Implement limits for revolute joints.

examples3d/joints3.rs

@@ -177,6 +177,85 @@ fn create_revolute_joints(
     }
 }
 
+fn create_revolute_joints_with_limits(
+    bodies: &mut RigidBodySet,
+    colliders: &mut ColliderSet,
+    joints: &mut JointSet,
+    origin: Point<f32>,
+) {
+    let ground = bodies.insert(
+        RigidBodyBuilder::new_static()
+            .translation(origin.coords)
+            .build(),
+    );
+
+    let platform1 = bodies.insert(
+        RigidBodyBuilder::new_dynamic()
+            .translation(origin.coords)
+            .build(),
+    );
+    colliders.insert_with_parent(
+        ColliderBuilder::cuboid(4.0, 0.2, 2.0).build(),
+        platform1,
+        bodies,
+    );
+
+    let shift = vector![0.0, 0.0, 6.0];
+    let platform2 = bodies.insert(
+        RigidBodyBuilder::new_dynamic()
+            .translation(origin.coords + shift)
+            .build(),
+    );
+    colliders.insert_with_parent(
+        ColliderBuilder::cuboid(4.0, 0.2, 2.0).build(),
+        platform2,
+        bodies,
+    );
+
+    let mut joint1 = RevoluteJoint::new(
+        Point::origin(),
+        Vector::z_axis(),
+        Point::origin(),
+        Vector::z_axis(),
+    );
+    joint1.limits_enabled = true;
+    joint1.limits = [-0.2, 0.2];
+    joints.insert(ground, platform1, joint1);
+
+    let mut joint2 = RevoluteJoint::new(
+        Point::origin(),
+        Vector::z_axis(),
+        Point::from(-shift),
+        Vector::z_axis(),
+    );
+    joint2.limits_enabled = true;
+    joint2.limits = [-0.3, 0.3];
+    joints.insert(platform1, platform2, joint2);
+
+    // Let’s add a couple of cuboids that will fall on the platforms, triggering the joint limits.
+    let cuboid_body1 = bodies.insert(
+        RigidBodyBuilder::new_dynamic()
+            .translation(origin.coords + vector![-2.0, 4.0, 0.0])
+            .build(),
+    );
+    colliders.insert_with_parent(
+        ColliderBuilder::cuboid(0.6, 0.6, 0.6).friction(1.0).build(),
+        cuboid_body1,
+        bodies,
+    );
+
+    let cuboid_body2 = bodies.insert(
+        RigidBodyBuilder::new_dynamic()
+            .translation(origin.coords + shift + vector![2.0, 16.0, 0.0])
+            .build(),
+    );
+    colliders.insert_with_parent(
+        ColliderBuilder::cuboid(0.6, 0.6, 0.6).friction(1.0).build(),
+        cuboid_body2,
+        bodies,
+    );
+}
+
 fn create_fixed_joints(
     bodies: &mut RigidBodySet,
     colliders: &mut ColliderSet,
@@ -442,6 +521,12 @@ pub fn init_world(testbed: &mut Testbed) {
         point![20.0, 0.0, 0.0],
         3,
     );
+    create_revolute_joints_with_limits(
+        &mut bodies,
+        &mut colliders,
+        &mut joints,
+        point![34.0, 0.0, 0.0],
+    );
     create_fixed_joints(
         &mut bodies,
         &mut colliders,

src/dynamics/joint/prismatic_joint.rs

@@ -19,6 +19,7 @@ pub struct PrismaticJoint {
     pub(crate) local_axis2: Unit<Vector<Real>>,
     pub(crate) basis1: [Vector<Real>; DIM - 1],
     pub(crate) basis2: [Vector<Real>; DIM - 1],
+
     /// The impulse applied by this joint on the first body.
     ///
     /// The impulse applied to the second body is given by `-impulse`.
@@ -29,6 +30,7 @@ pub struct PrismaticJoint {
     /// The impulse applied to the second body is given by `-impulse`.
     #[cfg(feature = "dim2")]
     pub impulse: Vector2<Real>,
+
     /// Whether or not this joint should enforce translational limits along its axis.
     pub limits_enabled: bool,
     /// The min an max relative position of the attached bodies along this joint's axis.

