feat: add warmstarting to contact constraints resolution

examples2d/s2d_joint_grid.rs

@@ -0,0 +1,68 @@
+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 mut impulse_joints = ImpulseJointSet::new();
+    let multibody_joints = MultibodyJointSet::new();
+
+    /*
+     * Ground
+     */
+    let ground = bodies.insert(RigidBodyBuilder::fixed());
+
+    /*
+     * Create the bridge.
+     */
+    let rad = 0.4;
+    let numi = 100;
+    let numk = 100;
+    let shift = 1.0;
+    let mut index = 0;
+    let mut handles = vec![RigidBodyHandle::invalid(); numi * numk];
+
+    for k in 0..numk {
+        for i in 0..numi {
+            let body_type = if k >= numk / 2 - 3 && k <= numk / 2 + 3 && i == 0 {
+                RigidBodyType::Fixed
+            } else {
+                RigidBodyType::Dynamic
+            };
+
+            let rigid_body = RigidBodyBuilder::new(body_type)
+                .translation(vector![k as f32 * shift, -(i as f32) * shift]);
+            let handle = bodies.insert(rigid_body);
+            let collider = ColliderBuilder::ball(rad);
+            colliders.insert_with_parent(collider, handle, &mut bodies);
+
+            if i > 0 {
+                let joint = RevoluteJointBuilder::new()
+                    .local_anchor1(point![0.0, -0.5 * shift])
+                    .local_anchor2(point![0.0, 0.5 * shift])
+                    .contacts_enabled(false);
+                impulse_joints.insert(handles[index - 1], handle, joint, true);
+            }
+
+            if k > 0 {
+                let joint = RevoluteJointBuilder::new()
+                    .local_anchor1(point![0.5 * shift, 0.0])
+                    .local_anchor2(point![-0.5 * shift, 0.0])
+                    .contacts_enabled(false);
+                impulse_joints.insert(handles[index - numi], handle, joint, true);
+            }
+
+            handles[index] = handle;
+            index += 1;
+        }
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, impulse_joints, multibody_joints);
+    testbed.look_at(point![0.0, 2.5], 20.0);
+}