基本的概念说明
上面的代码在制作基于2D的游戏时检查单位之间的冲突（例如友军飞机和敌方导弹）时非常有用。
这个代码的基本原理是使用中心距和两个圆的半径之和。 两个圆的中心距离可以用毕达哥拉斯定理求出，如果两个圆的半径之和大于这个中心距，那么这个物体就被认为是相撞的（如果不知道的话，可见图示说明）(Basic concept descr iption
The code above is useful for checking conflicts between units (such as friendly planes and enemy missiles) when making 2D-based games.
The basic principle of this code is to use the center distance and the sum of the radii of two circles. The distance between the centers of the two circles can be found by the Pythagorean theorem. If the sum of the radii of the two circles is greater than the center distance, the object is considered as a collision (If you do not know, you can see the illustrations))