Nanite skinned mesh does not respect disabled sections from skeletal mesh editor

Development Rendering
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1

Sections which are disabled on skeletal meshes still render when rendering skeletal meshes using nanite.

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I have the following hotfix in engine code (NaniteResources.cpp:2469) which appears to fix the issue, though I am not sure if that is the correct way to go about it:

// If Section is hidden, do not cast shadow
MaterialSection.bHidden = MeshObject->IsMaterialHidden(FirstLODIndex, MaterialSection.MaterialIndex);

// CHANGED CODE
MaterialSection.bHidden |= MeshSection.bDisabled;
// END CHANGED CODE

// If the material is NULL, or isn't flagged for use with skeletal meshes, it will be replaced by the default material.
UMaterialInterface* ShadingMaterial = InMeshDesc.GetMaterial(MaterialSection.MaterialIndex);
2

Steps to Reproduce
* Import a skeletal mesh asset with multiple sections (for example one cloth simulation section)

* In LOD 0 > Sections right click on one of the sections and select “Disable” on the section

* Toggle on Nanite Settings > Enable Nanite Support and press the “Apply Changes” button

* Drag an instance of this skeletal mesh into the scene

* Notice that the disabled section still renders in nanite, but does not render in the skeletal mesh previewer (where nanite is disabled on the debug component)

3

Hi Ted,

Thank you for the great bug report. I have fixed this in UE5Main in CL 45797729

Cheers,

Graham