Chapter 8. Collision Detection

Collision detection, in one form or another, is a staple of many animations and nearly all games. In this chapter you will see how to implement collision detection, from simple strategies involving bounding areas and intersecting rays, to detecting collisions between arbitrary polygons, circles, images, and sprites.

Most of this chapter deals with implementing the separating axis theorem (SAT), which is a highly accurate and widely used method for detecting collisions between polygons, both in two and three dimensions. You will see how to implement the SAT with Canvas, and how to extend it for circles, images, and sprites.

This chapter concludes with a look at a byproduct of the SAT, the minimum translation vector (MTV), that coincides with the shortest distance you must move a colliding object so that it’s no longer colliding. You can use that vector to decouple colliding objects, make objects stick to each other, and make objects bounce off each other.