[XeTeX] wrong kerning and slow processing with xelatex intexlive 2010

[Khaled Hosny]

On Wed, Oct 13, 2010 at 02:23:47PM +0100, John Was wrote:
> Just as a postscript to this thread, I've several times asked for
> (and still hope to see)  a custom kerning facility in XeTeX (this is
> already available in LuaTeX).  The idea would be that when you call
> up a font you can say ':kerning=mykern.krn' just as you can say
> ':mapping=tex-text'.  The file 'mykern.krn' would be something that
> the user writes to a specified syntax, and it would supplement
> (including overriding) the kerning information supplied by the font
> itself.  Any unsatisfactory pairings could then be sorted out by the
> user without the need to edit the font (which might be illegal).
> 
> Whenever I do mention this, a few people usually react to say that
> it would be a good idea - but perhaps too few to bring the task to
> the front of the hard-pressed programmers' queue.

XeTeX does not do OpenType processing (which includes kerning) on its
own, it "outsources" it to ICU library (statically linked, though, so
XeTeX specific patches are possible), so that custom kerning need to be
applied there, depending on how ICU reads OpenType data from fonts this
might not be trivial (I'd be surprised if it was) if possible at all.
The situation with LuaTeX is special because it has a (partial) font
editor library which naturally knows how to patch fonts (in the eyes of
the engine it is just a regular OpenType font, the patching is done
before the font is passed to the OpenType layout code).

Regards,
 Khaled

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