Adds enhanced determinism flag to PhysxCfg (#395)

# Description

This MR adds an `enableEnhancedDeterminism` flag to have improved
deterministic behavior from the physics engine. By default, this is
False to remain performant. However, it should be set to true for
imitation learning-like applications where you want to replay the
demonstrations.

## Type of change

- New feature (non-breaking change which adds functionality)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have run all the tests with `./orbit.sh --test` and they pass
- [x] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

docs/source/refs/issues.rst

@@ -36,6 +36,25 @@ over stepping different parts of the simulation app. However, at this point, the
 timeline for this feature request.
 
 
+Non-determinism in physics simulation
+-------------------------------------
+
+Due to GPU work scheduling, there's a possibility that runtime changes to simulation parameters
+may alter the order in which operations take place. This occurs because environment updates can
+happen while the GPU is occupied with other tasks. Due to the inherent nature of floating-point
+numeric storage, any modification to the execution ordering can result in minor changes in the
+least significant bits of output data. These changes may lead to divergent execution over the
+course of simulating thousands of environments and simulation frames.
+
+An illustrative example of this issue is observed with the runtime domain randomization of object's
+physics materials. This process can introduce both determinancy and simulation issues when executed
+on the GPU due to the way these parameters are passed from the CPU to the GPU in the lower-level APIs.
+Consequently, it is strongly advised to perform this operation only at setup time, before the
+environment stepping commences.
+
+For more information, please refer to the `PhysX Determinism documentation`_.
+
+
 Blank initial frames from the camera
 ------------------------------------
 
@@ -70,3 +89,4 @@ are stored in the instanceable asset's USD file and not in its stage reference's
 
 .. _instanceable assets: https://docs.omniverse.nvidia.com/app_isaacsim/app_isaacsim/tutorial_gym_instanceable_assets.html
 .. _Omniverse Isaac Sim documentation: https://docs.omniverse.nvidia.com/isaacsim/latest/known_issues.html
+.. _PhysX Determinism documentation: https://nvidia-omniverse.github.io/PhysX/physx/5.3.1/docs/BestPractices.html#determinism

source/extensions/omni.isaac.orbit/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.10.19"
+version = "0.10.20"
 
 # Description
 title = "ORBIT framework for Robot Learning"

source/extensions/omni.isaac.orbit/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.10.20 (2024-02-12)
+~~~~~~~~~~~~~~~~~~~~
+
+Added
+^^^^^
+
+* Adds :attr:`omni.isaac.orbit.sim.PhysxCfg.enable_enhanced_determinism` to enable improved
+  determinism from PhysX. Please note this comes at the expense of performance.
+
+
 0.10.19 (2024-02-08)
 ~~~~~~~~~~~~~~~~~~~~
 

source/extensions/omni.isaac.orbit/omni/isaac/orbit/sim/simulation_cfg.py

@@ -114,6 +114,14 @@ class PhysxCfg:
     enable_stabilization: bool = True
     """Enable/disable additional stabilization pass in solver. Default is True."""
 
+    enable_enhanced_determinism: bool = False
+    """Enable/disable improved determinism at the expense of performance. Defaults to False.
+
+    For more information on PhysX determinism, please check `here`_.
+
+    .. _here: https://nvidia-omniverse.github.io/PhysX/physx/5.3.1/docs/RigidBodyDynamics.html#enhanced-determinism
+    """
+
     bounce_threshold_velocity: float = 0.5
     """Relative velocity threshold for contacts to bounce (in m/s). Default is 0.5 m/s."""
 

source/extensions/omni.isaac.orbit/omni/isaac/orbit/sim/simulation_context.py

@@ -484,6 +484,8 @@ class SimulationContext(_SimulationContext):
         self._physics_context.enable_ccd(self.cfg.physx.enable_ccd)
         # -- GPU collision stack size
         physx_scene_api.CreateGpuCollisionStackSizeAttr(self.cfg.physx.gpu_collision_stack_size)
+        # -- Improved determinism by PhysX
+        physx_scene_api.CreateEnableEnhancedDeterminismAttr(self.cfg.physx.enable_enhanced_determinism)
 
         # -- Gravity
         # note: Isaac sim only takes the "up-axis" as the gravity direction. But physics allows any direction so we