coreGraphs和动画

http://www.jianshu.com/p/b71c3d450e8e

http://blog.csdn.net/volcan1987/article/details/9969455

http://my.oschina.net/joanfen/blog/150411

http://www.cnblogs.com/wengzilin/p/4250957.html

http://www.cnblogs.com/bucengyongyou/archive/2012/12/20/2826590.html

http://www.cocoachina.com/bbs/read.php?tid=95815