Wouldn't it be fun to actually play with these bouncy balls? Let's make a game where you aim the ball at a target using headshots. For this game, balls drop one at a time from above and bounce off your forehead (face), aiming for a target.
The feature we'll implement here is, when a ball drops from above your head, you bounce it off your face and aim for a target.
To implement this, create a cube as a child of the camera object (much like we did for the reticle cursor in Chapter 6, World Space UI). This provides a collider parented by the VR camera, so our head pose will move the face of the cube. I decided a cube-shaped collider will be better for this game than a sphere or capsule because it provides a flat face that will make the bounce direction more predictable. Balls will drop out of the sky. For a target, we'll use a flattened cylinder...