feat: add warmstarting to contact constraints resolution

examples2d/debug_vertical_column2.rs

@@ -0,0 +1,47 @@
+use rapier2d::prelude::*;
+use rapier_testbed2d::Testbed;
+
+pub fn init_world(testbed: &mut Testbed) {
+    /*
+     * World
+     */
+    let mut bodies = RigidBodySet::new();
+    let mut colliders = ColliderSet::new();
+    let impulse_joints = ImpulseJointSet::new();
+    let multibody_joints = MultibodyJointSet::new();
+
+    let num = 80;
+    let rad = 0.5;
+
+    /*
+     * Ground
+     */
+    let ground_size = 1.0;
+    let ground_thickness = 1.0;
+
+    let rigid_body = RigidBodyBuilder::fixed();
+    let ground_handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(ground_size, ground_thickness).friction(0.3);
+    colliders.insert_with_parent(collider, ground_handle, &mut bodies);
+
+    /*
+     * Create the cubes
+     */
+
+    for i in 0..num {
+        let y = i as f32 * rad * 2.0 + ground_thickness + rad;
+
+        // Build the rigid body.
+        let rigid_body = RigidBodyBuilder::dynamic().translation(vector![0.0, y]);
+        let handle = bodies.insert(rigid_body);
+        let collider = ColliderBuilder::cuboid(rad, rad).friction(0.3);
+        colliders.insert_with_parent(collider, handle, &mut bodies);
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, impulse_joints, multibody_joints);
+    // testbed.harness_mut().physics.gravity.y = -981.0;
+    testbed.look_at(point![0.0, 2.5], 5.0);
+}