ambient occlusion
references
recommended
Michael Bunnell. 2005. Dynamic ambient occlusion and indirect lighting (html). In Matt Pharr (ed.), GPU Gems 2. Addison Wesley. There is a corresponding white paper, video and demo here, just look for "dynamic ambient occlusion."
Martin Mittring. 2007. Finding next-gen - CryEngine 2. In ACM SIGGRAPH Course Notes. Corresponding presentation is here. The section on ambient occlusion isn't very long -- so may want to see figure 9.38 in the Real time Rendering book too.
Akenine-Moller, T., Haines, E., & Hoffman, N. (2018). Section 11.3 in Real-Time Rendering. AK Peters/CRC Press. (ncsu)
optional
As a bonus, we may also have a look at this paper by Luft et al. There is a video on the ACM page here.
Also, you can find more detail on obscurance here, in a paper from Zhukov et al. in 98, and an improved version especially for games here, which they published in 03.
McGuire, M., Mara, M., & Luebke, D. P. (2012, June). Scalable Ambient Obscurance. In High Performance Graphics (pp. 97-103). (site)
Bonet, Ruben Torres. 2020. The Dark Side Of Ray-Traced Ambient Occlusion (RTAO). Gamasutra, October 21, 2020.
demos
engine refs
manual
unreal: ssao, distanceao
unity: ssao, ssaobscure
videos
unity: ssao