Are you sure you can use Piccolo2D with Processing? I know it as a something with its own rendering method, so it is more concurrent of Processing (in a different domain, higher level with its scenegraph) than complementary. I can be wrong, of course.
Ah, I didn't know such library existed. It is GPL, so it is a no-no for me, as I don't want to release my code under this license (I prefer less constraining licenses, like the Piccolo2D one, based on the BSD one). I suppose the author changed the back-end of Piccolo2D from Java2D to Processing. Perhaps look at the Piccolo2D examples, they are quite complete. The scenegraph and zoomable interface can be useful in Processing, indeed.