[cairo] fast surface->surface rendering using glitz+cairo?

[Vladimir Vukicevic]

Right now in mozilla-land, we optimize images into server-side
Pixmaps, so that we can do a fast composite of the image into the
window drawable/pixmap/whichever.  If we're using glitz for rendering
though, Pixmaps won't help.  (On the flip side, cairo handled
rendering a xlib surface into a glitz surface just fine ;)

Ideally all I want is a texture -- but I guess I won't be able to do
that until glitz has render-to-texture support, so that you can create
an actual cairo surface for it.  I'm using pbuffers now, but using
pbuffers for this is rather expensive (we go through a lot of
pbuffers, too).

Is what I'm looking for really render-to-texture?  Or is there a
simpler way to accomplish what I want?  I don't really want to write a
large glitz-specific codepath, so it would have to be something that
can be expressed as a cairo surface.  Would a cairo surface that just
supports writing/reading its pixels be useful, backed with a texture? 
Any writing/reading operations would be slow, but using it as the
source for an operation with a glitz surface target should be fast..

    - Vlad