This is pretty interesting
https://www.eurogamer.net/articles/digitalfoundry-2019-metro-exodus-tech-interview
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With the release of DXR GI on PC we have to recall our discussions a few years back about real time global illumination (rough voxilisation of the game scene was mentioned back then as a possible real time solution for GI). What type of GI does Metro Exodus use on consoles currently? Does DXR GI have an influence on where 4A engine might go for next generation consoles?
Ben Archard: We use spherical harmonics grid around the camera which is smoothly updated from latest RSM data each frame. Plus a bunch of light-probes. It is relatively cheap solution and quite good in many cases, but it can leak lighting, and is too coarse to get something even remotely looking like indirect shadows. If next-gen consoles would be good at tracing the rays we would be completely "in".
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Let's talk about ray tracing on next-gen console hardware. How viable do you see it to be and what would alternatives be if not like RTX cards we see on PC? Could we see a future where consoles use something like a voxel GI solution while PC maintains its DXR path?
Ben Archard: it doesn't really matter - be it dedicated hardware or just enough compute power to do it in shader units, I believe it would be viable. For the current generation - yes, multiple solutions is the way to go.
This is also a question of how long you support a parallel pipeline for legacy PC hardware. A GeForce GTX 1080 isn't an out of date card as far as someone who bought one last year is concerned. So, these cards take a few years to phase out and for RT to become fully mainstream to the point where you can just assume it. And obviously on current generation consoles we need to have the voxel GI solution in the engine alongside the new RT solution. RT is the future of gaming, so the main focus is now on RT either way.
In terms of the viability of RT on next generation consoles, the hardware doesn't have to be specifically RTX cores. Those cores aren't the only thing that matters when it comes to ray tracing. They are fixed function hardware that speed up the calculations specifically relating to the BVH intersection tests. Those calculations can be done in standard compute if the computer cores are numerous and fast enough (which we believe they will be on the next gen consoles). In fact, any GPU that is running DX12 will be able to "run" DXR since DXR is just an extension of DX12.
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Full interview at the link.