We started pursuing Physically Based Shading during Black Ops, details of which I presented at SIG
https://blog.selfshadow.com/publications/s2013-shading-course/lazarov/s2013_pbs_black_ops_2_slides_v2.pdf
UnrealEngine4 PBR Shading Model 概述
https://www.cnblogs.com/TracePlus/p/4141833.html
虽然是概述，但内容并还是有些多，写上一篇PBR概念概述后，也在考虑怎么继续下去，最后还是觉得先多写一些东西再慢慢总结，所以还是尽量把这些年PBR相关的Paper精粹沉淀下来吧。
因为UE4开源的缘故，所以一开始还从它入手。相关的ppt和notebook可以从下面的链接下载，同期的黑色行动2（black op2）的PBR使用也是很有参考价值的，加上本文里也有OP2的IBL近似方法的介绍，如果没看过那也很值得下载的。
http://blog.selfshadow.com/publications/s2013-shading-course/
https://blog.selfshadow.com/publications/s2013-shading-course/lazarov/s2013_pbs_black_ops_2_slides_v2.pdf