Offscreen Rendering?

[kbonawitz]

How do I configure Xith3D to do offscreen rendering?  In particular, I would like to be able to make a call like view.getSnapshot(Canvas3D) to produce a BufferedImage, but without actually invoking the cost of drawing pixels onto the screen.  (In my application, I only need to compute some statistics about the difference between the 3D rendered image and a prerendered image.)

Thanks for your help.