Joint API and joint motors improvements

30 files changed, 1796 insertions, 769 deletions

diff --git a/src/dynamics/integration_parameters.rs b/src/dynamics/integration_parameters.rs
index 9e3f686..bab0fe2 100644
--- a/src/dynamics/integration_parameters.rs
+++ b/src/dynamics/integration_parameters.rs
@@ -18,10 +18,6 @@ pub struct IntegrationParameters {
     /// to numerical instabilities.
     pub min_ccd_dt: Real,
 
-    /// 0-1: how much of the velocity to dampen out in the constraint solver?
-    /// (default `1.0`).
-    pub velocity_solve_fraction: Real,
-
     /// 0-1: multiplier for how much of the constraint violation (e.g. contact penetration)
     /// will be compensated for during the velocity solve.
     /// If zero, you need to enable the positional solver.
@@ -35,6 +31,9 @@ pub struct IntegrationParameters {
     /// (default `0.25`).
     pub damping_ratio: Real,
 
+    pub joint_erp: Real,
+    pub joint_damping_ratio: Real,
+
     /// Amount of penetration the engine wont attempt to correct (default: `0.001m`).
     pub allowed_linear_error: Real,
     /// The maximal distance separating two objects that will generate predictive contacts (default: `0.002`).
@@ -89,12 +88,17 @@ impl IntegrationParameters {
 
     /// The ERP coefficient, multiplied by the inverse timestep length.
     pub fn erp_inv_dt(&self) -> Real {
-        0.8 / self.dt
+        self.erp / self.dt
+    }
+
+    /// The joint ERP coefficient, multiplied by the inverse timestep length.
+    pub fn joint_erp_inv_dt(&self) -> Real {
+        self.joint_erp / self.dt
     }
 
     /// The CFM factor to be used in the constraints resolution.
     pub fn cfm_factor(&self) -> Real {
-        // Compute CFM assuming a critically damped spring multiplied by the dampingratio.
+        // Compute CFM assuming a critically damped spring multiplied by the damping ratio.
         let inv_erp_minus_one = 1.0 / self.erp - 1.0;
 
         // let stiffness = 4.0 * damping_ratio * damping_ratio * projected_mass
@@ -124,6 +128,16 @@ impl IntegrationParameters {
         // in the constraints solver.
         1.0 / (1.0 + cfm_coeff)
     }
+
+    pub fn joint_cfm_coeff(&self) -> Real {
+        // Compute CFM assuming a critically damped spring multiplied by the damping ratio.
+        let inv_erp_minus_one = 1.0 / self.joint_erp - 1.0;
+        inv_erp_minus_one * inv_erp_minus_one
+            / ((1.0 + inv_erp_minus_one)
+                * 4.0
+                * self.joint_damping_ratio
+                * self.joint_damping_ratio)
+    }
 }
 
 impl Default for IntegrationParameters {
@@ -131,9 +145,10 @@ impl Default for IntegrationParameters {
         Self {
             dt: 1.0 / 60.0,
             min_ccd_dt: 1.0 / 60.0 / 100.0,
-            velocity_solve_fraction: 1.0,
             erp: 0.8,
             damping_ratio: 0.25,
+            joint_erp: 1.0,
+            joint_damping_ratio: 1.0,
             allowed_linear_error: 0.001, // 0.005
             prediction_distance: 0.002,
             max_velocity_iterations: 4,
diff --git a/src/dynamics/island_manager.rs b/src/dynamics/island_manager.rs
index 631cf7a..7cf16d6 100644
--- a/src/dynamics/island_manager.rs
+++ b/src/dynamics/island_manager.rs
@@ -136,36 +136,6 @@ impl IslandManager {
             .chain(self.active_kinematic_set.iter().copied())
     }
 
