Fix some solver issues

- Fix the wrong codepath taken  by the solver for contacts involving a collider without parent.
- Properly adress the non-linear treatment of the friction direction
- Simplify the sleeping strategy
- Add an impulse resolution multiplier

src/dynamics/solver/generic_velocity_ground_constraint.rs

@@ -0,0 +1,242 @@
+use crate::data::{BundleSet, ComponentSet};
+use crate::dynamics::solver::VelocityGroundConstraint;
+use crate::dynamics::{
+    IntegrationParameters, MultibodyJointSet, RigidBodyIds, RigidBodyMassProps, RigidBodyType,
+    RigidBodyVelocity,
+};
+use crate::geometry::{ContactManifold, ContactManifoldIndex};
+use crate::math::{Point, Real, DIM, MAX_MANIFOLD_POINTS};
+use crate::utils::WCross;
+
+use super::{VelocityGroundConstraintElement, VelocityGroundConstraintNormalPart};
+use crate::dynamics::solver::AnyGenericVelocityConstraint;
+#[cfg(feature = "dim2")]
+use crate::utils::WBasis;
+use na::DVector;
+
+#[derive(Copy, Clone, Debug)]
+pub(crate) struct GenericVelocityGroundConstraint {
+    // We just build the generic constraint on top of the velocity constraint,
+    // adding some information we can use in the generic case.
+    pub velocity_constraint: VelocityGroundConstraint,
+    pub j_id: usize,
+    pub ndofs2: usize,
+}
+
+impl GenericVelocityGroundConstraint {
+    pub fn generate<Bodies>(
+        params: &IntegrationParameters,
+        manifold_id: ContactManifoldIndex,
+        manifold: &ContactManifold,
+        bodies: &Bodies,
+        multibodies: &MultibodyJointSet,
+        out_constraints: &mut Vec<AnyGenericVelocityConstraint>,
+        jacobians: &mut DVector<Real>,
+        jacobian_id: &mut usize,
+        push: bool,
+    ) where
+        Bodies: ComponentSet<RigidBodyIds>
+            + ComponentSet<RigidBodyVelocity>
+            + ComponentSet<RigidBodyMassProps>
+            + ComponentSet<RigidBodyType>,
+    {
+        let inv_dt = params.inv_dt();
+        let erp_inv_dt = params.erp_inv_dt();
+
+        let mut handle1 = manifold.data.rigid_body1;
+        let mut handle2 = manifold.data.rigid_body2;
+        let flipped = manifold.data.relative_dominance < 0;
+
+        let (force_dir1, flipped_multiplier) = if flipped {
+            std::mem::swap(&mut handle1, &mut handle2);
+            (manifold.data.normal, -1.0)
+        } else {
+            (-manifold.data.normal, 1.0)
+        };
+
+        let (rb_vels1, world_com1) = if let Some(handle1) = handle1 {
+            let (vels1, mprops1): (&RigidBodyVelocity, &RigidBodyMassProps) =
+                bodies.index_bundle(handle1.0);
+            (*vels1, mprops1.world_com)
+        } else {
+            (RigidBodyVelocity::zero(), Point::origin())
+        };
+
+        let (rb_vels2, rb_mprops2): (&RigidBodyVelocity, &RigidBodyMassProps) =
+            bodies.index_bundle(handle2.unwrap().0);
+
+        let (mb2, link_id2) = handle2
+            .and_then(|h| multibodies.rigid_body_link(h))
+            .map(|m| (&multibodies[m.multibody], m.id))
+            .unwrap();
+        let mj_lambda2 = mb2.solver_id;
+
+        #[cfg(feature = "dim2")]
+        let tangents1 = force_dir1.orthonormal_basis();
+        #[cfg(feature = "dim3")]
+        let tangents1 = super::compute_tangent_contact_directions(
+            &force_dir1,
+            &rb_vels1.linvel,
+            &rb_vels2.linvel,
+        );
+
+        let multibodies_ndof = mb2.ndofs();
+        // For each solver contact we generate DIM constraints, and each constraints appends
+        // the multibodies jacobian and weighted jacobians
+        let required_jacobian_len =
+            *jacobian_id + manifold.data.solver_contacts.len() * multibodies_ndof * 2 * DIM;
+
+        if jacobians.nrows() < required_jacobian_len {
+            jacobians.resize_vertically_mut(required_jacobian_len, 0.0);
+        }
+
+        for (_l, manifold_points) in manifold
+            .data
+            .solver_contacts
+            .chunks(MAX_MANIFOLD_POINTS)
+            .enumerate()
+        {
+            let chunk_j_id = *jacobian_id;
+            let mut constraint = VelocityGroundConstraint {
+                dir1: force_dir1,
+                #[cfg(feature = "dim3")]
+                tangent1: tangents1[0],
+                elements: [VelocityGroundConstraintElement::zero(); MAX_MANIFOLD_POINTS],
+                im2: rb_mprops2.effective_inv_mass,
+                limit: 0.0,
+                mj_lambda2,
+                manifold_id,
+                manifold_contact_id: [0; MAX_MANIFOLD_POINTS],
+                num_contacts: manifold_points.len() as u8,
+            };
+
+            for k in 0..manifold_points.len() {
+                let manifold_point = &manifold_points[k];
+                let dp1 = manifold_point.point - world_com1;
+                let dp2 = manifold_point.point - rb_mprops2.world_com;
+
+                let vel1 = rb_vels1.linvel + rb_vels1.angvel.gcross(dp1);
