Shading Artifacts on HDA Instance Static mesh in UE4.25.3

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Hey all,

I'm looking for some guidance as to what to investigate in trying to fix this shading artifact I'm seeing on instance static meshes in UE4 4.25.3.

The attached gif shows the artifact I'm seeing. The mesh on sc L is just a static mesh dragged in from the content browser. The same mesh is on the right but instanced via an HDA from Houdini. I saw this on a more complicated set up but what we are looking at is a stripped down HDA that is just 6 points. I have tried using the a couple methods for the instancing (packed copy to points geo, straight points and unreal_instance attributes). The mesh is the same so it has the same import settings. A different mesh dropped on the HDA will show similar artifacts (i.e. “regular” mesh looks fine, instance mesh gets the dark ‘shadowing’).

The effect seems to be camera distance relative and only partially impacted by light position. It looks like broken normals or up vector but the mesh normals seem fine on the Left and, as a test, I've tried setting a manual up vector on the points in the HDA to no effect.

I've used HDA for basic layout / arrangement like this before; very simple stuff to be sure. Never seen a rendering artifact like this. Has anyone else seen this before? Suggestions on what to investigate next? Since the source mesh looks right, I'm more focused on the HDA and Houdini side of things…

Attachments:
hda_artifact.mp4 (3.6 MB)

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Tiny update:

in some continuing debugging, I've found the artifact is partially related to ray traced reflections in UE4. when I added a chrome like material to both the mesh and the instance static mesh and upped the max bounce for the refls (on the PPV) to 3, that filled in the “dark” portions of the artifact.

However, for a more normal diffuse material, you can still see the issue quite clearly. And it means the instance static meshes are still treated differently than the regular mesh, which still looks fine in all cases. So, partly sorted, but still not at a solution yet. :/
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Additional update. If I embed the mesh in question in a BP and instance that BP rather than the mesh itself, the HDA uses the HoudiniInstancedActorComponent rather than the HoudiniInstancedStaticMeshComponent.

The Actor Component method looks right and does not show the visual artifact.
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