First public release of Rapier.

src/dynamics/solver/velocity_ground_constraint.rs

@@ -0,0 +1,300 @@
+use super::{AnyVelocityConstraint, DeltaVel};
+use crate::math::{AngVector, Vector, DIM, MAX_MANIFOLD_POINTS};
+use crate::utils::{WAngularInertia, WBasis, WCross, WDot};
+
+use crate::dynamics::{IntegrationParameters, RigidBodySet};
+use crate::geometry::{ContactManifold, ContactManifoldIndex};
+use simba::simd::SimdPartialOrd;
+
+#[derive(Copy, Clone, Debug)]
+pub(crate) struct VelocityGroundConstraintElementPart {
+    pub gcross2: AngVector<f32>,
+    pub rhs: f32,
+    pub impulse: f32,
+    pub r: f32,
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+impl VelocityGroundConstraintElementPart {
+    fn zero() -> Self {
+        Self {
+            gcross2: na::zero(),
+            rhs: 0.0,
+            impulse: 0.0,
+            r: 0.0,
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+pub(crate) struct VelocityGroundConstraintElement {
+    pub normal_part: VelocityGroundConstraintElementPart,
+    pub tangent_part: [VelocityGroundConstraintElementPart; DIM - 1],
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+impl VelocityGroundConstraintElement {
+    pub fn zero() -> Self {
+        Self {
+            normal_part: VelocityGroundConstraintElementPart::zero(),
+            tangent_part: [VelocityGroundConstraintElementPart::zero(); DIM - 1],
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+pub(crate) struct VelocityGroundConstraint {
+    pub dir1: Vector<f32>, // Non-penetration force direction for the first body.
+    pub im2: f32,
+    pub limit: f32,
+    pub mj_lambda2: usize,
+    pub manifold_id: ContactManifoldIndex,
+    pub manifold_contact_id: usize,
+    pub num_contacts: u8,
+    pub elements: [VelocityGroundConstraintElement; MAX_MANIFOLD_POINTS],
+}
+
+impl VelocityGroundConstraint {
+    pub fn generate(
+        params: &IntegrationParameters,
+        manifold_id: ContactManifoldIndex,
+        manifold: &ContactManifold,
+        bodies: &RigidBodySet,
+        out_constraints: &mut Vec<AnyVelocityConstraint>,
+        push: bool,
+    ) {
+        let mut rb1 = &bodies[manifold.body_pair.body1];
+        let mut rb2 = &bodies[manifold.body_pair.body2];
+        let flipped = !rb2.is_dynamic();
+
+        if flipped {
+            std::mem::swap(&mut rb1, &mut rb2);
+        }
+
+        let mj_lambda2 = rb2.active_set_offset;
+        let force_dir1 = if flipped {
+            // NOTE: we already swapped rb1 and rb2
+            // so we multiply by rb1.position.
+            rb1.position * (-manifold.local_n2)
+        } else {
+            rb1.position * (-manifold.local_n1)
+        };
+
+        let warmstart_coeff = manifold.warmstart_multiplier * params.warmstart_coeff;
+
+        for (l, manifold_points) in manifold
+            .active_contacts()
+            .chunks(MAX_MANIFOLD_POINTS)
+            .enumerate()
+        {
+            #[cfg(not(target_arch = "wasm32"))]
+            let mut constraint = VelocityGroundConstraint {
+                dir1: force_dir1,
+                elements: [VelocityGroundConstraintElement::zero(); MAX_MANIFOLD_POINTS],
+                im2: rb2.mass_properties.inv_mass,
+                limit: manifold.friction,
+                mj_lambda2,
+                manifold_id,
+                manifold_contact_id: l * MAX_MANIFOLD_POINTS,
+                num_contacts: manifold_points.len() as u8,
+            };
+
+            // TODO: this is a WIP optimization for WASM platforms.
+            // For some reasons, the compiler does not inline the `Vec::push` method
+            // in this method. This generates two memset and one memcpy which are both very
+            // expansive.
+            // This would likely be solved by some kind of "placement-push" (like emplace in C++).
