Lumen GI and Reflections feedback thread

[Suthriel]

Thanks for those infos

In the Star Destroyer, getting perfect Surface Cache coverage isn’t going to matter much, since you’re outside of it (you don’t rely on the GI bounce from it much), and Screen Traces are likely handling most of the GI anyway with such small scale features.

Please don´t underestimate the urge to drive a camera straight through those superstructures for some extreme close-ups and dogfights in between those structures
And the inside of an SSD or ISD is just one crash through a window away

[Arkiras]

I’m aware emissive surfaces should not replace analytical lightsources, I mention this only in case this behavior is unintended; Emissive surfaces seem to completely stop emitting light in the LumenScene/SurfaceCache when scaled below a certain size:

Emissive surface disappears from lumen scene below a certain size

Seems like theres some non-uniformity to it, for example making a 95x95cm plane won’t emit light into the surface cache, but a 50x126cm plane will work just fine.

Also, what is the difference between the “Lumen Scene” and the “Surface Cache” view in the visualizer? Just the additional debug colors in the Surface Cache view? They seem identical otherwise.

I’m really looking for the 5.0 release (and the future of Lumen beyond that), you guys have done an incredible job all around.

[Farshid]

r.Lumen.ScreenProbeGather.MaxRayIntensity

Thank you
More tests

Path Tracing

Early Access

Preview 1 (again black ceiling !)

Path Tracing

Early Access

Preview 1 (default)

Preview 1
r.Lumen.ScreenProbeGather.MaxRayIntensity 100
r.Lumen.ScreenProbeGather.RadianceCache 0

the Early Access and path tracing are more clean , less noisy
preview 1 has high contrast shodow while the shadows are bright in path tracing and early access
corners are too dark in preview 1

[Rawalanche]

Lumen will never be able to do as many bounces as Path Tracer in realtime, and from your path tracer renders I can clearly see you are using way to excessive albedo on your bright materials, resulting in extremely unrealistic amount of light bounce. So the less realistic albedo ranges you stay within, the more discrepancy will there be between lumen and path tracer.

[AE_3DFX]

Wonder why such rule that features that might be broken cannot be fixed after lock period? This produces release that has wrongly working feature. Thanks.

[DaEmpty]

The documentation states that you will get problems below a certain size and mentioned it in different streams. You should not use emissive materials to replace all lights in the scene.

[Yaeko]

A bit of “Off Topic”, since I see more and more problems that come from a missunderstanding in how Lumen is used best, and its reliance on “simple” Meshes.

Tip: Forget about “how things have been done in the past”, its obsolete, Lumen will not work with these meshes/games.

The Mesh Distance Fields cant deal with very small features and/or large but complex/hollow meshes, which is why especially Architectural stuff appears very often in such posts.

How to do it then?

For Architectural Stuff:

• Each Wall at best is a single mesh, if it has a bunch of angles/corners, you need to seperate that out, otherwise it gets lost in the Mesh Distance Field.
• Do not merge things like Fences etc. (complex meshes) into a single one, keep them seperate, make use if Instanced Static Meshes for stuff like planks etc. (for easy setup)
• If it is a large scene, use Nanite, and make sure to re-use the same mesh as often as you can, for example: walls.
• If you use Nanite, dont use it for meshes with transparency, like windows, trees, etc.
• care for the thickness of your walls/roof etc.
• use actual lights for lights, tune down your emissive materials to a “its only for looks, not light” level.
• some faking required in certain situations

For Games related stuff:

• Create reusable pieces that arent too large, dont merge things.
• Instanced Static Meshes are your friend, make use of them, they can easily deal with all kinds of things. (especially walls, floor, ceilings etc.)
• Your individual “wall panels” can be thin, but the wall itself should have a certain thickness to prevent light leaks.
• Nanite, use it. If you dont… say bye to your drawcalls with all these meshes.
• Feel free to experiment with a lights “Gi contribution” value (or whatever its called) to get the look you want.
• Some faking still is required

You can have very complex scenes in Lumen, as long as you give it “simple stuff” to work with. I used Nanite to visualize the single meshes, allthough many of them are Instanced Static Meshes, especially the smaller wall Tiles.

What you can see in the image below should be around tens of thousands of meshes, if we also count the instances (not all of them are nanite, nanite doesnt like small meshes.)

==========

To get to the Star Destroyer further above, and how I would build it for lumen:

• 1:1 scale → forget about it.
• as a smale decorative object: the mesh you have is fine, lumens screen traces will deal with it.
• as a large decorative object:

I would cut it into pieces like this (Source for the image was the star wars fandom wiki):

The issue with the executor is:

• the center part is too complex to not be separated from the outer parts
• on a larger scale, the Mesh Distance fields cant represent the center part properly, maybe not even the outer parts and the sides.
• that thing is big in 1:1, if you want lumen to work with it at 1:1, you will end up with hundreds of pieces for the center part.
• Nanite is also required then (if build from cubes, which is possible)

The limiting factor for Lumen is not Lumen itself, but the Mesh Distance Fields level of Detail, and on a second level the cards generated based on that MDF.

Mesh-Separation is Key, the times of “merging” are over for UE5.

PS: My approach might not be “the best”, or “the most correct” one, but I had a lot of success with it since EA1, it just worked.

