Re: [emacs-bidi] RTL support

[Eli Zaretskii]

> Date: Tue, 22 Nov 2005 11:05:43 -0600
> From: Gregg Reynolds <address@hidden>
> 
> Regarding support for Arabic, Hebrew, etc. there are three elements:
> 
>    a.  RTL layout
>    b.  Shaping
>    c.  Bidi reordering

No, there are only two: shaping and Bidi reordering.  The former is
relevant for Arabic scripts alone, AFAIK (Hebrew certainly doesn't
need that, but I'm not sure whether there are scripts besides Arabic
that need it).

RTL layout is an integral part of bidi reordering.

> For myself, support for the first two, without bidi reordering, would be 
>   fantastic.  Usually when I work in Arabic, I don't need bidi support. 

I don't speak Arabic, so I cannot say how useful it is to have
right-to-left display without bidi reordering.  I _can_ tell you that
bidi support is a must for Hebrew (because numbers should be displayed
left to right), and the way Arabic related bidi features are specified
in the Unicode Bidirectional Algorithm makes me wonder how come such
an elaborate scheme (more complex than the scheme used in Hebrew) was
invented if Arabic can be written without it.

> So how hard would it be to add plain RTL layout first, and then Arabic 
> shaping?

I have no idea.  I certainly am not going to work on RTL without bidi.
If you want partial bidi support, you might try the m17n version or
hebeng.el (which you could hack to support Arabic).

As for Arabic shaping, I think some work was or is planned in the
Unicode branch.  You may wish to try searching the emacs-devel
archives for suitable keywords, I think Kenichi Handa posted some
messages there in the past.