Fixes to manager based environments to use in an extension (#541)

# Description

This PR adds in a few changes that enable the extension based workflow
to work properly.

The main changes are:
* Disable the check for a pre-existing `SimulationContext` in
`manager_based_env.py`
* Move gym spaces setup to load_managers as this can't be called yet in
extension workflow
* Only do `flush` calls if Isaac Sim version < 4.0

Fixes #540

## 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
`./isaaclab.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
- [ ] I have run all the tests with `./isaaclab.sh --test` and they pass
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [ ] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

---------
Signed-off-by: Hunter Hansen <50837800+hhansen-bdai@users.noreply.github.com>
Co-authored-by: Hunter Hansen <50837800+hhansen-bdai@users.noreply.github.com>

source/extensions/omni.isaac.lab/omni/isaac/lab/envs/manager_based_env.py

@@ -81,7 +81,11 @@ class ManagerBasedEnv:
             # since it gets confused with Isaac Sim's SimulationContext class
             self.sim: SimulationContext = SimulationContext(self.cfg.sim)
         else:
-            raise RuntimeError("Simulation context already exists. Cannot create a new one.")
+            # simulation context should only be created before the environment
+            # when in extension mode
+            if not builtins.ISAAC_LAUNCHED_FROM_TERMINAL:
+                raise RuntimeError("Simulation context already exists. Cannot create a new one.")
+            self.sim: SimulationContext = SimulationContext.instance()
 
         # print useful information
         print("[INFO]: Base environment:")

source/extensions/omni.isaac.lab/omni/isaac/lab/envs/manager_based_rl_env.py

@@ -81,15 +81,6 @@ class ManagerBasedRLEnv(ManagerBasedEnv, gym.Env):
         self.common_step_counter = 0
         # -- init buffers
         self.episode_length_buf = torch.zeros(self.num_envs, device=self.device, dtype=torch.long)
-
-        # setup the action and observation spaces for Gym
-        self._configure_gym_env_spaces()
-
-        # perform events at the start of the simulation
-        if "startup" in self.event_manager.available_modes:
-            self.event_manager.apply(mode="startup")
-
-        # print the environment information
         print("[INFO]: Completed setting up the environment...")
 
     """
@@ -128,6 +119,11 @@ class ManagerBasedRLEnv(ManagerBasedEnv, gym.Env):
         # -- curriculum manager
         self.curriculum_manager = CurriculumManager(self.cfg.curriculum, self)
         print("[INFO] Curriculum Manager: ", self.curriculum_manager)
+        # setup the action and observation spaces for Gym
+        self._configure_gym_env_spaces()
+        # perform events at the start of the simulation
+        if "startup" in self.event_manager.available_modes:
+            self.event_manager.apply(mode="startup")
 
     """
     Operations - MDP

source/extensions/omni.isaac.lab/omni/isaac/lab/scene/interactive_scene.py

@@ -12,6 +12,7 @@ import carb
 import omni.usd
 from omni.isaac.cloner import GridCloner
 from omni.isaac.core.prims import XFormPrimView
+from omni.isaac.version import get_version
 from pxr import PhysxSchema
 
 import omni.isaac.lab.sim as sim_utils
@@ -112,8 +113,13 @@ class InteractiveScene:
                     base_env_path=self.env_ns,
                     root_path=self.env_regex_ns.replace(".*", ""),
                 )
+
             self.filter_collisions(self._global_prim_paths)
 
+        # read isaac sim version (this includes build tag, release tag etc.)
+        # note: we do it once here because it reads the VERSION file from disk and is not expected to change.
+        self._isaac_sim_version = int(get_version()[0][0])
+
     def clone_environments(self, copy_from_source: bool = False):
         """Creates clones of the environment ``/World/envs/env_0``.
 
@@ -274,12 +280,12 @@ class InteractiveScene:
         # -- sensors
         for sensor in self._sensors.values():
             sensor.reset(env_ids)
-        # -- flush physics sim view if called in extension mode
-        # this is needed when using PhysX GPU pipeline since the data needs to be sent to the underlying
-        # PhysX buffers that might live on a separate device
-        # note: In standalone mode, this method is called in the `step()` method of the simulation context.
-        #   So we only need to flush when running in extension mode.
-        if builtins.ISAAC_LAUNCHED_FROM_TERMINAL:
+        if builtins.ISAAC_LAUNCHED_FROM_TERMINAL and self._isaac_sim_version < 4:
+            # -- flush physics sim view if called in extension mode and Isaac Sim version is < 4.0
+            # this is needed when using PhysX GPU pipeline since the data needs to be sent to the underlying
+            # PhysX buffers that might live on a separate device
+            # note: In standalone mode, this method is called in the `step()` method of the simulation context.
+            #   So we only need to flush when running in extension mode.
             sim_utils.SimulationContext.instance().physics_sim_view.flush()  # pyright: ignore [reportOptionalMemberAccess]
 
     def write_data_to_sim(self):
@@ -289,12 +295,12 @@ class InteractiveScene:
             articulation.write_data_to_sim()
         for rigid_object in self._rigid_objects.values():
             rigid_object.write_data_to_sim()
-        # -- flush physics sim view if called in extension mode
-        # this is needed when using PhysX GPU pipeline since the data needs to be sent to the underlying
-        # PhysX buffers that might live on a separate device
-        # note: In standalone mode, this method is called in the `step()` method of the simulation context.
-        #   So we only need to flush when running in extension mode.
-        if builtins.ISAAC_LAUNCHED_FROM_TERMINAL:
+        if builtins.ISAAC_LAUNCHED_FROM_TERMINAL and self._isaac_sim_version < 4:
+            # -- flush physics sim view if called in extension mode and Isaac Sim version is < 4.0
+            # this is needed when using PhysX GPU pipeline since the data needs to be sent to the underlying
+            # PhysX buffers that might live on a separate device
+            # note: In standalone mode, this method is called in the `step()` method of the simulation context.
+            #   So we only need to flush when running in extension mode.
             sim_utils.SimulationContext.instance().physics_sim_view.flush()  # pyright: ignore [reportOptionalMemberAccess]
 
     def update(self, dt: float) -> None: