[XeTeX] [luatex] Info on direction primitives/implementation

[Joseph Wright]

On 04/12/2012 15:55, Khaled Hosny wrote:
> IMO TeXXeT and all its incarnation has always been a hack to get RTL
> with the least modification as possible. Two main limitations I'm
> concerned about are the broken handling of specials (you can not get
> coloring or hyperlinks in RTL text without macro hacks with limited
> functionality) and lack of RTL math. On the other hand Omega's
> directionality code is more sophisticated and requires less adaptations
> at macro side (check the size of bidi package on how things can go wild
> with TeX--XeT), and it should allow for proper vertical typesetting in
> XeTeX as bonus.

I'd picked up the math mode point (although I'm not 100% sure on how
this works out with numerals, which don't always seem to be reversed
compared to the latin script order). The point about specials is one I
guess I'll look at by reading the bidi code and doing some tests.

As you might guess, my interest here steams from some LaTeX3
discussions, and one issue I'm trying to understand is whether the
TeX--XeT approach is really one that is sensible to try to support,
given the fact that the Omega approach exists. Certainly if you move
XeTeX from TeX--XeT to the Omega approach (with the LuaTeX fixes, I
guess), then this will be an easier thing to think about!

>> A slightly wider question which this leads me to: do I take it that
>> getting some (minor) additions to XeTeX might be possible? There was
>> some discussion last week about a few pdfTeX primitives that might be
>> useful.
> 
> Patches are always welcomed of course :) Right now work is mainly on
> layout side (replacing the abandoned ICU LayoutEngine with HarfBuzz,
> there is even a chance of replacing ATS/ATSU with Core Text, and old
> SilGraphite with Graphite2 engine) and further polishing of OpenType
> math.

Jonathan K. will tell you that my ability to write XeTeX patches is very
limited :-) I was thinking much less complicated than layout engines
(which all sounds very good!). I'll see what makes sense and perhaps be
in contact again.
--
Joseph Wright