[Test] Quadrupeds: relax import order (depends on #5826 + #5771)

scripts/demos/demo_helper.py

@@ -0,0 +1,91 @@
+# Copyright (c) 2022-2026, The Isaac Lab Project Developers (https://github.com/isaac-sim/IsaacLab/blob/main/CONTRIBUTORS.md).
+# All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
+"""
+This script contains helper functions for the demos.
+"""
+
+import textwrap
+from contextlib import contextmanager
+
+
+@contextmanager
+def resolve_backend_and_visualizer(args, newton_cfg=None):
+    """Resolve physics + visualizer cfgs from ``--physics`` / ``--visualizer``.
+
+    Yields ``(physics_cfg, visualizer_cfg)``. Kit is launched when required by
+    either the visualizer or the physics backend, and closed automatically on exit.
+    """
+
+    # Resolve physics cfg
+    if args.physics == "physx":
+        from isaaclab_physx.physics import PhysxCfg
+
+        physics_cfg = PhysxCfg()
+    elif args.physics == "newton_mjwarp":
+        from isaaclab_newton.physics import MJWarpSolverCfg, NewtonCfg
+
+        DEFAULT_NEWTON_CFG = NewtonCfg(
+            solver_cfg=MJWarpSolverCfg(
+                njmax=70,
+                nconmax=70,
+                ls_iterations=40,
+                cone="elliptic",
+                impratio=100,
+                ls_parallel=False,
+                integrator="implicitfast",
+            ),
+            num_substeps=2,
+        )
+        physics_cfg = newton_cfg or DEFAULT_NEWTON_CFG
+    else:
+        raise ValueError(f"Unsupported --physics value: {args.physics}")
+
+    # Resolve visualizer cfg
+    if not isinstance(args.visualizer, list) or len(args.visualizer) != 1:
+        raise ValueError("Demos support exactly one --visualizer value: kit or newton.")
+    viz_type = args.visualizer[0]
+    if viz_type == "kit":
+        from isaaclab_visualizers.kit import KitVisualizerCfg
+
+        visualizer_cfg = KitVisualizerCfg()
+    elif viz_type == "newton":
+        from isaaclab_visualizers.newton import NewtonVisualizerCfg
+
+        visualizer_cfg = NewtonVisualizerCfg()
+    else:
+        raise ValueError(f"Unsupported --visualizer value: {viz_type}")
+
+    # PhysX requires Isaac Sim Kit extensions even when rendering through a
+    # standalone visualizer such as Newton.
+    close_fn = None
+    if viz_type == "kit" or args.physics == "physx":
+        from isaaclab.app import AppLauncher
+
+        args.visualizer = [viz_type]
+        close_fn = AppLauncher(args).app.close
+
+    try:
+        yield physics_cfg, visualizer_cfg
+    finally:
+        # No-op for the newton visualizer; close Kit automatically upon exit
+        if close_fn is not None:
+            close_fn()
+
+
+def has_no_alive_visualizer_window(sim) -> bool:
+    """Check if there are no alive visualizer windows."""
+    visualizers = sim.visualizers or ()
+    return not any(v.is_running() and not v.is_closed for v in visualizers)
+
+
+def get_usage_examples(doc: str) -> str:
+    """Return usage examples from the module docstring."""
+    marker = ".. code-block:: bash"
+    if marker not in doc:
+        return ""
+
+    examples = textwrap.dedent(doc.split(marker, maxsplit=1)[1]).strip()
+    return "Examples:\n" + textwrap.indent(examples, "  ")

