UE 5.7 – Substrate + Clear Coat + Lumen HWRT causes colorfill square artifact

[Allan_Portilho]

II’m experiencing a rendering artifact in UE 5.7 that I can’t resolve.

Setup:

• Substrate material with Clear Coat layer

• Lumen Hardware Ray Tracing reflections enabled

• “Max Roughness to Trace” set to anything other than 0.2 (e.g., 0.4, 0.6, 0.8)

Issue:
A small colorfill square / tile artifact appears on screen. It stays fixed in the same place (not moving with geometry). Disabling Hardware Ray Tracing makes it disappear. Switching reflections to Screen Space turns the square black.

What I’ve tried (none worked):

• Updated the BIOS of my Motherboard

• Updated NVIDIA driver to latest

• Deleted Intermediate, Saved, DerivedDataCache

• Tried console variables:

  • r.Lumen.Reflections.MaxRoughnessToTraceClamp 0

  • r.Lumen.Reflections.Temporal.NeighborhoodClampScale 0

  • r.Lumen.Reflections.SamplePerPixel 1

  • r.Lumen.Reflections.SpatialFilter 0

  • r.Lumen.Reflections.RadianceCache 0

  • r.LumenScene.Radiosity.ProbeSpacing 2

  • r.raytracing.nanite.mode 1

• The artifact remains. Only setting r.Lumen.Reflections.Temporal 0 changes it from a square to a bloom flare (not a fix).

Question:
Is this a known Substrate + Clear Coat + Lumen HWRT bug in 5.7? Are there any working workarounds besides disabling Substrate or lowering Max Roughness?

Thanks for any help.

[Data_Vision (Léo Paul Ossola)]

Hi !
I happen to have the same exact issue but i didn’t dig in as deep as you did. I did find that Max roughness to trace changed it and i do have HWRT and substrate so we must experience the exact same issue.

As for a solution, well it’s in fact pretty easy to overcome ! I use 5% overscan and that is enough to make it go away. I’m rendering so i just added an extra node in my movie render graph, but i’m pretty sure you can do it at runtime with a cinecamera.

But this does need to be looked at. Did you open a bug report ?

[The_Distiller]

Experiencing the exact same thing. Let’s hope this gets fixed for 5.8.

500×500 2.84 KB

The substrate automotive materials produce a NaN/bad pixel in the top left corner, when using any multi coated material. This is happening on multiple Windows machines with different configurations (3090 to 5090). [image]

[ChrisRapid94]

Hi Allan. I had the same issue, I have the “same” setup that you have too. What I found that worked for me was actually to add / remove a CVAR.
r.Lumen.Reflections.maxRoughnessToTrace -1

This took away the entire bug for me and I will flag this to Epic as well. I really hope this helps you out, let me know.

Kind regards, C

[McSwiff]

This has been fixed in 5.8, but if you’re stuck on 5.7 you can manually patch in the fix as it’s just a buildin shader that needs fixin.

Substrate Automotive - Coated materials produce NaN/bad pixel

Hello! This is a “known” issue on 5.7 and will be fixed in 5.8. The change which addressed that was checked in CL 51211767 on our main line (Github). [image] I hope this helps. /Charles.

So in \UE_5.7\Engine\Shaders\Private\StochasticLighting\StochasticLightingTileClassification.usf
On line 636 (if in Vanilla) add if (bIsAnyValid)

Then just restart your engine, or execute the console command RecompileShaders changed, and it’ll be fixed.

[Data_Vision (Léo Paul Ossola)]

Well thanks ! Didn’t understand that you could simply modify the .usf without recompiling the engine. That’s a really simple fix that should have been made more clear..