src/dynamics/joint/revolute_joint.rs

@@ -24,6 +24,15 @@ pub struct RevoluteJoint {
     /// The impulse applied to the second body is given by `-impulse`.
     pub impulse: Vector5<Real>,
 
+    /// Whether or not this joint should enforce translational limits along its axis.
+    pub limits_enabled: bool,
+    /// The min an max relative position of the attached bodies along this joint's axis.
+    pub limits: [Real; 2],
+    /// The impulse applied by this joint on the first body to enforce the position limit along this joint's axis.
+    ///
+    /// The impulse applied to the second body is given by `-impulse`.
+    pub limits_impulse: Real,
+
     /// The target relative angular velocity the motor will attempt to reach.
     pub motor_target_vel: Real,
     /// The target relative angle along the joint axis the motor will attempt to reach.
@@ -67,6 +76,9 @@ impl RevoluteJoint {
             basis2: local_axis2.orthonormal_basis(),
             impulse: na::zero(),
             world_ang_impulse: na::zero(),
+            limits_enabled: false,
+            limits: [-Real::MAX, Real::MAX],
+            limits_impulse: 0.0,
             motor_target_vel: 0.0,
             motor_target_pos: 0.0,
             motor_stiffness: 0.0,
@@ -82,7 +94,9 @@ impl RevoluteJoint {
     /// Can a SIMD constraint be used for resolving this joint?
     pub fn supports_simd_constraints(&self) -> bool {
         // SIMD revolute constraints don't support motors right now.
-        self.motor_max_impulse == 0.0 || (self.motor_stiffness == 0.0 && self.motor_damping == 0.0)
+        !self.limits_enabled
+            && (self.motor_max_impulse == 0.0
+                || (self.motor_stiffness == 0.0 && self.motor_damping == 0.0))
     }
 
     /// Set the spring-like model used by the motor to reach the desired target velocity and position.
@@ -120,21 +134,31 @@ impl RevoluteJoint {
         body_pos1: &Isometry<Real>,
         body_pos2: &Isometry<Real>,
     ) -> Real {
-        let motor_axis1 = body_pos1 * self.local_axis1;
-        let ref1 = body_pos1 * self.basis1[0];
-        let ref2 = body_pos2 * self.basis2[0];
+        Self::estimate_motor_angle_from_params(
+            &(body_pos1 * self.local_axis1),
+            &(body_pos1 * self.basis1[0]),
+            &(body_pos2 * self.basis2[0]),
+            self.motor_last_angle,
+        )
+    }
 
-        let last_angle_cycles = (self.motor_last_angle / Real::two_pi()).trunc() * Real::two_pi();
+    pub fn estimate_motor_angle_from_params(
+        axis1: &Unit<Vector<Real>>,
+        tangent1: &Vector<Real>,
+        tangent2: &Vector<Real>,
+        motor_last_angle: Real,
+    ) -> Real {
+        let last_angle_cycles = (motor_last_angle / Real::two_pi()).trunc() * Real::two_pi();
 
         // Measure the position between 0 and 2-pi
-        let new_angle = if ref1.cross(&ref2).dot(&motor_axis1) < 0.0 {
-            Real::two_pi() - ref1.angle(&ref2)
+        let new_angle = if tangent1.cross(&tangent2).dot(&axis1) < 0.0 {
+            Real::two_pi() - tangent1.angle(&tangent2)
         } else {
-            ref1.angle(&ref2)
+            tangent1.angle(&tangent2)
         };
 
         // The last angle between 0 and 2-pi
-        let last_angle_zero_two_pi = self.motor_last_angle - last_angle_cycles;
+        let last_angle_zero_two_pi = motor_last_angle - last_angle_cycles;
 
         // Figure out the smallest angle differance.
         let mut angle_diff = new_angle - last_angle_zero_two_pi;
@@ -144,6 +168,6 @@ impl RevoluteJoint {
             angle_diff += Real::two_pi()
         }
 