scripts/demos/quadrupeds.py

@@ -8,41 +8,53 @@
 
 .. code-block:: bash
 
-    # Usage
+    # Usage with the default PhysX backend (launches Isaac Sim Kit by default).
     ./isaaclab.sh -p scripts/demos/quadrupeds.py
+    ./isaaclab.sh -p scripts/demos/quadrupeds.py --visualizer kit
+    ./isaaclab.sh -p scripts/demos/quadrupeds.py --physics physx
+    ./isaaclab.sh -p scripts/demos/quadrupeds.py --physics physx --visualizer kit
+
+    # Usage with the kit-less Newton (MJWarp) backend (launches Isaac Sim Kit by default).
+    ./isaaclab.sh -p scripts/demos/quadrupeds.py --physics newton_mjwarp
+    ./isaaclab.sh -p scripts/demos/quadrupeds.py --physics newton_mjwarp --visualizer kit
+
+    # Usage with the Newton (MJWarp) backend without Kit (launches Newton visualizer).
+    ./isaaclab.sh -p scripts/demos/quadrupeds.py --physics newton_mjwarp --visualizer newton
+
+    # Usage with the PhysX backend and Newton visualizer.
+    # PhysX still launches Isaac Sim Kit headless because it depends on Kit extensions.
+    ./isaaclab.sh -p scripts/demos/quadrupeds.py --physics physx --visualizer newton
 
 """
 
-"""Launch Isaac Sim Simulator first."""
+"""Parse CLI first so we can decide whether to launch Isaac Sim Kit."""
 
 import argparse
 
+from demo_helper import get_usage_examples, has_no_alive_visualizer_window, resolve_backend_and_visualizer
+
 from isaaclab.app import AppLauncher
 
 # add argparse arguments
-parser = argparse.ArgumentParser(description="This script demonstrates different legged robots.")
+parser = argparse.ArgumentParser(
+    description="This script demonstrates different legged robots.",
+    epilog=get_usage_examples(str(__doc__)),
+    formatter_class=argparse.RawDescriptionHelpFormatter,
+)
+parser.add_argument("--physics", default="physx", choices=["physx", "newton_mjwarp"], help="Physics backend.")
 # append AppLauncher cli args
 AppLauncher.add_app_launcher_args(parser)
 # demos should open Kit visualizer by default
 parser.set_defaults(visualizer=["kit"])
 # parse the arguments
 args_cli = parser.parse_args()
 
-# launch omniverse app
-app_launcher = AppLauncher(args_cli)
-simulation_app = app_launcher.app
-
-"""Rest everything follows."""
-
 import numpy as np
 import torch
 
 import isaaclab.sim as sim_utils
 from isaaclab.assets import Articulation
 
-##
-# Pre-defined configs
-##
 from isaaclab_assets.robots.anymal import ANYMAL_B_CFG, ANYMAL_C_CFG, ANYMAL_D_CFG  # isort:skip
 from isaaclab_assets.robots.spot import SPOT_CFG  # isort:skip
 from isaaclab_assets.robots.unitree import UNITREE_A1_CFG, UNITREE_GO1_CFG, UNITREE_GO2_CFG  # isort:skip
@@ -124,14 +136,15 @@ def design_scene() -> tuple[dict, list[list[float]]]:
     return scene_entities, origins
 
 
-def run_simulator(sim: sim_utils.SimulationContext, entities: dict[str, Articulation], origins: torch.Tensor):
+def run_simulator(sim, entities: dict, origins):
     """Runs the simulation loop."""
     # Define simulation stepping
     sim_dt = sim.get_physics_dt()
     sim_time = 0.0
     count = 0
     # Simulate physics
-    while simulation_app.is_running():
+    # Exit when every visualizer window has been closed (works for kit and newton)
+    while not has_no_alive_visualizer_window(sim):
         # reset
         if count % 200 == 0:
             # reset counters
@@ -175,24 +188,27 @@ def run_simulator(sim: sim_utils.SimulationContext, entities: dict[str, Articula
 
