Stepping into the world
Once the world has been created, the simulation must actually be run. You can do this by calling the Step function of the b2World class, usually in the update function of your game, as follows:
world_->Step(dt, 8, 3);
The three parameters passed to the Step function are the time-step, the number of velocity iterations, and the number of position iterations, respectively. The variable dt passed into the Step function is passed to us from the update function of our GameWorld class, and the value held by dt is that of a variable time-step. We use the term variable to describe this value because the amount of time the Cocos2d-x engine will take to finish one single tick might vary continuously.
One drawback of using a variable time-step is that it makes the entire simulation hardware dependent. Thus the simulation might run faster on a machine having a powerful configuration, while it might run significantly slower on a machine having a poor configuration. Considering...
