Re: Gnome 2 Screenshot - Tamil Xft rendering seems broken

[Thuraiappah Vaseeharan <t_vasee yahoo com>]

Vikram Subramanian <glueview yahoo com> writes:
> Is there be some change required to the Tamil Xft
> module?

Owen Taylor:
>>Well, it would be nice to support the OpenType Indic stuff :-), I
>>don't have much of a feeling for how much work that would be ... all
>>the necessary OpenType parsing code should be there, but isn't
>>necessarily tested at all.
 
It hould be relatively easy to implement this for Tamil if OTL table parsing 
code is available as Tamil doesn't need a lot of OpenType features as other 
Indic languages. 

As an example, the Unicode editor Yudit (www.yudit.org) now supports Tamil 
fully using both OpenType fonts [1] and X11 fonts with 
PANGO_LIGATURE_HACK. 

Yudit doesn't use freetype (or Pango), but Gaspar Sinai, the author of Yudit, 
was able to write the code for getting the necessary Tamil ligature 
information from the OTL/PANGO_LIGATURE_HACK in a few days ;-)

The tamil xft module currently uses arbitary PUA code points for tamil 
ligatures. This should not be the case. With OpenType, it is not necessary to 
have any codepoints associated with the ligature glyphs at all. We can use 
the GSUB table to get the ligature information. 

All the tamil xft module has to do is:

o do vowel sign re-ordering
o identify (consonant + vowel sign) clusters and query the font for 
appropriate ligatures

This is exactly what the tamil module does presently with the X fonts via the 
PANGO_LIGATURE_HACK. IMHO, we should extend the same logic for OpenType fonts 
also, especially if the open type table parsing code is available in Pango.

-Vasee

[1] The (shareware) font code2000.ttf has the necessary OTL tables for Tamil. 
Also, it is easy to add these tables to existing Tamil fonts using (free as 
in beer) tools like MS VOLT.