Fix some solver issues

- Fix the wrong codepath taken  by the solver for contacts involving a collider without parent.
- Properly adress the non-linear treatment of the friction direction
- Simplify the sleeping strategy
- Add an impulse resolution multiplier

examples2d/drum2.rs

@@ -0,0 +1,81 @@
+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();
+
+    /*
+     * Create the boxes
+     */
+    let num = 30;
+    let rad = 0.2;
+
+    let shift = rad * 2.0;
+    let centerx = shift * num as f32 / 2.0;
+    let centery = shift * num as f32 / 2.0;
+
+    for i in 0usize..num {
+        for j in 0usize..num {
+            let x = i as f32 * shift - centerx;
+            let y = j as f32 * shift - centery;
+
+            // Build the rigid body.
+            let rigid_body = RigidBodyBuilder::new_dynamic()
+                .translation(vector![x, y])
+                .build();
+            let handle = bodies.insert(rigid_body);
+            let collider = ColliderBuilder::cuboid(rad, rad).build();
+            colliders.insert_with_parent(collider, handle, &mut bodies);
+        }
+    }
+
+    /*
+     * Setup a velocity-based kinematic rigid body.
+     */
+    let platform_body = RigidBodyBuilder::new_kinematic_velocity_based().build();
+    let velocity_based_platform_handle = bodies.insert(platform_body);
+
+    let sides = [
+        (10.0, 0.25, vector![0.0, 10.0]),
+        (10.0, 0.25, vector![0.0, -10.0]),
+        (0.25, 10.0, vector![10.0, 0.0]),
+        (0.25, 10.0, vector![-10.0, 0.0]),
+    ];
+    let balls = [
+        (1.25, vector![6.0, 6.0]),
+        (1.25, vector![-6.0, 6.0]),
+        (1.25, vector![6.0, -6.0]),
+        (1.25, vector![-6.0, -6.0]),
+    ];
+
+    for (hx, hy, pos) in sides {
+        let collider = ColliderBuilder::cuboid(hx, hy).translation(pos).build();
+        colliders.insert_with_parent(collider, velocity_based_platform_handle, &mut bodies);
+    }
+    for (r, pos) in balls {
+        let collider = ColliderBuilder::ball(r).translation(pos).build();
+        colliders.insert_with_parent(collider, velocity_based_platform_handle, &mut bodies);
+    }
+
+    /*
+     * Setup a callback to control the platform.
+     */
+    testbed.add_callback(move |_, physics, _, _| {
+        // Update the velocity-based kinematic body by setting its velocity.
+        if let Some(platform) = physics.bodies.get_mut(velocity_based_platform_handle) {
+            platform.set_angvel(-0.15, true);
+        }
+    });
+
+    /*
+     * Run the simulation.
+     */
+    testbed.set_world(bodies, colliders, impulse_joints, multibody_joints);
+    testbed.look_at(point![0.0, 1.0], 40.0);
+}