Particle Emitter + GPU Dynamics Error in Isaac Sim Extension

[mephiengineer]

Hi everyone,

I’m working on a custom extension trying to combine the modified trajectory_generator_example ( Lula Trajectory Generator — Isaac Sim Documentation ), and with a a particle emitter (based on FluidBallEmitterDemo.py).

Separately, both work nicely. Even an extention I made out of the FluidBallEmitterDemo works good.

Issue:

When I run taskspace trajectory movement (i need this type of movement only), I get the error:

[omni.physx.plugin] Particles feature is only supported on GPU. Please enable GPU dynamics flag in Property/Scene of physics scene!

This happens with both: Use_Instancer = True or False

What should happen:

Robot follows a Cartesian path (continuous IK update). - works

Particle system/emitter is started from the same button and updated every physics step. - error (some primitives spawned but do not behave as physical particles).

What I have tried so far:

1. Explicitly setting GPU dynamics via PhysxSceneAPI. In Physics/Scene the Checkmark “Enable GPU dynamics” looks activated

2. finding the actual UsdPhysics.Scene in the stage, enabling GPU dynamics on that scene, using the same scene path as simulation_owner when creating particle system

Isaac versions

5.1.0
5.0.0

Operating System
Windows 11

[PeterNV]

Hi, Can you try to enable GPU dynamics globally via SimulationManager to see if that works?

from isaacsim.core.simulation_manager import SimulationManager

#Enable GPU dynamics BEFORE creating particle system or starting timeline
SimulationManager.enable_gpu_dynamics(flag=True)

[mephiengineer]

Hi, thanks for your reply!

I tried a few placements for the GPU dynamics enable:

First, in scenario.py SimulationManager.enable_gpu_dynamics(flag=True) before particle creation. Did not work.

Second, i tried to place it inside _setup_taskspace_particles() (right before add_physx_particle_system) Did not work.

I also tried to place it in ui_builder.py right before timeline.play() Did not work.

Third, I tried to moved it so it runs on import of the mentioned Lula trajectory generator example:

a) at the top of scenario.py Did not work.

b) in extension.py before importing UIBuilder/scenario:

from isaacsim.core.simulation_manager import SimulationManager

SimulationManager.enable_gpu_dynamics(flag=True)

Nothing worked. The error message remained always the same.

[PeterNV]

Seems the issue is that the Lula trajectory generator might be creating or resetting the physics scene in a way that disables GPU dynamics after you’ve enabled it. Can you check if GPU dynamics is actually enabled with following code?

from pxr import PhysxSchema, UsdPhysics

def check_gpu_dynamics():
    stage = omni.usd.get_context().get_stage()
    physics_scene_path = "/physicsScene"  # or your scene path
    physics_scene = stage.GetPrimAtPath(physics_scene_path)
    
    physx_api = PhysxSchema.PhysxSceneAPI(physics_scene)
    gpu_enabled = physx_api.GetEnableGPUDynamicsAttr().Get()
    
    print(f"GPU Dynamics enabled: {gpu_enabled}")
    return gpu_enabled

[mephiengineer]

So, enabling GPU dynamics globally via SimulationManager.enable_gpu_dynamics(flag=True) before the timeline starts and before creating the particle system remains in my code

What i did: I added the check_gpu_dynamics() diagnostic at multiple points in scenario.py. Results:

After LulaKinematicsSolver created: False

After reset(): False (after pressing the reset button )

At start of setup_taskspace_trajectory(): False

After explicitly setting PhysxSceneAPI.enableGPUDynamics = True: True

(here is the code for that step:

def _enable_gpu_dynamics(self):

stage = omni.usd.get_context().get_stage()

scene_prim = self._get_or_create_physics_scene_prim(stage)

physx_scene_api = PhysxSchema.PhysxSceneAPI.Apply(scene_prim)

physx_scene_api.CreateEnableGPUDynamicsAttr(True)

self._physics_scene_path = scene_prim.GetPath().pathString

return self._physics _scene_path

But I still get the aforement ioned error…

PS Initially, both my robot (“kuka”) and the physicsScene were outside of /World. moving them all under /World ( screenshot)

does not help either and i become the False and True flags in the same order as described above

[PeterNV]

So enabling GPU dynamics via SimulationManager.enable_gpu_dynamics(flag=True) is working as expected. I have no idea what’s the issue now. If you have a minimal repro case, we can take a further look.