Merge pull request #579 from dimforge/joints-improvements

Feat: implement a "small-steps" velocity-based constraints solver + joint improvements

1 files changed, 64 insertions, 0 deletions

diff --git a/examples3d/spring_joints3.rs b/examples3d/spring_joints3.rs
new file mode 100644
index 0000000..3336402
--- /dev/null
+++ b/examples3d/spring_joints3.rs
@@ -0,0 +1,64 @@
+use rapier3d::prelude::*;
+use rapier_testbed3d::Testbed;
+
+pub fn init_world(testbed: &mut Testbed) {
+    /*
+     * World
+     */
+    let mut bodies = RigidBodySet::new();
+    let mut colliders = ColliderSet::new();
+    let mut impulse_joints = ImpulseJointSet::new();
+    let multibody_joints = MultibodyJointSet::new();
+
+    /*
+     * Fixed ground to attach one end of the joints.
+     */
+    let rigid_body = RigidBodyBuilder::fixed();
+    let ground_handle = bodies.insert(rigid_body);
+
+    /*
+     * Spring joints with a variety of spring parameters.
+     * The middle one has uses critical damping.
+     */
+    let num = 30;
+    let radius = 0.5;
+    let mass = Ball::new(radius).mass_properties(1.0).mass();
+    let stiffness = 1.0e3;
+    let critical_damping = 2.0 * (stiffness * mass).sqrt();
+    for i in 0..=num {
+        let x_pos = -6.0 + 1.5 * i as f32;
+        let ball_pos = point![x_pos, 4.5, 0.0];
+        let rigid_body = RigidBodyBuilder::dynamic()
+            .translation(ball_pos.coords)
+            .can_sleep(false);
+        let handle = bodies.insert(rigid_body);
+        let collider = ColliderBuilder::ball(radius);
+        colliders.insert_with_parent(collider, handle, &mut bodies);
+
+        let damping_ratio = i as f32 / (num as f32 / 2.0);
+        let damping = damping_ratio * critical_damping;
+        let joint = SpringJointBuilder::new(0.0, stiffness, damping)
+            .local_anchor1(ball_pos - Vector::y() * 3.0);
+        impulse_joints.insert(ground_handle, handle, joint, true);
+
+        // Box that will fall on to of the springed balls, makes the simulation funier to watch.
+        let rigid_body =
+            RigidBodyBuilder::dynamic().translation(ball_pos.coords + Vector::y() * 5.0);
+        let handle = bodies.insert(rigid_body);
+        let collider = ColliderBuilder::cuboid(radius, radius, radius).density(100.0);
+        colliders.insert_with_parent(collider, handle, &mut bodies);
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world_with_params(
+        bodies,
+        colliders,
+        impulse_joints,
+        multibody_joints,
+        vector![0.0, -9.81, 0.0],
+        (),
+    );
+    testbed.look_at(point![15.0, 5.0, 42.0], point![13.0, 1.0, 1.0]);
+}