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bevy/examples/games/game_menu.rs
Joseph d66c868e6f
Expressively define plugins using functions (#11080) 
# Objective

Plugins are an incredible tool for encapsulating functionality. They are
low-key one of Bevy's best features. Combined with rust's module and
privacy system, it's a match made in heaven.

The one downside is that they can be a little too verbose to define. 90%
of all plugin definitions look something like this:

```rust
pub struct MyPlugin;

impl Plugin for MyPlugin {
    fn build(&self, app: &mut App) {
        app.init_resource::<CameraAssets>()
           .add_event::<SetCamera>()
           .add_systems(Update, (collect_set_camera_events, drive_camera).chain());
    }
}
```

Every so often it gets a little spicier:

```rust
pub struct MyGenericPlugin<T>(PhantomData<T>);

impl<T> Default for MyGenericPlugin<T> { 
    fn default() -> Self { ... }
 }

impl<T> Plugin for MyGenericPlugin<T> { ... }
```

This is an annoying amount of boilerplate. Ideally, plugins should be
focused and small in scope, which means any app is going to have a *lot*
of them. Writing a plugin should be as easy as possible, and the *only*
part of this process that carries any meaning is the body of `fn build`.

## Solution

Implement `Plugin` for functions that take `&mut App` as a parameter.

The two examples above now look like this:

```rust
pub fn my_plugin(app: &mut App) {
    app.init_resource::<CameraAssets>()
       .add_event::<SetCamera>()
       .add_systems(Update, (collect_set_camera_events, drive_camera).chain());
} 

pub fn my_generic_plugin<T>(app: &mut App) {
    // No need for PhantomData, it just works.
}
```

Almost all plugins can be written this way, which I believe will make
bevy code much more attractive. Less boilerplate and less meaningless
indentation. More plugins with smaller scopes.

---

## Changelog

The `Plugin` trait is now implemented for all functions that take `&mut
App` as their only parameter. This is an abbreviated way of defining
plugins with less boilerplate than manually implementing the trait.

---------

Co-authored-by: Federico Rinaldi <gisquerin@gmail.com>
2024-01-27 02:40:15 +00:00

