Refactor SoftContacts algorithm

src/jaxsim/api/contact.py

@@ -186,7 +186,9 @@ def collidable_point_dynamics(
             # Note that the material deformation rate is always returned in the mixed frame
             # C[W] = (W_p_C, [W]). This is convenient for integration purpose.
             W_f_Ci, (CW_ṁ,) = jax.vmap(soft_contacts.compute_contact_forces)(
-                W_p_Ci, W_ṗ_Ci, data.state.contact.tangential_deformation
+                position=W_p_Ci,
+                velocity=W_ṗ_Ci,
+                tangential_deformation=data.state.contact.tangential_deformation,
             )
             aux_data = dict(m_dot=CW_ṁ)
 

src/jaxsim/rbda/contacts/__init__.py

@@ -0,0 +1,8 @@
+from .common import ContactModel, ContactsParams, ContactsState
+from .relaxed_rigid import (
+    RelaxedRigidContacts,
+    RelaxedRigidContactsParams,
+    RelaxedRigidContactsState,
+)
+from .rigid import RigidContacts, RigidContactsParams, RigidContactsState
+from .soft import SoftContacts, SoftContactsParams, SoftContactsState

src/jaxsim/rbda/contacts/common.py

@@ -7,15 +7,20 @@
 import jaxsim.typing as jtp
 from jaxsim.utils import JaxsimDataclass
 
+try:
+    from typing import Self
+except ImportError:
+    from typing_extensions import Self
 
-class ContactsState(abc.ABC):
+
+class ContactsState(JaxsimDataclass):
     """
     Abstract class storing the state of the contacts model.
     """
 
     @classmethod
     @abc.abstractmethod
-    def build(cls, **kwargs) -> ContactsState:
+    def build(cls: type[Self], **kwargs) -> Self:
         """
         Build the contact state object.
 
@@ -26,7 +31,7 @@ def build(cls, **kwargs) -> ContactsState:
 
     @classmethod
     @abc.abstractmethod
-    def zero(cls, **kwargs) -> ContactsState:
+    def zero(cls: type[Self], **kwargs) -> Self:
         """
         Build a zero contact state.
 
@@ -36,7 +41,7 @@ def zero(cls, **kwargs) -> ContactsState:
         pass
 
     @abc.abstractmethod
-    def valid(self, **kwargs) -> bool:
+    def valid(self, **kwargs) -> jtp.BoolLike:
         """
         Check if the contacts state is valid.
         """
@@ -50,18 +55,20 @@ class ContactsParams(JaxsimDataclass):
 
     @classmethod
     @abc.abstractmethod
-    def build(cls) -> ContactsParams:
+    def build(cls: type[Self], **kwargs) -> Self:
         """
         Create a `ContactsParams` instance with specified parameters.
+
         Returns:
             The `ContactsParams` instance.
         """
         pass
 
     @abc.abstractmethod
-    def valid(self, *args, **kwargs) -> bool:
+    def valid(self, **kwargs) -> jtp.BoolLike:
         """
         Check if the parameters are valid.
+
         Returns:
             True if the parameters are valid, False otherwise.
         """
@@ -83,8 +90,8 @@ class ContactModel(JaxsimDataclass):
     @abc.abstractmethod
     def compute_contact_forces(
         self,
-        position: jtp.Vector,
-        velocity: jtp.Vector,
+        position: jtp.VectorLike,
+        velocity: jtp.VectorLike,
         **kwargs,
     ) -> tuple[jtp.Vector, tuple[Any, ...]]:
         """

src/jaxsim/rbda/contacts/relaxed_rigid.py

@@ -16,6 +16,11 @@
 
 from .common import ContactModel, ContactsParams, ContactsState
 
+try:
+    from typing import Self
+except ImportError:
+    from typing_extensions import Self
+
 
 @jax_dataclasses.pytree_dataclass
 class RelaxedRigidContactsParams(ContactsParams):
@@ -106,7 +111,8 @@ def __eq__(self, other: RelaxedRigidContactsParams) -> bool:
 
     @classmethod
     def build(
-        cls,
+        cls: type[Self],
+        *,
         time_constant: jtp.FloatLike | None = None,
         damping_coefficient: jtp.FloatLike | None = None,
         d_min: jtp.FloatLike | None = None,
@@ -119,7 +125,7 @@ def build(
         mu: jtp.FloatLike | None = None,
         max_iterations: jtp.IntLike | None = None,
         tolerance: jtp.FloatLike | None = None,
-    ) -> RelaxedRigidContactsParams:
+    ) -> Self:
         """Create a `RelaxedRigidContactsParams` instance"""
 
         return cls(
@@ -132,7 +138,8 @@ def build(
             }
         )
 
-    def valid(self) -> bool:
+    def valid(self) -> jtp.BoolLike:
+
         return bool(
             jnp.all(self.time_constant >= 0.0)
             and jnp.all(self.damping_coefficient > 0.0)
@@ -155,18 +162,19 @@ class RelaxedRigidContactsState(ContactsState):
     def __eq__(self, other: RelaxedRigidContactsState) -> bool:
         return hash(self) == hash(other)
 
