Multi pass rendering faster with foveated rendering?

I just checked the PSVR2 URP GDC video and it mentions multi pass rendering being quite a bit faster when foveated rendering is enabled compared to single pass rendering.
Normally single pass is the preferred choice, so this blew my mind.

Could anyone give some details in why multi pass is faster for this?
And could this also be the case for Quest 2, etc?

https://www.youtube.com/watch?v=5z55_k0MgGA

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Hi DevDunk

I can clarify a few things from the video but for more details on the PS VR2 side you would need to post your question on the PlayStation developer forums which you should have access to if you are a registered PlayStation developer.

The CPU and GPU architecture on the Quest 2 will be very different to that on the PS5 + PS VR2 so I wouldn't generalize the PS VR2 results onto other platforms.

Nnanna mentions in the presentation that he is talking about GPU timings between single-pass and multi-pass and that multi-pass generally has a much higher CPU cost compared to single-pass. You can also see in the non foveated rendering case that the single-pass GPU performance is slightly faster than the multi-pass GPU performance 48.2ms compared to 51ms.

In this case if you were not using foveated rendering for PS VR2 then single-pass would still be the preferred choice.

If you were using foveated rendering then you get a benefit with both but more of a benefit if you are using multi-pass. With foveated rendering the preferred choice might well now depend on how much CPU and GPU cost your game generates as with multi-pass you will most likely have a higher CPU cost but a lower GPU cost when compared to single-pass on the PS VR2.

Cheers

Robin


Thanks for the answer. If I get into PlayStation developing I will repost it there.
I mostly was wondering if this translates to any other platforms, because PC has the same x86 architecture as well.
But it might be renderer specific

Hi DevDunk

The foveated rendering approach we take on each platform tends to be quite different based on the capabilities of the graphics API and hardware features available. The different foveated rendering approaches will have different performance characteristics and quality trade offs, though they should all be faster than without using foveated rendering.

So I wouldn't generalize the PS VR2 results onto other platforms.

Cheers

Robin

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Thanks for the answers!