[FriBidi] fribidi_reorder_runs()

[Behdad Esfahbod]

I'll try to put it back in FriBidi.  The rollback was necessary because the
original commit was exposing structs that we didn't want to.

On Wed, Feb 8, 2017 at 10:20 AM, Eduardo Castiñeyra <
eduardo at brainstorm3d.com> wrote:

>
>
> On 2/8/2017 7:02 PM, Eli Zaretskii wrote:
>
>> Cc: fribidi at lists.freedesktop.org
>>> From: Eduardo Castiñeyra <eduardo at brainstorm3d.com>
>>> Date: Wed, 8 Feb 2017 16:59:04 +0100
>>>
>>> On 2/7/2017 5:19 PM, Eli Zaretskii wrote:
>>>
>>>> From: Eduardo Castiñeyra <eduardo at brainstorm3d.com>
>>>>> Date: Tue, 7 Feb 2017 16:39:01 +0100
>>>>>
>>>>> It turned out that our incorrect way to integrate fribidi and harfbuzz
>>>>> (let fribidi reorder all the characters and shape as full LTR in
>>>>> harfbuzz) is "surprisingly" causing problems.
>>>>>
>>>>> The problem is mainly with the parenthesis. It looks like the shaper
>>>>> should flip the direction of the parenthesis when it belongs to a RTL
>>>>> run.
>>>>>
>>>> Shouldn't reordering mirror parentheses if their level is even?
>>>>
>>> AFAIK, parenthesis are neutral, they inherit the direction of the text
>>> surrounding them
>>>
>> Yes, and if the surrounding text is RTL, the parentheses should be
>> mirrored as part of reordering.  See L4 in the UBA (a.k.a. "UAX#9")
>> description.  It says:
>>
>>    A character is depicted by a mirrored glyph if and only if (a) the
>>    resolved directionality of that character is R, and (b) the
>>    Bidi_Mirrored property value of that character is Yes.
>>
>>
> That makes sense. Nevertheless the direction of the parenthesis is just an
> example of why we need that fribidi_reorder_runs function which was what my
> question was actually about.
>
> I think that, in a glyph based renderer, changing the direction of the
> parenthesis should be on harfbuzz's roof not fribidi. fribidi's
> responsibility would be limited to reordering the runs and labeling them
> with their level.
>
> Behdad proposed an algorithm to reorder the runs ourselves
>
> https://github.com/behdad/linear-reorder/blob/master/linear-reorder.c
>
> but he also implemented it in FriBiDi and then rolled it back.  Of course
> we'd rather use the one implemented in FriBiDi as soon as it is available.
> Hence my question.
>
>
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> fribidi at lists.freedesktop.org
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>



-- 
behdad
http://behdad.org/
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