how do i enable lumen multibounce? i can only get it in the native raytracer.
i can get it below 60 too. runs decent tho for what i’m asking from my lil gpu. 75% dlss.
and yes… raytraced glass has both the front and the interior wall reflection.
I asked the lumen team about this a while ago, the response was that it would be possible and that they’ve laid the groundwork for it already (if I understand their message), but that given how leaky the fallback radiance cache can be, it may not give very good results.
I compiled a custom version of UE pulled down from _main, multibounce reflections isn’t even a month old as a feature (based on the github dates at least).
Epic’s old RT system is powerful, but it also has limited interaction and awareness of other lighting systems. The tremendous virtue of lumen is that it’s so well-integrated into all the other lighting and rendering systems, so it’s more of the ‘just works’ indirect lighting that’s been sought after for so long. It’s also cheaper by a fair bit, as Epic did very good work optimizing their RT pipeline.
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about that temporal noise. done some thinking. i think that’s cause the lightcache doesn’t exist behind the camera. if you have rough materials in the shot you gotta raytrace the whole scene behind you with multiple random scattered rays to composite the color you would see. this is very demanding. reflection tracing offscreen is easy with pure rays but is very hard with rough materials.
I believe you are right about most of that. While I’m no light transport researcher, I’m relatively familiar with the most common rendering algorithms, and I’ve read the lumen papers quite a few times because I was completely mystified by how the technology worked.
If by ‘lightcache’ you mean the lumen surface cache, that is actually designed to be world-space persistent, located in the surroundings of the player. You are correct on the concept of reflection coherence, as rays coming off of very smooth surfaces have little-to-no inherit noise. The rougher the reflection, the harder it is to reconstruct into a stable image.
Granted, this is with rays. At one point, Epic considered prefiltered cone tracing for lumen reflections, which could resolve surfaces of any roughness with little to no noise. Ultimately too many drawbacks to be implemented, but it was on the table for the time.\
PS if anyone from the Lumen team reads this, please correct anything I may be misunderstanding.
Also, for anyone interested, came in yesterday:
While I don’t know performance implications at the moment, I believe they could be fairly more performant than the original RT reflections, given the lumen team’s work to develop a much smaller RT payload and better pipeline management.
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Looks like a step toward lightmap GI support
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forking it too, rn. gotta check this out.
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compile took hours. but i got it to run. this is spicy. hell yeah. intentionally forced a bit of roughness. i know it’s not a proper surface cache stresstest, but it like the result of this.
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You can expect next colors from 3 input color.
Here you can check the 3 colors(which is circled green. Results are 3 red color.)
There are green triangle this represent 3 input colors which are green circle and draw infinite lines and symmerty lines for each points from green triangle.
You can see green triangle. Find a symmetry line that through green triangle points you must go through green line from extended lines that is important. (find symmetry line from extended lines. From extended lines you drew just before and to the each of the green triangle points)
You can find one specific point that satisfies through all green triangle points.
If you have any questions I’ll answer for you. My first language is not english so I have some troubles to describe this logic.
If you have questions or need more detail let me know.
Question / problem; for an archviz project I’m using Lumen + VR. In this project, the material on the roof is behaving like ‘drunk’. All other meshes and materials are fine.
- When walking in VR, the rooftile material goes a bit up and down.
- IT’s PC-vr and it only happens in the headset, the spectator view is ok. Also there’s no problem when the project is played in first person mode.
- Tried changing materials (its an old rooftile from Quixel), added some extra edges to split-up the roof surface.
- Also tried using customized UVs in the material
- No FFR is active, using VSM + TSR
- If Lumen is disabled and GPUlightmass is used - all is fine so I guess its Lumen & VR related.
- Using 5.1.1, RTX4090 + latest Studio drivers
Any suggestions ?
Lightmass+lumen reflections I take it? How’s the temporal stability?
nope. that’s not lightmass. all live. it’s all lumen. and on epic settings. no dlss plugin yet. i intentionally removed the wall too. GI probes and surface cache on the left side. quinn is lit by GI probes too. ofc it doesn’t propagate into the reflection. but ima cut my train of thought here. chill friday.
ofc the reflection is still temporally unstable, cause it’s rough, but that’s fine. noise is my friend. 
I guess this is just referring to improved shadow/occlusion? Tried 5.2 as well as main and Lumen GI still doesn’t affect grooms. Which leads to big visuals discrepancies. Quite annoying since everything else is so coherent at this point.
No issues with 5.2 Lumen on my end (so far).
I was going to make a post about it but forgot to: SWRT in 5.2 is a beast in my testing. Now that the global distance field can pull from surface cache cards and the cache supports feedback for SW reflections, I’ve gotten really high-quality results.
In the sci-fi hall scene, SWRT and non hit-lighting HWRT look very similar even at near-perfect specularity, the real difference being HWRT had less light-leaking. The only way to make a real visual difference was to enable hit lighting with multiple bounces.
SWRT
HWRT
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I actually found an issue, something that always existed, but I just was reminded of it due to the “new lumen” being a lot brighter, and me not having adjusted stuff yet.
Lumen lacks “depth awareness” for its screenspace-part I guess:
As is visible in this image, Lumen creates either reflections or bounce-light for stuff that it shouldnt. The Lasers are nowhere near the ground, so that they would create an “aura” like this around themselves.
There also is massive ghosting with this “side effect” of Lumen.
Obviously, this will mostly go away again after I adjusted all brightness for the new lumen settings, since this comes from 5.0, which was different.
In general, I would like it, if we could completely exclude something from Lumen, because there are situations where Lumen becomes really difficult to “keep under control”.
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This is really only an issue for translucent surfaces, and I assume it’s because they don’t write to the depth buffer
example
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One of the changenotes I read on lumen from 5.1 onwards was that, on account of the increased image stability and firefly suppression, they were able to double maximum energy per-ray to facilitate closer to ground truth GI. What you’re saying makes complete sense, and it also makes me wonder how updates to lumen technology would necessitate art direction tweaks in the future.
got around to blockout a piece of clone wars city. good for ronin 2072 too. it’s nice to have both baked GI and live lumen for multibounce reflections. skyscrapers are a thing. gotta cheat a bit cause the ligthmaps are not in the reflection, but it works for the main focal point of potential gameplay at this spac(e)ious scale. also got the possibility of long exposure for engine exhaust plumes or slow explosions in the closer range cache on top of the static GI.
it’s also pretty darn stable at city scale. long distances and smaller angles of incidence? good stuff.
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