-    @staticmethod
-    def build() -> RelaxedRigidContactsState:
+    @classmethod
+    def build(cls: type[Self]) -> Self:
         """Create a `RelaxedRigidContactsState` instance"""
 
-        return RelaxedRigidContactsState()
+        return cls()
 
-    @staticmethod
-    def zero(model: js.model.JaxSimModel) -> RelaxedRigidContactsState:
+    @classmethod
+    def zero(cls: type[Self]) -> Self:
         """Build a zero `RelaxedRigidContactsState` instance from a `JaxSimModel`."""
-        return RelaxedRigidContactsState.build()
 
-    def valid(self, model: js.model.JaxSimModel) -> bool:
+        return cls.build()
+
+    def valid(self, *, model: js.model.JaxSimModel) -> jtp.BoolLike:
         return True
 
 
@@ -182,10 +190,12 @@ class RelaxedRigidContacts(ContactModel):
         default_factory=FlatTerrain
     )
 
+    @jax.jit
     def compute_contact_forces(
         self,
-        position: jtp.Vector,
-        velocity: jtp.Vector,
+        position: jtp.VectorLike,
+        velocity: jtp.VectorLike,
+        *,
         model: js.model.JaxSimModel,
         data: js.data.JaxSimModelData,
         link_forces: jtp.MatrixLike | None = None,

src/jaxsim/rbda/contacts/rigid.py

@@ -14,6 +14,11 @@
 
 from .common import ContactModel, ContactsParams, ContactsState
 
+try:
+    from typing import Self
+except ImportError:
+    from typing_extensions import Self
+
 
 @jax_dataclasses.pytree_dataclass
 class RigidContactsParams(ContactsParams):
@@ -50,19 +55,22 @@ def __eq__(self, other: RigidContactsParams) -> bool:
 
     @classmethod
     def build(
-        cls,
+        cls: type[Self],
+        *,
         mu: jtp.FloatLike | None = None,
         K: jtp.FloatLike | None = None,
         D: jtp.FloatLike | None = None,
-    ) -> RigidContactsParams:
+    ) -> Self:
         """Create a `RigidContactParams` instance"""
-        return RigidContactsParams(
+
+        return cls(
             mu=mu or cls.__dataclass_fields__["mu"].default,
             K=K or cls.__dataclass_fields__["K"].default,
             D=D or cls.__dataclass_fields__["D"].default,
         )
 
-    def valid(self) -> bool:
+    def valid(self) -> jtp.BoolLike:
+
         return bool(
             jnp.all(self.mu >= 0.0)
             and jnp.all(self.K >= 0.0)
@@ -77,18 +85,19 @@ class RigidContactsState(ContactsState):
     def __eq__(self, other: RigidContactsState) -> bool:
         return hash(self) == hash(other)
 
-    @staticmethod
-    def build(**kwargs) -> RigidContactsState:
+    @classmethod
+    def build(cls: type[Self]) -> Self:
         """Create a `RigidContactsState` instance"""
 
-        return RigidContactsState()
+        return cls()
 
-    @staticmethod
-    def zero(**kwargs) -> RigidContactsState:
+    @classmethod
+    def zero(cls: type[Self]) -> Self:
         """Build a zero `RigidContactsState` instance from a `JaxSimModel`."""
-        return RigidContactsState.build()
 
-    def valid(self, **kwargs) -> bool:
+        return cls.build()
+
+    def valid(self) -> jtp.BoolLike:
         return True
 
 
@@ -117,7 +126,8 @@ def detect_contacts(
             terrain_height: The height of the terrain at the collidable point position.
 
         Returns:
-            A tuple containing the activation state of the collidable points and the contact penetration depth h.
+            A tuple containing the activation state of the collidable points
+            and the contact penetration depth h.
         """
 
         # TODO: reduce code duplication with js.contact.in_contact
@@ -154,8 +164,8 @@ def compute_impact_velocity(
 
         Args:
             inactive_collidable_points: The activation state of the collidable points.
-            M: The mass matrix of the system.
-            J_WC: The Jacobian matrix of the collidable points.
+            M: The mass matrix of the system (in mixed representation).
+            J_WC: The Jacobian matrix of the collidable points (in mixed representation).
             data: The `JaxSimModelData` instance.
         """
 
@@ -206,10 +216,12 @@ def impact_velocity(
 
         return BW_ν_post_impact
 
+    @jax.jit
     def compute_contact_forces(
         self,
-        position: jtp.Vector,
-        velocity: jtp.Vector,
+        position: jtp.VectorLike,
+        velocity: jtp.VectorLike,
+        *,
         model: js.model.JaxSimModel,
         data: js.data.JaxSimModelData,
         link_forces: jtp.MatrixLike | None = None,