Add a 2D demo for locking rotation.

examples2d/all_examples2.rs

@@ -16,6 +16,7 @@ mod damping2;
 mod debug_box_ball2;
 mod heightfield2;
 mod joints2;
+mod locked_rotation2;
 mod platform2;
 mod pyramid2;
 mod restitution2;
@@ -59,6 +60,7 @@ pub fn main() {
         ("Damping", damping2::init_world),
         ("Heightfield", heightfield2::init_world),
         ("Joints", joints2::init_world),
+        ("Locked rotations", locked_rotation2::init_world),
         ("Platform", platform2::init_world),
         ("Pyramid", pyramid2::init_world),
         ("Restitution", restitution2::init_world),

examples2d/locked_rotation2.rs

@@ -0,0 +1,63 @@
+use na::Point2;
+use rapier2d::dynamics::{JointSet, RigidBodyBuilder, RigidBodySet};
+use rapier2d::geometry::{ColliderBuilder, ColliderSet};
+use rapier_testbed2d::Testbed;
+
+// This shows a bug when a cylinder is in contact with a very large
+// but very thin cuboid. In this case the EPA returns an incorrect
+// contact normal, resulting in the cylinder falling through the floor.
+pub fn init_world(testbed: &mut Testbed) {
+    /*
+     * World
+     */
+    let mut bodies = RigidBodySet::new();
+    let mut colliders = ColliderSet::new();
+    let joints = JointSet::new();
+
+    /*
+     * The ground
+     */
+    let ground_size = 5.0;
+    let ground_height = 0.1;
+
+    let rigid_body = RigidBodyBuilder::new_static()
+        .translation(0.0, -ground_height)
+        .build();
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(ground_size, ground_height).build();
+    colliders.insert(collider, handle, &mut bodies);
+
+    /*
+     * A rectangle that only rotate.
+     */
+    let rigid_body = RigidBodyBuilder::new_dynamic()
+        .translation(0.0, 3.0)
+        .lock_translations()
+        .build();
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(2.0, 0.6).build();
+    colliders.insert(collider, handle, &mut bodies);
+
+    /*
+     * A tilted capsule that cannot rotate.
+     */
+    let rigid_body = RigidBodyBuilder::new_dynamic()
+        .translation(0.0, 5.0)
+        .rotation(1.0)
+        .lock_rotations()
+        .build();
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::capsule_y(0.6, 0.4).build();
+    colliders.insert(collider, handle, &mut bodies);
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, joints);
+    testbed.look_at(Point2::new(0.0, 0.0), 40.0);
+}
+
+fn main() {
+    let testbed = Testbed::from_builders(0, vec![("Boxes", init_world)]);
+    testbed.run()
+}

examples2d/platform2.rs

@@ -61,7 +61,7 @@ pub fn init_world(testbed: &mut Testbed) {
      * Setup a callback to control the platform.
      */
     testbed.add_callback(move |_, physics, _, _, time| {
-        let mut platform = physics.bodies.get_mut(platform_handle).unwrap();
+        let platform = physics.bodies.get_mut(platform_handle).unwrap();
         let mut next_pos = *platform.position();
 
         let dt = 0.016;