-    /*
-    #[cfg(feature = "parallel")]
-    #[inline(always)]
-    #[allow(dead_code)]
-    pub(crate) fn foreach_active_island_body_mut_internal_parallel<Set>(
-        &self,
-        island_id: usize,
-        bodies: &mut Set,
-        f: impl Fn(RigidBodyHandle, &mut RigidBody) + Send + Sync,
-    ) where
-        Set: ComponentSet<T>,
-    {
-        use std::sync::atomic::Ordering;
-
-        let island_range = self.active_islands[island_id]..self.active_islands[island_id + 1];
-        let bodies = std::sync::atomic::AtomicPtr::new(&mut bodies as *mut _);
-        self.active_dynamic_set[island_range]
-            .par_iter()
-            .for_each_init(
-                || bodies.load(Ordering::Relaxed),
-                |bodies, handle| {
-                    let bodies: &mut Set = unsafe { std::mem::transmute(*bodies) };
-                    if let Some(rb) = bodies.get_mut_internal(handle.0) {
-                        f(*handle, rb)
-                    }
-                },
-            );
-    }
-     */
-
     #[cfg(feature = "parallel")]
     pub(crate) fn active_island_range(&self, island_id: usize) -> std::ops::Range<usize> {
         self.active_islands[island_id]..self.active_islands[island_id + 1]
@@ -203,7 +173,7 @@ impl IslandManager {
         // NOTE: the `.rev()` is here so that two successive timesteps preserve
         // the order of the bodies in the `active_dynamic_set` vec. This reversal
         // does not seem to affect performances nor stability. However it makes
-        // debugging slightly nicer so we keep this rev.
+        // debugging slightly nicer.
         for h in self.active_dynamic_set.drain(..).rev() {
             let can_sleep = &mut self.can_sleep;
             let stack = &mut self.stack;
diff --git a/src/dynamics/joint/fixed_joint.rs b/src/dynamics/joint/fixed_joint.rs
index c7ca904..192b7d9 100644
--- a/src/dynamics/joint/fixed_joint.rs
+++ b/src/dynamics/joint/fixed_joint.rs
@@ -1,10 +1,11 @@
-use crate::dynamics::{JointAxesMask, JointData};
+use crate::dynamics::{GenericJoint, GenericJointBuilder, JointAxesMask};
 use crate::math::{Isometry, Point, Real};
 
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
 #[derive(Copy, Clone, Debug, PartialEq)]
+#[repr(transparent)]
 pub struct FixedJoint {
-    data: JointData,
+    data: GenericJoint,
 }
 
 impl Default for FixedJoint {
@@ -14,48 +15,100 @@ impl Default for FixedJoint {
 }
 
 impl FixedJoint {
+    #[must_use]
     pub fn new() -> Self {
-        #[cfg(feature = "dim2")]
-        let mask = JointAxesMask::X | JointAxesMask::Y | JointAxesMask::ANG_X;
-        #[cfg(feature = "dim3")]
-        let mask = JointAxesMask::X
-            | JointAxesMask::Y
-            | JointAxesMask::Z
-            | JointAxesMask::ANG_X
-            | JointAxesMask::ANG_Y
-            | JointAxesMask::ANG_Z;
-
-        let data = JointData::default().lock_axes(mask);
+        let data = GenericJointBuilder::new(JointAxesMask::LOCKED_FIXED_AXES).build();
         Self { data }
     }
 
     #[must_use]
+    pub fn local_frame1(&self) -> &Isometry<Real> {
+        &self.data.local_frame1
+    }
+
+    pub fn set_local_frame1(&mut self, local_frame: Isometry<Real>) -> &mut Self {
+        self.data.set_local_frame1(local_frame);
+        self
+    }
+
+    #[must_use]
+    pub fn local_frame2(&self) -> &Isometry<Real> {
+        &self.data.local_frame2
+    }
+
+    pub fn set_local_frame2(&mut self, local_frame: Isometry<Real>) -> &mut Self {
+        self.data.set_local_frame2(local_frame);
+        self
+    }
+
+    #[must_use]
+    pub fn local_anchor1(&self) -> Point<Real> {
+        self.data.local_anchor1()
+    }
+
+    pub fn set_local_anchor1(&mut self, anchor1: Point<Real>) -> &mut Self {
+        self.data.set_local_anchor1(anchor1);
+        self
+    }
+
+    #[must_use]
+    pub fn local_anchor2(&self) -> Point<Real> {
+        self.data.local_anchor2()
+    }
+
+    pub fn set_local_anchor2(&mut self, anchor2: Point<Real>) -> &mut Self {
+        self.data.set_local_anchor2(anchor2);
+        self
+    }
+}
+
+impl Into<GenericJoint> for FixedJoint {
+    fn into(self) -> GenericJoint {
+        self.data
+    }
+}
+
+#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+#[derive(Copy, Clone, Debug, PartialEq, Default)]
+pub struct FixedJointBuilder(FixedJoint);
+
+impl FixedJointBuilder {
+    pub fn new() -> Self {
+        Self(FixedJoint::new())
+    }
+
+    #[must_use]
     pub fn local_frame1(mut self, local_frame: Isometry<Real>) -> Self {
-        self.data = self.data.local_frame1(local_frame);
+        self.0.set_local_frame1(local_frame);
         self
     }
 
