Lumen GI and Reflections feedback thread

[Uno1982]

@Krzysztof.N

I’ve exposed r.Lumen.Supported.SM5 in UE5-Main, which you can integrate in order to re-enable DX11 support. Maybe will be able to get that into a hotfix.

Thank you so much!

@Krzysztof.N

And if not, and you have a good proof

Lumen no longer working in UE5.5 DX11 SM5

5.5 release notes even mention SM5 Lumen support. [image] [image] Nah we have it running on APUs and really cheap non HWRT pixel streaming machines from 5.1 - 5.4 its literally the way to get performant GI in UE5 (GTX 1070 my guy … not even RTX) I track source changes and I’m almost for certain the Fortnite and UEFN DX12 requirement likely got pushed into UE5.5 main and it was an unintended side affect. Wouldn’t be the first time I’ve seen this.

What do you mean good proof? Look at the thread I linked. If you do nothing other than swap the rhi in a 3rd person template nanite isn’t involved. You can cut SM6 from the equation entirely and then toss out VSM and Lumen in 5.5.0 release as I’ve shown there. Your still SM5 apples to apples without any sm6 supported features. Your memory footprint increases simply due to the rhi and the low level driver and hardware efficiency. This obviously is slower simply by handling a different RHIT and a larger memory footprint.

DX11 SM5 - 4.26ms starting cost (235fps)

DX12 SM5 - 5.41ms (184fps)
zero changes other than rhi results in (but why even run dx12 with sm5?)
Note: the memory footprint difference

Literally nothing more than paying twice the RHIT cost and larger memory footprint as GPU Time is almost identical

DX12 SM6 - 9.58ms (104fps)
zero change other than lumen is now enabled since its locked behind sm6

That’s a total loss of about 123% of the initial starting ms on DX11 SM5. If I could enable lumen in DX11 I would have provided a 1:1 comparison as in 5.4 its like 65% difference with no HWRT involved in pipeline at all with DX12 vs DX11 SM5 Lumen SWRT only. I’ll be happy to follow up here with 5.4 results if you like?

While your correct in that it is features being enabled as you move up in rhi and shader models between DX12 SM5 and SM6 … that has nothing to do with the DX11 SM5 to DX12 SM5 rhi swap… SWRT doesn’t even work in SM5 UE5.5 so no lumen cost to factor in here. Nanite doesn’t work without VSM which requires SM6.

HWRT doesn’t come enabled by default in the template so that’s not a factor until bUseHardwareRTWhenAvailable kicks in for lumen in DX12 sm6.

Also… forcing this path and removing SWRT entirely just because DX12 is where your focusing is taking away the option entirely would throw out the baby with the bathwater.

Update:
As a follow up to this I just tested vulkan SM5 and Lumen SWRT does still work in that RHI however it appears to be frame locked to 60htz no matter what vsync settings you apply and even if you set maxFPS to 10000