Forward+ base overhead?

Graphics Render Pipelines
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1

I recently started using URP for the first time since I tested LWRP years ago, and was quite excited mainly because of Forward+.

I was pleasantly surprised URP is now much better than it used to be, and outperforms built-in, in most of the tests and benchmarks I’ve done recently using Forward rendering in VR.

However I had a bit of a shock with Forward+, it performs significantly worse than expected.

I tested two scenes - one with 1 directional light, one with plenty of point lights. In both scenes Forward+ used about 30% more GPU than Forward. Both tests were Android compiled to two very different devices with an Adreno 650. A phone with a Snapdragon 870 chipset, and a Quest 2. Both have an Adreno 650 but the Quest 2 is pushing almost twice as many pixels per frame (1440p Vs FHD+) so if the cost was per pixel, you’d think the baseline overhead would be more, but actually it wasn’t. So what is this overhead exactly?

For obvious reasons Deferred has a baseline cost, however I was under the impression Forward+ didn’t, and was simply Forward with support for many realtime lights without needing to render an object multiple times for multiple lights.

Is this to be expected? Is it known that Forward+ has a higher baseline cost than Forward?

2

I’m running into the same issue, unfortunately. Which makes it not worth it to use the GPU Resident Drawer with that requiring Forward+.

3

Yes facing the same problem. Forward+ is performing worse. There is no use of so much hyped GPU Resident Drawer if Forward+ is already lowering FPS on Meta Quest 2.

4

Think about it — after switching to clustered, every frame has to send a large amount of cluster light culling results to the GPU. How could that possibly be low-cost?

5

Low cost? Perhaps not. But the cost that it has kind of negates the advantage it’s supposed to have over Forward. The cost is too much, and edging on deferred’s level of GPU overhead.

The only reason it would be an atrractive option over deferred is if you absolutely have to have MSAA, which VR does, but then again the GPU overhead is too crippling for standalone VR.

I opted for my own light culling system with Forward, it’s much faster.

6

I saw your question about Forward+ overhead and thought this might be relevant. It’s a GPU-driven Forward+ shader on the Asset Store:
GPUDrivenForwardPlus