     #[must_use]
     pub fn local_frame2(mut self, local_frame: Isometry<Real>) -> Self {
-        self.data = self.data.local_frame2(local_frame);
+        self.0.set_local_frame2(local_frame);
         self
     }
 
     #[must_use]
     pub fn local_anchor1(mut self, anchor1: Point<Real>) -> Self {
-        self.data = self.data.local_anchor1(anchor1);
+        self.0.set_local_anchor1(anchor1);
         self
     }
 
     #[must_use]
     pub fn local_anchor2(mut self, anchor2: Point<Real>) -> Self {
-        self.data = self.data.local_anchor2(anchor2);
+        self.0.set_local_anchor2(anchor2);
         self
     }
+
+    #[must_use]
+    pub fn build(self) -> FixedJoint {
+        self.0
+    }
 }
 
-impl Into<JointData> for FixedJoint {
-    fn into(self) -> JointData {
-        self.data
+impl Into<GenericJoint> for FixedJointBuilder {
+    fn into(self) -> GenericJoint {
+        self.0.into()
     }
 }
diff --git a/src/dynamics/joint/generic_joint.rs b/src/dynamics/joint/generic_joint.rs
new file mode 100644
index 0000000..7455b0d
--- /dev/null
+++ b/src/dynamics/joint/generic_joint.rs
@@ -0,0 +1,501 @@
+use na::SimdRealField;
+
+use crate::dynamics::solver::MotorParameters;
+use crate::dynamics::{FixedJoint, MotorModel, PrismaticJoint, RevoluteJoint};
+use crate::math::{Isometry, Point, Real, Rotation, UnitVector, Vector, SPATIAL_DIM};
+use crate::utils::WBasis;
+
+#[cfg(feature = "dim3")]
+use crate::dynamics::SphericalJoint;
+
+#[cfg(feature = "dim3")]
+bitflags::bitflags! {
+    #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+    pub struct JointAxesMask: u8 {
+        const X = 1 << 0;
+        const Y = 1 << 1;
+        const Z = 1 << 2;
+        const ANG_X = 1 << 3;
+        const ANG_Y = 1 << 4;
+        const ANG_Z = 1 << 5;
+        const LOCKED_REVOLUTE_AXES = Self::X.bits | Self::Y.bits | Self::Z.bits | Self::ANG_Y.bits | Self::ANG_Z.bits;
+        const LOCKED_PRISMATIC_AXES = Self::Y.bits | Self::Z.bits | Self::ANG_X.bits | Self::ANG_Y.bits | Self::ANG_Z.bits;
+        const LOCKED_FIXED_AXES = Self::X.bits | Self::Y.bits | Self::Z.bits | Self::ANG_X.bits | Self::ANG_Y.bits | Self::ANG_Z.bits;
+        const LOCKED_SPHERICAL_AXES = Self::X.bits | Self::Y.bits | Self::Z.bits;
+        const FREE_REVOLUTE_AXES = Self::ANG_X.bits;
+        const FREE_PRISMATIC_AXES = Self::X.bits;
+        const FREE_FIXED_AXES = 0;
+        const FREE_SPHERICAL_AXES = Self::ANG_X.bits | Self::ANG_Y.bits | Self::ANG_Z.bits;
+    }
+}
+
+#[cfg(feature = "dim2")]
+bitflags::bitflags! {
+    #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+    pub struct JointAxesMask: u8 {
+        const X = 1 << 0;
+        const Y = 1 << 1;
+        const ANG_X = 1 << 2;
+        const LOCKED_REVOLUTE_AXES = Self::X.bits | Self::Y.bits;
+        const LOCKED_PRISMATIC_AXES = Self::Y.bits | Self::ANG_X.bits;
+        const LOCKED_FIXED_AXES = Self::X.bits | Self::Y.bits | Self::ANG_X.bits;
+        const FREE_REVOLUTE_AXES = Self::ANG_X.bits;
+        const FREE_PRISMATIC_AXES = Self::X.bits;
+        const FREE_FIXED_AXES = 0;
+    }
+}
+
+#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub enum JointAxis {
+    X = 0,
+    Y,
+    #[cfg(feature = "dim3")]
+    Z,
+    AngX,
+    #[cfg(feature = "dim3")]
+    AngY,
+    #[cfg(feature = "dim3")]
+    AngZ,
+}
+
+impl From<JointAxis> for JointAxesMask {