+            // In the mean time, a workaround is to "push" using `.resize_with` and `::uninit()` to
+            // avoid spurious copying.
+            // Is this optimization beneficial when targeting non-WASM platforms?
+            //
+            // NOTE: joints have the same problem, but it is not easy to refactor the code that way
+            // for the moment.
+            #[cfg(target_arch = "wasm32")]
+            let constraint = if push {
+                let new_len = out_constraints.len() + 1;
+                unsafe {
+                    out_constraints.resize_with(new_len, || {
+                        AnyVelocityConstraint::NongroupedGround(
+                            std::mem::MaybeUninit::uninit().assume_init(),
+                        )
+                    });
+                }
+                out_constraints
+                    .last_mut()
+                    .unwrap()
+                    .as_nongrouped_ground_mut()
+                    .unwrap()
+            } else {
+                unreachable!(); // We don't have parallelization on WASM yet, so this is unreachable.
+            };
+
+            #[cfg(target_arch = "wasm32")]
+            {
+                constraint.dir1 = force_dir1;
+                constraint.im2 = rb2.mass_properties.inv_mass;
+                constraint.limit = manifold.friction;
+                constraint.mj_lambda2 = mj_lambda2;
+                constraint.manifold_id = manifold_id;
+                constraint.manifold_contact_id = l * MAX_MANIFOLD_POINTS;
+                constraint.num_contacts = manifold_points.len() as u8;
+            }
+
+            for k in 0..manifold_points.len() {
+                let manifold_point = &manifold_points[k];
+                let (p1, p2) = if flipped {
+                    // NOTE: we already swapped rb1 and rb2
+                    // so we multiply by rb2.position.
+                    (
+                        rb1.position * manifold_point.local_p2,
+                        rb2.position * manifold_point.local_p1,
+                    )
+                } else {
+                    (
+                        rb1.position * manifold_point.local_p1,
+                        rb2.position * manifold_point.local_p2,
+                    )
+                };
+                let dp2 = p2.coords - rb2.position.translation.vector;
+                let dp1 = p1.coords - rb1.position.translation.vector;
+                let vel1 = rb1.linvel + rb1.angvel.gcross(dp1);
+                let vel2 = rb2.linvel + rb2.angvel.gcross(dp2);
+
+                // Normal part.
+                {
+                    let gcross2 = rb2
+                        .world_inv_inertia_sqrt
+                        .transform_vector(dp2.gcross(-force_dir1));
+
+                    let r = 1.0 / (rb2.mass_properties.inv_mass + gcross2.gdot(gcross2));
+                    let rhs = -vel2.dot(&force_dir1)
+                        + vel1.dot(&force_dir1)
+                        + manifold_point.dist.max(0.0) * params.inv_dt();
+                    let impulse = manifold_points[k].impulse * warmstart_coeff;
+
+                    constraint.elements[k].normal_part = VelocityGroundConstraintElementPart {
+                        gcross2,
+                        rhs,
+                        impulse,
+                        r,
+                    };
+                }
+
+                // Tangent parts.