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//! This example will display a simple menu using Bevy UI where you can start a new game,
//! change some settings or quit. There is no actual game, it will just display the current
//! settings for 5 seconds before going back to the menu.
use bevy::prelude::*;
const TEXT_COLOR: Color = Color::rgb(0.9, 0.9, 0.9);
// Enum that will be used as a global state for the game
#[derive(Clone, Copy, Default, Eq, PartialEq, Debug, Hash, States)]
enum GameState {
#[default]
Splash,
Menu,
Game,
}
// One of the two settings that can be set through the menu. It will be a resource in the app
#[derive(Resource, Debug, Component, PartialEq, Eq, Clone, Copy)]
enum DisplayQuality {
Low,
Medium,
High,
}
// One of the two settings that can be set through the menu. It will be a resource in the app
#[derive(Resource, Debug, Component, PartialEq, Eq, Clone, Copy)]
struct Volume(u32);
fn main() {
App::new()
.add_plugins(DefaultPlugins)
// Insert as resource the initial value for the settings resources
.insert_resource(DisplayQuality::Medium)
.insert_resource(Volume(7))
// Declare the game state, whose starting value is determined by the `Default` trait
.init_state::<GameState>()
.add_systems(Startup, setup)
// Adds the plugins for each state
.add_plugins((splash::splash_plugin, menu::menu_plugin, game::game_plugin))
.run();
}
fn setup(mut commands: Commands) {
commands.spawn(Camera2dBundle::default());
}
mod splash {
use bevy::prelude::*;
use super::{despawn_screen, GameState};
// This plugin will display a splash screen with Bevy logo for 1 second before switching to the menu
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)),
);
}
// State used for the current menu screen
#[derive(Clone, Copy, Default, Eq, PartialEq, Debug, Hash, States)]
enum MenuState {
Main,
Settings,
SettingsDisplay,
SettingsSound,
#[default]
Disabled,
}
// Tag component used to tag entities added on the main menu screen
#[derive(Component)]
struct OnMainMenuScreen;
// Tag component used to tag entities added on the settings menu screen
#[derive(Component)]
struct OnSettingsMenuScreen;
// Tag component used to tag entities added on the display settings menu screen
#[derive(Component)]
struct OnDisplaySettingsMenuScreen;
// Tag component used to tag entities added on the sound settings menu screen
#[derive(Component)]
struct OnSoundSettingsMenuScreen;
const NORMAL_BUTTON: Color = Color::rgb(0.15, 0.15, 0.15);
const HOVERED_BUTTON: Color = Color::rgb(0.25, 0.25, 0.25);
const HOVERED_PRESSED_BUTTON: Color = Color::rgb(0.25, 0.65, 0.25);
const PRESSED_BUTTON: Color = Color::rgb(0.35, 0.75, 0.35);
// Tag component used to mark which setting is currently selected
#[derive(Component)]
struct SelectedOption;
// All actions that can be triggered from a button click
#[derive(Component)]
enum MenuButtonAction {
Play,
Settings,
SettingsDisplay,
SettingsSound,
BackToMainMenu,
BackToSettings,
Quit,
}
// This system handles changing all buttons color based on mouse interaction
fn button_system(
mut interaction_query: Query<
(&Interaction, &mut BackgroundColor, Option<&SelectedOption>),
(Changed<Interaction>, With<Button>),
>,
) {
for (interaction, mut color, selected) in &mut interaction_query {
*color = match (*interaction, selected) {
(Interaction::Pressed, _) | (Interaction::None, Some(_)) => PRESSED_BUTTON.into(),
(Interaction::Hovered, Some(_)) => HOVERED_PRESSED_BUTTON.into(),
(Interaction::Hovered, None) => HOVERED_BUTTON.into(),
(Interaction::None, None) => NORMAL_BUTTON.into(),
}
}
}
// This system updates the settings when a new value for a setting is selected, and marks
// the button as the one currently selected
fn setting_button<T: Resource + Component + PartialEq + Copy>(
interaction_query: Query<(&Interaction, &T, Entity), (Changed<Interaction>, With<Button>)>,
mut selected_query: Query<(Entity, &mut BackgroundColor), With<SelectedOption>>,
mut commands: Commands,
mut setting: ResMut<T>,
) {
for (interaction, button_setting, entity) in &interaction_query {
if *interaction == Interaction::Pressed && *setting != *button_setting {
let (previous_button, mut previous_color) = selected_query.single_mut();
*previous_color = NORMAL_BUTTON.into();
commands.entity(previous_button).remove::<SelectedOption>();
commands.entity(entity).insert(SelectedOption);
*setting = *button_setting;
}
}
}
fn menu_setup(mut menu_state: ResMut<NextState<MenuState>>) {
menu_state.set(MenuState::Main);
}
fn main_menu_setup(mut commands: Commands, asset_server: Res<AssetServer>) {
// Common style for all buttons on the screen
let button_style = Style {
width: Val::Px(250.0),
height: Val::Px(65.0),
margin: UiRect::all(Val::Px(20.0)),
justify_content: JustifyContent::Center,
align_items: AlignItems::Center,
..default()
};
let button_icon_style = Style {
width: Val::Px(30.0),
// This takes the icons out of the flexbox flow, to be positioned exactly
position_type: PositionType::Absolute,