+    fn from(axis: JointAxis) -> Self {
+        JointAxesMask::from_bits(1 << axis as usize).unwrap()
+    }
+}
+
+#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub struct JointLimits<N> {
+    pub min: N,
+    pub max: N,
+    pub impulse: N,
+}
+
+impl<N: SimdRealField<Element = Real>> Default for JointLimits<N> {
+    fn default() -> Self {
+        Self {
+            min: -N::splat(Real::MAX),
+            max: N::splat(Real::MAX),
+            impulse: N::splat(0.0),
+        }
+    }
+}
+
+#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub struct JointMotor {
+    pub target_vel: Real,
+    pub target_pos: Real,
+    pub stiffness: Real,
+    pub damping: Real,
+    pub max_force: Real,
+    pub impulse: Real,
+    pub model: MotorModel,
+}
+
+impl Default for JointMotor {
+    fn default() -> Self {
+        Self {
+            target_pos: 0.0,
+            target_vel: 0.0,
+            stiffness: 0.0,
+            damping: 0.0,
+            max_force: Real::MAX,
+            impulse: 0.0,
+            model: MotorModel::AccelerationBased, // VelocityBased,
+        }
+    }
+}
+
+impl JointMotor {
+    pub(crate) fn motor_params(&self, dt: Real) -> MotorParameters<Real> {
+        let (erp_inv_dt, cfm_coeff, cfm_gain) =
+            self.model
+                .combine_coefficients(dt, self.stiffness, self.damping);
+        MotorParameters {
+            erp_inv_dt,
+            cfm_coeff,
+            cfm_gain,
+            // keep_lhs,
+            target_pos: self.target_pos,
+            target_vel: self.target_vel,
+            max_impulse: self.max_force * dt,
+        }
+    }
+}
+
+#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub struct GenericJoint {
+    pub local_frame1: Isometry<Real>,
+    pub local_frame2: Isometry<Real>,
+    pub locked_axes: JointAxesMask,
+    pub limit_axes: JointAxesMask,
+    pub motor_axes: JointAxesMask,
+    pub limits: [JointLimits<Real>; SPATIAL_DIM],
+    pub motors: [JointMotor; SPATIAL_DIM],
+}
+
+impl Default for GenericJoint {
+    fn default() -> Self {
+        Self {
+            local_frame1: Isometry::identity(),
+            local_frame2: Isometry::identity(),
+            locked_axes: JointAxesMask::empty(),
+            limit_axes: JointAxesMask::empty(),
+            motor_axes: JointAxesMask::empty(),
+            limits: [JointLimits::default(); SPATIAL_DIM],
+            motors: [JointMotor::default(); SPATIAL_DIM],
+        }
+    }
+}
+
+impl GenericJoint {
+    #[must_use]
+    pub fn new(locked_axes: JointAxesMask) -> Self {
+        *Self::default().lock_axes(locked_axes)
+    }
+
+    /// Can this joint use SIMD-accelerated constraint formulations?
+    pub(crate) fn supports_simd_constraints(&self) -> bool {
+        self.limit_axes.is_empty() && self.motor_axes.is_empty()
+    }
+
+    fn complete_ang_frame(axis: UnitVector<Real>) -> Rotation<Real> {
+        let basis = axis.orthonormal_basis();
+
+        #[cfg(feature = "dim2")]
+        {
+            use na::{Matrix2, Rotation2, UnitComplex};
+            let mat = Matrix2::from_columns(&[axis.into_inner(), basis[0]]);
+            let rotmat = Rotation2::from_matrix_unchecked(mat);
+            UnitComplex::from_rotation_matrix(&rotmat)
+        }
+
+        #[cfg(feature = "dim3")]
+        {
+            use na::{Matrix3, Rotation3, UnitQuaternion};
+            let mat = Matrix3::from_columns(&[axis.into_inner(), basis[0], basis[1]]);
