: Ray tracing has two quality settings: high and ultra. Ultra setting traces up to one ray per pixel, with all the denoising and accumulation running in full. The high setting traces up to 0.5 rays per pixel, essentially in a checkerboard pattern, and one of the denoising passes runs as checkerboard.
At Gamescom it was mentioned that the ray tracing for global illumination is done at three rays per pixel, so there have been some big changes then?
So, for Gamescom we had three rays. After Gamescom, we rebuilt everything with the focus on high quality denoising and temporal accumulation of ray data across multiple frames. We have a specifically crafted "denoising" TAA at the end of the pipeline, because stochastic techniques will be noisy by nature.
A lot of work, ideas and tricks were implemented to make it real-time. It was a multi-people and even multi-company effort with Nvidia's cooperation.
Interesting interview here: https://www.eurogamer.net/articles/digitalfoundry-2019-metro-exodus-tech-interview
On the one hand, some things sound great, like how they believe next-gen consoles could do some RT themselves. On the other, that it requires such a concerted effort to get it implemented in a game means it's going to be difficult for games in general to do the same, at least for a while still. Truly, it's looking more and more like RTX's start is going to really be with the next-gen GPUs, with Turing being more of an appetiser.