http://game-develop.net/blog/?p=291
具体源文件
https://files.cnblogs.com/zack/%E4%BC%98%E5%8C%96%E6%88%90%E7%A6%BB%E6%95%A3%E7%82%B9%E8%BF%9E%E7%BA%BF%E7%9A%84AStar.zip