 def main():
     """Main function."""
-
-    # Initialize the simulation context
-    sim = sim_utils.SimulationContext(sim_utils.SimulationCfg(dt=0.01))
-    # Set main camera
-    sim.set_camera_view(eye=[2.5, 2.5, 2.5], target=[0.0, 0.0, 0.0])
-    # design scene
-    scene_entities, scene_origins = design_scene()
-    scene_origins = torch.tensor(scene_origins, device=sim.device)
-    # Play the simulator
-    sim.reset()
-    # Now we are ready!
-    print("[INFO]: Setup complete...")
-    # Run the simulator
-    run_simulator(sim, scene_entities, scene_origins)
+    with resolve_backend_and_visualizer(args_cli) as (physics_cfg, visualizer_cfg):
+        # define simulation configuration
+        sim_cfg = sim_utils.SimulationCfg(
+            dt=0.005, device=args_cli.device, physics=physics_cfg, visualizer_cfgs=[visualizer_cfg]
+        )
+        # Initialize the simulation context
+        sim = sim_utils.SimulationContext(sim_cfg)
+        # Set main camera
+        sim.set_camera_view(eye=[2.5, 2.5, 2.5], target=[0.0, 0.0, 0.0])
+        # design scene
+        scene_entities, scene_origins = design_scene()
+        # convert origins to tensor
+        scene_origins = torch.tensor(scene_origins, device=sim.device)
+        # Play the simulator
+        sim.reset()
+        # Now we are ready!
+        print("[INFO]: Setup complete...")
+        # Run the simulator
+        run_simulator(sim, scene_entities, scene_origins)
 
 
 if __name__ == "__main__":
     # run the main function
     main()
-    # close sim app
-    simulation_app.close()

source/isaaclab/changelog.d/jichuanh-defer-asset-pxr-imports.rst

@@ -0,0 +1,7 @@
+Fixed
+^^^^^
+
+* Fixed ``from isaaclab.assets import Articulation`` and ``from isaaclab.sim import SimulationContext``
+  loading ``pxr`` at module-import time, which forced :class:`~isaaclab.app.AppLauncher`
+  to run before any such import and blocked kit-less workflows that bind these
+  classes at module top.

source/isaaclab/isaaclab/assets/asset_base.py

@@ -15,14 +15,12 @@
 import torch
 import warp as wp
 
-from pxr import Usd
-
 import isaaclab.sim as sim_utils
 from isaaclab.physics import PhysicsEvent, PhysicsManager
-from isaaclab.sim.simulation_context import SimulationContext
-from isaaclab.sim.utils.stage import get_current_stage
 
 if TYPE_CHECKING:
+    from pxr import Usd
+
     from .asset_base_cfg import AssetBaseCfg
 
 
@@ -81,7 +79,7 @@ def __init__(self, cfg: AssetBaseCfg):
         # flag for whether the asset is initialized
         self._is_initialized = False
         # get stage handle
-        self.stage: Usd.Stage = get_current_stage()
+        self.stage: Usd.Stage = sim_utils.get_current_stage()
 
         # spawn the asset
         # determine path where prims should exist after spawn
@@ -208,11 +206,11 @@ def set_debug_vis(self, debug_vis: bool) -> bool:
         # toggle debug visualization handles (Kit/omni only for PhysX backend)
         if debug_vis:
             if self._debug_vis_handle is None:
-                sim_ctx = SimulationContext.instance()
+                sim_ctx = sim_utils.SimulationContext.instance()
                 if sim_ctx is not None:
                     self._debug_vis_handle = sim_ctx.vis_marker_registry.add_debug_vis_callback(self)
         else:
-            sim_ctx = SimulationContext.instance()
+            sim_ctx = sim_utils.SimulationContext.instance()
             if sim_ctx is not None:
                 sim_ctx.vis_marker_registry.clear_debug_vis_callback(self)
             else:
@@ -353,7 +351,7 @@ def _debug_vis_callback(self, event):
 
     def _register_callbacks(self):
         """Registers physics lifecycle callbacks via the current backend's physics manager."""
-        physics_mgr_cls = SimulationContext.instance().physics_manager
+        physics_mgr_cls = sim_utils.SimulationContext.instance().physics_manager
 
         # note: use weakref on callbacks to ensure that this object can be deleted when its destructor is called.
         obj_ref = weakref.proxy(self)
@@ -397,15 +395,15 @@ def _initialize_callback(self, event):
             :attr:`PhysicsEvent.PHYSICS_READY` is dispatched by the current backend.
         """
         if not self._is_initialized:
-            self._backend = SimulationContext.instance().physics_manager.get_backend()
-            self._device = SimulationContext.instance().physics_manager.get_device()
+            self._backend = sim_utils.SimulationContext.instance().physics_manager.get_backend()
+            self._device = sim_utils.SimulationContext.instance().physics_manager.get_device()
             self._initialize_impl()
             self._is_initialized = True
 
