游戏在主循环中增加了一个复杂的碰撞检查后，开始出现掉帧，怪物元素量大时，原本60的fps只剩20~30之间；
引用cocos2d官方的一段话：
Basically all the cocos2d-iphone, Chipmunk or CocosBuilder Reader APIs are going to perform almost at native speed. But you should pay attention to the following scenarios:
The performance could be slow down while the garbage collector is run. Workaround: Do not create many JS objects. Reuse as many as possible
Having a complex main loop could slow down the performance. Workaround: Profile your JS code, and if you can't further optimize it, write the expensive parts in Objective-C and create JS bindings for those functions.
掉帧现象部分来自于主循环运算量过大，60fps的游戏， 主循环每秒运算60次， 可以减少主循环中不必要的运算；
怪物每帧移动，施法，判断碰撞等，可以改为每5帧判断一次，运算量会小很多；
具体的做法，是在主循环中获取当前时间戳，运行动作后记录时间戳， 下次运行时当前时间和最后记录的时间戳达到一定时间以上，再进行动作；
本次调整后的游戏表现及体验均未有影响，fps又稳定在58以上；