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

[Behdad Esfahbod]

On Tue, Nov 12, 2019 at 5:30 AM Ebrahim Byagowi <ebraminio at gmail.com> wrote:

> 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.
>

I'm hesitant to do that.  The reason I want to expose this is such that
clients can do that while we figure out how to implement justification.


> > [..] even the ones that do NOT use cursive joining.
>
> Guess this a property of a font rather than a buffer?
>

It's property of how font is designed.  Some glyphs in the font might, and
others not.


> 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.
>

Interesting.  Can you provide test results for this?  Let's understand what
changed.


> > [,,] 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/
>> _______________________________________________
>> HarfBuzz mailing list
>> HarfBuzz at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/harfbuzz
>
>

-- 
behdad
http://behdad.org/
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