Core Animation是对OpenGL ES的Objective-C封装，具有与OpenGL ES几乎等价的高性能，却隐藏了OpenGL ES的复杂性。

https://www.cnblogs.com/feng9exe/p/6723056.html

https://www.cnblogs.com/feng9exe/p/8848663.html

https://www.cnblogs.com/feng9exe/p/9436833.html

http://ios.jobbole.com/92237/

https://www.cnblogs.com/feng9exe/p/8848570.html

https://www.cnblogs.com/feng9exe/p/7339569.html

https://www.cnblogs.com/feng9exe/p/8883872.html

https://www.cnblogs.com/feng9exe/p/8856857.htm

http://www.cnblogs.com/fengmin/p/5702240.html

iOS UI（绘图）的几张原理图