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

Aditya Bhargava ab31 at ualberta.ca
Thu Feb 17 07:39:07 CET 2011

On Wed, Feb 16, 2011 at 11:32 PM, Taco Hoekwater <taco at elvenkind.com> wrote:

> 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).

Xelatex also needs the special handling to be explicitly specified: without
the [Script=Devanagari] parameter to fontspec it doesn't render it
correctly.  I know very little about these things, but shouldn't the Unicode
range be enough of a hint to enable the special handling? At any rate, given
xelatex's behaviour, I don't expect that having to manually specify the
script would be of any added hindrance to anybody using it (vs. xelatex,
that is).

On Wed, Feb 16, 2011 at 8:15 AM, Khaled Hosny <khaledhosny at eglug.org> wrote:

> 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.

Thanks; I've emailed him (assuming I got the right Hans).

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