Much of gameplay derives from how agents in the game world (players, enemies, puzzle pieces, interactive items, etc) interact with each other. This is the domain of physics, the rules of how physical (or game) objects interact. In a sense the game physics define how the game’s simulation will unfold.

While game physics often correlate to the physics of the world we inhabit they don’t have to! In fact, most game physics approaches at least simplify real-world physics models to allow for real-time processing, and some abandon real-world physics altogether.

When games do try to implement realistic physics, they typically start with rigid body dynamics, a simplification of real-world physics where objects are represented as a rigid body and a point mass. In games, the rigid body is essentially the collision shape we covered in chapter 4, and a point mass represents the object’s position as a vector, and the mass as a float.

In this chapter we’ll examine how to implement rigid body physics in games.