-        self.motor_last_angle + angle_diff
+        motor_last_angle + angle_diff
     }
 }

src/dynamics/solver/joint_constraint/prismatic_velocity_constraint.rs

@@ -256,8 +256,8 @@ impl PrismaticVelocityConstraint {
 
             limits_impulse_limits.0 = if max_enabled { -Real::INFINITY } else { 0.0 };
             limits_impulse_limits.1 = if min_enabled { Real::INFINITY } else { 0.0 };
-
             limits_active = min_enabled || max_enabled;
+
             if limits_active {
                 limits_rhs = (anchor_linvel2.dot(&axis2) - anchor_linvel1.dot(&axis1))
                     * params.velocity_solve_fraction;

src/dynamics/solver/joint_constraint/revolute_position_constraint.rs

@@ -21,6 +21,11 @@ pub(crate) struct RevolutePositionConstraint {
 
     ang_inv_lhs: AngularInertia<Real>,
 
+    limits_enabled: bool,
+    limits: [Real; 2],
+
+    motor_last_angle: Real,
+
     local_anchor1: Point<Real>,
     local_anchor2: Point<Real>,
 
@@ -61,6 +66,9 @@ impl RevolutePositionConstraint {
             position2: ids2.active_set_offset,
             local_basis1: cparams.basis1,
             local_basis2: cparams.basis2,
+            limits_enabled: cparams.limits_enabled,
+            limits: cparams.limits,
+            motor_last_angle: cparams.motor_last_angle,
         }
     }
 
@@ -119,6 +127,31 @@ impl RevolutePositionConstraint {
                 Rotation::new(self.ii2.transform_vector(-ang_impulse)) * position2.rotation;
         }
 
+        /*
+         * Limits part.
+         */
+        if self.limits_enabled {
+            let angle = RevoluteJoint::estimate_motor_angle_from_params(
+                &(position1 * self.local_axis1),
+                &(position1 * self.local_basis1[0]),
+                &(position2 * self.local_basis2[0]),
+                self.motor_last_angle,
+            );
+            let ang_error = (angle - self.limits[1]).max(0.0) - (self.limits[0] - angle).max(0.0);
+
+            if ang_error != 0.0 {
+                let axis2 = position2 * self.local_axis2;
+                let ang_impulse = self
+                    .ang_inv_lhs
+                    .transform_vector(*axis2 * ang_error * params.joint_erp);
+
+                position1.rotation =
+                    Rotation::new(self.ii1.transform_vector(ang_impulse)) * position1.rotation;
+                position2.rotation =
+                    Rotation::new(self.ii2.transform_vector(-ang_impulse)) * position2.rotation;
+            }
+        }
+
         positions[self.position1 as usize] = position1;
         positions[self.position2 as usize] = position2;
     }
@@ -133,9 +166,14 @@ pub(crate) struct RevolutePositionGroundConstraint {
     anchor1: Point<Real>,
     local_anchor2: Point<Real>,
     axis1: Unit<Vector<Real>>,
-    local_axis2: Unit<Vector<Real>>,
-
     basis1: [Vector<Real>; 2],
+
+    limits_enabled: bool,
+    limits: [Real; 2],
+
+    motor_last_angle: Real,
+
+    local_axis2: Unit<Vector<Real>>,
     local_basis2: [Vector<Real>; 2],
 }
 
@@ -189,6 +227,9 @@ impl RevolutePositionGroundConstraint {
             position2: ids2.active_set_offset,
             basis1,
             local_basis2,
+            limits_enabled: cparams.limits_enabled,
+            limits: cparams.limits,
+            motor_last_angle: cparams.motor_last_angle,
         }
     }
 
@@ -230,6 +271,25 @@ impl RevolutePositionGroundConstraint {
             position2.rotation = Rotation::new(-ang_error) * position2.rotation;
         }
 
+        /*
+         * Limits part.
+         */
+        if self.limits_enabled {
+            let angle = RevoluteJoint::estimate_motor_angle_from_params(
+                &self.axis1,
+                &self.basis1[0],
+                &(position2 * self.local_basis2[0]),
+                self.motor_last_angle,
+            );
+            let ang_error = (angle - self.limits[1]).max(0.0) - (self.limits[0] - angle).max(0.0);
+
+            if ang_error != 0.0 {
+                let axis2 = position2 * self.local_axis2;
+                position2.rotation =
+                    Rotation::new(*axis2 * -ang_error * params.joint_erp) * position2.rotation;
+            }
+        }
+
         positions[self.position2 as usize] = position2;
     }
 }

src/dynamics/solver/joint_constraint/revolute_velocity_constraint.rs

@@ -30,6 +30,12 @@ pub(crate) struct RevoluteVelocityConstraint {
     motor_axis1: Vector<Real>,
     motor_axis2: Vector<Real>,
 
