Adds invalidation of physics handles when simulation is stopped (#332)

# Description

Since we now handle the PhysX views directly, we need to make sure they
are deleted properly when the simulation is stopped. This MR adds the
missing implementation for invalidating the views in all sensors and
asset classes.

## Type of change

- Bug fix (non-breaking change which fixes an issue)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [ ] 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
- [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

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

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.10.8"
+version = "0.10.9"
 
 # Description
 title = "ORBIT framework for Robot Learning"

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

 Changelog
 ---------
 
+0.10.9 (2023-12-21)
+~~~~~~~~~~~~~~~~~~~
+
+Fixed
+^^^^^
+
+* Fixed invalidation of physics views inside the asset and sensor classes. Earlier, they were left initialized
+  even when the simulation was stopped. This caused issues when closing the application.
+
+
 0.10.8 (2023-12-20)
 ~~~~~~~~~~~~~~~~~~~
 

source/extensions/omni.isaac.orbit/omni/isaac/orbit/assets/rigid_object/rigid_object.py

@@ -383,3 +383,16 @@ class RigidObject(AssetBase):
         # -- heading direction of root
         forward_w = math_utils.quat_apply(self._data.root_quat_w, self.FORWARD_VEC_B)
         self._data.heading_w[:] = torch.atan2(forward_w[:, 1], forward_w[:, 0])
+
+    """
+    Internal simulation callbacks.
+    """
+
+    def _invalidate_initialize_callback(self, event):
+        """Invalidates the scene elements."""
+        # call parent
+        super()._invalidate_initialize_callback(event)
+        # set all existing views to None to invalidate them
+        self._physics_sim_view = None
+        self._root_physx_view = None
+        self._body_physx_view = None

source/extensions/omni.isaac.orbit/omni/isaac/orbit/sensors/camera/camera.py

@@ -554,3 +554,14 @@ class Camera(SensorBase):
         data = convert_to_torch(data, device=self.device)
         # return the data and info
         return data, info
+
+    """
+    Internal simulation callbacks.
+    """
+
+    def _invalidate_initialize_callback(self, event):
+        """Invalidates the scene elements."""
+        # call parent
+        super()._invalidate_initialize_callback(event)
+        # set all existing views to None to invalidate them
+        self._view = None

source/extensions/omni.isaac.orbit/omni/isaac/orbit/sensors/contact_sensor/contact_sensor.py

@@ -291,3 +291,16 @@ class ContactSensor(SensorBase):
             frame_origins = pose.view(-1, self._num_bodies, 7)[:, :, :3]
         # visualize
         self.contact_visualizer.visualize(frame_origins.view(-1, 3), marker_indices=marker_indices.view(-1))
+
+    """
+    Internal simulation callbacks.
+    """
+
+    def _invalidate_initialize_callback(self, event):
+        """Invalidates the scene elements."""
+        # call parent
+        super()._invalidate_initialize_callback(event)
+        # set all existing views to None to invalidate them
+        self._physics_sim_view = None
+        self._body_physx_view = None
+        self._contact_physx_view = None

source/extensions/omni.isaac.orbit/omni/isaac/orbit/sensors/frame_transformer/frame_transformer.py

@@ -351,3 +351,15 @@ class FrameTransformer(SensorBase):
         # Update the visualized markers
         if self.frame_visualizer is not None:
             self.frame_visualizer.visualize(self._data.target_pos_w.view(-1, 3), self._data.target_rot_w.view(-1, 4))
+
+    """
+    Internal simulation callbacks.
+    """
+
+    def _invalidate_initialize_callback(self, event):
+        """Invalidates the scene elements."""
+        # call parent
+        super()._invalidate_initialize_callback(event)
+        # set all existing views to None to invalidate them
+        self._physics_sim_view = None
+        self._frame_physx_view = None

source/extensions/omni.isaac.orbit/omni/isaac/orbit/sensors/ray_caster/ray_caster.py

@@ -279,3 +279,15 @@ class RayCaster(SensorBase):
     def _debug_vis_callback(self, event):
         # show ray hit positions
         self.ray_visualizer.visualize(self._data.ray_hits_w.view(-1, 3))
+
+    """
+    Internal simulation callbacks.
+    """
+
+    def _invalidate_initialize_callback(self, event):
+        """Invalidates the scene elements."""
+        # call parent
+        super()._invalidate_initialize_callback(event)
+        # set all existing views to None to invalidate them
+        self._physics_sim_view = None
+        self._view = None

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

@@ -201,7 +201,7 @@ class SimulationContext(_SimulationContext):
             self._app_control_on_stop_handle = timeline_event_stream.create_subscription_to_pop_by_type(
                 int(omni.timeline.TimelineEventType.STOP),
                 lambda *args, obj=weakref.proxy(self): obj._app_control_on_stop_callback(*args),
-                order=10,
+                order=15,
             )
         else:
             self._app_control_on_stop_handle = None