切空间（TBN矩阵介绍）

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/wodownload2/article/details/88823754

http://www.opengl-tutorial.org/intermediate-tutorials/tutorial-13-normal-mapping/
https://www.nvidia.com/object/real-time-normal-map-dxt-compression.html