说明：  Box2D 是一个用于游戏的 2D 刚体仿真库。程序员可以在他们的游戏里使用它，它可以使物体的运动更加可信，让世界看起来更具交互性。从游戏的视角来看，物理引擎就是一个程序性动画(procedural animation)的系统，而不是由动画师去移动你的物体。你可以让牛顿来做导演。 Box2D 是用可移植的 C++ 来写成的。引擎中定义的大部分类型都有 b2 前缀，希望这能消除它和你游戏引擎之间的名字冲突
(Box2D is a 2D rigid body simulation library for games. Programmers can use it in their games to make objects move in believable ways and make the game world more interactive. From the game s point of view a physics engine is just a system for procedural animation. Box2D is written in portable C++. Most of the types defined in the engine begin with the b2 prefix. Hopefully this is sufficient to avoid name clashing with your game engine. )