respond_to_mouse_wheel_press.md

Respond to a mouse wheel press

This chapter shows how to respond to a mouse wheel press.

!!! note "Not ready for yet"

This section remains unfinished until feedback about the previous sections
has been received.

The idea is to do something upon a mouse wheel press.

This chapter introduces:

• TODO

First test: an empty App has no players

Forces us to write count_n_players.

fn test_empty_app_has_no_players() {
    let mut app = App::new();
    assert_eq!(count_n_players(&mut app), 0);
}

Second test: our App has a player

fn test_create_app_has_a_player() {
    let mut app = create_app();
    app.update();
    assert_eq!(count_n_players(&mut app), 1);
}

Third test: player is at the origin

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

Fourth test: player position changes upon mouse wheel turn

fn test_player_responds_to_mouse_wheel_press() {
    let mut app = create_app();
    assert!(app.is_plugin_added::<InputPlugin>());
    app.update();

    // Not moved yet
    assert_eq!(get_player_position(&mut app), Vec2::new(0.0, 0.0));

    // Press the left mouse button
    app.world_mut()
        .resource_mut::<ButtonInput<MouseButton>>()
        .press(MouseButton::Middle);

    app.update();

    // Position must have changed now
    assert_ne!(get_player_position(&mut app), Vec2::new(0.0, 0.0));
}

Conclusion

We can now create an App with something that responds to a mouse wheel press. We have tested everything that the App does!

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