This is now dated, because Gl Graphics is kind of implemented in Processing 3. Nonetheless, code works different, so I might publish an update (code is on the shelf already in the near future.
Demonstration of the ease of use to use Processing for Compositing. A combination of examples of the Gl Graphics library and the SimpleParticleSystem code from Daniel Shiffman.
Please note that Gl Graphics doesn’t work in Processing 2.0 beta yet.
For explanation see comments in the code.