[luatex] luatex's (mis-)handling of Unicode Devanagari vowel signs and ligatures

[Taco Hoekwater]

On 02/16/11 16:15, Khaled Hosny wrote:
> There is currently no support for Indic scripts in our OpenType layout
> engine, simply because no one asked for it.
> 
> Since Hans don't read any of these languages, he will need help from
> someone who can. So if you are interested in digging into this finding
> relivant specs, fonts, reference renderings and so (be warned, Indic
> support is OpenType is a big mess with basically two incompatible
> standards one deprecated but there are many fonts out there using it),
> then contact Hans and I think he would be interested in such help.

The problem with complex scripts is that they sometimes need more
support that just turning on opentype features. For example,
in Arabic script, there is a the need to analyze the relative
location of the characters (initial, medial, final, isolated).
This process is not actually encoded in the font itself, it has
to be done by the engine based on whether or not the engine
believes it is in Arabic mode (yes, that it is indeed a little
fuzzy).

It looks like the Devanagari script processing depends on a similar
non-encoded presumed logic in the engine, and that is the information
that Hans currently does not have (and therefore does not implement).

Best wishes,
Taco