+    limits_active: bool,
+    limits_impulse: Real,
+    limits_rhs: Real,
+    limits_inv_lhs: Real,
+    limits_impulse_limits: (Real, Real),
+
     basis1: Matrix3x2<Real>,
     basis2: Matrix3x2<Real>,
 
@@ -145,8 +151,11 @@ impl RevoluteVelocityConstraint {
             joint.motor_damping,
         );
 
-        if stiffness != 0.0 {
+        if stiffness != 0.0 || joint.limits_enabled {
             motor_angle = joint.estimate_motor_angle(&poss1.position, &poss2.position);
+        }
+
+        if stiffness != 0.0 {
             motor_rhs += (motor_angle - joint.motor_target_pos) * stiffness;
         }
 
@@ -167,6 +176,47 @@ impl RevoluteVelocityConstraint {
             motor_rhs /= gamma;
         }
 
+        /*
+         * Setup limit constraint.
+         */
+        let mut limits_active = false;
+        let mut limits_rhs = 0.0;
+        let mut limits_inv_lhs = 0.0;
+        let mut limits_impulse_limits = (0.0, 0.0);
+        let mut limits_impulse = 0.0;
+
+        if joint.limits_enabled {
+            // TODO: we should allow predictive constraint activation.
+
+            let (min_limit, max_limit) = (joint.limits[0], joint.limits[1]);
+            let min_enabled = motor_angle < min_limit;
+            let max_enabled = max_limit < motor_angle;
+
+            limits_impulse_limits.0 = if max_enabled { -Real::INFINITY } else { 0.0 };
+            limits_impulse_limits.1 = if min_enabled { Real::INFINITY } else { 0.0 };
+            limits_active = min_enabled || max_enabled;
+
+            if limits_active {
+                limits_rhs = (vels2.angvel.dot(&motor_axis2) - vels1.angvel.dot(&motor_axis1))
+                    * params.velocity_solve_fraction;
+
+                limits_rhs += ((motor_angle - max_limit).max(0.0)
+                    - (min_limit - motor_angle).max(0.0))
+                    * velocity_based_erp_inv_dt;
+
+                limits_inv_lhs = crate::utils::inv(
+                    motor_axis2.dot(&ii2.transform_vector(motor_axis2))
+                        + motor_axis1.dot(&ii1.transform_vector(motor_axis1)),
+                );
+
+                limits_impulse = joint
+                    .limits_impulse
+                    .max(limits_impulse_limits.0)
+                    .min(limits_impulse_limits.1)
+                    * params.warmstart_coeff;
+            }
+        }
+
         /*
          * Adjust the warmstart impulse.
          * If the velocity along the free axis is somewhat high,
@@ -205,6 +255,11 @@ impl RevoluteVelocityConstraint {
             motor_axis2,
             motor_impulse,
             motor_angle,
+            limits_impulse,
+            limits_impulse_limits,
+            limits_active,
+            limits_inv_lhs,
+            limits_rhs,
         }
     }
 
@@ -228,7 +283,7 @@ impl RevoluteVelocityConstraint {
             .transform_vector(ang_impulse2 + self.r2.gcross(lin_impulse2));
 
         /*
-         * Motor
+         * Warmstart motor.
          */
         if self.motor_inv_lhs != 0.0 {
             mj_lambda1.angular += self
@@ -239,6 +294,14 @@ impl RevoluteVelocityConstraint {
                 .transform_vector(self.motor_axis2 * self.motor_impulse);
         }
 
+        // Warmstart limits.
+        if self.limits_active {
+            let limit_impulse1 = -self.motor_axis2 * self.limits_impulse;
+            let limit_impulse2 = self.motor_axis2 * self.limits_impulse;
+            mj_lambda1.angular += self.ii1_sqrt.transform_vector(limit_impulse1);
+            mj_lambda2.angular += self.ii2_sqrt.transform_vector(limit_impulse2);
+        }
+
         mj_lambdas[self.mj_lambda1 as usize] = mj_lambda1;
         mj_lambdas[self.mj_lambda2 as usize] = mj_lambda2;
     }
@@ -270,6 +333,31 @@ impl RevoluteVelocityConstraint {
             .transform_vector(ang_impulse2 + self.r2.gcross(lin_impulse2));
     }
 
