docs/bevy/examples/state/states.rs 5.3 K · 160 lines · raw · history

1 //! This example illustrates how to use [`States`] for high-level app control flow.
2 //! States are a powerful but intuitive tool for controlling which logic runs when.
3 //! You can have multiple independent states, and the [`OnEnter`] and [`OnExit`] schedules
4 //! can be used to great effect to ensure that you handle setup and teardown appropriately.
5 //!
6 //! In this case, we're transitioning from a `Menu` state to an `InGame` state.
7
8 use bevy::{
9 picking::hover::Hovered,
10 prelude::*,
11 ui_widgets::{Activate, ActivateOnPress, Button},
12 };
13
14 fn main() {
15 let mut app = App::new();
16 app.add_plugins(DefaultPlugins)
17 .init_state::<AppState>() // Alternatively we could use .insert_state(AppState::Menu)
18 .add_systems(Startup, setup)
19 // This system runs when we enter `AppState::Menu`, during the `StateTransition` schedule.
20 // All systems from the exit schedule of the state we're leaving are run first,
21 // and then all systems from the enter schedule of the state we're entering are run second.
22 .add_systems(OnEnter(AppState::Menu), setup_menu)
23 // By contrast, update systems are stored in the `Update` schedule. They simply
24 // check the value of the `State<T>` resource to see if they should run each frame.
25 .add_systems(Update, hover_style.run_if(in_state(AppState::Menu)))
26 .add_observer(on_activate_start_game.run_if(in_state(AppState::Menu)))
27 .add_systems(OnExit(AppState::Menu), cleanup_menu)
28 .add_systems(OnEnter(AppState::InGame), setup_game)
29 .add_systems(
30 Update,
31 (movement, change_color).run_if(in_state(AppState::InGame)),
32 );
33
34 #[cfg(feature = "bevy_dev_tools")]
35 app.add_systems(Update, bevy::dev_tools::states::log_transitions::<AppState>);
36 #[cfg(not(feature = "bevy_dev_tools"))]
37 warn!("Enable feature bevy_dev_tools to log state transitions");
38
39 app.run();
40 }
41
42 #[derive(Debug, Clone, Copy, Default, Eq, PartialEq, Hash, States)]
43 enum AppState {
44 #[default]
45 Menu,
46 InGame,
47 }
48
49 #[derive(Resource)]
50 struct MenuData {
51 button_entity: Entity,
52 }
53
54 const NORMAL_BUTTON: Color = Color::srgb(0.15, 0.15, 0.15);
55 const HOVERED_BUTTON: Color = Color::srgb(0.25, 0.25, 0.25);
56
57 fn setup(mut commands: Commands) {
58 commands.spawn(Camera2d);
59 }
60
61 fn setup_menu(mut commands: Commands) {
62 let button_entity = commands
63 .spawn((
64 Node {
65 // center button
66 width: percent(100),
67 height: percent(100),
68 justify_content: JustifyContent::Center,
69 align_items: AlignItems::Center,
70 ..default()
71 },
72 children![(
73 Button,
74 ActivateOnPress,
75 Hovered::default(),
76 Node {
77 width: px(150),
78 height: px(65),
79 // horizontally center child text
80 justify_content: JustifyContent::Center,
81 // vertically center child text
82 align_items: AlignItems::Center,
83 ..default()
84 },
85 BackgroundColor(NORMAL_BUTTON),
86 children![(
87 Text::new("Play"),
88 TextFont {
89 font_size: FontSize::Px(33.0),
90 ..default()
91 },
92 TextColor(Color::srgb(0.9, 0.9, 0.9)),
93 )],
94 )],
95 ))
96 .id();
97 commands.insert_resource(MenuData { button_entity });
98 }
99
100 fn on_activate_start_game(_: On<Activate>, mut next_state: ResMut<NextState<AppState>>) {
101 next_state.set(AppState::InGame);
102 }
103
104 fn hover_style(
105 mut button_query: Query<(&Hovered, &mut BackgroundColor), (Changed<Hovered>, With<Button>)>,
106 ) {
107 for (hovered, mut color) in &mut button_query {
108 if hovered.get() {
109 *color = HOVERED_BUTTON.into();
110 } else {
111 *color = NORMAL_BUTTON.into();
112 }
113 }
114 }
115
116 fn cleanup_menu(mut commands: Commands, menu_data: Res<MenuData>) {
117 commands.entity(menu_data.button_entity).despawn();
118 }
119
120 fn setup_game(mut commands: Commands, asset_server: Res<AssetServer>) {
121 commands.spawn(Sprite::from_image(asset_server.load("branding/icon.png")));
122 }
123
124 const SPEED: f32 = 100.0;
125 fn movement(
126 time: Res<Time>,
127 input: Res<ButtonInput<KeyCode>>,
128 mut query: Query<&mut Transform, With<Sprite>>,
129 ) {
130 for mut transform in &mut query {
131 let mut direction = Vec3::ZERO;
132 if input.pressed(KeyCode::ArrowLeft) {
133 direction.x -= 1.0;
134 }
135 if input.pressed(KeyCode::ArrowRight) {
136 direction.x += 1.0;
137 }
138 if input.pressed(KeyCode::ArrowUp) {
139 direction.y += 1.0;
140 }
141 if input.pressed(KeyCode::ArrowDown) {
142 direction.y -= 1.0;
143 }
144
145 if direction != Vec3::ZERO {
146 transform.translation += direction.normalize() * SPEED * time.delta_secs();
147 }
148 }
149 }
150
151 fn change_color(time: Res<Time>, mut query: Query<&mut Sprite>) {
152 for mut sprite in &mut query {
153 let new_color = LinearRgba {
154 blue: ops::sin(time.elapsed_secs() * 0.5) + 2.0,
155 ..LinearRgba::from(sprite.color)
156 };
157
158 sprite.color = new_color.into();
159 }
160 }