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

Khaled Hosny khaledhosny at eglug.org
Tue Dec 4 16:55:11 CET 2012

On Tue, Dec 04, 2012 at 02:52:59PM +0000, Joseph Wright wrote:
> [Moved from the LuaTeX list as this moves me to XeTeX!]
> On 04/12/2012 14:33, Khaled Hosny wrote:
> > On Tue, Dec 04, 2012 at 01:52:19PM +0000, Joseph Wright wrote:
> >> Very useful, thanks. Point about detail understood: at the moment I'm
> >> trying to get my head around the entire area, and to see how the LuaTeX
> >> version contrasts with the pdfTeX/XeTeX approach.
> > 
> > In the last few days I have been fancying the idea of scrapping TeX--XeT
> > from XeTeX and replacing it with code from Aleph (with LuaTeX
> > modifications backported to it), but no work has been done so far (and
> > probably never will, I always underestimate how hard things are).
> > 
> > Regards,
> > Khaled
> Hello Khaled,
> That suggests that TeX--XeT is not providing the tools required to do a
> decent job in XeTeX: is that a fair reading? (I'd guess that there were
> reasons for the Omega/Aleph/LuaTeX move from TeX--XeT to other
> approaches, but as a non-expert was not sure how to read it.)

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.

> 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


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