I wrote a program that places random colored spheres throughout a scene, and then creates a "viewing screen" sphere in the center. It's called the "viewing screen" sphere because what I do is send out rays from the sphere and see what spheres (if any) the ray intersects and then I map that color on to the "viewing sphere".
Here is the code (compiles on an SGI with Open Inventor):
Time spent: 3 hours
Date: Spring 2001