Move a camera

This chapter shows how to move a camera.

The idea is to give a camera a velocity, making the camera move on screen.

This chapter introduces nothing new.

First test: our App needs a camera velocity

fn test_can_create_app_with_a_velocity() {
    let velocity = Vec2::new(0.2, 0.1);
    create_app(velocity);
}

Second test: an empty App has no camera

fn test_empty_app_has_no_moving_cameras() {
    let mut app = App::new();
    app.update();
    assert_eq!(count_n_moving_cameras(&mut app), 0);
}

Third test: our App has a camera

fn test_create_app_has_a_moving_camera() {
    let velocity = Vec2::new(0.0, 0.0);
    let mut app = create_app(velocity);
    app.update();
    assert_eq!(count_n_moving_cameras(&mut app), 1);
}

Fourth test: camera starts at origin

fn test_camera_starts_at_origin() {
    let velocity = Vec2::new(0.0, 0.0);
    let mut app = create_app(velocity);
    app.update();
    assert_eq!(get_camera_position(&mut app), Vec2::new(0.0, 0.0));
}

Fifth test: camera moves

fn test_moving_camera_moves() {
    let velocity = Vec2::new(1.2, 3.4);
    let mut app = create_app(velocity);
    app.update();
    assert_ne!(get_camera_position(&mut app), Vec2::new(0.0, 0.0));
}

main.rs

fn main() {
    let velocity = Vec2::new(0.2, 0.1);
    let mut app = create_app(velocity);
    app.add_plugins(DefaultPlugins);
    app.run();
}

Conclusion

We can now create an App with a camera that moves. When running the App, we can see the camera moves. We have tested everything that the App does!

Full code can be found at https://github.com/richelbilderbeek/bevy_tdd_book_move_camera.