Merge pull request #146 from dimforge/implicit_friction_cone

Projection friction impulses on an implicit cone instead of a pyramid approximation.

1 files changed, 61 insertions, 109 deletions

diff --git a/src/dynamics/solver/velocity_ground_constraint_wide.rs b/src/dynamics/solver/velocity_ground_constraint_wide.rs
index 8e9f3a1..ba1c46a 100644
--- a/src/dynamics/solver/velocity_ground_constraint_wide.rs
+++ b/src/dynamics/solver/velocity_ground_constraint_wide.rs
@@ -1,51 +1,26 @@
-use super::{AnyVelocityConstraint, DeltaVel};
+use super::{
+    AnyVelocityConstraint, DeltaVel, VelocityGroundConstraintElement,
+    VelocityGroundConstraintNormalPart,
+};
 use crate::dynamics::{IntegrationParameters, RigidBodySet};
 use crate::geometry::{ContactManifold, ContactManifoldIndex};
 use crate::math::{
     AngVector, AngularInertia, Point, Real, SimdReal, Vector, DIM, MAX_MANIFOLD_POINTS, SIMD_WIDTH,
 };
-use crate::utils::{WAngularInertia, WBasis, WCross, WDot};
+#[cfg(feature = "dim2")]
+use crate::utils::WBasis;
+use crate::utils::{WAngularInertia, WCross, WDot};
 use num::Zero;
 use simba::simd::{SimdPartialOrd, SimdValue};
 
 #[derive(Copy, Clone, Debug)]
-pub(crate) struct WVelocityGroundConstraintElementPart {
-    pub gcross2: AngVector<SimdReal>,
-    pub rhs: SimdReal,
-    pub impulse: SimdReal,
-    pub r: SimdReal,
-}
-
-impl WVelocityGroundConstraintElementPart {
-    pub fn zero() -> Self {
-        Self {
-            gcross2: AngVector::zero(),
-            rhs: SimdReal::zero(),
-            impulse: SimdReal::zero(),
-            r: SimdReal::zero(),
-        }
-    }
-}
-
-#[derive(Copy, Clone, Debug)]
-pub(crate) struct WVelocityGroundConstraintElement {
-    pub normal_part: WVelocityGroundConstraintElementPart,
-    pub tangent_parts: [WVelocityGroundConstraintElementPart; DIM - 1],
-}
-
-impl WVelocityGroundConstraintElement {
-    pub fn zero() -> Self {
-        Self {
-            normal_part: WVelocityGroundConstraintElementPart::zero(),
-            tangent_parts: [WVelocityGroundConstraintElementPart::zero(); DIM - 1],
-        }
-    }
-}
-
-#[derive(Copy, Clone, Debug)]
 pub(crate) struct WVelocityGroundConstraint {
     pub dir1: Vector<SimdReal>, // Non-penetration force direction for the first body.
-    pub elements: [WVelocityGroundConstraintElement; MAX_MANIFOLD_POINTS],
+    #[cfg(feature = "dim3")]
+    pub tangent1: Vector<SimdReal>, // One of the friction force directions.
+    #[cfg(feature = "dim3")]
+    pub tangent_rot1: na::UnitComplex<SimdReal>, // Orientation of the tangent basis wrt. the reference basis.
+    pub elements: [VelocityGroundConstraintElement<SimdReal>; MAX_MANIFOLD_POINTS],
     pub num_contacts: u8,
     pub im2: SimdReal,
     pub limit: SimdReal,
@@ -104,13 +79,23 @@ impl WVelocityGroundConstraint {
         let warmstart_coeff = warmstart_multiplier * SimdReal::splat(params.warmstart_coeff);
         let num_active_contacts = manifolds[0].data.num_active_contacts();
 
+        #[cfg(feature = "dim2")]
+        let tangents1 = force_dir1.orthonormal_basis();
+        #[cfg(feature = "dim3")]
+        let (tangents1, tangent_rot1) =
+            super::compute_tangent_contact_directions(&force_dir1, &linvel1, &linvel2);
+
         for l in (0..num_active_contacts).step_by(MAX_MANIFOLD_POINTS) {
             let manifold_points = array![|ii| &manifolds[ii].data.solver_contacts[l..]; SIMD_WIDTH];
             let num_points = manifold_points[0].len().min(MAX_MANIFOLD_POINTS);
 
             let mut constraint = WVelocityGroundConstraint {
                 dir1: force_dir1,
-                elements: [WVelocityGroundConstraintElement::zero(); MAX_MANIFOLD_POINTS],
+                #[cfg(feature = "dim3")]
+                tangent1: tangents1[0],
+                #[cfg(feature = "dim3")]
+                tangent_rot1,
+                elements: [VelocityGroundConstraintElement::zero(); MAX_MANIFOLD_POINTS],
                 im2,
                 limit: SimdReal::splat(0.0),
                 mj_lambda2,
@@ -158,7 +143,7 @@ impl WVelocityGroundConstraint {
                     rhs +=
                         dist.simd_min(SimdReal::zero()) * (velocity_based_erp_inv_dt * is_resting);
 
-                    constraint.elements[k].normal_part = WVelocityGroundConstraintElementPart {
+                    constraint.elements[k].normal_part = VelocityGroundConstraintNormalPart {
                         gcross2,
                         rhs,
                         impulse: impulse * warmstart_coeff,
@@ -167,29 +152,25 @@ impl WVelocityGroundConstraint {
                 }
 
