Apply SDF mesh conversion before the enviorment is replicated

Author: vidurv-nvidia

source/isaaclab_newton/isaaclab_newton/cloner/newton_replicate.py

@@ -69,7 +69,7 @@ def _build_newton_builder_from_mapping(
     # SDF collision requires original triangle meshes for mesh.build_sdf().
     # Convex hull approximation destroys the source geometry, so shapes
     # matching SDF patterns must be excluded from approximation here.
-    # _apply_sdf_config() will build the SDF on these meshes later.
+    # _apply_sdf_config() builds the SDF on each prototype after approximation.
     cfg = PhysicsManager._cfg
     sdf_cfg = getattr(cfg, "sdf_cfg", None) if cfg is not None else None
     body_pats = [re.compile(x) for x in sdf_cfg.body_patterns] if sdf_cfg and sdf_cfg.body_patterns else None
@@ -111,6 +111,10 @@ def _build_newton_builder_from_mapping(
                     p.approximate_meshes("convex_hull", shape_indices=approx_indices, keep_visual_shapes=True)
             else:
                 p.approximate_meshes("convex_hull", keep_visual_shapes=True)
+        # Build SDF on prototype before add_builder copies it N times.
+        # Mesh objects are shared by reference, so SDF is built once and
+        # all environments inherit it.
+        NewtonManager._apply_sdf_config(p)
         protos[src_path] = p
 
     # create a separate world for each environment (heterogeneous spawning)

source/isaaclab_newton/isaaclab_newton/physics/newton_manager.py

@@ -608,12 +608,11 @@ def start_simulation(cls) -> None:
         """
         logger.debug(f"Builder: {cls._builder}")
 
-        # Create builder from USD stage if not provided
+        # Create builder from USD stage if not provided.
+        # When the builder was set externally (e.g. by newton_replicate),
+        # SDF was already applied on the prototype before replication.
         if cls._builder is None:
             cls.instantiate_builder_from_stage()
-        else:
-            # Builder was set externally (e.g. by newton_replicate) — still apply SDF
-            cls._apply_sdf_config(cls._builder)
 
         logger.info("Dispatching MODEL_INIT callbacks")
         cls.dispatch_event(PhysicsEvent.MODEL_INIT)