Today I came across this impressive rendering library here:
http://www.antigrain.com/
It is licensed under GPL and from what I read it seems to be able to
solve the performance issues people here where facing with the Cairo
Java2D backend.
There seems to be work done on a Antigrain backend for Cairo, maybe
this would be an easy way to find out:
http://lists.freedesktop.org/archives/cairo/2006-September/008028.html
http://ehielscher.org/agg-surface.php
Also of interest:
http://lists.motion-twin.com/pipermail/neko/2006-June/001136.html
Best,
Jürg