is a font bug in Ezra SIL; if a font has positioning rules for yod > + hireq, and also has a precomposed yod-hireq glyph, the two should look > identical. A font that gives the impression that entering U+FB1D will result > in one appearance, while <U+05D9, U+05B4> will result in something > different, is misleading its users. Indeed. > As for what harfbuzz should do: currently, it deliberately uses the > precomposed Hebrew presentation-form glyphs, because there are many > (generally older) fonts out there that lack good (or any) mark positioning > rules, and so decomposed sequences look terrible. Using the presentation > forms gives a much better result. > > However, perhaps we should try to be more sophisticated, and do something > like "compose to the presentation forms if the font doesn't have GPOS mark > positioning; otherwise prefer decomposed sequences". Yes, this what I had in mind, similar to what HarfBuzz currently does for Arabic presentation forms shaping. Regards, Khaled _______________________________________________ HarfBuzz mailing list [email protected] http://lists.freedesktop.org/mailman/listinfo/harfbuzz
