GPU dynamics flag only takes effect after manually opening physicsScene in the GUI

[dgarcialopez]

I’m having problems setting GPU dynamics programatically in the physicsScene for a scene with a ParticleSystem. The physicalScene correctly sets the GPU flag but apparently is not applied even if you stop/start the simulation. It only makes effect if you manually click on the physicsScene in the GUI.

To demostrate this error, I’ve created a simple script loading a usd reference which contains a cube with a ParticleSystem already set. Find attached the usd file and the script used.

from omni.isaac.kit import SimulationApp

CONFIG = {"renderer": "RayTracedLighting", "headless": False}
simulation_app = SimulationApp(CONFIG)

from omni.isaac.core import SimulationContext, utils  # noqa E402

simulation_context = SimulationContext(stage_units_in_meters=1.0)

# Configure the physics scene to use GPU dynamics for particles (fluids)
physics_context = simulation_context.get_physics_context()
physics_context.enable_ccd(False)
physics_context.enable_gpu_dynamics(True)

# Loading the cube with the particle sampler as a reference
utils.stage.add_reference_to_stage("particle_cube.usda", "/cube_reference")

simulation_app.update()
simulation_context.initialize_physics()
simulation_context.play()

while simulation_app.is_running():
    simulation_context.step(render=True)

simulation_context.stop()
simulation_app.close()

particle_cube.usda (286.7 KB)

I also tried to programatically create the cube and the ParticleSystem in python (without the usd reference) and the problem persist.

Check in the video that the ParticleSystem only works after I click on the physicsScene and the GPU flag was correctly set.

Thanks!

[AlesBorovicka]

That might indicate some IsaacSim script issues, you can try to directly access the physicsScene prim and set the attribute, which is what the script should do.

        physx_scene = PhysxSchema.PhysxSceneAPI.Apply(physics_scene.GetPrim())
        physx_scene.CreateEnableGPUDynamicsAttr().Set(True)

@kellyg I guess is would be expected to work right?

[PARKBONG]

Hi, Since I have the same problem, I applied for your recommendation.

scene_path = "/home/bong/.local/share/ov/pkg/isaac_sim-2022.2.1/standalone_examples/My_Demo/USD/Deformable.usd"
open_stage(usd_path=scene_path)
world = World(physics_dt=1/60, stage_units_in_meters=0.01)
world._physics_context.enable_gpu_dynamics(flag=True)

# ADDED --------------------------------------------------------------------------
from pxr import PhysxSchema
import omni.usd
stage = omni.usd.get_context().get_stage()
physics_scene = stage.GetPrimAtPath("/Root/PhysicsScene")
physx_scene = PhysxSchema.PhysxSceneAPI.Apply(physics_scene)
physx_scene.CreateEnableGPUDynamicsAttr().Set(True)
# ADDED --------------------------------------------------------------------------

But it doesn’t work. How can I solve this issue?

[PARKBONG]

And… should I turn off the ccd to use gpu_dynamics?

Thanks!

[AlesBorovicka]

I think the setting might get overridden by IsaacSim scripts, because GPU dynamics is enabled by default, I would try to move the attribute change right before the play.

No CCD is unrelated you can leave it on or off as you wish.

[dgarcialopez]

Thanks for the fast reply @AlesBorovicka

I also tried with PhysxSchema with the same result.

I don’t know if it helps to spot the issue but I realized that if you initialize the SimulationContext with cuda the error doesn’t appear:

simulation_context = SimulationContext(stage_units_in_meters=1.0, backend="torch", device="cuda")

Although the particle system doesn’t work because Fabric (Flatcache) doesn’t support it, right?

[AlesBorovicka]

Sorry I am not very familiar with all IsaacSim scripts, I am working mostly on the physics side.

So yes I think you need to set the device to CUDA to enable the GPU simulation, the particles should move, the update through Fabric/Flatcache is supported since 104.1 Kit release (help → about should tell you what version you do use).

However since particles are pretty much not supported by IsaacSim, I am wondering why do you use the script at all? Why dont you just simulate stuff through regular python and USD APIs? If things work fine through UI?

[dgarcialopez]

I’m using Isaac Sim 2022.2.1 with Kit 104.2. Launching Isaac from python doesn’t have the Help tab but I assume is using the same Kit version.

I didn’t know that particles where not fully supported on Isaac. For me they work good, except fot the issue explained in this post. I’m developing a project that needs to simulate fluids and connects to ROS, that’s why is handy to have a python script launching the simulation

With the line I posted previously, which set Fabric/Flatcache, the particles aren’t moving but no error appears. Maybe Fabric for particles is not supported by Isaac yet?

[AlesBorovicka]

I see, makes sense.

Well for particles you need GPU enabled, so the CUDA device should be set, that sounds good. Why particles dont move I am not sure, that sounds like a bug. I hope Kelly can comment more on the IsaacSim side, they should work with standalone physics simulation .

[kellyg]

We had some issues with deformable rendering with the GPU pipeline, it’s possible the issue also appears for particles. I will confirm this on our end.

For now, you can initialize the SimulationContext with cpu device, adding set_defaults=False to the arguments so that it does not override the default settings for enabling GPU simulation. It seems like a bug to me that we cannot override the setting somehow, even though the UI reflects the change.

[dgarcialopez]

Thanks @kellyg! I tried with set_defaults=False and works fine for now. Looking forward for the final solution.