http://dev.wo.com.cn/bbs/viewthread.jsp?tid=141767&page=1
http://blog.csdn.net/lvxiangan/article/details/17167827
http://o0o0o0o.iteye.com/blog/670834
http://code4app.com/ios/Core-Animation-Fun-House/4fe421816803fa3856000000
http://www.cnblogs.com/xdream86/p/3250782.html