[Farshid]

my main question is why early access is more similar to path tracer ?
why preview 1 create too much shadow ? I see dark Floor and Ceiling in every scene

lumen has limitation in bounces
but this realtime lighting system has pre calculated Mesh Distance Field which offline path tracer does not has

[Arkiras]

You’ve misunderstood the purpose of my post, I’m not seeking advice. I’m aware of what the best practices are for using Lumen with emissives, I am merely mentioning there is a tipping point based on object size at which emissive light becomes completely ignored by the Lumen Scene and Surface Cache, in case this behavior is unintended.

[Daniel_Wright]

@Arkiras

missive surfaces seem to completely stop emitting light in the LumenScene/SurfaceCache when scaled below a certain size:

We have a new setting to work around this: set ‘Emissive Light Source’ on the component

By default Lumen culls small objects from Lumen Scene for realtime performance, but you can override this when you know it is an important source of light.

Also, what is the difference between the “Lumen Scene” and the “Surface Cache” view in the visualizer? Just the additional debug colors in the Surface Cache view? They seem identical otherwise.

Just the error coloring, we found it too distracting to be always present in Lumen Scene, where you are usually looking more at the lighting match rather than the Surface Cache coverage.

[Daniel_Wright]

@AE_3DFX

Wonder why such rule that features that might be broken cannot be fixed after lock period? This produces release that has wrongly working feature.

This stuff is all outside of my control, but basically to release a stable software product with hundreds of programmers working on it, you have to slowly reduce the severity of bugs that are allowed to be fixed (as each fix to a bug has a chance of causing another bug). In the end, only major issues can be fixed, and Thursday is that deadline.

[AE_3DFX]

Thank you sir for very good answer

[Tycholarfero1 (Tycholarfero)]

Hi all, brand new user to the forum, can’t embed as many pics as I would have liked, or links! So this will be pretty awkward as a post!! Had to copy and paste the post on Pastebin, maybe eventually I’ll have a high enough post count so that this doesn’t become an issue again. lumen stuff - Pastebin.com

• Word for word from Pastebin so there’s post consistency

I noticed that the deadline is for tomorrow so I just have two things I’ve noticed that may be bugs but honestly I have no idea, I wanted to throw them out there before then so at least they’re known.

1. I have noticed something strange going on since at least EA 2 when you have a large reflective texture for the ground and you have an element going up a certain point above floor level, seems to invert the tallest object and blow it up in scale in the reflection and it seems to also contribute to scene lighting for whatever reason.
   -On Pastebin-

The mannequin in the reflection also remains even when the actual mannequin is hidden too, it seems only to fix when I rebuild reflection captures.
-On Pastebin-

2. I have no idea if it’s just me, but emissives are sometimes wack and now seem to behave much more inconsistently for me than they did in EA 2, they’ve become much more splotchy, even with hardware ray tracing on, and I think I noticed that their cut off is much smaller than it used to be, but I can’t really verify all that much and may just have bad memory already.
   -On Pastebin-

Something else I have noticed is that on a scene that I was trying out previously in EA 2, the emissives looked normal in the lumen scene but in Preview 1 it’s now seemingly completely broken and I have little idea why, I have my doubts that this is a lumen issue itself and may just be on my end as I am not very competent, but it’s been strange regardless. Emissive cut off definitely wasn’t this bad before though on this scene, my poor memory remembers this much at least.
-On Pastebin-

On the much more positive side to what I’ve tried so far, the Assetsville Town pack now looks absolutely gorgeous, and there’s even SSS on the blocky tarp both with and without hardware RT on.
-On Pastebin-

I’ve not noticed this in other parts of the map so I don’t believe it’s due to light leak, it’s a gorgeous effect!

[Daniel_Wright]

Preview 1 (again black ceiling !)
the Early Access and path tracing are more clean , less noisy
preview 1 has high contrast shodow while the shadows are bright in path tracing and early access
corners are too dark in preview 1

Thanks for this test project. Both of the maps have good Surface Cache coverage.

You had Hardware Ray Tracing for the project disabled, but it’s definitely a requirement for clean architecture like this. With Hardware Ray Tracing, the dark ceiling is fixed:

You can see why Software Ray Tracing is so dark if you look at the Lumen Reflection View viewmode, Software Ray Tracing just doesn’t have enough precision to represent the small window openings.

Disabling ‘Affect Distance Field Lighting’ on the window frames opens them up:

Now Software Ray Tracing is giving similar brightness results to Hardware Ray Tracing, but still lower quality.

[Yaeko]

are you planning to improve precision etc. as gpus get faster over time?

[Farshid]

Last test for preview 1
thank @ for answering community

Path tracing

early access - similar to path tracing - (hardware raytracing off)

Preview 1 (very strange ceiling) - (hardware raytracing off)

preview 1 is downgrade in quality and upgarde in performance (fps)
but I’m sure
Epic genius developers will take ue5 to the next level

[Braitenbug]

Changing the distance field resolution could help. How does the last shot look in lumen scene?

[Farshid]

First Scene
early access Lumen Scene

early access Lumen GI

early access mesh distance fields

Preview 1 Lumen Scene

Preview 1 Lumen surface cache

Preview 1 mesh distance fields

[Farshid]

in Early access there is some light in Ceiling in Lumen Scene

but Lumen Scene in preview 1 is complete Black !

Luemen Scene in Early Access

Luemen Scene in Preview 1 (black seling in lumen scene)

[Farshid]

Second Scene
early access Lumen Scene

early access mesh distance fields

Preview 1 Lumen Scene

Preview 1 Lumen surface cache

Preview 1 mesh distance fields