Lumen GI and Reflections feedback thread

Hi everyone, I’m starting this thread for feedback and discussion about Lumen GI and Reflections in UE5.

We’re under a lot of pressure with internal deadlines so can’t promise responses, but we will read everything here.

Lumen team is:
Daniel Wright
Krzysztof Narkowicz
Patrick Kelly

(Slightly outdated docs from Early Access, new ones in progress)
Lumen documentation
Lumen technical details documentation

New Lumen developments since Early Access:

  • Full Hardware Ray Tracing pipeline for Lumen GI and Reflections
  • Shipped on next gen consoles in ‘The Matrix Awakens’
  • Support for large view ranges with Far Field Hardware Ray Tracing
  • Feedback driven Surface Cache, giving higher quality in reflections
  • Improved Final Gather quality, especially visible on foliage
  • Improved Reflections denoiser, especially for glossy reflections and behind moving objects
  • Glossy reflections on translucency (not mirror)
  • Translucency Final Gather, which improves global illumination quality on translucency and Volumetric Fog
  • Landscape support
  • Radiosity Final Gather, which improves the quality of multi-bounce global illumination and GI seen in reflections
  • Lumen settings exposed to the UI, for quality / performance tradeoffs
  • Subsurface / Two Sided Foliage shading models supported
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Great work epic team, I’m experiencing much improved performance and visual fidelity going from EA2 to Preview 1.

I was curious about the improvements on translucent reflections using lumen.

Changes list “Glossy reflections on translucency” but whatever I try, i can’t seem to get sharper reflections on a glass like surface than this:

Is there any specific setting to enable that i have overlooked?

Also, I am generally still experiencing quite noticable grain/noise in direct shadows as seen on the white surface (more visible when downloading the attached image, web compression and forum scaling reduced the effect in the image).

I’m assuming this relates to virtual shadow maps, but I have yet to find a setting or console command that is able to effectively reduce the amount of noise at the cost of performance. Any tips?

Will lumen reflections on single layer water surfaces make it for 5.0 final?

I really like the improvements, lighting seems much more consistent and stable in UE5P compared to EA2 (and its nice to see Landscape support!)

I would really like to know if there are any plans to improve support for chaos geometry collections, currently they don’t appear to generate distance fields and as a result have no representation in the Lumen scene.

Everything seems cleaner and more stable but i have a problem with a converted project from EA2. In 5.0 Preview the Level is way darker with the same settings and i don’t quite know what to do.


The dark scene is in 5.0 Preview.

Nevermind :slight_smile: during converting to 5.0 Preview the postprocessing broke and didnt take the manual exposure min (0) max (1) into account.

Changes list “Glossy reflections on translucency” but whatever I try, i can’t seem to get sharper reflections on a glass like surface than this:

That’s all we have for now, Lumen Reflections on translucency can’t produce mirror reflections. No one is happy with it so expect future improvements.

Also, I am generally still experiencing quite noticable grain/noise in direct shadows as seen on the white surface

Yes that noise is from Virtual Shadow Map filtering, not Lumen. You can find quality / performance tradeoffs for it in Engine\Config\BaseScalability.ini, specifically these:

r.Shadow.Virtual.SMRT.RayCountDirectional=8
r.Shadow.Virtual.SMRT.SamplesPerRayDirectional=4

4 Likes

Will lumen reflections on single layer water surfaces make it for 5.0 final?

We won’t have Single Layer Water reflections for 5.0 unfortunately. It’s a glaring omission, any level using water looks broken. We’ll try to have this for 5.1. In the meantime you have to change water to opaque or stick with the SSR.

I would really like to know if there are any plans to improve support for chaos geometry collections, currently they don’t appear to generate distance fields and as a result have no representation in the Lumen scene.

We’d like to implement distance fields for Geometry Collections but it would be pretty far down the priority list. Hardware Ray Tracing already supports Geometry Collections, however as a dynamically deforming mesh, it will cause an acceleration structure rebuild every frame so you’ll have to watch out for the performance cost.

3 Likes

Thanks for the reply, I’m glad to hear it’s at least something you hope to implement (even if it is a ways off).

