A camera following the player in a 2D game.

follow_camera_system_2d.rs

/// 2D player following camera system. Needs to be dispatched after the Transform-Bundle, to avoid jittering,
/// but before the Render-Bundle.
pub struct FollowCameraSystem;

impl<'s> System<'s> for FollowCameraSystem{
    type SystemData = (
        WriteStorage<'s, Transform>,
        ReadStorage<'s, CPlayer>,
        ReadStorage<'s, Camera>,
    );

    fn run(&mut self, (mut transforms, players, camera) : Self::SystemData){
        let mut transform_camera = Transform::default();
        if let Some((transform, player)) = (&transforms, &players).join().next() {
            // TODO: Dont use camera-offset in Player, instead make it a component of the Camera entity?
            transform_camera.translation[0] = transform.translation[0] - player.camera_offset.0;
            transform_camera.translation[1] = transform.translation[1] - player.camera_offset.1;
        }

        if let Some((transform, _)) = (&mut transforms, &camera).join().next() {
            transform.translation[0] = transform_camera.translation[0];
            transform.translation[1] = transform_camera.translation[1];
        }
    }
}