Refactor the parallel solver code the same way we did with the non-parallel solver.

src/dynamics/solver/joint_constraint/fixed_position_constraint_wide.rs

@@ -0,0 +1,53 @@
+use super::{FixedPositionConstraint, FixedPositionGroundConstraint};
+use crate::dynamics::{FixedJoint, IntegrationParameters, JointIndex, RigidBody};
+use crate::math::{AngularInertia, Isometry, Point, Real, Rotation, Vector, SIMD_WIDTH};
+use crate::utils::WAngularInertia;
+use na::Unit;
+
+// TODO: this does not uses SIMD optimizations yet.
+#[derive(Debug)]
+pub(crate) struct WFixedPositionConstraint {
+    constraints: [FixedPositionConstraint; SIMD_WIDTH],
+}
+
+impl WFixedPositionConstraint {
+    pub fn from_params(
+        rbs1: [&RigidBody; SIMD_WIDTH],
+        rbs2: [&RigidBody; SIMD_WIDTH],
+        cparams: [&FixedJoint; SIMD_WIDTH],
+    ) -> Self {
+        Self {
+            constraints: array![|ii| FixedPositionConstraint::from_params(rbs1[ii], rbs2[ii], cparams[ii]); SIMD_WIDTH],
+        }
+    }
+
+    pub fn solve(&self, params: &IntegrationParameters, positions: &mut [Isometry<Real>]) {
+        for constraint in &self.constraints {
+            constraint.solve(params, positions);
+        }
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct WFixedPositionGroundConstraint {
+    constraints: [FixedPositionGroundConstraint; SIMD_WIDTH],
+}
+
+impl WFixedPositionGroundConstraint {
+    pub fn from_params(
+        rbs1: [&RigidBody; SIMD_WIDTH],
+        rbs2: [&RigidBody; SIMD_WIDTH],
+        cparams: [&FixedJoint; SIMD_WIDTH],
+        flipped: [bool; SIMD_WIDTH],
+    ) -> Self {
+        Self {
+            constraints: array![|ii| FixedPositionGroundConstraint::from_params(rbs1[ii], rbs2[ii], cparams[ii], flipped[ii]); SIMD_WIDTH],
+        }
+    }
+
+    pub fn solve(&self, params: &IntegrationParameters, positions: &mut [Isometry<Real>]) {
+        for constraint in &self.constraints {
+            constraint.solve(params, positions);
+        }
+    }
+}