Goals

Pro:

• There are blocks with arbitrary shapes.
• They're displayed correctly, with clipping.
• You can't fly through stationary blocks.
• There is motion (the trains).
• There are interesting curves (the tracks).
• You can interact with the world by flipping switches.

Con:

• The motion is only along predefined tracks. (Predefined by commands in a scene file, not hard-coded.)
• There is no real physics. In particular, you can't tip the trains over at high speed or crash them into each other.
• Blocks have to be convex.