[HarfBuzz] Exposing attachment tree / Arabic joining to shaping clients

[Ebrahim Byagowi]

This is very interesting Behdad. Can this have Kashida priority also, like
what harfbuzz-old
<https://github.com/harfbuzz/harfbuzz-old/blob/master/src/harfbuzz-arabic.c#L402>
had.

> [..] even the ones that do NOT use cursive joining.

Guess this a property of a font rather than a buffer? IranNastaliq had
broken Kashida justification in IE6 but not in IE7, so Microsoft probably
has some insight to this, how to detect a font (or a buffer) is not useful
for Kashida justification.

> [,,] The latter definitely belongs to the pos buffer

Guess can't provide much help here. Just about shape of the API, maybe like
the way unsafe to break, hb_buffer_get_glyph_flags, is exposed, would be
useful for Arabic joining info and guess exposing priority can be done in
the some way but we can just forget about it for now.

Thanks!

On Thu, Oct 31, 2019 at 11:12 PM Behdad Esfahbod <behdad at behdad.org> wrote:

> Hi,
>
> For reason that many of you know (letter-spacing, Arabic elongation, other
> postprocessing) I like to expose attachment data to the shaping clients.
> There's two separate pieces so far:
>
> - The Arabic joining info, which is applicable to all Arabic-like fonts
> even the ones that do NOT use cursive joining.
>
> - Mark attachment and cursive attachment.  These form a tree with a
> attachment-type enum.
>
> I'm not sure which slots in the pos buffer to expose this in.  The latter
> definitely belongs to the pos buffer, whereas the former is more a property
> of the text.  So I feel like we should expose them separately.
>
> Ideas?
>
> --
> behdad
> http://behdad.org/
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> HarfBuzz at lists.freedesktop.org
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