Add params.velocity_based_erp_inv_dt() helper

src/dynamics/integration_parameters.rs

@@ -181,6 +181,12 @@ impl IntegrationParameters {
             self.dt = 1.0 / inv_dt
         }
     }
+
+    /// Convenience: `velocity_based_erp / dt`
+    #[inline]
+    pub(crate) fn velocity_based_erp_inv_dt(&self) -> Real {
+        self.velocity_based_erp * self.inv_dt()
+    }
 }
 
 impl Default for IntegrationParameters {

src/dynamics/solver/joint_constraint/ball_velocity_constraint.rs

@@ -50,9 +50,8 @@ impl BallVelocityConstraint {
         let im1 = rb1.effective_inv_mass;
         let im2 = rb2.effective_inv_mass;
 
-        let mut rhs = params.velocity_solve_fraction * (vel2 - vel1);
+        let rhs = (vel2 - vel1) * params.velocity_solve_fraction
-
+            + (anchor_world2 - anchor_world1) * params.velocity_based_erp_inv_dt();
-        rhs += params.velocity_based_erp * params.inv_dt() * (anchor_world2 - anchor_world1);
 
         let lhs;
         let cmat1 = anchor1.gcross_matrix();
@@ -293,9 +292,9 @@ impl BallVelocityGroundConstraint {
         let im2 = rb2.effective_inv_mass;
         let vel1 = rb1.linvel + rb1.angvel.gcross(anchor1);
         let vel2 = rb2.linvel + rb2.angvel.gcross(anchor2);
-        let mut rhs = params.velocity_solve_fraction * (vel2 - vel1);
 
-        rhs += params.velocity_based_erp * params.inv_dt() * (anchor_world2 - anchor_world1);
+        let rhs = (vel2 - vel1) * params.velocity_solve_fraction
+            + (anchor_world2 - anchor_world1) * params.velocity_based_erp_inv_dt();
 
         let cmat2 = anchor2.gcross_matrix();
 

src/dynamics/solver/joint_constraint/fixed_velocity_constraint.rs

@@ -112,26 +112,23 @@ impl FixedVelocityConstraint {
                 lin_dvel.x, lin_dvel.y, lin_dvel.z, ang_dvel.x, ang_dvel.y, ang_dvel.z,
             );
 
-        if params.velocity_based_erp != 0.0 {
+        let velocity_based_erp_inv_dt = params.velocity_based_erp_inv_dt();
+        if velocity_based_erp_inv_dt != 0.0 {
             let error = anchor2 * anchor1.inverse();
             let lin_err = error.translation.vector;
 
             #[cfg(feature = "dim2")]
             {
                 let ang_err = error.rotation.angle();
-                rhs += params.velocity_based_erp
+                rhs += Vector3::new(lin_err.x, lin_err.y, ang_err) * velocity_based_erp_inv_dt;
-                    * params.inv_dt()
-                    * Vector3::new(lin_err.x, lin_err.y, ang_err);
             }
 
             #[cfg(feature = "dim3")]
             {
                 let ang_err = error.rotation.scaled_axis();
-                rhs += params.velocity_based_erp
+                rhs += Vector6::new(
-                    * params.inv_dt()
-                    * Vector6::new(
                     lin_err.x, lin_err.y, lin_err.z, ang_err.x, ang_err.y, ang_err.z,
-                    );
+                ) * velocity_based_erp_inv_dt;
             }
         }
 
@@ -326,16 +323,14 @@ impl FixedVelocityGroundConstraint {
                 lin_dvel.x, lin_dvel.y, lin_dvel.z, ang_dvel.x, ang_dvel.y, ang_dvel.z,
             );
 
-        if params.velocity_based_erp != 0.0 {
+        let velocity_based_erp_inv_dt = params.velocity_based_erp_inv_dt();
+        if velocity_based_erp_inv_dt != 0.0 {
             // let error = anchor2 * anchor1.inverse();
             // let lin_err = error.translation.vector;
             // let ang_err = error.rotation;
 
             // Doesn't quite do what it should
-            // let target_pos = anchor1.lerp_slerp(
+            // let target_pos = anchor1.lerp_slerp(&anchor2, velocity_based_erp_inv_dt);
-            //     &anchor2,
-            //     params.velocity_based_erp * params.inv_dt(),
-            // );
             // let error = target_pos * anchor1.inverse();
             // let lin_err = error.translation.vector;
 
@@ -345,19 +340,15 @@ impl FixedVelocityGroundConstraint {
             #[cfg(feature = "dim2")]
             {
                 let ang_err = ang_err.angle();
-                rhs += params.velocity_based_erp
+                rhs += Vector3::new(lin_err.x, lin_err.y, ang_err) * velocity_based_erp_inv_dt;
-                    * params.inv_dt()
-                    * Vector3::new(lin_err.x, lin_err.y, ang_err);
             }
 
             #[cfg(feature = "dim3")]
             {
                 let ang_err = ang_err.scaled_axis();
-                rhs += params.velocity_based_erp
+                rhs += Vector6::new(
-                    * params.inv_dt()
-                    * Vector6::new(
                     lin_err.x, lin_err.y, lin_err.z, ang_err.x, ang_err.y, ang_err.z,
-                    );
+                ) * velocity_based_erp_inv_dt;
             }
         }
 

src/dynamics/solver/velocity_constraint.rs

@@ -147,6 +147,8 @@ impl VelocityConstraint {
         assert_eq!(manifold.data.relative_dominance, 0);
 
         let inv_dt = params.inv_dt();
+        let velocity_based_erp_inv_dt = params.velocity_based_erp_inv_dt();
+
         let rb1 = &bodies[manifold.data.body_pair.body1];
         let rb2 = &bodies[manifold.data.body_pair.body2];
         let mj_lambda1 = rb1.active_set_offset;
@@ -250,10 +252,7 @@ impl VelocityConstraint {
                         * (vel1 - vel2).dot(&force_dir1);
                     rhs += manifold_point.dist.max(0.0) * inv_dt;
                     rhs *= params.velocity_solve_fraction;
-                    rhs += is_resting
+                    rhs += is_resting * velocity_based_erp_inv_dt * manifold_point.dist.min(0.0);
-                        * params.velocity_based_erp
-                        * inv_dt
-                        * manifold_point.dist.min(0.0);
 
                     constraint.elements[k].normal_part = VelocityConstraintElementPart {
                         gcross1,

src/dynamics/solver/velocity_ground_constraint.rs

@@ -64,6 +64,8 @@ impl VelocityGroundConstraint {
         push: bool,
     ) {
         let inv_dt = params.inv_dt();
+        let velocity_based_erp_inv_dt = params.velocity_based_erp_inv_dt();
+
         let mut rb1 = &bodies[manifold.data.body_pair.body1];
         let mut rb2 = &bodies[manifold.data.body_pair.body2];
         let flipped = manifold.data.relative_dominance < 0;
@@ -162,10 +164,7 @@ impl VelocityGroundConstraint {
                         * (vel1 - vel2).dot(&force_dir1);
                     rhs += manifold_point.dist.max(0.0) * inv_dt;
                     rhs *= params.velocity_solve_fraction;
-                    rhs += is_resting
+                    rhs += is_resting * velocity_based_erp_inv_dt * manifold_point.dist.min(0.0);
-                        * params.velocity_based_erp
-                        * inv_dt
-                        * manifold_point.dist.min(0.0);
 
                     constraint.elements[k].normal_part = VelocityGroundConstraintElementPart {
                         gcross2,