Add one-way platform + conveyor belt demos.

examples2d/one_way_platforms2.rs

@@ -0,0 +1,143 @@
+use na::{Point2, Vector2};
+use rapier2d::dynamics::{JointSet, RigidBodyBuilder, RigidBodySet};
+use rapier2d::geometry::{ColliderBuilder, ColliderHandle, ColliderSet};
+use rapier2d::pipeline::{ContactModificationContext, PhysicsHooks, PhysicsHooksFlags};
+use rapier_testbed2d::Testbed;
+
+struct OneWayPlatformHook {
+    platform1: ColliderHandle,
+    platform2: ColliderHandle,
+}
+
+impl PhysicsHooks for OneWayPlatformHook {
+    fn active_hooks(&self) -> PhysicsHooksFlags {
+        PhysicsHooksFlags::MODIFY_SOLVER_CONTACTS
+    }
+
+    fn modify_solver_contacts(&self, context: &mut ContactModificationContext) {
+        // The allowed normal for the first platform is its local +y axis, and the
+        // allowed normal for the second platform is its local -y axis.
+        //
+        // Now we have to be careful because the `manifold.local_n1` normal points
+        // toward the outside of the shape of `context.co1`. So we need to flip the
+        // allowed normal direction if the platform is in `context.collider_handle2`.
+        //
+        // Therefore:
+        // - If context.collider_handle1 == self.platform1 then the allowed normal is +y.
+        // - If context.collider_handle2 == self.platform1 then the allowed normal is -y.
+        // - If context.collider_handle1 == self.platform2 then its allowed normal +y needs to be flipped to -y.
+        // - If context.collider_handle2 == self.platform2 then the allowed normal -y needs to be flipped to +y.
+        let mut allowed_local_n1 = Vector2::zeros();
+
+        if context.collider_handle1 == self.platform1 {
+            allowed_local_n1 = Vector2::y();
+        } else if context.collider_handle2 == self.platform1 {
+            // Flip the allowed direction.
+            allowed_local_n1 = -Vector2::y();
+        }
+
+        if context.collider_handle1 == self.platform2 {
+            allowed_local_n1 = -Vector2::y();
+        } else if context.collider_handle2 == self.platform2 {
+            // Flip the allowed direction.
+            allowed_local_n1 = -Vector2::y();
+        }
+
+        // Call the helper function that simulates one-way platforms.
+        context.update_as_oneway_platform(&allowed_local_n1, 0.1);
+
+        // Set the surface velocity of the accepted contacts.
+        let surface_velocity = if context.collider_handle1 == self.platform1
+            || context.collider_handle2 == self.platform2
+        {
+            -12.0
+        } else {
+            12.0
+        };
+
+        for contact in context.solver_contacts.iter_mut() {
+            contact.surface_velocity.x = surface_velocity;
+        }
+    }
+}
+
+pub fn init_world(testbed: &mut Testbed) {
+    /*
+     * World
+     */
+    let mut bodies = RigidBodySet::new();
+    let mut colliders = ColliderSet::new();
+    let joints = JointSet::new();
+
+    /*
+     * Ground
+     */
+    let rigid_body = RigidBodyBuilder::new_static().build();
+    let handle = bodies.insert(rigid_body);
+
+    let collider = ColliderBuilder::cuboid(25.0, 0.5)
+        .translation(30.0, 2.0)
+        .modify_contacts(true)
+        .build();
+    let platform1 = colliders.insert(collider, handle, &mut bodies);
+    let collider = ColliderBuilder::cuboid(25.0, 0.5)
+        .translation(-30.0, -2.0)
+        .modify_contacts(true)
+        .build();
+    let platform2 = colliders.insert(collider, handle, &mut bodies);
+
+    /*
+     * Setup the one-way platform hook.
+     */
+    let physics_hooks = OneWayPlatformHook {
+        platform1,
+        platform2,
+    };
+
+    /*
+     * Spawn cubes at regular intervals and apply a custom gravity
+     * depending on their position.
+     */
+    testbed.add_callback(move |mut window, mut graphics, physics, _, run_state| {
+        if run_state.timestep_id % 50 == 0 && physics.bodies.len() <= 7 {
+            // Spawn a new cube.
+            let collider = ColliderBuilder::cuboid(1.5, 2.0).build();
+            let body = RigidBodyBuilder::new_dynamic()
+                .translation(20.0, 10.0)
+                .build();
+            let handle = physics.bodies.insert(body);
+            physics
+                .colliders
+                .insert(collider, handle, &mut physics.bodies);
+
+            if let (Some(graphics), Some(window)) = (&mut graphics, &mut window) {
+                graphics.add(window, handle, &physics.bodies, &physics.colliders);
+            }
+        }
+
+        physics.bodies.foreach_active_dynamic_body_mut(|_, body| {
+            if body.position().translation.y > 1.0 {
+                body.set_gravity_scale(1.0, false);
+            } else if body.position().translation.y < -1.0 {
+                body.set_gravity_scale(-1.0, false);
+            }
+        });
+    });
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world_with_params(
+        bodies,
+        colliders,
+        joints,
+        Vector2::new(0.0, -9.81),
+        physics_hooks,
+    );
+    testbed.look_at(Point2::new(0.0, 0.0), 20.0);
+}
+
+fn main() {
+    let testbed = Testbed::from_builders(0, vec![("Boxes", init_world)]);
+    testbed.run()
+}