+            let rotmat = Rotation3::from_matrix_unchecked(mat);
+            UnitQuaternion::from_rotation_matrix(&rotmat)
+        }
+    }
+
+    pub fn lock_axes(&mut self, axes: JointAxesMask) -> &mut Self {
+        self.locked_axes |= axes;
+        self
+    }
+
+    pub fn set_local_frame1(&mut self, local_frame: Isometry<Real>) -> &mut Self {
+        self.local_frame1 = local_frame;
+        self
+    }
+
+    pub fn set_local_frame2(&mut self, local_frame: Isometry<Real>) -> &mut Self {
+        self.local_frame2 = local_frame;
+        self
+    }
+
+    #[must_use]
+    pub fn local_axis1(&self) -> UnitVector<Real> {
+        self.local_frame1 * Vector::x_axis()
+    }
+
+    pub fn set_local_axis1(&mut self, local_axis: UnitVector<Real>) -> &mut Self {
+        self.local_frame1.rotation = Self::complete_ang_frame(local_axis);
+        self
+    }
+
+    #[must_use]
+    pub fn local_axis2(&self) -> UnitVector<Real> {
+        self.local_frame2 * Vector::x_axis()
+    }
+
+    pub fn set_local_axis2(&mut self, local_axis: UnitVector<Real>) -> &mut Self {
+        self.local_frame2.rotation = Self::complete_ang_frame(local_axis);
+        self
+    }
+
+    #[must_use]
+    pub fn local_anchor1(&self) -> Point<Real> {
+        self.local_frame1.translation.vector.into()
+    }
+
+    pub fn set_local_anchor1(&mut self, anchor1: Point<Real>) -> &mut Self {
+        self.local_frame1.translation.vector = anchor1.coords;
+        self
+    }
+
+    #[must_use]
+    pub fn local_anchor2(&self) -> Point<Real> {
+        self.local_frame2.translation.vector.into()
+    }
+
+    pub fn set_local_anchor2(&mut self, anchor2: Point<Real>) -> &mut Self {
+        self.local_frame2.translation.vector = anchor2.coords;
+        self
+    }
+
+    #[must_use]
+    pub fn limits(&self, axis: JointAxis) -> Option<&JointLimits<Real>> {
+        let i = axis as usize;
+        if self.limit_axes.contains(axis.into()) {
+            Some(&self.limits[i])
+        } else {
+            None
+        }
+    }
+
+    pub fn set_limits(&mut self, axis: JointAxis, limits: [Real; 2]) -> &mut Self {
+        let i = axis as usize;
+        self.limit_axes |= axis.into();
+        self.limits[i].min = limits[0];
+        self.limits[i].max = limits[1];
+        self
+    }
+
+    #[must_use]
+    pub fn motor_model(&self, axis: JointAxis) -> Option<MotorModel> {
+        let i = axis as usize;
+        if self.motor_axes.contains(axis.into()) {
+            Some(self.motors[i].model)
+        } else {
+            None
+        }
+    }
+
+    /// Set the spring-like model used by the motor to reach the desired target velocity and position.
+    pub fn set_motor_model(&mut self, axis: JointAxis, model: MotorModel) -> &mut Self {
+        self.motors[axis as usize].model = model;
+        self
+    }
+
+    /// Sets the target velocity this motor needs to reach.
+    pub fn set_motor_velocity(
+        &mut self,
+        axis: JointAxis,
+        target_vel: Real,
+        factor: Real,
+    ) -> &mut Self {
+        self.set_motor(
+            axis,
+            self.motors[axis as usize].target_pos,
+            target_vel,
+            0.0,
+            factor,
+        )
+    }
+
+    /// Sets the target angle this motor needs to reach.
+    pub fn set_motor_position(
+        &mut self,
