Translucency Glitches using Lumen

Development Rendering
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1

Hi there,

My 5.3 scene is using

  • Lumen Reflections
  • ScreenSpace GI
  • Rasterized Translucency

When opaque material geometry is behind translucent material geometry I get this artifacts:

image
image571×461 40 KB

It looks like a glitch in screen space, when I move the camera. It glows immensly depending on the view, so those pixel values has to be quite big and it happens before the tonemapper. Does not matter if the geometry behind uses Nanite or not.

I can reproduce this with a basic translucent material (happens for Translucent and ThinTranslucent):

image
image867×731 107 KB

What I found after many tests:

  • “r.Lumen.Reflections.BilateralFilter 0” gets rid of those glitches. This is not a solution though, as it causes sporadic editor and package crashes with something like “reflectionState->ResolveVarianceHistoryRT == nullptr || ReflectionState->ResolveVarianceHistoryRT”. (I will post the full error as soon as it appears again)
  • I also found “r.Lumen.TranslucencyReflections.FrontLayer.Allow 0” or “r.Lumen.TranslucencyReflections.FrontLayer.Enable 0” to get rid of the glitch as well. But might not be a solution for every scene.
  • It gets reduced when I decrease “r.Lumen.TranslucencyReflections.FrontLayer.RelativeDepthThreshold” to super low values like 0.000001, but persists.
  • As soon as I use Lumen GI instead or do not use Lumen Reflections instead, it also goes away.

All those insights could give a clue to a rendering engineer of Epic on what is going on under the hood.

Did someone stumbled apon this and has other “solutions” or even real ones?
Does anybody can think of what is going on, to understand this bug better?

Thank you very much in advance!

Basti

2

Here is the error message after the sudden crashes:

Assertion failed: ReflectionState->ResolveVarianceHistoryRT == nullptr || ReflectionState->ResolveVarianceHistoryRT->GetDesc().Extent == HistoryEffectiveResolution [File:D:\build\++UE5\Sync\Engine\Source\Runtime\Renderer\Private\Lumen\LumenReflections.cpp] [Line: 889]

UnrealEditor_Renderer!FDeferredShadingSceneRenderer::RenderLumenReflections() [D:\build\++UE5\Sync\Engine\Source\Runtime\Renderer\Private\Lumen\LumenReflections.cpp:1292]
UnrealEditor_Renderer!FDeferredShadingSceneRenderer::RenderDiffuseIndirectAndAmbientOcclusion() [D:\build\++UE5\Sync\Engine\Source\Runtime\Renderer\Private\IndirectLightRendering.cpp:1056]
UnrealEditor_Renderer!FDeferredShadingSceneRenderer::Render() [D:\build\++UE5\Sync\Engine\Source\Runtime\Renderer\Private\DeferredShadingRenderer.cpp:3884]
UnrealEditor_Renderer!RenderViewFamilies_RenderThread() [D:\build\++UE5\Sync\Engine\Source\Runtime\Renderer\Private\SceneRendering.cpp:4574]
UnrealEditor_Renderer!`FRendererModule::BeginRenderingViewFamilies'::`87'::<lambda_3>::operator()() [D:\build\++UE5\Sync\Engine\Source\Runtime\Renderer\Private\SceneRendering.cpp:4848]
UnrealEditor_Renderer!TEnqueueUniqueRenderCommandType<`FRendererModule::BeginRenderingViewFamilies'::`87'::FDrawSceneCommandName,`FRendererModule::BeginRenderingViewFamilies'::`87'::<lambda_3> >::DoTask() [D:\build\++UE5\Sync\Engine\Source\Runtime\RenderCore\Public\RenderingThread.h:209]
UnrealEditor_Renderer!TGraphTask<TEnqueueUniqueRenderCommandType<`FRendererModule::BeginRenderingViewFamilies'::`87'::FDrawSceneCommandName,`FRendererModule::BeginRenderingViewFamilies'::`87'::<lambda_3> > >::ExecuteTask() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Public\Async\TaskGraphInterfaces.h:1265]
UnrealEditor_Core!FNamedTaskThread::ProcessTasksNamedThread() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:758]
UnrealEditor_Core!FNamedTaskThread::ProcessTasksUntilQuit() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:649]
UnrealEditor_RenderCore!RenderingThreadMain() [D:\build\++UE5\Sync\Engine\Source\Runtime\RenderCore\Private\RenderingThread.cpp:411]
UnrealEditor_RenderCore!FRenderingThread::Run() [D:\build\++UE5\Sync\Engine\Source\Runtime\RenderCore\Private\RenderingThread.cpp:537]
UnrealEditor_Core!FRunnableThreadWin::Run() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Windows\WindowsRunnableThread.cpp:149]