[BUG] `UsdGeom.TetMesh` does not render

[dogganon]

Description

Steps to reproduce:

0. Open IsaacSim in GUI mode.
1. Run create_simulation_tetmesh(stage, "/World/TetMesh", add_surface=True) from https://docs.omniverse.nvidia.com/kit/docs/omni_physics/107.3/dev_guide/deformables_beta/deformable_beta.html#single-mesh-volume-deformable
2. Observe the viewport, the created tetmesh does not render:

@vick-yu

Isaac Sim version

5.0.0

Operating System (OS)

Debian 6.1.137-1

GPU Name

RTX 3060

GPU Driver and CUDA versions

Driver Version: 535.247.01 CUDA Version: 12.2

Logs

No response

Additional information

No response

[PeterL-NV]

Hi, The mesh created by create_simulation_tetmesh(stage, "/World/TetMesh", add_surface=True) is a UsdGeom.TetMesh, which is meant for volumetric (tetrahedral) simulation and collision—not for rendering visible geometry in Isaac Sim. By default, UsdGeom.TetMesh only stores the tetrahedral volume data. The surface faces used for simulation are typically stored as surfaceFaceVertexIndices, which helps with collision, but rendering engines expect triangle or quad meshes (UsdGeom.Mesh) for visualization.

[dogganon]

@PeterL-NV This is inconsistent with the openusd specification. UsdGeomTetMesh inherits from UsdGeomImageable, which is a "base class for all prims that may require rendering or visualization of some sort." And UsdGeomTetMesh seems to be the only geometry in the UsdGeomImageable family that does not render in isaacsim so far.

[PeterL-NV]

Hi, Apologize for my previous reply, you're right UsdGeom.TetMesh is renderable. The rendering just doesn't work with Fabric Scene Delegate(FSD) enabled. Can you try to disable FSD as a WAR for now? This will be fixed in a future release and is under track. Here's how to switch FSD: Edit > Preferences > Rendering > Fabric Scene Delegate > Enable Fabric delegate

[dogganon]

@PeterL-NV Turned off FSD through the /app/useFabricSceneDelegate=false setting and UsdGeom.TetMesh finally renders.. Well it turns out UsdGeom.Plane was also not renderable under FSD so I hope that will be fixed as well. It appears that UsdGeom.TetMesh is mostly used in the proposed USD Deformable Bodies schema so it's best that the bug gets fixed by the time the schema gets standardized.