+        axis: JointAxis,
+        target_pos: Real,
+        stiffness: Real,
+        damping: Real,
+    ) -> &mut Self {
+        self.set_motor(axis, target_pos, 0.0, stiffness, damping)
+    }
+
+    pub fn set_motor_max_force(&mut self, axis: JointAxis, max_force: Real) -> &mut Self {
+        self.motors[axis as usize].max_force = max_force;
+        self
+    }
+
+    #[must_use]
+    pub fn motor(&self, axis: JointAxis) -> Option<&JointMotor> {
+        let i = axis as usize;
+        if self.motor_axes.contains(axis.into()) {
+            Some(&self.motors[i])
+        } else {
+            None
+        }
+    }
+
+    /// Configure both the target angle and target velocity of the motor.
+    pub fn set_motor(
+        &mut self,
+        axis: JointAxis,
+        target_pos: Real,
+        target_vel: Real,
+        stiffness: Real,
+        damping: Real,
+    ) -> &mut Self {
+        self.motor_axes |= axis.into();
+        let i = axis as usize;
+        self.motors[i].target_vel = target_vel;
+        self.motors[i].target_pos = target_pos;
+        self.motors[i].stiffness = stiffness;
+        self.motors[i].damping = damping;
+        self
+    }
+}
+
+macro_rules! joint_conversion_methods(
+    ($as_joint: ident, $as_joint_mut: ident, $Joint: ty, $axes: expr) => {
+        #[must_use]
+        pub fn $as_joint(&self) -> Option<&$Joint> {
+            if self.locked_axes == $axes {
+                // SAFETY: this is OK because the target joint type is
+                //         a `repr(transparent)` newtype of `Joint`.
+                Some(unsafe { std::mem::transmute(self) })
+            } else {
+                None
+            }
+        }
+
+        #[must_use]
+        pub fn $as_joint_mut(&mut self) -> Option<&mut $Joint> {
+            if self.locked_axes == $axes {
+                // SAFETY: this is OK because the target joint type is
+                //         a `repr(transparent)` newtype of `Joint`.
+                Some(unsafe { std::mem::transmute(self) })
+            } else {
+                None
+            }
+        }
+    }
+);
+
+impl GenericJoint {
+    joint_conversion_methods!(
+        as_revolute,
+        as_revolute_mut,
+        RevoluteJoint,
+        JointAxesMask::LOCKED_REVOLUTE_AXES
+    );
+    joint_conversion_methods!(
+        as_fixed,
+        as_fixed_mut,
+        FixedJoint,
+        JointAxesMask::LOCKED_FIXED_AXES
+    );
+    joint_conversion_methods!(
+        as_prismatic,
+        as_prismatic_mut,
+        PrismaticJoint,
+        JointAxesMask::LOCKED_PRISMATIC_AXES
+    );
+
+    #[cfg(feature = "dim3")]
+    joint_conversion_methods!(
+        as_spherical,
+        as_spherical_mut,
+        SphericalJoint,
+        JointAxesMask::LOCKED_SPHERICAL_AXES
+    );
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct GenericJointBuilder(GenericJoint);
+
+impl GenericJointBuilder {
+    #[must_use]
+    pub fn new(locked_axes: JointAxesMask) -> Self {
+        Self(GenericJoint::new(locked_axes))
+    }
+
+    #[must_use]
+    pub fn lock_axes(mut self, axes: JointAxesMask) -> Self {
+        self.0.lock_axes(axes);
+        self
+    }
+
+    #[must_use]
+    pub fn local_frame1(mut self, local_frame: Isometry<Real>) -> Self {
+        self.0.set_local_frame1(local_frame);
+        self
+    }
+
+    #[must_use]
+    pub fn local_frame2(mut self, local_frame: Isometry<Real>) -> Self {
