pub fn in_state<S>(state: S) -> impl FnMut(Option<Res<'_, State<S>>>) + Clonewhere
S: States,Expand description
Generates a Condition-satisfying closure that returns true
if the state machine is currently in state.
Will return false if the state does not exist or if not in state.
§Example
#[derive(States, Clone, Copy, Default, Eq, PartialEq, Hash, Debug)]
enum GameState {
#[default]
Playing,
Paused,
}
world.init_resource::<State<GameState>>();
app.add_systems((
// `in_state` will only return true if the
// given state equals the given value
play_system.run_if(in_state(GameState::Playing)),
pause_system.run_if(in_state(GameState::Paused)),
));
fn play_system(mut counter: ResMut<Counter>) {
counter.0 += 1;
}
fn pause_system(mut counter: ResMut<Counter>) {
counter.0 -= 1;
}
// We default to `GameState::Playing` so `play_system` runs
app.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 1);
*world.resource_mut::<State<GameState>>() = State::new(GameState::Paused);
// Now that we are in `GameState::Pause`, `pause_system` will run
app.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 0);Examples found in repository?
More examples
examples/games/game_menu.rs (line 60)
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pub fn splash_plugin(app: &mut App) {
// As this plugin is managing the splash screen, it will focus on the state `GameState::Splash`
app
// When entering the state, spawn everything needed for this screen
.add_systems(OnEnter(GameState::Splash), splash_setup)
// While in this state, run the `countdown` system
.add_systems(Update, countdown.run_if(in_state(GameState::Splash)))
// When exiting the state, despawn everything that was spawned for this screen
.add_systems(OnExit(GameState::Splash), despawn_screen::<OnSplashScreen>);
}
// Tag component used to tag entities added on the splash screen
#[derive(Component)]
struct OnSplashScreen;
// Newtype to use a `Timer` for this screen as a resource
#[derive(Resource, Deref, DerefMut)]
struct SplashTimer(Timer);
fn splash_setup(mut commands: Commands, asset_server: Res<AssetServer>) {
let icon = asset_server.load("branding/icon.png");
// Display the logo
commands
.spawn((
NodeBundle {
style: Style {
align_items: AlignItems::Center,
justify_content: JustifyContent::Center,
width: Val::Percent(100.0),
height: Val::Percent(100.0),
..default()
},
..default()
},
OnSplashScreen,
))
.with_children(|parent| {
parent.spawn(ImageBundle {
style: Style {
// This will set the logo to be 200px wide, and auto adjust its height
width: Val::Px(200.0),
..default()
},
image: UiImage::new(icon),
..default()
});
});
// Insert the timer as a resource
commands.insert_resource(SplashTimer(Timer::from_seconds(1.0, TimerMode::Once)));
}
// Tick the timer, and change state when finished
fn countdown(
mut game_state: ResMut<NextState<GameState>>,
time: Res<Time>,
mut timer: ResMut<SplashTimer>,
) {
if timer.tick(time.delta()).finished() {
game_state.set(GameState::Menu);
}
}
}
mod game {
use bevy::prelude::*;
use super::{despawn_screen, DisplayQuality, GameState, Volume, TEXT_COLOR};
// This plugin will contain the game. In this case, it's just be a screen that will
// display the current settings for 5 seconds before returning to the menu
pub fn game_plugin(app: &mut App) {
app.add_systems(OnEnter(GameState::Game), game_setup)
.add_systems(Update, game.run_if(in_state(GameState::Game)))
.add_systems(OnExit(GameState::Game), despawn_screen::<OnGameScreen>);
}
// Tag component used to tag entities added on the game screen
#[derive(Component)]
struct OnGameScreen;
#[derive(Resource, Deref, DerefMut)]
struct GameTimer(Timer);
fn game_setup(
mut commands: Commands,
display_quality: Res<DisplayQuality>,
volume: Res<Volume>,
) {
commands
.spawn((
NodeBundle {
style: Style {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
// center children
align_items: AlignItems::Center,
justify_content: JustifyContent::Center,
..default()
},
..default()
},
OnGameScreen,
))
.with_children(|parent| {
// First create a `NodeBundle` for centering what we want to display
parent
.spawn(NodeBundle {
style: Style {
// This will display its children in a column, from top to bottom
flex_direction: FlexDirection::Column,
// `align_items` will align children on the cross axis. Here the main axis is
// vertical (column), so the cross axis is horizontal. This will center the
// children
align_items: AlignItems::Center,
..default()
},
background_color: Color::BLACK.into(),
..default()
})
.with_children(|parent| {
// Display two lines of text, the second one with the current settings
parent.spawn(
TextBundle::from_section(
"Will be back to the menu shortly...",
TextStyle {
font_size: 80.0,
color: TEXT_COLOR,
..default()
},
)
.with_style(Style {
margin: UiRect::all(Val::Px(50.0)),
..default()
}),
);
parent.spawn(
TextBundle::from_sections([
TextSection::new(
format!("quality: {:?}", *display_quality),
TextStyle {
font_size: 60.0,
color: Color::BLUE,
..default()
},
),
TextSection::new(
" - ",
TextStyle {
font_size: 60.0,
color: TEXT_COLOR,
..default()
},
),
TextSection::new(
format!("volume: {:?}", *volume),
TextStyle {
font_size: 60.0,
color: Color::GREEN,
..default()
},
),
])
.with_style(Style {
margin: UiRect::all(Val::Px(50.0)),
..default()
}),
);
});
});
// Spawn a 5 seconds timer to trigger going back to the menu
commands.insert_resource(GameTimer(Timer::from_seconds(5.0, TimerMode::Once)));
}
// Tick the timer, and change state when finished
fn game(
time: Res<Time>,
mut game_state: ResMut<NextState<GameState>>,
mut timer: ResMut<GameTimer>,
) {
if timer.tick(time.delta()).finished() {
game_state.set(GameState::Menu);
}
}
}
mod menu {
use bevy::{app::AppExit, prelude::*};
use super::{despawn_screen, DisplayQuality, GameState, Volume, TEXT_COLOR};
// This plugin manages the menu, with 5 different screens:
// - a main menu with "New Game", "Settings", "Quit"
// - a settings menu with two submenus and a back button
// - two settings screen with a setting that can be set and a back button
pub fn menu_plugin(app: &mut App) {
app
// At start, the menu is not enabled. This will be changed in `menu_setup` when
// entering the `GameState::Menu` state.
