Nowadays, it seems like everybody in the world has played or will play a physics-based game at some point in their lives. Box2D is by far the most popular engine in the casual games arena. The commands you learned here can be found in pretty much every port of the engine, including a JavaScript one that is growing in popularity as we speak.

Setting up the engine and getting it up and running is remarkably simple—perhaps too much so. A lot of testing and value tweaking goes into developing a Box2D game and pretty soon you learn that keeping the engine performing as you wish is the most important skill to master when developing physics-based games. Picking the right values for friction, density, restitution, damping, time step, PTM ratio, and so on can make or break your game.

In the next chapter, we'll continue to use Box2D, but we'll focus on what else Cocos2d-x can do to help us organize our games.