Re: Pango and SILGraphite was Re: Possible Pango 1.4 ideas

[Owen Taylor <otaylor redhat com>]

"Daniel Glassey" <danglassey ntlworld com> writes:

> Hi,
> After hearing about the discussion of ideas for pango 1.4 a 
> discussion has started on the silgraphite list about the possibility 
> of integrating graphite into pango.
> 
> SILGraphite (graphite.sil.org) is a library for providing "rendering 
> capabilities for complex non-Roman writing systems"/"extensible 
> complex script behavior"
> 
> It is written in C++ but C wrappers for use in C-based projects are 
> being considered - so it would have to be some kind of plugin - it 
> isn't for a single writing system and is just for all graphite-
> compiled fonts so I'm not sure if it will fit into the current 
> engine/plugin system.
> 
> It is currently being ported to linux 
> (www.sf.net/projects/silgraphite) and being integrated into windows 
> Mozilla and hopefully others later (sila.mozdev.org)
> 
> Would this be feasible/useful for 1.4? We need to work on a detailed 
> API proposal and patches , but is it conceptually the kind of thing 
> you would be interested in? also, see summaries below.

Right now, Pango selects a single shaper module for each Unicode
range.  There is no provision to check if a font has GDL tables, and
use a different Graphite specific shaper module.

It wouldn't be impossible to add such a facility (it would require
some extensions to fontconfig, but these extensions are needed already
to deal with fonts that have, say, Arabic glyphs without the Arabic
OpenType tables.)

The goals of the Graphite project are obviously a little different
than for Pango. I'm not sure that the extra capabilities that Graphite
support would offer really excites me that much, personally.

To state something that may be a bit controversial, my opinion is that
the set of "hard" scripts out there is pretty finite, and not going to
go up in the future. Rather than trying to make it possible to handle
arbitrary new scripts, I think time would be better spent creating the
necessary specifications, fonts, and code to fit the dozen or so
remaining complex scripts into OpenType.

(The set of live scripts in Unicode that Pango doesn't handle for
OpenType fonts, is, to my knowledge: Sinhala, Lao, Khmer, Mongolian,
Tibetan, Syriac, Hanunoo, Buhid, Tagbanwa. As far as I know, the 
set of arguably live complex scripts not yet encoded in Unicode is 
pretty small too.)

Really, I see the challenge for Pango at this point not as supporting
more scripts, but supporting the ones we already handle better.

So, I guess my opinion would be I'm not particularly interested in
adding a dependency on Graphite. But if someone was interested in
working on adding the necessary pieces to the Pango core so that
external Graphite support could be plugged in on top of Pango, I'd be
happy to work with them.

Regards,
                                        Owen