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//! This example illustrates the use of [`SubStates`] for more complex state handling patterns.
//!
//! [`SubStates`] are [`States`] that only exist while the App is in another [`State`]. They can
//! be used to create more complex patterns while relying on simple enums, or to de-couple certain
//! elements of complex state objects.
//!
//! In this case, we're transitioning from a `Menu` state to an `InGame` state, at which point we create
//! a substate called `IsPaused` to track whether the game is paused or not.
use bevy::prelude::*;
use ui::*;
#[derive(Debug, Clone, Copy, Default, Eq, PartialEq, Hash, States)]
enum AppState {
#[default]
Menu,
InGame,
}
// In this case, instead of deriving `States`, we derive `SubStates`
#[derive(Debug, Clone, Copy, Default, Eq, PartialEq, Hash, SubStates)]
// And we need to add an attribute to let us know what the source state is
// and what value it needs to have. This will ensure that unless we're
// in [`AppState::InGame`], the [`IsPaused`] state resource
// will not exist.
#[source(AppState = AppState::InGame)]
enum IsPaused {
#[default]
Running,
Paused,
}
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.init_state::<AppState>()
.add_sub_state::<IsPaused>() // We set the substate up here.
// Most of these remain the same
.add_systems(Startup, setup)
.add_systems(OnEnter(AppState::Menu), setup_menu)
.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(OnEnter(IsPaused::Paused), setup_paused_screen)
.add_systems(
OnExit(IsPaused::Paused),
clear_state_bound_entities(IsPaused::Paused),
)
.add_systems(
Update,
(
// Instead of relying on [`AppState::InGame`] here, we're relying on
// [`IsPaused::Running`], since we don't want movement or color changes
// if we're paused
(movement, change_color).run_if(in_state(IsPaused::Running)),
// The pause toggle, on the other hand, needs to work whether we're
// paused or not, so it uses [`AppState::InGame`] instead.
toggle_pause.run_if(in_state(AppState::InGame)),
),
)
.add_systems(Update, log_transitions)
.run();
}
fn menu(
mut next_state: ResMut<NextState<AppState>>,
mut interaction_query: Query<
(&Interaction, &mut UiImage),
(Changed<Interaction>, With<Button>),
>,
) {
for (interaction, mut image) in &mut interaction_query {
let color = &mut image.color;
match *interaction {
Interaction::Pressed => {
*color = PRESSED_BUTTON;
next_state.set(AppState::InGame);
}
Interaction::Hovered => {
*color = HOVERED_BUTTON;
}
Interaction::None => {
*color = NORMAL_BUTTON;
}
}
}
}
fn cleanup_menu(mut commands: Commands, menu_data: Res<MenuData>) {
commands.entity(menu_data.button_entity).despawn_recursive();
}
const SPEED: f32 = 100.0;
fn movement(
time: Res<Time>,
input: Res<ButtonInput<KeyCode>>,
mut query: Query<&mut Transform, With<Sprite>>,
) {
for mut transform in &mut query {
let mut direction = Vec3::ZERO;
if input.pressed(KeyCode::ArrowLeft) {
direction.x -= 1.0;
}
if input.pressed(KeyCode::ArrowRight) {
direction.x += 1.0;
}
if input.pressed(KeyCode::ArrowUp) {
direction.y += 1.0;
}
if input.pressed(KeyCode::ArrowDown) {
direction.y -= 1.0;
}
if direction != Vec3::ZERO {
transform.translation += direction.normalize() * SPEED * time.delta_seconds();
}
}
}
fn change_color(time: Res<Time>, mut query: Query<&mut Sprite>) {
for mut sprite in &mut query {
let new_color = LinearRgba {
blue: (time.elapsed_seconds() * 0.5).sin() + 2.0,
..LinearRgba::from(sprite.color)
};
sprite.color = new_color.into();
}
}
fn toggle_pause(
input: Res<ButtonInput<KeyCode>>,
current_state: Res<State<IsPaused>>,
mut next_state: ResMut<NextState<IsPaused>>,
) {
if input.just_pressed(KeyCode::Space) {
next_state.set(match current_state.get() {
IsPaused::Running => IsPaused::Paused,
IsPaused::Paused => IsPaused::Running,
});
}
}
#[derive(Component)]
struct StateBound<S: States>(S);
fn clear_state_bound_entities<S: States>(
state: S,
) -> impl Fn(Commands, Query<(Entity, &StateBound<S>)>) {
move |mut commands, query| {
for (entity, bound) in &query {
if bound.0 == state {
commands.entity(entity).despawn_recursive();
}
}
}
}
/// print when an `AppState` transition happens
fn log_transitions(mut transitions: EventReader<StateTransitionEvent<AppState>>) {
for transition in transitions.read() {
info!(
"transition: {:?} => {:?}",
transition.before, transition.after
);
}
}
mod ui {
use crate::*;
#[derive(Resource)]
pub struct MenuData {
pub button_entity: Entity,
}
pub const NORMAL_BUTTON: Color = Color::srgb(0.15, 0.15, 0.15);
pub const HOVERED_BUTTON: Color = Color::srgb(0.25, 0.25, 0.25);
pub const PRESSED_BUTTON: Color = Color::srgb(0.35, 0.75, 0.35);
pub fn setup(mut commands: Commands) {
commands.spawn(Camera2dBundle::default());
}
pub fn setup_menu(mut commands: Commands) {
let button_entity = commands
.spawn(NodeBundle {
style: Style {
// center button
width: Val::Percent(100.),
height: Val::Percent(100.),
justify_content: JustifyContent::Center,
align_items: AlignItems::Center,
..default()
},
..default()
})
.with_children(|parent| {
parent
.spawn(ButtonBundle {
style: Style {
width: Val::Px(150.),
height: Val::Px(65.),
// horizontally center child text
justify_content: JustifyContent::Center,
// vertically center child text
align_items: AlignItems::Center,
..default()
},
image: UiImage::default().with_color(NORMAL_BUTTON),
..default()
})
.with_children(|parent| {
parent.spawn(TextBundle::from_section(
"Play",
TextStyle {
font_size: 40.0,
color: Color::srgb(0.9, 0.9, 0.9),
..default()
},
));
});
})
.id();
commands.insert_resource(MenuData { button_entity });
}
pub fn setup_game(mut commands: Commands, asset_server: Res<AssetServer>) {
commands.spawn(SpriteBundle {
texture: asset_server.load("branding/icon.png"),
..default()
});
}
pub fn setup_paused_screen(mut commands: Commands) {
commands
.spawn((
StateBound(IsPaused::Paused),
NodeBundle {
style: Style {
// center button
width: Val::Percent(100.),
height: Val::Percent(100.),
justify_content: JustifyContent::Center,
align_items: AlignItems::Center,
flex_direction: FlexDirection::Column,
row_gap: Val::Px(10.),
..default()
},
..default()
},
))
.with_children(|parent| {
parent
.spawn(NodeBundle {
style: Style {
width: Val::Px(400.),
height: Val::Px(400.),
// horizontally center child text
justify_content: JustifyContent::Center,
// vertically center child text
align_items: AlignItems::Center,
..default()
},
background_color: NORMAL_BUTTON.into(),
..default()
})
.with_children(|parent| {
parent.spawn(TextBundle::from_section(
"Paused",
TextStyle {
font_size: 40.0,
color: Color::srgb(0.9, 0.9, 0.9),
..default()
},
));
});
});
}
}