+                let vel2 = rb_vels2.linvel + rb_vels2.angvel.gcross(dp2);
+
+                constraint.limit = manifold_point.friction;
+                constraint.manifold_contact_id[k] = manifold_point.contact_id;
+
+                // Normal part.
+                {
+                    let torque_dir2 = dp2.gcross(-force_dir1);
+                    let inv_r2 = mb2
+                        .fill_jacobians(
+                            link_id2,
+                            -force_dir1,
+                            #[cfg(feature = "dim2")]
+                            na::vector!(torque_dir2),
+                            #[cfg(feature = "dim3")]
+                            torque_dir2,
+                            jacobian_id,
+                            jacobians,
+                        )
+                        .0;
+
+                    let r = crate::utils::inv(inv_r2);
+
+                    let is_bouncy = manifold_point.is_bouncy() as u32 as Real;
+                    let is_resting = 1.0 - is_bouncy;
+
+                    let mut rhs_wo_bias = (1.0 + is_bouncy * manifold_point.restitution)
+                        * (vel1 - vel2).dot(&force_dir1);
+                    rhs_wo_bias += manifold_point.dist.max(0.0) * inv_dt;
+                    rhs_wo_bias *= is_bouncy + is_resting * params.velocity_solve_fraction;
+                    let rhs_bias =
+                        /* is_resting * */ erp_inv_dt * manifold_point.dist.min(0.0);
+
+                    constraint.elements[k].normal_part = VelocityGroundConstraintNormalPart {
+                        gcross2: na::zero(), // Unused for generic constraints.
+                        rhs: rhs_wo_bias + rhs_bias,
+                        rhs_wo_bias,
+                        impulse: na::zero(),
+                        r,
+                    };
+                }
+
+                // Tangent parts.
+                {
+                    constraint.elements[k].tangent_part.impulse = na::zero();
+
+                    for j in 0..DIM - 1 {
+                        let torque_dir2 = dp2.gcross(-tangents1[j]);
+                        let inv_r2 = mb2
+                            .fill_jacobians(
+                                link_id2,
+                                -tangents1[j],
+                                #[cfg(feature = "dim2")]
+                                na::vector![torque_dir2],
+                                #[cfg(feature = "dim3")]
+                                torque_dir2,
+                                jacobian_id,
+                                jacobians,
+                            )
+                            .0;
+
+                        let r = crate::utils::inv(inv_r2);
+
+                        let rhs = (vel1 - vel2
+                            + flipped_multiplier * manifold_point.tangent_velocity)
+                            .dot(&tangents1[j]);
+
+                        constraint.elements[k].tangent_part.rhs[j] = rhs;
+
+                        // FIXME: in 3D, we should take into account gcross[0].dot(gcross[1])
+                        // in lhs. See the corresponding code on the `velocity_constraint.rs`
+                        // file.
+                        constraint.elements[k].tangent_part.r[j] = r;
+                    }
+                }
+            }
+
+            let constraint = GenericVelocityGroundConstraint {
+                velocity_constraint: constraint,
+                j_id: chunk_j_id,
+                ndofs2: mb2.ndofs(),
+            };
+
+            if push {
+                out_constraints.push(AnyGenericVelocityConstraint::NongroupedGround(constraint));
+            } else {
+                out_constraints[manifold.data.constraint_index + _l] =
+                    AnyGenericVelocityConstraint::NongroupedGround(constraint);
+            }
+        }
+    }
+
+    pub fn solve(
+        &mut self,
+        jacobians: &DVector<Real>,
+        generic_mj_lambdas: &mut DVector<Real>,
+        solve_restitution: bool,
+        solve_friction: bool,
+    ) {
+        let mj_lambda2 = self.velocity_constraint.mj_lambda2 as usize;
+
+        let elements = &mut self.velocity_constraint.elements
+            [..self.velocity_constraint.num_contacts as usize];
+        VelocityGroundConstraintElement::generic_solve_group(
+            elements,
+            jacobians,
+            self.velocity_constraint.limit,
+            self.ndofs2,
+            self.j_id,
+            mj_lambda2,
+            generic_mj_lambdas,
+            solve_restitution,
+            solve_friction,
+        );
+    }
+
+    pub fn writeback_impulses(&self, manifolds_all: &mut [&mut ContactManifold]) {
+        self.velocity_constraint.writeback_impulses(manifolds_all);
+    }
+
+    pub fn remove_bias_from_rhs(&mut self) {
+        self.velocity_constraint.remove_bias_from_rhs();
+    }
+}