http://www.3drender.com/glossary/fresneleffect.htm
http://kylehalladay.com/all/graphics/2014/02/23/Fresnel-Shaders.html
http://www.reddit.com/r/Unity3D/comments/1yp8l0/i_wrote_a_tutorial_and_released_a_free_shader/
原文：http://www.cnblogs.com/lilei9110/p/4565694.html