khaledhosny at eglug.org
Sat Sep 24 15:43:41 CEST 2011
On Thu, Sep 22, 2011 at 11:57:16PM +0200, Stephan Hennig wrote:
> schrieb Stephan Hennig:
> > schrieb Khaled Hosny:
> >> Arabic handling in luatex (or rather luatex based packages) is done by
> >> OpenType layout features processed by lua code, no engine techniques are
> >> involved.
> > Is OpenType powerful enough to solve all script related typesetting
> > problems in Arabic typography?
> OK, I've read a (very) little bit about typesetting Arabic script and
> found in <URL:http://en.wikipedia.org/wiki/Complex_script>
> > Context-sensitive shaping (ligatures), where a character may change
> > its shape, dependent on its location and/or the surrounding
> > characters. For example, a character in Arabic script can have as
> > many as four different shape-forms, depending on context.
> As far as I know, OpenType uses (more or less) simple rules rather than
> patterns for contextual features (I may be wrong with that). Does that
> mean, glyph substitution in Arabic script can be managed by rules only?
OpenType is a mix of both; there are basic features where the font
provides simple substitution lists and the OpenType engine (in our case
entirely written in lua) have to do contextual analysis using predefined
algorithms to decide where and when to apply those features e.g.
initial, medial, final and isolated forms in Arabic. But there is also
contextual features with more complex rules in which the font embeds all
the knowledge about the context in which features are applied, and this
is used for less straight forward cases where the context are font
dependant rather than defined by script orthography.
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