     def _invalidate_initialize_callback(self, event):
         """Invalidates the scene elements."""
         self._is_initialized = False
-        sim_ctx = SimulationContext.instance()
+        sim_ctx = sim_utils.SimulationContext.instance()
         if sim_ctx is not None:
             sim_ctx.vis_marker_registry.clear_debug_vis_callback(self)
         else:
@@ -438,7 +436,7 @@ def _clear_callbacks(self) -> None:
         if self._prim_deletion_handle is not None:
             self._prim_deletion_handle.deregister()
             self._prim_deletion_handle = None
-        sim_ctx = SimulationContext.instance()
+        sim_ctx = sim_utils.SimulationContext.instance()
         if sim_ctx is not None:
             sim_ctx.vis_marker_registry.clear_debug_vis_callback(self)
         else:

source/isaaclab/isaaclab/sim/simulation_context.py

@@ -17,10 +17,7 @@
 import toml
 import torch
 
-from pxr import Gf, Usd, UsdGeom, UsdPhysics, UsdUtils
-
 import isaaclab.sim as sim_utils
-import isaaclab.sim.utils.stage as stage_utils
 from isaaclab.app.settings_manager import SettingsManager
 from isaaclab.envs.utils.recording_hooks import run_recording_hooks_after_visualizers
 from isaaclab.markers.vis_marker_registry import VisMarkerRegistry
@@ -32,12 +29,13 @@
 from isaaclab.renderers.render_context import RenderContext
 from isaaclab.scene_data import SceneDataProvider
 from isaaclab.sim.service_locator import ServiceLocator
-from isaaclab.sim.utils import create_new_stage
 from isaaclab.utils.string import clear_resolve_matching_names_cache
 from isaaclab.utils.version import has_kit
 from isaaclab.visualizers.base_visualizer import BaseVisualizer
 
 if TYPE_CHECKING:
+    from pxr import Usd
+
     from isaaclab.cloner.clone_plan import ClonePlan
 
 from .simulation_cfg import SimulationCfg
@@ -111,13 +109,17 @@ def __init__(self, cfg: SimulationCfg | None = None):
         if type(self)._instance is not None:
             return  # Already initialized
 
+        from pxr import UsdUtils  # noqa: PLC0415
+
+        from isaaclab.sim.utils import stage as stage_utils  # noqa: PLC0415
+
         # Store config
         self.cfg = SimulationCfg() if cfg is None else cfg
 
         # Get or create stage based on config
         stage_cache = UsdUtils.StageCache.Get()
         if self.cfg.create_stage_in_memory:
-            self.stage = create_new_stage()
+            self.stage = sim_utils.create_new_stage()
         else:
             # Prefer the thread-local current stage (set by create_new_stage / test fixtures)
             # over cache lookup, since the cache may contain stale stages from prior tests.
@@ -126,7 +128,7 @@ def __init__(self, cfg: SimulationCfg | None = None):
                 self.stage = current
             else:
                 all_stages = stage_cache.GetAllStages() if stage_cache.Size() > 0 else []  # type: ignore[union-attr]
-                self.stage = all_stages[0] if all_stages else create_new_stage()
+                self.stage = all_stages[0] if all_stages else sim_utils.create_new_stage()
 
         # Ensure stage is in the USD cache
         stage_id = stage_cache.GetId(self.stage).ToLongInt()  # type: ignore[union-attr]
@@ -322,6 +324,8 @@ def _apply_nested(data: dict[str, Any], path: str = "") -> None:
 
     def _init_usd_physics_scene(self) -> None:
         """Create and configure the USD physics scene."""
+        from pxr import Gf, UsdGeom, UsdPhysics  # noqa: PLC0415
+
         cfg = self.cfg
         with sim_utils.use_stage(self.stage):
             # Set stage conventions for metric units
@@ -913,7 +917,7 @@ def clear_instance(cls) -> None:
 
             # Tear down the stage. We skip clear_stage() (prim-by-prim deletion) since
             # close_stage() + app shutdown destroy the entire stage at once.
-            stage_utils.close_stage()
+            sim_utils.close_stage()
 
             # Discard cached name-resolution data from destroyed assets
             clear_resolve_matching_names_cache()