Rigid body collision

Here’s the most important thing you need to know about rigid body physics: It’s all about collisions. You may have noticed your active rigid bodies colliding – crashing into one another and reacting in a realistic way that would be time-consuming to animate. Forces such as gravity are a piece of cake – heck, we can simulate gravity with two keyframes and quadratic interpolation – but collisions? Collisions are where things get interesting.

Take this wall made of bricks, where each brick is an active rigid body. Knocking over brick walls is a fun exercise; we’re going to make one of these ourselves soon:

Figure 12.11: A simple wall of bricks on frame 1

Looks decent enough, right? It’ll stay upright until we knock it over with something else, right?

Wrong! It exploded because you were careless with collisions:

Figure 12.12: Same wall, frame 12

This sort...