[FriBidi] fribidi_reorder_runs()

[Eduardo Castiñeyra]

Thanks Behdad!

On 2/8/2017 10:33 PM, Behdad Esfahbod wrote:
> 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 <mailto:eduardo at brainstorm3d.com>> wrote:
>
>
>
>     On 2/8/2017 7:02 PM, Eli Zaretskii wrote:
>
>             Cc: fribidi at lists.freedesktop.org
>             <mailto:fribidi at lists.freedesktop.org>
>             From: Eduardo Castiñeyra <eduardo at brainstorm3d.com
>             <mailto: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
>                     <mailto: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
>     <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.
>
>
>     _______________________________________________
>     fribidi mailing list
>     fribidi at lists.freedesktop.org <mailto:fribidi at lists.freedesktop.org>
>     https://lists.freedesktop.org/mailman/listinfo/fribidi
>     <https://lists.freedesktop.org/mailman/listinfo/fribidi>
>
>
>
>
> -- 
> behdad
> http://behdad.org/

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