ABSTRACT
In this chapter we’ll be concerned with a very straightforward question: How do we tell when two geometric entities are intersecting? This knowledge proves useful in many cases throughout a game engine. The most obvious is collision detection and response. Rather than have game objects pass through each other, we want them to push against each other and respond realistically. In the real world, this is a simple problem. Solid objects are solid; due to their physical properties, they just don’t interpenetrate. But in the virtual world we have to create these constraints ourselves. Despite the fact that we have completely defined the geometry of our game objects, we still need to provide methods to detect when they interpenetrate. Only when we have a way to handle this can we write the code to perform the proper response.
