Add debug demos for rigid-body change tracking.

examples3d/all_examples3.rs

@@ -16,6 +16,7 @@ mod damping3;
 mod debug_boxes3;
 mod debug_cylinder3;
 mod debug_infinite_fall3;
+mod debug_rollback3;
 mod debug_triangle3;
 mod debug_trimesh3;
 mod domino3;
@@ -86,6 +87,7 @@ pub fn main() {
         ("(Debug) trimesh", debug_trimesh3::init_world),
         ("(Debug) cylinder", debug_cylinder3::init_world),
         ("(Debug) infinite fall", debug_infinite_fall3::init_world),
+        ("(Debug) rollback", debug_rollback3::init_world),
     ];
 
     // Lexicographic sort, with stress tests moved at the end of the list.

examples3d/debug_rollback3.rs

@@ -0,0 +1,77 @@
+use na::{Isometry3, Point3, Vector3};
+use rapier3d::dynamics::{JointSet, RigidBodyBuilder, RigidBodySet};
+use rapier3d::geometry::{ColliderBuilder, ColliderSet};
+use rapier_testbed3d::Testbed;
+
+pub fn init_world(testbed: &mut Testbed) {
+    /*
+     * World
+     */
+    let mut bodies = RigidBodySet::new();
+    let mut colliders = ColliderSet::new();
+    let joints = JointSet::new();
+    /*
+     * Ground.
+     */
+    let ground_size = 20.0;
+    let ground_height = 0.1;
+
+    let rigid_body = RigidBodyBuilder::new_static()
+        .translation(0.0, -ground_height, 0.0)
+        .build();
+    let ground_handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(ground_size, ground_height, 0.4)
+        .friction(0.15)
+        // .restitution(0.5)
+        .build();
+    colliders.insert(collider, ground_handle, &mut bodies);
+
+    /*
+     * Rolling ball
+     */
+    let rb = RigidBodyBuilder::new_dynamic()
+        .translation(0.0, 0.2, 0.0)
+        .linvel(10.0, 0.0, 0.0)
+        .build();
+    let ball_handle = bodies.insert(rb);
+    let collider = ColliderBuilder::ball(0.1).density(100.0).build();
+    colliders.insert(collider, ball_handle, &mut bodies);
+
+    let mut linvel = Vector3::zeros();
+    let mut angvel = Vector3::zeros();
+    let mut pos = Isometry3::identity();
+    let mut step = 0;
+    let snapped_frame = 51;
+
+    testbed.add_callback(move |_, physics, _, _, _| {
+        step += 1;
+        let mut ball = physics.bodies.get_mut(ball_handle).unwrap();
+
+        if step == snapped_frame {
+            linvel = *ball.linvel();
+            angvel = *ball.angvel();
+            pos = *ball.position();
+        }
+
+        if step == 100 {
+            ball.set_linvel(linvel, true);
+            ball.set_angvel(angvel, true);
+            ball.set_position(pos, true);
+            step = snapped_frame;
+        }
+
+        let ground = physics.bodies.get_mut(ground_handle).unwrap();
+        ground.set_position(Isometry3::translation(0.0, step as f32 * 0.001, 0.0), false);
+    });
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, joints);
+    testbed.look_at(Point3::new(10.0, 10.0, 10.0), Point3::origin());
+}
+
+fn main() {
+    let testbed = Testbed::from_builders(0, vec![("Boxes", init_world)]);
+    testbed.run()
+}