https://www.gamedevs.org/uploads/comparative-study-of-ssao-methods.pdf
https://www.activision.com/cdn/research/Practical_Real_Time_Strategies_for_Accurate_Indirect_Occlusion_NEW%20VERSION_COLOR.pdf
Practical Real-Time Strategies for Accurate Indirect Occlusion (Jorge Jiménez)
https://research.activision.com/publications/archives/practical-real-time-strategies-for-accurate-indirect-occlusion
基础的ao 方案
1.hdao 一个pair pos ， dot他们的normal ， 大于0同向形成ao
2.
3.
4.hbao horizon based
5. gtao在hbao的基础上 多了cosin weighting
这个cos有两部分一部分是normal的投影 一部分是cos（n-theta）
这两部分用的都是 projected normal
6
7
ssdo是ao的补充方案
This allows for colored and
directed shadows in the result. Furthermore, SSDO has an optional
second pass that approximates one diffuse indirect bounce of light.
This is done by sampling nearby values of direct radiance gathered
in the first pass. Color bleeding effects as known from ray-traced
global illumination solutions are thereby possible.
一些gi信息 比如coloredshadodw和间接光的diffuse 部分和 color bleeding