+        self.0.set_local_frame2(local_frame);
+        self
+    }
+
+    #[must_use]
+    pub fn local_axis1(mut self, local_axis: UnitVector<Real>) -> Self {
+        self.0.set_local_axis1(local_axis);
+        self
+    }
+
+    #[must_use]
+    pub fn local_axis2(mut self, local_axis: UnitVector<Real>) -> Self {
+        self.0.set_local_axis2(local_axis);
+        self
+    }
+
+    #[must_use]
+    pub fn local_anchor1(mut self, anchor1: Point<Real>) -> Self {
+        self.0.set_local_anchor1(anchor1);
+        self
+    }
+
+    #[must_use]
+    pub fn local_anchor2(mut self, anchor2: Point<Real>) -> Self {
+        self.0.set_local_anchor2(anchor2);
+        self
+    }
+
+    #[must_use]
+    pub fn limits(mut self, axis: JointAxis, limits: [Real; 2]) -> Self {
+        self.0.set_limits(axis, limits);
+        self
+    }
+
+    /// Set the spring-like model used by the motor to reach the desired target velocity and position.
+    #[must_use]
+    pub fn motor_model(mut self, axis: JointAxis, model: MotorModel) -> Self {
+        self.0.set_motor_model(axis, model);
+        self
+    }
+
+    /// Sets the target velocity this motor needs to reach.
+    #[must_use]
+    pub fn motor_velocity(mut self, axis: JointAxis, target_vel: Real, factor: Real) -> Self {
+        self.0.set_motor_velocity(axis, target_vel, factor);
+        self
+    }
+
+    /// Sets the target angle this motor needs to reach.
+    #[must_use]
+    pub fn motor_position(
+        mut self,
+        axis: JointAxis,
+        target_pos: Real,
+        stiffness: Real,
+        damping: Real,
+    ) -> Self {
+        self.0
+            .set_motor_position(axis, target_pos, stiffness, damping);
+        self
+    }
+
+    /// Configure both the target angle and target velocity of the motor.
+    #[must_use]
+    pub fn set_motor(
+        mut self,
+        axis: JointAxis,
+        target_pos: Real,
+        target_vel: Real,
+        stiffness: Real,
+        damping: Real,
+    ) -> Self {
+        self.0
+            .set_motor(axis, target_pos, target_vel, stiffness, damping);
+        self
+    }
+
+    #[must_use]
+    pub fn motor_max_force(mut self, axis: JointAxis, max_force: Real) -> Self {
+        self.0.set_motor_max_force(axis, max_force);
+        self
+    }
+
+    #[must_use]
+    pub fn build(self) -> GenericJoint {
+        self.0
+    }
+}
diff --git a/src/dynamics/joint/impulse_joint/impulse_joint.rs b/src/dynamics/joint/impulse_joint/impulse_joint.rs
index f3f4f7c..993542a 100644
--- a/src/dynamics/joint/impulse_joint/impulse_joint.rs
+++ b/src/dynamics/joint/impulse_joint/impulse_joint.rs
@@ -1,4 +1,4 @@
-use crate::dynamics::{ImpulseJointHandle, JointData, RigidBodyHandle};
+use crate::dynamics::{GenericJoint, ImpulseJointHandle, RigidBodyHandle};
 use crate::math::{Real, SpacialVector};
 
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
@@ -10,7 +10,7 @@ pub struct ImpulseJoint {
     /// Handle to the second body attached to this joint.
     pub body2: RigidBodyHandle,
 
-    pub data: JointData,
+    pub data: GenericJoint,
     pub impulses: SpacialVector<Real>,
 
     // A joint needs to know its handle to simplify its removal.
diff --git a/src/dynamics/joint/impulse_joint/impulse_joint_set.rs b/src/dynamics/joint/impulse_joint/impulse_joint_set.rs
index 51d5989..8677772 100644
--- a