Skipping attachment creation

Omniverse Isaac Sim
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1

Hello, I have an error when using the deformable body attachments in the last Isaac Sim 2023.1.0-hotfix.1 release.

It can be reproduced with the extsPhysics/omni.physx.demos-105.1.10-5.1/omni/physxdemos/scenes/DeformableBodyAttachmentsDemo.py. If we set the left blob deformable body simulation_hexahedral_resolution to 64 (it can also be changed in the Mesh/Physcs/Deformable Body UI).

deformableUtils.add_physx_deformable_body(stage, blob_left_mesh.GetPath(), collision_simplification=False, simulation_hexahedral_resolution=64)

This change sets more attachment points but when the simulation starts the attachment is not properly created. The left blob is actually detached from the cube, showing this error:

[Error] [omni.physx.plugin] Invalid attachment point detected for attachment /blobLeft/attachment. Skipping attachment creation.

I think, this issue is not related to simulation_hexahedral_resolution but it is due to a limit on the number of attachment points that can be handled by PhysxSchema.PhysxPhysicsAttachment. As another example, a low resolution deformable body attached into a large overlap object (more attachment points) causes the same error.

I tested this with the previous 2022.2.1 release and it did not have this issue, it maintained correctly attached the blob, independently of the number of attached points.

Best

attach_4
attach_41152×735 592 KB

attach_3
attach_31152×735 643 KB

attach_2
attach_21152×735 671 KB

attach_1
attach_11152×735 709 KB

attach_0
attach_01152×735 687 KB

3

I followed your steps using Isaac Sim 2023.1.0-hotfix. 1 release but unfortunately, I was unable to reproduce the bug. Could you please verify again from a clean installation?

4

Another thing I found unusual is that from your attached screenshots, the number of visual tets on the left blob has increased significantly. If you only changed simulation_hexahedral_resolution, the number of visual tets should not increase as only the simulation tets are affected. Increasing the number of simulation tets will make the left blob much more stretchable than the right blob but will not change the number of visual tets.