Changes to RawMesh.FaceMaterialIndices working for lods with Reduction Settings|Percent Trianles==100 only

Development Asset Creation
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1

Hi. My code here is changing indices in RawMesh.FaceMaterialIndices but to no effect. That only seems to work for LOD0 and not the other ones. Any idea why?

bool modified = false;
FRawMesh mesh;
auto& sourceModel = staticMesh->SourceModels[lod];
sourceModel.RawMeshBulkData->LoadRawMesh(mesh);

auto& faceMaterialIndices = mesh.FaceMaterialIndices;
for (int32 F = faceMaterialIndices.Num() - 1; F != -1; F--)
{
	if (faceMaterialIndices[F] == material)
	{
		faceMaterialIndices[F] = replacement;
		modified = true;
	}
}

if (modified == true)
{
	sourceModel.RawMeshBulkData->SaveRawMesh(mesh);
	staticMesh->Build();
}
2

Update: I tracked this issue to be triggered by changing LOD#|Reduction Settings|Percent Triangles to be something other that 100. Expectedly, MeshUtilities.cpp test just that (“ReductionSettings.PercentTriangles < 1.0f”).

3

staticMesh->SourceModels[lod].ReductionSettings.BaseLODModel = lod;
Case solved.