@yedefei Builderboy2005 has a useful scenario: http://www.greenfoot.org/scenarios/532 This 3d program uses z buffering, which can be useful for you, since raycasting (what nccb has scenarios for) is a bit limited I think.

This scenario is explained from the beginning in the greenfoot book: http://www.amazon.com/Introduction-Programming-Greenfoot-Object-Oriented-Simulations/dp/0136037534 And there are many people who just post scenarios from that book on this site, and I always wonder why.