                 // tangent parts.
-                let tangents1 = force_dir1.orthonormal_basis();
-
-                for j in 0..DIM - 1 {
-                    #[cfg(feature = "dim2")]
-                    let impulse = SimdReal::from(
+                #[cfg(feature = "dim2")]
+                let impulse = [SimdReal::from(
+                    array![|ii| manifold_points[ii][k].data.tangent_impulse; SIMD_WIDTH],
+                )];
+                #[cfg(feature = "dim3")]
+                let impulse = tangent_rot1
+                    * na::Vector2::from(
                         array![|ii| manifold_points[ii][k].data.tangent_impulse; SIMD_WIDTH],
                     );
-                    #[cfg(feature = "dim3")]
-                    let impulse = SimdReal::from(
-                        array![|ii| manifold_points[ii][k].data.tangent_impulse[j]; SIMD_WIDTH],
-                    );
+                constraint.elements[k].tangent_part.impulse = impulse;
 
+                for j in 0..DIM - 1 {
                     let gcross2 = ii2.transform_vector(dp2.gcross(-tangents1[j]));
                     let r = SimdReal::splat(1.0) / (im2 + gcross2.gdot(gcross2));
                     let rhs = (vel1 - vel2 + tangent_velocity * flipped_sign).dot(&tangents1[j]);
 
-                    constraint.elements[k].tangent_parts[j] =
-                        WVelocityGroundConstraintElementPart {
-                            gcross2,
-                            rhs,
-                            impulse: impulse * warmstart_coeff,
-                            r,
-                        };
+                    constraint.elements[k].tangent_part.gcross2[j] = gcross2;
+                    constraint.elements[k].tangent_part.r[j] = r;
+                    constraint.elements[k].tangent_part.rhs[j] = rhs;
                 }
             }
 
@@ -212,19 +193,14 @@ impl WVelocityGroundConstraint {
             ),
         };
 
-        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_parts[j];
-                mj_lambda2.linear += tangents1[j] * (-self.im2 * elt.impulse);
-                mj_lambda2.angular += elt.gcross2 * elt.impulse;
-            }
-        }
+        VelocityGroundConstraintElement::warmstart_group(
+            &self.elements[..self.num_contacts as usize],
+            &self.dir1,
+            #[cfg(feature = "dim3")]
+            &self.tangent1,
+            self.im2,
+            &mut mj_lambda2,
+        );
 
         for ii in 0..SIMD_WIDTH {
             mj_lambdas[self.mj_lambda2[ii] as usize].linear = mj_lambda2.linear.extract(ii);
@@ -235,46 +211,22 @@ impl WVelocityGroundConstraint {
     pub fn solve(&mut self, mj_lambdas: &mut [DeltaVel<Real>]) {
         let mut mj_lambda2 = DeltaVel {
             linear: Vector::from(
-                array![ |ii| mj_lambdas[ self.mj_lambda2[ii] as usize].linear; SIMD_WIDTH],
+                array![|ii| mj_lambdas[ self.mj_lambda2[ii] as usize].linear; SIMD_WIDTH],
             ),
             angular: AngVector::from(
-                array![ |ii| mj_lambdas[ self.mj_lambda2[ii] as usize].angular; SIMD_WIDTH],
+                array![|ii| mj_lambdas[ self.mj_lambda2[ii] as usize].angular; SIMD_WIDTH],
             ),
         };
 
-        // Solve friction first.
-        let tangents1 = self.dir1.orthonormal_basis();
-
-        for i in 0..self.num_contacts as usize {
-            let normal_elt = &self.elements[i].normal_part;
-
-            for j in 0..DIM - 1 {
-                let elt = &mut self.elements[i].tangent_parts[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 non-penetration after friction.
-        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).simd_max(SimdReal::zero());
-            let dlambda = new_impulse - elt.impulse;
-            elt.impulse = new_impulse;
-
-            mj_lambda2.linear += self.dir1 * (-self.im2 * dlambda);
-            mj_lambda2.angular += elt.gcross2 * dlambda;
-        }
+        VelocityGroundConstraintElement::solve_group(
+            &mut self.elements[..self.num_contacts as usize],
+            &self.dir1,
+            #[cfg(feature = "dim3")]
+            &self.tangent1,
+            self.im2,
+            self.limit,
+            &mut mj_lambda2,
+        );
 
         for ii in 0..SIMD_WIDTH {
             mj_lambdas[self.mj_lambda2[ii] as usize].linear = mj_lambda2.linear.extract(ii);
@@ -286,11 +238,12 @@ impl WVelocityGroundConstraint {
     pub fn writeback_impulses(&self, manifolds_all: &mut [&mut ContactManifold]) {
         for k in 0..self.num_contacts as usize {
             let impulses: [_; SIMD_WIDTH] = self.elements[k].normal_part.impulse.into();
-            let tangent_impulses: [_; SIMD_WIDTH] =
-                self.elements[k].tangent_parts[0].impulse.into();
+            #[cfg(feature = "dim2")]
+            let tangent_impulses: [_; SIMD_WIDTH] = self.elements[k].tangent_part.impulse[0].into();
             #[cfg(feature = "dim3")]
-            let bitangent_impulses: [_; SIMD_WIDTH] =
-                self.elements[k].tangent_parts[1].impulse.into();
+            let tangent_impulses = self
+                .tangent_rot1
+                .inverse_transform_vector(&self.elements[k].tangent_part.impulse);
 
             for ii in 0..SIMD_WIDTH {
                 let manifold = &mut manifolds_all[self.manifold_id[ii]];
@@ -304,8 +257,7 @@ impl WVelocityGroundConstraint {
                 }
                 #[cfg(feature = "dim3")]
                 {
-                    active_contact.data.tangent_impulse =
-                        [tangent_impulses[ii], bitangent_impulses[ii]];
+                    active_contact.data.tangent_impulse = tangent_impulses.extract(ii);
                 }
             }
         }