feat: add warmstarting to contact constraints resolution

examples2d/s2d_high_mass_ratio_1.rs

@@ -0,0 +1,66 @@
+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 extent = 1.0;
+    let friction = 0.5;
+
+    /*
+     * Ground
+     */
+    let ground_width = 66.0 * extent;
+
+    let rigid_body = RigidBodyBuilder::fixed();
+    let ground_handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::segment(
+        point![-0.5 * 2.0 * ground_width, 0.0],
+        point![0.5 * 2.0 * ground_width, 0.0],
+    )
+    .friction(friction);
+    colliders.insert_with_parent(collider, ground_handle, &mut bodies);
+
+    /*
+     * Create the cubes
+     */
+
+    for j in 0..3 {
+        let mut count = 10;
+        let offset = -20.0 * extent + 2.0 * (count as f32 + 1.0) * extent * j as f32;
+        let mut y = extent;
+
+        while count > 0 {
+            for i in 0..count {
+                let coeff = i as f32 - 0.5 * count as f32;
+                let yy = if count == 1 { y + 2.0 } else { y };
+                let position = vector![2.0 * coeff * extent + offset, yy];
+                let rigid_body = RigidBodyBuilder::dynamic().translation(position);
+                let parent = bodies.insert(rigid_body);
+
+                let collider = ColliderBuilder::cuboid(extent, extent)
+                    .density(if count == 1 {
+                        (j as f32 + 1.0) * 100.0
+                    } else {
+                        1.0
+                    })
+                    .friction(friction);
+                colliders.insert_with_parent(collider, parent, &mut bodies);
+            }
+
+            count -= 1;
+            y += 2.0 * extent;
+        }
+    }
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, impulse_joints, multibody_joints);
+    testbed.look_at(point![0.0, 2.5], 20.0);
+}