1 files changed, 139 insertions, 0 deletions
diff --git a/src/dynamics/solver/joint_constraint/fixed_position_constraint.rs b/src/dynamics/solver/joint_constraint/fixed_position_constraint.rs
new file mode 100644
index 0000000..24001cd
--- /dev/null
+++ b/src/dynamics/solver/joint_constraint/fixed_position_constraint.rs
@@ -0,0 +1,139 @@
+use crate::dynamics::{FixedJoint, IntegrationParameters, RigidBody};
+use crate::math::{AngularInertia, Isometry, Point, Rotation};
+use crate::utils::WAngularInertia;
+
+#[derive(Debug)]
+pub(crate) struct FixedPositionConstraint {
+    position1: usize,
+    position2: usize,
+    local_anchor1: Isometry<f32>,
+    local_anchor2: Isometry<f32>,
+    local_com1: Point<f32>,
+    local_com2: Point<f32>,
+    im1: f32,
+    im2: f32,
+    ii1: AngularInertia<f32>,
+    ii2: AngularInertia<f32>,
+
+    lin_inv_lhs: f32,
+    ang_inv_lhs: AngularInertia<f32>,
+}
+
+impl FixedPositionConstraint {
+    pub fn from_params(rb1: &RigidBody, rb2: &RigidBody, cparams: &FixedJoint) -> Self {
+        let ii1 = rb1.world_inv_inertia_sqrt.squared();
+        let ii2 = rb2.world_inv_inertia_sqrt.squared();
+        let im1 = rb1.mass_properties.inv_mass;
+        let im2 = rb2.mass_properties.inv_mass;
+        let lin_inv_lhs = 1.0 / (im1 + im2);
+        let ang_inv_lhs = (ii1 + ii2).inverse();
+
+        Self {
+            local_anchor1: cparams.local_anchor1,
+            local_anchor2: cparams.local_anchor2,
+            position1: rb1.active_set_offset,
+            position2: rb2.active_set_offset,
+            im1,
+            im2,
+            ii1,
+            ii2,
+            local_com1: rb1.mass_properties.local_com,
+            local_com2: rb2.mass_properties.local_com,
+            lin_inv_lhs,
+            ang_inv_lhs,
+        }
+    }
+
+    pub fn solve(&self, params: &IntegrationParameters, positions: &mut [Isometry<f32>]) {
+        let mut position1 = positions[self.position1 as usize];
+        let mut position2 = positions[self.position2 as usize];
+
+        // Angular correction.
+        let anchor1 = position1 * self.local_anchor1;
+        let anchor2 = position2 * self.local_anchor2;
+        let ang_err = anchor2.rotation * anchor1.rotation.inverse();
+        #[cfg(feature = "dim3")]
+        let ang_impulse = self
+            .ang_inv_lhs
+            .transform_vector(ang_err.scaled_axis() * params.joint_erp);
+        #[cfg(feature = "dim2")]
+        let ang_impulse = self
+            .ang_inv_lhs
+            .transform_vector(ang_err.angle() * params.joint_erp);
+        position1.rotation =
+            Rotation::new(self.ii1.transform_vector(ang_impulse)) * position1.rotation;
+        position2.rotation =
+            Rotation::new(self.ii2.transform_vector(-ang_impulse)) * position2.rotation;
+
+        // Linear correction.
+        let anchor1 = position1 * Point::from(self.local_anchor1.translation.vector);
+        let anchor2 = position2 * Point::from(self.local_anchor2.translation.vector);
+        let err = anchor2 - anchor1;
+        let impulse = err * (self.lin_inv_lhs * params.joint_erp);
+        position1.translation.vector += self.im1 * impulse;
+        position2.translation.vector -= self.im2 * impulse;
+
+        positions[self.position1 as usize] = position1;
+        positions[self.position2 as usize] = position2;
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct FixedPositionGroundConstraint {
+    position2: usize,
+    anchor1: Isometry<f32>,
+    local_anchor2: Isometry<f32>,
+    local_com2: Point<f32>,
+    im2: f32,
+    ii2: AngularInertia<f32>,
+    impulse: f32,
+}
+
+impl FixedPositionGroundConstraint {
+    pub fn from_params(
+        rb1: &RigidBody,
+        rb2: &RigidBody,
+        cparams: &FixedJoint,
+        flipped: bool,
+    ) -> Self {
+        let anchor1;
+        let local_anchor2;
+
+        if flipped {
+            anchor1 = rb1.predicted_position * cparams.local_anchor2;
+            local_anchor2 = cparams.local_anchor1;
+        } else {
+            anchor1 = rb1.predicted_position * cparams.local_anchor1;
+            local_anchor2 = cparams.local_anchor2;
+        };
+
+        Self {
+            anchor1,
+            local_anchor2,
+            position2: rb2.active_set_offset,
+            im2: rb2.mass_properties.inv_mass,
+            ii2: rb2.world_inv_inertia_sqrt.squared(),
+            local_com2: rb2.mass_properties.local_com,
+            impulse: 0.0,
+        }
+    }
+
+    pub fn solve(&self, params: &IntegrationParameters, positions: &mut [Isometry<f32>]) {
+        let mut position2 = positions[self.position2 as usize];
+
+        // Angular correction.
+        let anchor2 = position2 * self.local_anchor2;
+        let ang_err = anchor2.rotation * self.anchor1.rotation.inverse();
+        position2.rotation = ang_err.powf(-params.joint_erp) * position2.rotation;
+
+        // Linear correction.
+        let anchor1 = Point::from(self.anchor1.translation.vector);
+        let anchor2 = position2 * Point::from(self.local_anchor2.translation.vector);
+        let err = anchor2 - anchor1;
+        // NOTE: no need to divide by im2 just to multiply right after.
+        let impulse = err * params.joint_erp;
+        position2.translation.vector -= impulse;
+
+        positions[self.position2 as usize] = position2;
+    }
+}