Merge remote-tracking branch 'upstream/develop' into esekkin/camera-refactor

Author: nvsekkin

source/isaaclab/docs/CHANGELOG.rst

@@ -34,6 +34,17 @@ Removed
   now managed internally by the renderer backend and are not part of the public API.
 
 
+4.5.28 (2026-04-10)
+~~~~~~~~~~~~~~~~~~~
+
+Added
+^^^^^
+
+* Added :meth:`~isaaclab.physics.PhysicsManager.wait_for_playing` hook and
+  integrated it into :meth:`~isaaclab.sim.SimulationContext.step` so the
+  training loop blocks while the Kit GUI timeline is paused.
+
+
 4.5.27 (2026-04-08)
 ~~~~~~~~~~~~~~~~~~~
 

source/isaaclab/isaaclab/physics/physics_manager.py

@@ -324,6 +324,11 @@ def stop(cls) -> None:
         """Stop physics simulation. Default is no-op."""
         pass
 
+    @classmethod
+    def wait_for_playing(cls) -> None:
+        """Block until the timeline is playing. Default is no-op."""
+        pass
+
     @classmethod
     def get_backend(cls) -> str:
         """Get the tensor backend being used ("numpy" or "torch")."""

source/isaaclab/isaaclab/sim/simulation_context.py

@@ -654,9 +654,15 @@ def reset(self, soft: bool = False) -> None:
     def step(self, render: bool = True) -> None:
         """Step physics and optionally render.
 
+        If the timeline is paused (e.g. via the GUI), this method blocks and keeps
+        the visualizer responsive until the timeline is resumed or stopped.
+
         Args:
             render: Whether to render the scene after stepping. Defaults to True.
         """
+        # Block while the GUI timeline is paused so the entire training loop freezes.
+        # See: https://github.com/isaac-sim/IsaacLab/issues/4279
+        self.physics_manager.wait_for_playing()
         self._physics_step_count += 1
         self.physics_manager.step()
         if render and self.is_rendering:

source/isaaclab_physx/config/extension.toml

@@ -1,7 +1,7 @@
 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.5.13"
+version = "0.5.14"
 
 # Description
 title = "PhysX simulation interfaces for IsaacLab core package"

source/isaaclab_physx/docs/CHANGELOG.rst

@@ -1,6 +1,20 @@
 Changelog
 ---------
 
+0.5.14 (2026-04-06)
+~~~~~~~~~~~~~~~~~~~
+
+Fixed
+^^^^^
+
+* Fixed the simulation training loop not pausing when the Kit GUI timeline is
+  paused. :meth:`~isaaclab_physx.physics.PhysxManager.wait_for_playing` now
+  blocks and keeps the GUI responsive until the timeline is resumed or stopped.
+* Fixed articulation visualization freezing after pausing and unpausing the
+  simulation through the headed GUI in Isaac Sim 5.1+. Articulation meshes now
+  remain visually updated after resuming.
+
+
 0.5.13 (2026-03-25)
 ~~~~~~~~~~~~~~~~~~~
 

source/isaaclab_physx/isaaclab_physx/physics/physx_manager.py

@@ -28,7 +28,7 @@
 import omni.physx
 import omni.timeline
 import omni.usd
-from pxr import Sdf
+from pxr import Sdf, UsdUtils
 
 import isaaclab.sim as sim_utils
 from isaaclab.physics import CallbackHandle, PhysicsEvent, PhysicsManager
@@ -290,6 +290,30 @@ def stop(cls) -> None:
         # Pump events so timeline callbacks fire synchronously
         omni.kit.app.get_app().update()
 
+    @classmethod
+    def wait_for_playing(cls) -> None:
+        """Block until the timeline is playing, keeping the GUI responsive.
+
+        After resume, forces a fabric re-sync so articulation meshes unfreeze.
+        See: https://github.com/isaac-sim/IsaacLab/issues/4279
+        """
+        if cls._timeline.is_playing():
+            return
+        app = omni.kit.app.get_app()
+        while not cls._timeline.is_playing():
+            app.update()
+            if cls._timeline.is_stopped():
+                break
+        # Force fabric to re-sync articulation transforms after resume.
+        # detach/attach resets the FabricManager, then we immediately push
+        # current poses so the first render after resume shows correct state.
+        if not cls._timeline.is_stopped():
+            cls._re_sync_fabric()
+            if cls._view is not None:
+                cls._view.update_articulations_kinematic()
+            if cls._update_fabric is not None:
+                cls._update_fabric(0.0, 0.0)
+
     @classmethod
     def close(cls) -> None:
         """Clean up physics resources."""
@@ -585,6 +609,42 @@ def _load_fabric(cls) -> None:
         sim.set_setting("/isaaclab/fabric_enabled", use_fabric)  # type: ignore[union-attr]
         sim.set_setting("/physics/visualizationDisplaySimulationOutput", False)  # type: ignore[union-attr]
 
+    @classmethod
+    def _re_sync_fabric(cls) -> None:
+        """Force the PhysX fabric extension to re-synchronize after a pause/resume transition.
+
+        Starting with PhysX fabric 107.3.21 (Isaac Sim 5.1), the FabricManager skips writing
+        initial articulation poses to fabric on subsequent resumes, causing articulation meshes
+        to freeze visually while physics continues to run.
+
+        The workaround detaches and re-attaches the USD stage on the fabric interface, forcing
+        the FabricManager to fully reinitialize and write transforms into fabric so that Hydra
+        picks them up.
+        """
+        if cls._fabric is None:
+            return
+        sim = PhysicsManager._sim
+        if sim is None:
+            return
+        stage = sim.stage
+        if stage is None:
+            return
+        stage_id = UsdUtils.StageCache.Get().GetId(stage).ToLongInt()
+        if stage_id <= 0:
+            return
+        try:
+            cls._fabric.detach_stage()
+        except Exception:
+            logger.warning("Failed to detach fabric stage during re-sync. Articulation visuals may be stale.")
+            return
+        try:
+            cls._fabric.attach_stage(stage_id)
+        except Exception:
+            logger.error(
+                "Could not re-attach fabric stage. Articulation visuals will be broken until next reset.",
+                exc_info=True,
+            )
+
     @classmethod
     def _warmup_and_create_views(cls) -> None:
         """Warm-start physics and create simulation views."""