[luatex] Fribidi for LuaTeX

[Idris Samawi Hamid ادريس سماوي حامد]

Salaam, Vafa, all

On Tue, 19 Jul 2011 02:24:02 -0600, Vafa Khalighi <vafa018 at gmail.com>
wrote:

> True but at least I think luatex can provides something similar to  what
> XeTeX provides by its ICU layout engine and the rest (which obviously is
> much complicated and needs more testing) can be done either by a
> preprocessor or done entirely in lua.
>
>
> Which thereby makes a generic solution impossible. Omega translation
>> processing struggled with this mix of 'pure text', 'macro expansion',
>> 'packages content' and it never worked out in complex situations. For me
>> this is a pretty good reason for not adding any hard coded bidi (or foo  
>> or
>> bar or whatever) behavior to core luatex but stick to either external
>> libraries (preprocessing or whatever) and/or solutions written in lua  
>> that
>> nicely interact with the macro packages concepts. (Well, that's the main
>> reason for having lua as extension language in the first place).

I am feeling deja vu here ;-)

We must all remember that luatex has a different philosophy from xetex
etc. luatex provides the most basic, low-level, bi-directionality as
perfectly as possible.

OTOH, luatex is _not_ interested in deifying any particular paradigm of
rules for processing bidi text. Compare with the Open Type engine: That's
done by lua extensions. Similarly, bidi in mkiv will be done by lua
extensions which can easily be modified and parameterized as needed.

For example, I may want to use Arabic-numerals in a Persian-typesetting
context or vice versa. Hardcoding the bidi algorithm makes that
inconvenient. Also, the bidi algorithm is not perfect: it mixes the needs
of an editor or verbatim mode with those of real life typography. These
features should be flexible and capable of being turned on and off.
Consider an Arabic paragraph that's all in Arabic except the first word in
English. It makes no sense to force an LR par in that case.

Sometimes you want to turn bidi features off, or at least deprecate them,
in verbatim. See the features of SC Unipad -- perhaps the best
implementation of the bidi algorithm -- for example.

Parts of the bidi algorithm can be part of a solution to the overall
question of bidi typography, but it makes more sense in the luatex
philosophy to decouple that algorithm from the core and build a bidi
paradigm -- or even paradigms in the plural -- than to hardcode one.

For those who like the xetex paradigm, it's best to use xetex. xetex and
luatex involve different philosophical approaches. Using lua, anyone
interested can develop their own bidi engine on top of luatex. Similarly,
if someone does not like the way mkiv does open type. it's just a matter
of writing another OT engine in lua instead of recompiling luatex.

Best wishes
Idris
-- 
Professor Idris Samawi Hamid, Editor-in-Chief
International Journal of Shīʿī Studies
Department of Philosophy
Colorado State University
Fort Collins, CO 80523