+                {
+                    let tangents1 = force_dir1.orthonormal_basis();
+
+                    for j in 0..DIM - 1 {
+                        let gcross2 = rb2
+                            .world_inv_inertia_sqrt
+                            .transform_vector(dp2.gcross(-tangents1[j]));
+                        let r = 1.0 / (rb2.mass_properties.inv_mass + gcross2.gdot(gcross2));
+                        let rhs = -vel2.dot(&tangents1[j]) + vel1.dot(&tangents1[j]);
+                        #[cfg(feature = "dim2")]
+                        let impulse = manifold_points[k].tangent_impulse * warmstart_coeff;
+                        #[cfg(feature = "dim3")]
+                        let impulse = manifold_points[k].tangent_impulse[j] * warmstart_coeff;
+
+                        constraint.elements[k].tangent_part[j] =
+                            VelocityGroundConstraintElementPart {
+                                gcross2,
+                                rhs,
+                                impulse,
+                                r,
+                            };
+                    }
+                }
+            }
+
+            #[cfg(not(target_arch = "wasm32"))]
+            if push {
+                out_constraints.push(AnyVelocityConstraint::NongroupedGround(constraint));
+            } else {
+                out_constraints[manifold.constraint_index + l] =
+                    AnyVelocityConstraint::NongroupedGround(constraint);
+            }
+        }
+    }
+
+    pub fn warmstart(&self, mj_lambdas: &mut [DeltaVel<f32>]) {
+        let mut mj_lambda2 = DeltaVel::zero();
+        let tangents1 = self.dir1.orthonormal_basis();
+
+        for i in 0..self.num_contacts as usize {
+            let elt = &self.elements[i].normal_part;
+            mj_lambda2.linear += self.dir1 * (-self.im2 * elt.impulse);
+            mj_lambda2.angular += elt.gcross2 * elt.impulse;
+
+            for j in 0..DIM - 1 {
+                let elt = &self.elements[i].tangent_part[j];
+                mj_lambda2.linear += tangents1[j] * (-self.im2 * elt.impulse);
+                mj_lambda2.angular += elt.gcross2 * elt.impulse;
+            }
+        }
+
+        mj_lambdas[self.mj_lambda2 as usize].linear += mj_lambda2.linear;
+        mj_lambdas[self.mj_lambda2 as usize].angular += mj_lambda2.angular;
+    }
+
+    pub fn solve(&mut self, mj_lambdas: &mut [DeltaVel<f32>]) {
+        let mut mj_lambda2 = mj_lambdas[self.mj_lambda2 as usize];
+
+        // Solve friction.
+        let tangents1 = self.dir1.orthonormal_basis();
+
+        for i in 0..self.num_contacts as usize {
+            for j in 0..DIM - 1 {
+                let normal_elt = &self.elements[i].normal_part;
+                let elt = &mut self.elements[i].tangent_part[j];
+                let dimpulse = -tangents1[j].dot(&mj_lambda2.linear)
+                    + elt.gcross2.gdot(mj_lambda2.angular)
+                    + elt.rhs;
+                let limit = self.limit * normal_elt.impulse;
+                let new_impulse = (elt.impulse - elt.r * dimpulse).simd_clamp(-limit, limit);
+                let dlambda = new_impulse - elt.impulse;
+                elt.impulse = new_impulse;
+
+                mj_lambda2.linear += tangents1[j] * (-self.im2 * dlambda);
+                mj_lambda2.angular += elt.gcross2 * dlambda;
+            }
+        }
+
+        // Solve penetration.
+        for i in 0..self.num_contacts as usize {
+            let elt = &mut self.elements[i].normal_part;
+            let dimpulse =
+                -self.dir1.dot(&mj_lambda2.linear) + elt.gcross2.gdot(mj_lambda2.angular) + elt.rhs;
+            let new_impulse = (elt.impulse - elt.r * dimpulse).max(0.0);
+            let dlambda = new_impulse - elt.impulse;
+            elt.impulse = new_impulse;
+
+            mj_lambda2.linear += self.dir1 * (-self.im2 * dlambda);
+            mj_lambda2.angular += elt.gcross2 * dlambda;
+        }
+
+        mj_lambdas[self.mj_lambda2 as usize] = mj_lambda2;
+    }
+
+    // FIXME: duplicated code. This is exactly the same as in the non-ground velocity constraint.
+    pub fn writeback_impulses(&self, manifolds_all: &mut [&mut ContactManifold]) {
+        let manifold = &mut manifolds_all[self.manifold_id];
+        let k_base = self.manifold_contact_id;
+
+        for k in 0..self.num_contacts as usize {
+            let active_contacts = manifold.active_contacts_mut();
+            active_contacts[k_base + k].impulse = self.elements[k].normal_part.impulse;
+            #[cfg(feature = "dim2")]
+            {
+                active_contacts[k_base + k].tangent_impulse =
+                    self.elements[k].tangent_part[0].impulse;
+            }
+            #[cfg(feature = "dim3")]
+            {
+                active_contacts[k_base + k].tangent_impulse = [
+                    self.elements[k].tangent_part[0].impulse,
+                    self.elements[k].tangent_part[1].impulse,
+                ];
+            }
+        }
+    }
+}