http://www.martinpalko.com/muli-compile-unity/
http://forum.unity3d.com/threads/tutorial-shade-more-efficiently-taking-advantage-of-multi-compile-shaders.222088/
http://docs.unity3d.com/Manual/SL-MultipleProgramVariants.html
原文：http://www.cnblogs.com/lilei9110/p/4516996.html