Re: [Render] OpenType support in Pango

[Owen Taylor <otaylor redhat com>]

bstell netscape com (Brian Stell) writes:

> Owen Taylor wrote:
> 
> > ...
> > - A simple Arabic shaper (again using some code from the
> >    FreeType 1 distro) that uses that shapes Arabic using
> >    the glue layer.
> >
> > This is currently only handling GSUB (contextual variants and
> > ligatures) though most of the GPOS code is there and just needs to be
> > hooked up and tested/debugged.
> 
> Do you intend to draw each (vertically) positioned character with a
> separate draw call?
> 
> Should we consider an API that allows an app to pass an array of positions
> along
> with the data?
> 
> This would be useful for line justification as well.

The output of the Pango shaping process is a array of independently
positioned glyphs. (Each glyph is accompanied by an advance
width, and x and y offsets from the origin determined by
the advanced widths and the baseline.)

Currently, I just use a request per glyph, both for the X backend
and for the Xft/Xrender backend. I could optimize this at render
time by taking into account knowledge of the natural advance
widths of the glyphs. A request that took multiple positioned
glyphs would also be an optimization.

Neither is all that important an optimization - the wire encoding of
text for drawing is not an important efficiency bottleneck in
most cases, but they wouldn't hurt.

Regards,
                                        Owen