[luatex] a bidi package for LaTeX in LuaTeX

Khaled Hosny khaledhosny at eglug.org
Mon Mar 30 01:13:41 CEST 2009

On Mon, Mar 30, 2009 at 12:31:29AM +0200, Yannis Haralambous wrote:
> The problem comes from the way Arabic script is segmentated. Breaking  
> glyphs between letters is a bad choice. Take for example a medial noon  
> followed by a fah. The stroke starting from the top of the medial noon  
> and arriving at the highest position of the fah should be unique,  
> unbreakable and perfectly drawn.

This could have been fairly to do in OpenType of there is many to many
GSUB lookup, then one would have the connecting stroke as a single
glyph (may be several ones with different lengths for justification) and
noon/feh - connecting stroke glyphs, then the sequence <noon><feh> would be
replaced by <noon - stroke><stroke><feh - stroke>. But unfortunately
OpenType doesn't allow such replacement (Graphite does, BTW).

But another, more complicated approach would be having to variant
feh/noon glyphs, each with his half of that unique connecting stroke and
using contextual substitution lookups. But having connecting strokes
with different lengths will complicate it further; we'll need tow new
glyphs for each length and reverse contextual substitution to make sure
that of one glyph (say feh) is replaced by the longer variant, the
corresponding longer noon get used too.

Just my two cents.


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