Fix particle collisions for disabled USD colliders (#3785)

Author: mmichelis

CHANGELOG.md

@@ -105,6 +105,7 @@
 - Fix panel-parallel RCM-blocked LLT factorization hanging when a matrix ends in a partial tile.
 - Fix USD capsule, cylinder, and cone visual and site scaling to follow the authored primitive axis.
 - Fix MJCF contact pairs ignoring properties inherited from pair default classes.
+- Fix disabled USD colliders participating in particle collisions when visual shape loading is disabled.
 - Fix `ArticulationView.is_fixed_base` for roots with zero effective degrees of freedom, including fully locked D6 joints. (#3727)
 - Fix USD plane visual width and length to scale along the axes defined by the `UsdGeomPlane` schema, and orient X- and Y-axis plane visuals along the authored axis.
 - Validate `ArticulationView` mask shapes and devices before launching selection kernels. (#3448)

newton/_src/utils/import_usd.py

@@ -3928,7 +3928,7 @@ def _record_fallback_collider_mass_information(
 
                 if not collider_is_enabled:
                     no_collision_shapes.add(shape_id)
-                    builder.shape_flags[shape_id] &= ~ShapeFlags.COLLIDE_SHAPES
+                    builder.shape_flags[shape_id] &= ~(ShapeFlags.COLLIDE_SHAPES | ShapeFlags.COLLIDE_PARTICLES)
 
     # Approximate meshes. ``physics:approximation`` belongs to
     # UsdPhysicsMeshCollisionAPI and is scoped to collision: it says which shape to

newton/tests/test_import_usd.py

@@ -5257,8 +5257,8 @@ def test_static_gaussian_respects_loading_flag(self):
         self.assertNotIn(gaussian.GetPath().pathString, result_no_visuals["path_shape_map"])
 
     @unittest.skipUnless(USD_AVAILABLE, "Requires usd-core")
-    def test_disabled_static_collider_loads_as_visual(self):
-        """Load disabled static colliders as visual-only shapes."""
+    def test_disabled_static_collider_has_no_collision_flags(self):
+        """Disable shape and particle collisions regardless of visual loading."""
         from pxr import Usd, UsdGeom, UsdPhysics
 
         stage = Usd.Stage.CreateInMemory()
@@ -5271,8 +5271,15 @@ def test_disabled_static_collider_loads_as_visual(self):
         flags = builder.shape_flags[result["path_shape_map"][collider.GetPath().pathString]]
 
         self.assertFalse(flags & ShapeFlags.COLLIDE_SHAPES)
+        self.assertFalse(flags & ShapeFlags.COLLIDE_PARTICLES)
         self.assertFalse(flags & ShapeFlags.VISIBLE)
 
+        headless_builder = newton.ModelBuilder()
+        headless_result = headless_builder.add_usd(stage, load_visual_shapes=False)
+        headless_flags = headless_builder.shape_flags[headless_result["path_shape_map"][collider.GetPath().pathString]]
+        self.assertFalse(headless_flags & ShapeFlags.COLLIDE_SHAPES)
+        self.assertFalse(headless_flags & ShapeFlags.COLLIDE_PARTICLES)
+
     @unittest.skipUnless(USD_AVAILABLE, "Requires usd-core")
     def test_granular_loading_flags(self):
         """Test the granular control over sites and visual shapes loading."""