feat: implement new "small-steps" solver + joint improvements

src/dynamics/rigid_body.rs

@@ -7,7 +7,7 @@ use crate::geometry::{
     ColliderHandle, ColliderMassProps, ColliderParent, ColliderPosition, ColliderSet, ColliderShape,
 };
 use crate::math::{AngVector, Isometry, Point, Real, Rotation, Vector};
-use crate::utils::WCross;
+use crate::utils::SimdCross;
 use num::Zero;
 
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
@@ -36,6 +36,7 @@ pub struct RigidBody {
     /// The dominance group this rigid-body is part of.
     pub(crate) dominance: RigidBodyDominance,
     pub(crate) enabled: bool,
+    pub(crate) additional_solver_iterations: usize,
     /// User-defined data associated to this rigid-body.
     pub user_data: u128,
 }
@@ -64,6 +65,7 @@ impl RigidBody {
             dominance: RigidBodyDominance::default(),
             enabled: true,
             user_data: 0,
+            additional_solver_iterations: 0,
         }
     }
 
@@ -72,6 +74,27 @@ impl RigidBody {
         self.ids = Default::default();
     }
 
+    /// Set the additional number of solver iterations run for this rigid-body and
+    /// everything interacting with it.
+    ///
+    /// See [`Self::set_additional_solver_iterations`] for additional information.
+    pub fn additional_solver_iterations(&self) -> usize {
+        self.additional_solver_iterations
+    }
+
+    /// Set the additional number of solver iterations run for this rigid-body and
+    /// everything interacting with it.
+    ///
+    /// Increasing this number will help improve simulation accuracy on this rigid-body
+    /// and every rigid-body interacting directly or indirectly with it (through joints
+    /// or contacts). This implies a performance hit.
+    ///
+    /// The default value is 0, meaning [`IntegrationParameters::num_solver_iterations`] will
+    /// be used as number of solver iterations for this body.
+    pub fn set_additional_solver_iterations(&mut self, additional_iterations: usize) {
+        self.additional_solver_iterations = additional_iterations;
+    }
+
     /// The activation status of this rigid-body.
     pub fn activation(&self) -> &RigidBodyActivation {
         &self.activation
@@ -1030,6 +1053,11 @@ pub struct RigidBodyBuilder {
     pub enabled: bool,
     /// An arbitrary user-defined 128-bit integer associated to the rigid-bodies built by this builder.
     pub user_data: u128,
+    /// The additional number of solver iterations run for this rigid-body and
+    /// everything interacting with it.
+    ///
+    /// See [`RigidBody::set_additional_solver_iterations`] for additional information.
+    pub additional_solver_iterations: usize,
 }
 
 impl RigidBodyBuilder {
@@ -1051,6 +1079,7 @@ impl RigidBodyBuilder {
             dominance_group: 0,
             enabled: true,
             user_data: 0,
+            additional_solver_iterations: 0,
         }
     }
 
@@ -1090,6 +1119,15 @@ impl RigidBodyBuilder {
         Self::new(RigidBodyType::Dynamic)
     }
 
+    /// Sets the additional number of solver iterations run for this rigid-body and
+    /// everything interacting with it.
+    ///
+    /// See [`RigidBody::set_additional_solver_iterations`] for additional information.
+    pub fn additional_solver_iterations(mut self, additional_iterations: usize) -> Self {
+        self.additional_solver_iterations = additional_iterations;
+        self
+    }
+
     /// Sets the scale applied to the gravity force affecting the rigid-body to be created.
     pub fn gravity_scale(mut self, scale_factor: Real) -> Self {
         self.gravity_scale = scale_factor;
@@ -1311,6 +1349,7 @@ impl RigidBodyBuilder {
         rb.vels.angvel = self.angvel;
         rb.body_type = self.body_type;
         rb.user_data = self.user_data;
+        rb.additional_solver_iterations = self.additional_solver_iterations;
 
         if self.additional_mass_properties
             != RigidBodyAdditionalMassProps::MassProps(MassProperties::zero())