// Current screen in the menu is handled by an independent state from `GameState`
.init_state::<MenuState>()
.add_systems(OnEnter(GameState::Menu), menu_setup)
// Systems to handle the main menu screen
.add_systems(OnEnter(MenuState::Main), main_menu_setup)
.add_systems(OnExit(MenuState::Main), despawn_screen::<OnMainMenuScreen>)
// Systems to handle the settings menu screen
.add_systems(OnEnter(MenuState::Settings), settings_menu_setup)
.add_systems(
OnExit(MenuState::Settings),
despawn_screen::<OnSettingsMenuScreen>,
)
// Systems to handle the display settings screen
.add_systems(
OnEnter(MenuState::SettingsDisplay),
display_settings_menu_setup,
)
.add_systems(
Update,
(setting_button::<DisplayQuality>.run_if(in_state(MenuState::SettingsDisplay)),),
)
.add_systems(
OnExit(MenuState::SettingsDisplay),
despawn_screen::<OnDisplaySettingsMenuScreen>,
)
// Systems to handle the sound settings screen
.add_systems(OnEnter(MenuState::SettingsSound), sound_settings_menu_setup)
.add_systems(
Update,
setting_button::<Volume>.run_if(in_state(MenuState::SettingsSound)),
)
.add_systems(
OnExit(MenuState::SettingsSound),
despawn_screen::<OnSoundSettingsMenuScreen>,
)
// Common systems to all screens that handles buttons behavior
.add_systems(
Update,
(menu_action, button_system).run_if(in_state(GameState::Menu)),
);
}examples/ecs/generic_system.rs (line 42)
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fn main() {
App::new()
.add_plugins(DefaultPlugins)
.init_state::<AppState>()
.add_systems(Startup, setup_system)
.add_systems(
Update,
(
print_text_system,
transition_to_in_game_system.run_if(in_state(AppState::MainMenu)),
),
)
// Cleanup systems.
// Pass in the types your system should operate on using the ::<T> (turbofish) syntax
.add_systems(OnExit(AppState::MainMenu), cleanup_system::<MenuClose>)
.add_systems(OnExit(AppState::InGame), cleanup_system::<LevelUnload>)
.run();
}examples/2d/bounding_2d.rs (line 19)
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fn main() {
App::new()
.add_plugins(DefaultPlugins)
.init_state::<Test>()
.add_systems(Startup, setup)
.add_systems(
Update,
(update_text, spin, update_volumes, update_test_state),
)
.add_systems(
PostUpdate,
(
render_shapes,
(
aabb_intersection_system.run_if(in_state(Test::AabbSweep)),
circle_intersection_system.run_if(in_state(Test::CircleSweep)),
ray_cast_system.run_if(in_state(Test::RayCast)),
aabb_cast_system.run_if(in_state(Test::AabbCast)),
bounding_circle_cast_system.run_if(in_state(Test::CircleCast)),
),
render_volumes,
)
.chain(),
)
.run();
}examples/games/alien_cake_addict.rs (line 38)
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fn main() {
App::new()
.add_plugins(DefaultPlugins)
.init_resource::<Game>()
.insert_resource(BonusSpawnTimer(Timer::from_seconds(
5.0,
TimerMode::Repeating,
)))
.init_state::<GameState>()
.add_systems(Startup, setup_cameras)
.add_systems(OnEnter(GameState::Playing), setup)
.add_systems(
Update,
(
move_player,
focus_camera,
rotate_bonus,
scoreboard_system,
spawn_bonus,
)
.run_if(in_state(GameState::Playing)),
)
.add_systems(OnExit(GameState::Playing), teardown)
.add_systems(OnEnter(GameState::GameOver), display_score)
.add_systems(
Update,
(
gameover_keyboard.run_if(in_state(GameState::GameOver)),
bevy::window::close_on_esc,
),
)
.add_systems(OnExit(GameState::GameOver), teardown)
.run();
}examples/ecs/state.rs (line 21)
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fn main() {
App::new()
.add_plugins(DefaultPlugins)
.init_state::<AppState>() // Alternatively we could use .insert_state(AppState::Menu)
.add_systems(Startup, setup)
// This system runs when we enter `AppState::Menu`, during the `StateTransition` schedule.
// All systems from the exit schedule of the state we're leaving are run first,
// and then all systems from the enter schedule of the state we're entering are run second.
.add_systems(OnEnter(AppState::Menu), setup_menu)
// By contrast, update systems are stored in the `Update` schedule. They simply
// check the value of the `State<T>` resource to see if they should run each frame.
.add_systems(Update, menu.run_if(in_state(AppState::Menu)))
.add_systems(OnExit(AppState::Menu), cleanup_menu)
.add_systems(OnEnter(AppState::InGame), setup_game)
.add_systems(
Update,
(movement, change_color).run_if(in_state(AppState::InGame)),
)
.add_systems(Update, log_transitions)
.run();
}