[BUG FIX] Fix support of Hybrid entity with non-fixed base link. (#2040)

* Fix support of Hybrid entity with non-fixed base link.
* Increase tolerance of flaky unit test.

Author: duburcqa

genesis/engine/entities/hybrid_entity.py

@@ -66,7 +66,6 @@ def __init__(
 
         if isinstance(morph, gs.morphs.URDF):
             # set up rigid part
-            morph.fixed = material.fixed  # NOTE: use hybrid material to determine this
             if material.use_default_coupling:
                 gs.logger.info("Use default coupling in hybrid. Overwrite `needs_coup` in rigid material to True")
                 material_rigid._needs_coup = True
@@ -84,10 +83,9 @@ def __init__(
             augment_link_world_coords(part_rigid)
 
             # set soft parts based on rigid links
-            if material._func_instantiate_soft_from_rigid is None:
-                func_instantiate_soft_from_rigid = default_func_instantiate_soft_from_rigid
-            else:
-                func_instantiate_soft_from_rigid = material._func_instantiate_soft_from_rigid
+            func_instantiate_soft_from_rigid = (
+                material._func_instantiate_soft_from_rigid or default_func_instantiate_soft_from_rigid
+            )
             part_soft = func_instantiate_soft_from_rigid(
                 scene=scene,
                 part_rigid=part_rigid,

genesis/engine/materials/hybrid.py

@@ -14,8 +14,6 @@ class Hybrid(Material):
         The material of the rigid body.
     material_soft: gs.materials.base.Material
         The material of the soft body.
-    fixed: bool, optional
-        Whether the rigid entity is with a fixed base link. Default is False.
     use_default_coupling: bool, optional
         Whether to use default solver coupling. Default is False
     damping: float, optional
@@ -36,7 +34,6 @@ def __init__(
         self,
         material_rigid,
         material_soft,
-        fixed=True,
         use_default_coupling=False,
         damping=0.0,
         thickness=0.05,
@@ -50,7 +47,6 @@ def __init__(
         self._material_rigid = material_rigid
         self._material_soft = material_soft
         self._thickness = thickness
-        self._fixed = fixed
         self._use_default_coupling = use_default_coupling
         self._damping = damping
         self._soft_dv_coef = soft_dv_coef
@@ -73,11 +69,6 @@ def thickness(self):
         """The thickness to instantiate soft skin."""
         return self._thickness
 
-    @property
-    def fixed(self):
-        """Whether the rigid entity is with a fixed base link."""
-        return self._fixed
-
     @property
     def use_default_coupling(self):
         """Whether to use default solver coupling."""

genesis/engine/scene.py

@@ -398,11 +398,11 @@ def add_entity(
                     f"Unsupported `surface.vis_mode` for material {material}: '{surface.vis_mode}'. Expected one of: ['particle', 'recon']."
                 )
 
-        elif isinstance(material, (gs.materials.SF.Smoke)):
+        elif isinstance(material, gs.materials.SF.Smoke):
             if surface.vis_mode is None:
                 surface.vis_mode = "particle"
 
-            if surface.vis_mode not in ["particle"]:
+            if surface.vis_mode not in ("particle",):
                 gs.raise_exception(
                     f"Unsupported `surface.vis_mode` for material {material}: '{surface.vis_mode}'. Expected one of: ['particle', 'recon']."
                 )
@@ -416,20 +416,20 @@ def add_entity(
                     f"Unsupported `surface.vis_mode` for material {material}: '{surface.vis_mode}'. Expected one of: ['visual', 'particle', 'recon']."
                 )
 
-        elif isinstance(material, (gs.materials.FEM.Base)):
+        elif isinstance(material, gs.materials.FEM.Base):
             if surface.vis_mode is None:
                 surface.vis_mode = "visual"
 
-            if surface.vis_mode not in ["visual"]:
+            if surface.vis_mode not in ("visual",):
                 gs.raise_exception(
                     f"Unsupported `surface.vis_mode` for material {material}: '{surface.vis_mode}'. Expected one of: ['visual']."
                 )
 
-        elif isinstance(material, (gs.materials.Hybrid)):  # determine the visual of the outer soft part
+        elif isinstance(material, gs.materials.Hybrid):  # determine the visual of the outer soft part
             if surface.vis_mode is None:
                 surface.vis_mode = "particle"
 
-            if surface.vis_mode not in ["particle", "visual"]:
+            if surface.vis_mode not in ("particle", "visual"):
                 gs.raise_exception(
                     f"Unsupported `surface.vis_mode` for material {material}: '{surface.vis_mode}'. Expected one of: ['particle', 'visual']."
                 )

genesis/engine/simulator.py

@@ -165,30 +165,21 @@ def __init__(
     def _add_entity(self, morph: Morph, material, surface, visualize_contact=False):
         if isinstance(material, gs.materials.Tool):
             entity = self.tool_solver.add_entity(self.n_entities, material, morph, surface)
-
         elif isinstance(material, gs.materials.Avatar):
             entity = self.avatar_solver.add_entity(self.n_entities, material, morph, surface, visualize_contact)
-
         elif isinstance(material, gs.materials.Rigid):
             entity = self.rigid_solver.add_entity(self.n_entities, material, morph, surface, visualize_contact)
-
         elif isinstance(material, gs.materials.MPM.Base):
             entity = self.mpm_solver.add_entity(self.n_entities, material, morph, surface)
-
         elif isinstance(material, gs.materials.SPH.Base):
             entity = self.sph_solver.add_entity(self.n_entities, material, morph, surface)
-
         elif isinstance(material, gs.materials.PBD.Base):
             entity = self.pbd_solver.add_entity(self.n_entities, material, morph, surface)
-
         elif isinstance(material, gs.materials.FEM.Base):
             entity = self.fem_solver.add_entity(self.n_entities, material, morph, surface)
-
         elif isinstance(material, gs.materials.Hybrid):
-            entity = HybridEntity(
-                self.n_entities, self.scene, material, morph, surface
-            )  # adding to solver is handled in the hybrid entity
-
+            # Note that adding to solver is handled in the hybrid entity
+            entity = HybridEntity(self.n_entities, self.scene, material, morph, surface)
         else:
             gs.raise_exception(f"Material not supported.: {material}")
 

genesis/engine/solvers/mpm_solver.py

@@ -182,14 +182,10 @@ def build(self):
         self._coupler = self.sim._coupler
 
         if self.is_active:
-            if self._enable_CPIC:
-                gs.logger.warning(
-                    "Kernel compilation takes longer when running MPM solver in CPIC mode. Please be patient."
+            if self._enable_CPIC and self._sim.requires_grad:
+                gs.raise_exception(
+                    "CPIC is not supported in differentiable mode yet. Submit a feature request if you need it."
                 )
-                if self._sim.requires_grad:
-                    gs.raise_exception(
-                        "CPIC is not supported in differentiable mode yet. Submit a feature request if you need it."
-                    )
 
             self.init_particle_fields()
             self.init_grid_fields()

tests/test_integration.py

@@ -318,4 +318,4 @@ def test_franka_panda_grasp_fem_entity(primitive_type, show_viewer):
         franka.control_dofs_force(np.array([-1.0, -1.0]), fingers_dof)
         scene.step()
     box_pos_post = obj.get_state().pos.mean(dim=-2)
-    assert_allclose(box_pos_f, box_pos_post, atol=5e-4)
+    assert_allclose(box_pos_f, box_pos_post, atol=1e-3)