[Devel] Re: [Kannada] Re: Problem with freetype rendering of an Indic opentype font

[Lars Knoll]

On Sunday 07 September 2003 23:37, Arun Sharma wrote:
> On Thu, Sep 04, 2003 at 10:24:10PM +0200, Werner LEMBERG wrote:
> > > I see a problem with the freetype rendering of this unicode string:
> > >
> > > "0xcb7 0xccd"
> > >
> > > Using Microsoft tunga.ttf (A kannada font that ships with Windows
> > > XP).  In fact, the problem manifests itself with all other
> > > consonants too, including 0xcb7.
> >
> > I don't have time to investigate but it seems to me that some
> > contextual shaping is happening.  If this is true it is not a problem
> > of FreeType 2 (which doesn't support OpenType directly for the moment)
> > but rather a problem one level higher where Indic scripts are handled,
> > probably within the Pango library.  Owen?

I did some investigations and the problem seems to lie within the freetype 1 
open type code used by Qt and pango. The font uses chain substitutions to 
achieve correct rendering of this combination and these seem to work 
incorrectly. Up do now I didn't find time to dig into this in more detail.

> ok, I did some more investigation. Here's a partial dump of the font.
> According to this rule, glyph 0x62 should've been substituted by glyph
> 0xb0. But for some reason, it's not happening.
>
> Does this ring a bell ?

The lookup table you quite below is actually a subtable of some chain 
substitution table as far as I can tell. 

>    <Lookup> <!-- 36 -->
>       <LookupType>SINGLE</LookupType>
[...]

I'll try to have a closer look in the next days if time allows.

Cheers,
Lars