> On May 24, 2020, at 6:34 PM, Eli Zaretskii <e...@gnu.org> wrote:
>
>> From: Khaled Hosny <dr.khaled.ho...@gmail.com>
>> Date: Sun, 24 May 2020 18:00:45 +0200
>> Cc: harfbuzz@lists.freedesktop.org
>>
>
>> This, for example, ensures that HarfBuzz can do basic Arabic-like shaping
>> across item boundaries e.g. if you break items in the middle of an Arabic
>> word (due to font change, for example), you still get the
>> initial/medial/final forms across the boundary as appropriate. Or to put a
>> combining mark at the start of a paragraph on a dotted circle as it
>> otherwise has no base.
>>
>> If this is not possible, then you can try to pass enough context, like reach
>> back and forward to first character that is not a combining mark. This may
>> or may not be enough.
>>
>> Shaping space-delimited words is orthogonal to that, context is better be
>> always provided.
>
> So this sounds like passing a physical line that ends in a newline
> should be good enough? Or are there issues that cross newlines as
> well?
It should be enough.
>
> And what is a "paragraph" in this context?
The same as in UAX#9.
>> Some fonts do have OpenType lookups that interact with space (e.g. kerning
>> pairs involving space, or even substitutions involving space), so shaping
>> words independently will give suboptimal result. You can use HarfBuzz API to
>> find out if the font has OpenType layout rules involving space, or decide to
>> live with this limitation.
>
> Which API provides this information?
https://harfbuzz.github.io/harfbuzz-hb-ot-layout.html#hb-ot-layout-lookup-collect-glyphs
But requires some understanding of how OpenType lookups are structured.
Checking how Firefox uses it might help.
Regards,
Khaled
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