Description

Begin Map
Begin Level
Begin Actor Class=/Script/Engine.StaticMeshActor Name=Plane_2 Archetype=/Script/Engine.StaticMeshActor'/Script/Engine.Default__StaticMeshActor'
Begin Object Class=/Script/Engine.StaticMeshComponent Name="StaticMeshComponent0" Archetype=StaticMeshComponent'/Script/Engine.Default__StaticMeshActor:StaticMeshComponent0'
End Object
Begin Object Name="StaticMeshComponent0"
StaticMesh=StaticMesh'"/Engine/BasicShapes/Plane.Plane"'
StaticMeshImportVersion=1
StaticMeshDerivedDataKey="STATICMESH_F9378A28F161444987BACE79B2590E57_228332BAE0224DD294E232B87D83948FQuadricMeshReduction_V1$2e0_3F8C76BE469D6CAEBDC47F82BF709939000000000100000001000000000000000000000001000000010000000000000000000000010000000001000000000000010000000000803F0000803F0000803F0000803F00000000050000004E6F6E650030000000803F0000803F0000000000000041000000000000A0420303030000000000000000LS0MNSzzzzzzzz0"
MaterialStreamingRelativeBoxes(0)=67043328
OverrideMaterials(0)=Material'"/Engine/BasicShapes/BasicShapeMaterial.BasicShapeMaterial"'
VisibilityId=2
RelativeLocation=(X=-40.000000,Y=40.000000,Z=160.000000)
RelativeScale3D=(X=5.000000,Y=5.500000,Z=1.000000)
CustomProperties
End Object
StaticMeshComponent="StaticMeshComponent0"
RootComponent="StaticMeshComponent0"
ActorLabel="Plane"
End Actor
Begin Actor Class=/Script/Engine.StaticMeshActor Name=Cube_5 Archetype=/Script/Engine.StaticMeshActor'/Script/Engine.Default__StaticMeshActor'
Begin Object Class=/Script/Engine.StaticMeshComponent Name="StaticMeshComponent0" Archetype=StaticMeshComponent'/Script/Engine.Default__StaticMeshActor:StaticMeshComponent0'
End Object
Begin Object Name="StaticMeshComponent0"
StaticMesh=StaticMesh'"/Engine/BasicShapes/Cube.Cube"'
StaticMeshDerivedDataKey="STATICMESH_F9378A28F161444987BACE79B2590E57_228332BAE0224DD294E232B87D83948FQuadricMeshReduction_V1$2e0_26D666F86459324BE77D4F6A1939C6698000000000100000001000000000000000100000001000000010000000000000000000000000000004000000000000000020000000000803F0000803F0000803F0000004000000000050000004E6F6E650030000000803F0000803F000000000000004100000000000034420303030000000000000000LS0MNSzzzzzzzz0"
MaterialStreamingRelativeBoxes(0)=4294901760
OverrideMaterials(0)=Material'"/Engine/BasicShapes/BasicShapeMaterial.BasicShapeMaterial"'
VisibilityId=3
RelativeLocation=(X=-90.000000,Y=200.000000,Z=20.000000)
CustomProperties
End Object
StaticMeshComponent="StaticMeshComponent0"
RootComponent="StaticMeshComponent0"
ActorLabel="Cube"
End Actor
End Level
Begin Surface
End Surface
End Map

Steps to Reproduce

Copy the Text below in Description section and paste it into a New default level, built lighting

You will see lightmap artifacts(black and white blocks) on the Box mesh

The Box is inside the shadow of a Plane which is a single face mesh.

Duplicate the Plane mesh and flip it to have both top and down side faces, rebuilt lighting, the artifacts is gone

PS: in 4.23 it has no issue; In 4.24 release notes it has one note: "New: Lightmass—Improved dark corner mitigation by storing backfacing hits fraction inside irradiance cache records and marking texels as unmapped when their interpolated backfacing fraction > 0.5." I'm not exact sure what this notes means but feel like related

  [Link Removed]

[Link Removed]
 
 
 
 

Have Comments or More Details?

There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-94177 in the post.

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Duplicate
ComponentUE - Rendering - Lumen
Affects Versions4.244.25
Target Fix4.26
CreatedJun 9, 2020
ResolvedJun 10, 2020
UpdatedSep 19, 2021