+    fn solve_limits(&mut self, mj_lambda1: &mut DeltaVel<Real>, mj_lambda2: &mut DeltaVel<Real>) {
+        if self.limits_active {
+            let limits_torquedir1 = -self.motor_axis2;
+            let limits_torquedir2 = self.motor_axis2;
+
+            let ang_vel1 = self.ii1_sqrt.transform_vector(mj_lambda1.angular);
+            let ang_vel2 = self.ii2_sqrt.transform_vector(mj_lambda2.angular);
+
+            let ang_dvel = limits_torquedir1.dot(&ang_vel1)
+                + limits_torquedir2.dot(&ang_vel2)
+                + self.limits_rhs;
+            let new_impulse = (self.limits_impulse - ang_dvel * self.limits_inv_lhs)
+                .max(self.limits_impulse_limits.0)
+                .min(self.limits_impulse_limits.1);
+            let dimpulse = new_impulse - self.limits_impulse;
+            self.limits_impulse = new_impulse;
+
+            let ang_impulse1 = limits_torquedir1 * dimpulse;
+            let ang_impulse2 = limits_torquedir2 * dimpulse;
+
+            mj_lambda1.angular += self.ii1_sqrt.transform_vector(ang_impulse1);
+            mj_lambda2.angular += self.ii2_sqrt.transform_vector(ang_impulse2);
+        }
+    }
+
     fn solve_motors(&mut self, mj_lambda1: &mut DeltaVel<Real>, mj_lambda2: &mut DeltaVel<Real>) {
         if self.motor_inv_lhs != 0.0 {
             let ang_vel1 = self.ii1_sqrt.transform_vector(mj_lambda1.angular);
@@ -294,6 +382,7 @@ impl RevoluteVelocityConstraint {
         let mut mj_lambda1 = mj_lambdas[self.mj_lambda1 as usize];
         let mut mj_lambda2 = mj_lambdas[self.mj_lambda2 as usize];
 
+        self.solve_limits(&mut mj_lambda1, &mut mj_lambda2);
         self.solve_dofs(&mut mj_lambda1, &mut mj_lambda2);
         self.solve_motors(&mut mj_lambda1, &mut mj_lambda2);
 
@@ -310,6 +399,7 @@ impl RevoluteVelocityConstraint {
             revolute.prev_axis1 = self.motor_axis1;
             revolute.motor_last_angle = self.motor_angle;
             revolute.motor_impulse = self.motor_impulse;
+            revolute.limits_impulse = self.limits_impulse;
         }
     }
 }
@@ -333,6 +423,12 @@ pub(crate) struct RevoluteVelocityGroundConstraint {
     motor_max_impulse: Real,
     motor_angle: Real, // Exists just for writing it into the joint.
 
+    limits_active: bool,
+    limits_impulse: Real,
+    limits_rhs: Real,
+    limits_inv_lhs: Real,
+    limits_impulse_limits: (Real, Real),
+
     basis2: Matrix3x2<Real>,
 
     im2: Real,
@@ -458,8 +554,11 @@ impl RevoluteVelocityGroundConstraint {
             joint.motor_damping,
         );
 
-        if stiffness != 0.0 {
+        if stiffness != 0.0 || joint.limits_enabled {
             motor_angle = joint.estimate_motor_angle(&poss1.position, &poss2.position);
+        }
+
+        if stiffness != 0.0 {
             motor_rhs += (motor_angle - joint.motor_target_pos) * stiffness;
         }
 
@@ -480,6 +579,43 @@ impl RevoluteVelocityGroundConstraint {
         let motor_impulse = na::clamp(joint.motor_impulse, -motor_max_impulse, motor_max_impulse)
             * params.warmstart_coeff;
 
