Lightmass crashes when importing USD from Blender

Development Rendering
1

When I export a thing in USD format from Blender, building lighting with Lightmass almost always crashed with the following crash (or variant of it):


LightingResults: Error: <None> === Lightmass crashed: ===
Assertion failed: (Index >= 0) & (Index < ArrayNum) [File:D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Core\Public\Containers/Array.h] [Line: 674]
Array index out of bounds: 187008 from an array of size 187008
0x00007ffba3e47c57 UnrealLightmass-Core.dll!UnknownFunction ]
0x00007ff652fee5a8 UnrealLightmass.exe!DispatchCheckVerify<void,<lambda_84c2653a153346a64e79e460f0ea2f49> >() ]
0x00007ff652fb568a UnrealLightmass.exe!Lightmass::FStaticMeshStaticLightingMesh::GetTriangleIndices() ]
0x00007ff652f2c35a UnrealLightmass.exe!Lightmass::FEmbreeGeometry::FEmbreeGeometry() ]
0x00007ff652f35fbb UnrealLightmass.exe!Lightmass::FEmbreeAggregateMesh::AddMesh() ]
0x00007ff652f867b5 UnrealLightmass.exe!Lightmass::FStaticLightingSystem::FStaticLightingSystem() ]
0x00007ff652f3a529 UnrealLightmass.exe!Lightmass::BuildStaticLighting() ]
0x00007ff652f610d7 UnrealLightmass.exe!Lightmass::LightmassMain() ]
0x00007ff652f7f8d3 UnrealLightmass.exe!main() ]
0x00007ff652fe6c64 UnrealLightmass.exe!__scrt_common_main_seh() ]
0x00007ffc57556fd4 KERNEL32.DLL!UnknownFunction ]
0x00007ffc57a9cec1 ntdll.dll!UnknownFunction ]
0x00007ffc55413e49 KERNELBASE.dll!UnknownFunction ]
0x00007ffba4082db6 UnrealLightmass-Core.dll!UnknownFunction ]
0x00007ffba4086197 UnrealLightmass-Core.dll!UnknownFunction ]
0x00007ffba3eb3b2d UnrealLightmass-Core.dll!UnknownFunction ]
0x00007ffba3e45935 UnrealLightmass-Core.dll!UnknownFunction ]
0x00007ffba3e47c90 UnrealLightmass-Core.dll!UnknownFunction ]
0x00007ff652fee5a8 UnrealLightmass.exe!DispatchCheckVerify<void,<lambda_84c2653a153346a64e79e460f0ea2f49> >() ]
0x00007ff652fb568a UnrealLightmass.exe!Lightmass::FStaticMeshStaticLightingMesh::GetTriangleIndices() ]
0x00007ff652f2c35a UnrealLightmass.exe!Lightmass::FEmbreeGeometry::FEmbreeGeometry() ]
0x00007ff652f35fbb UnrealLightmass.exe!Lightmass::FEmbreeAggregateMesh::AddMesh() ]
0x00007ff652f867b5 UnrealLightmass.exe!Lightmass::FStaticLightingSystem::FStaticLightingSystem() ]
0x00007ff652f3a529 UnrealLightmass.exe!Lightmass::BuildStaticLighting() ]
0x00007ff652f610d7 UnrealLightmass.exe!Lightmass::LightmassMain() ]
0x00007ff652f7f8d3 UnrealLightmass.exe!main() ]
0x00007ff652fe6c64 UnrealLightmass.exe!__scrt_common_main_seh() ]
0x00007ffc57556fd4 KERNEL32.DLL!UnknownFunction ]
0x00007ffc57a9cec1 ntdll.dll!UnknownFunction ]

Has anyone experience something like this before? For some simple object, i.e. just a new Suzanne from Blender, it works fine. But anything reasonable complex gets a failure like this. (But also sometimes also with just Suzanne.)

(I have a very beefy machine so hardware issues are not very likely).

2

Yes, I have the same issues with my test scene. I will do some more tests with Houdini. It might be because there is no second uv map generated for lightmass.

3

I did a quick check on my usd scene which I export from blender and in UE the UVs are missing. However if I rename the UV set in blender from the default name “UVMap” to “st” the UVs are showing up in UE an lightmass doesn’t crash anylonger. Give that a shot.

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