A couple other unrelated questions:

  1. I noticed that the surface cache now seems to produce a pink debug color under certain circumstances. What is this? Do we need to be concerned by it?
  2. While troubleshooting this I also discovered that the distance field resolution scale now goes up to 100(!). Do we need to be concerned about performance (other than memory cost) when increasing the DF resolution scale on meshes?

I tried testing the stack o bot project with UE5preview1
and I noticed i didn’t see lumen in the landscape, but I read that’s a new feature, how can i turn it on?

Great work! Works pretty well, for a reason switching from ue5 ea to ue5 preview increased my framerate quite a lot! Thanks !

Would be handy if these were exposed in the light.

  1. I noticed that the surface cache now seems to produce a pink debug color under certain circumstances. What is this? Do we need to be concerned by it?

The pink areas mean that mesh has too complex of an interior for the Surface Cache to cover, and you won’t get any light bouncing off of them (and they’ll be black in reflections). You can increase MaxLumenMeshCards in the Static Mesh’s BuildSettings to a degree. If that’s not enough you may need to split the mesh into multiple with simpler interiors. Generally a small amount of pink is not a big deal, but if it’s a whole wall of your room then you have a problem. The docs have more on the limitations of the Surface Cache.

  1. While troubleshooting this I also discovered that the distance field resolution scale now goes up to 100(!). Do we need to be concerned about performance (other than memory cost) when increasing the DF resolution scale on meshes?

The scale can be large, but internally Mesh Distance Fields can only be 2x higher than was possible in UE4. There’s no significant performance difference from large scales, it’s mostly a disk size cost.

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I tried testing the stack o bot project with UE5preview1 and I noticed i didn’t see lumen in the landscape, but I read that’s a new feature, how can i turn it on?

Landscape should work automatically, there’s nothing you have to do to turn it on. Do you see it in your Lumen Scene viewmode? Does it work in any other levels containing Landscape?

Awesome to see and try the release of the latest UE5 build! Can’t wait for the final 5.0 launch.

Meanwhile started to test Preview and faced couple of issues with reflection and translucency:

  1. It looks like Ray Traced reflections are working now with Translucent objects (YAY!) but have some issues - glass type materials has some bleached look with translucency appearing washed out white-ish and reflections are working in a similar way to Hit Lighting mode without any GI reflections. And as been shown before in this thread switching Translucency mode to Raster leads to very lowres, blurry reflections

  2. Clear chrome/mirror material reflections look blurry for some reason. In Early Access Lumen reflections looked a bit sharper. But in both versions (Early Access and Preview) Lumen reflections look very splotchy. It looks like it’s due to lowres GI reflection quality.


Are there any setting I missing which can help to improve both scenarios (ray traced translucency & reflection on translucent objects and reflection quality on mirror materials)?

Thank you!

oh I see it now for some reason, maybe it was open with EA, and I didn’t notice. now it’s just the foliage that shows up as black in the lumen scene

Hi,
Will there be an update for double-sided surfaces and foliages? Back surfaces are too dark. Currently, Landscape grass types and painted foliages do not seem to support Lumen. Lumen does not seem stable in natural environments.


I mean this: CryEngine (SVOGI)

forest0

forest2

Thanks

Hi everyone. I did some tests with Preview 1 and with many neat improvements I’ve run into a problem with my metal materials package. How did they look on UE4:



And how they looks in UE5 Preview 1:



Anything that was not fully matte now appears so blurry…

Switching back to Screen Space Reflections in UE5 Preview 1 works brings sharpness back but at some roughness values material becomes black for some reason:


So I have tons of black artifacts from my roughness maps in random places.

You could try playing around with the reflection threshold in the ppv or via console. Not sure if that will solve it!

Btw is this rly the best reflection quality possible on translucent materials? I could not find a single console command or setting giving me better results.

r.Lumen.TranslucencyReflections - everything I tried here did not give me better results. Just crashes.

All lumen related settings I tried changing did not affect the translucent reflections at all.

Left: Glass Right: Chrome

1 Like