[XeTeX] Auto Font and Language Package in XeTeX

[Khaled Hosny]

On Mon, Dec 20, 2010 at 12:59:45PM +0100, Paul Isambert wrote:
> Selon Arthur Reutenauer <arthur.reutenauer at normalesup.org>:
> 
> > > Incidentally, does anyone know whether there is a LuaTeX version of the
> > > XeTeXintercharclass behaviour that would let this package be rewritten
> > > for LuaTeX with minimal effort?
> >
> >   Paul Isambert has written code to that effect, but I'm not sure he has
> > made it into a package yet.
> 
> 
> I haven't indeed. It's quite low on my priority list, all the more as mimicking
> interchartoks isn't totally possible in LuaTeX, although the most significant
> part of the mechanism can be reproduced.
> 
> Anyway judging from what I understand Michiel's package does, an
> interchartoks-like code in LuaTeX won't work, because it'll really be an
> ``inter-node'' mechanism, and (glyph) nodes already have their fonts attached to
> them, whereas the package is supposed to change fonts.
> 
> The solution would rather be: get the nodes as soon as possible, e.g. in the
> ligaturing callback, and set the font number for each node according to its
> unicode value. That means no such thing as "\fontspec{A font}" is usable here;
> instead, you must go low-level and grab the fonts by their numbers. Such numbers
> can be retrieved from the control sequences passed to the \font primitive with
> Lua's font.id(<name>). An extension to fontspec would be infinitely simpler than
> an independent package.

I long had that on my todo list, but I'm yet to figure out a proper user
interface for it; one needs to take care of different font styles,
optical sizes etc. e.g. English ARABIC {\it english ARABIC} should work
and get the Arabic text assigned the proper italic font and so on.

The code at lua end is quit trivial, once the script->font mapping is
defined which is actually the tricky part.

Regards,
 Khaled

-- 
 Khaled Hosny
 Arabic localiser and member of Arabeyes.org team
 Free font developer