+        /*
+         * Setup limit constraint.
+         */
+        let mut limits_active = false;
+        let mut limits_rhs = 0.0;
+        let mut limits_inv_lhs = 0.0;
+        let mut limits_impulse_limits = (0.0, 0.0);
+        let mut limits_impulse = 0.0;
+
+        if joint.limits_enabled {
+            // TODO: we should allow predictive constraint activation.
+            let (min_limit, max_limit) = (joint.limits[0], joint.limits[1]);
+            let min_enabled = motor_angle < min_limit;
+            let max_enabled = max_limit < motor_angle;
+
+            limits_impulse_limits.0 = if max_enabled { -Real::INFINITY } else { 0.0 };
+            limits_impulse_limits.1 = if min_enabled { Real::INFINITY } else { 0.0 };
+            limits_active = min_enabled || max_enabled;
+
+            if limits_active {
+                limits_rhs = (vels2.angvel.dot(&axis2) - vels1.angvel.dot(&axis1))
+                    * params.velocity_solve_fraction;
+
+                limits_rhs += ((motor_angle - max_limit).max(0.0)
+                    - (min_limit - motor_angle).max(0.0))
+                    * velocity_based_erp_inv_dt;
+
+                limits_inv_lhs = crate::utils::inv(axis2.dot(&ii2.transform_vector(axis2)));
+
+                limits_impulse = joint
+                    .limits_impulse
+                    .max(limits_impulse_limits.0)
+                    .min(limits_impulse_limits.1)
+                    * params.warmstart_coeff;
+            }
+        }
+
         let result = RevoluteVelocityGroundConstraint {
             joint_id,
             mj_lambda2: ids2.active_set_offset,
@@ -496,6 +632,11 @@ impl RevoluteVelocityGroundConstraint {
             motor_max_impulse,
             motor_rhs,
             motor_angle,
+            limits_impulse,
+            limits_impulse_limits,
+            limits_active,
+            limits_inv_lhs,
+            limits_rhs,
         };
 
         AnyJointVelocityConstraint::RevoluteGroundConstraint(result)
@@ -521,6 +662,12 @@ impl RevoluteVelocityGroundConstraint {
                 .transform_vector(self.motor_axis2 * self.motor_impulse);
         }
 
+        // Warmstart limits.
+        if self.limits_active {
+            let limit_impulse2 = self.motor_axis2 * self.limits_impulse;
+            mj_lambda2.angular += self.ii2_sqrt.transform_vector(limit_impulse2);
+        }
+
         mj_lambdas[self.mj_lambda2 as usize] = mj_lambda2;
     }
 
@@ -542,6 +689,24 @@ impl RevoluteVelocityGroundConstraint {
             .transform_vector(ang_impulse + self.r2.gcross(lin_impulse));
     }
 
+    fn solve_limits(&mut self, mj_lambda2: &mut DeltaVel<Real>) {
+        if self.limits_active {
+            let limits_torquedir2 = self.motor_axis2;
+
+            let ang_vel2 = self.ii2_sqrt.transform_vector(mj_lambda2.angular);
+
+            let ang_dvel = limits_torquedir2.dot(&ang_vel2) + self.limits_rhs;
+            let new_impulse = (self.limits_impulse - ang_dvel * self.limits_inv_lhs)
+                .max(self.limits_impulse_limits.0)
+                .min(self.limits_impulse_limits.1);
+            let dimpulse = new_impulse - self.limits_impulse;
+            self.limits_impulse = new_impulse;
+
+            let ang_impulse2 = limits_torquedir2 * dimpulse;
+            mj_lambda2.angular += self.ii2_sqrt.transform_vector(ang_impulse2);
+        }
+    }
+
     fn solve_motors(&mut self, mj_lambda2: &mut DeltaVel<Real>) {
         if self.motor_inv_lhs != 0.0 {
             let ang_vel2 = self.ii2_sqrt.transform_vector(mj_lambda2.angular);
@@ -563,6 +728,7 @@ impl RevoluteVelocityGroundConstraint {
     pub fn solve(&mut self, mj_lambdas: &mut [DeltaVel<Real>]) {
         let mut mj_lambda2 = mj_lambdas[self.mj_lambda2 as usize];
 
+        self.solve_limits(&mut mj_lambda2);
         self.solve_dofs(&mut mj_lambda2);
         self.solve_motors(&mut mj_lambda2);
 
@@ -576,6 +742,7 @@ impl RevoluteVelocityGroundConstraint {
             revolute.impulse = self.impulse;
             revolute.motor_impulse = self.motor_impulse;
             revolute.motor_last_angle = self.motor_angle;
+            revolute.limits_impulse = self.limits_impulse;
         }
     }
 }