[HarfBuzz] Better handling variation selectors

[Konstantin Ritt]

Hi Behdad, list,

the alternative you've suggested does make sense;
but in my opinion, it is better to change the API now, until 1.0, to make
it more intuitive/cleaner than be a hostage of some "tricky" cases for the
next 10-15-20 years...

Regards,
Konstantin


2013/6/7 Behdad Esfahbod <behdad at behdad.org>

> On 13-04-20 05:49 AM, Jonathan Kew wrote:
> >
> > The remaining question is what to do about a VS that was part of a valid
> > sequence, but the font being used didn't handle it.
>
> So, apparently Mongolian fonts in the wild implement the Mongolian
> Variation
> Selectors using GSUB, not cmap. [1]
>
> So, we either need to keep the "unused" variation selectors in the glyph
> stream, or remove the Mongolian ones from the cmap processing.
>
> Fixing this the way I like would require a change to the get_glyph()
> callback
> API.  Right now we have:
>
> typedef hb_bool_t
> (*hb_font_get_glyph_func_t) (hb_font_t *font, void *font_data,
>                              hb_codepoint_t unicode,
>                              hb_codepoint_t variation_selector,
>                              hb_codepoint_t *glyph,
>                              void *user_data);
>
> Now ideally I would have wanted to split that in two:
>
>   bool get_glyph (unicode)
>
> and
>
>   bool get_glyph_variant (unicode, selector)
>
> but I'm afraid it's too late to make such a change.  Instead, I propose
> that
> we just change the semantics of the existing call and expect that callbacks
> return false if the requested variant is not available, and then we will
> call
> them back with variation_selector=0 and will retain the glyph for the
> selector
> in the glyph stream.
>
> Makes sense?
>
>
> [1] https://bugs.freedesktop.org/show_bug.cgi?id=65258
>
> --
> behdad
> http://behdad.org/
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