// The icon will be close to the left border of the button
left: Val::Px(10.0),
..default()
};
let button_text_style = TextStyle {
font_size: 40.0,
color: TEXT_COLOR,
..default()
};
commands
.spawn((
NodeBundle {
style: Style {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
align_items: AlignItems::Center,
justify_content: JustifyContent::Center,
..default()
},
..default()
},
OnMainMenuScreen,
))
.with_children(|parent| {
parent
.spawn(NodeBundle {
style: Style {
flex_direction: FlexDirection::Column,
align_items: AlignItems::Center,
..default()
},
background_color: Color::CRIMSON.into(),
..default()
})
.with_children(|parent| {
// Display the game name
parent.spawn(
TextBundle::from_section(
"Bevy Game Menu UI",
TextStyle {
font_size: 80.0,
color: TEXT_COLOR,
..default()
},
)
.with_style(Style {
margin: UiRect::all(Val::Px(50.0)),
..default()
}),
);
// Display three buttons for each action available from the main menu:
// - new game
// - settings
// - quit
parent
.spawn((
ButtonBundle {
style: button_style.clone(),
background_color: NORMAL_BUTTON.into(),
..default()
},
MenuButtonAction::Play,
))
.with_children(|parent| {
let icon = asset_server.load("textures/Game Icons/right.png");
parent.spawn(ImageBundle {
style: button_icon_style.clone(),
image: UiImage::new(icon),
..default()
});
parent.spawn(TextBundle::from_section(
"New Game",
button_text_style.clone(),
));
});
parent
.spawn((
ButtonBundle {
style: button_style.clone(),
background_color: NORMAL_BUTTON.into(),
..default()
},
MenuButtonAction::Settings,
))
.with_children(|parent| {
let icon = asset_server.load("textures/Game Icons/wrench.png");
parent.spawn(ImageBundle {
style: button_icon_style.clone(),
image: UiImage::new(icon),
..default()
});
parent.spawn(TextBundle::from_section(
"Settings",
button_text_style.clone(),
));
});
parent
.spawn((
ButtonBundle {
style: button_style,
background_color: NORMAL_BUTTON.into(),
..default()
},
MenuButtonAction::Quit,
))
.with_children(|parent| {
let icon = asset_server.load("textures/Game Icons/exitRight.png");
parent.spawn(ImageBundle {
style: button_icon_style,
image: UiImage::new(icon),
..default()
});
parent.spawn(TextBundle::from_section("Quit", button_text_style));
});
});
});
}
fn settings_menu_setup(mut commands: Commands) {
let button_style = Style {
width: Val::Px(200.0),
height: Val::Px(65.0),
margin: UiRect::all(Val::Px(20.0)),
justify_content: JustifyContent::Center,
align_items: AlignItems::Center,
..default()
};
let button_text_style = TextStyle {
font_size: 40.0,
color: TEXT_COLOR,
..default()
};
commands
.spawn((
NodeBundle {
style: Style {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
align_items: AlignItems::Center,
justify_content: JustifyContent::Center,
..default()
},
..default()
},
OnSettingsMenuScreen,
))
.with_children(|parent| {
parent
.spawn(NodeBundle {
style: Style {
flex_direction: FlexDirection::Column,
align_items: AlignItems::Center,
..default()
},
background_color: Color::CRIMSON.into(),
..default()
})
.with_children(|parent| {
for (action, text) in [
(MenuButtonAction::SettingsDisplay, "Display"),
(MenuButtonAction::SettingsSound, "Sound"),
(MenuButtonAction::BackToMainMenu, "Back"),
] {
parent
.spawn((
ButtonBundle {
style: button_style.clone(),
background_color: NORMAL_BUTTON.into(),
..default()
},
action,
))
.with_children(|parent| {
parent.spawn(TextBundle::from_section(
text,
button_text_style.clone(),
));
});
}
});
});
}
fn display_settings_menu_setup(mut commands: Commands, display_quality: Res<DisplayQuality>) {
let button_style = Style {
width: Val::Px(200.0),
height: Val::Px(65.0),
margin: UiRect::all(Val::Px(20.0)),
justify_content: JustifyContent::Center,
align_items: AlignItems::Center,
..default()
};
let button_text_style = TextStyle {
font_size: 40.0,
color: TEXT_COLOR,
..default()
};
commands
.spawn((
NodeBundle {
style: Style {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
align_items: AlignItems::Center,
justify_content: JustifyContent::Center,
..default()
},
..default()
},
OnDisplaySettingsMenuScreen,
))
.with_children(|parent| {
parent
.spawn(NodeBundle {
style: Style {
flex_direction: FlexDirection::Column,
align_items: AlignItems::Center,
..default()
},
background_color: Color::CRIMSON.into(),
..default()
})
.with_children(|parent| {
// Create a new `NodeBundle`, this time not setting its `flex_direction`. It will
// use the default value, `FlexDirection::Row`, from left to right.
parent
.spawn(NodeBundle {
style: Style {
align_items: AlignItems::Center,
..default()
},
background_color: Color::CRIMSON.into(),
..default()
})
.with_children(|parent| {
// Display a label for the current setting
parent.spawn(TextBundle::from_section(
"Display Quality",
button_text_style.clone(),
));
// Display a button for each possible value
for quality_setting in [
DisplayQuality::Low,
DisplayQuality::Medium,
DisplayQuality::High,
] {
let mut entity = parent.spawn((
ButtonBundle {
style: Style {
width: Val::Px(150.0),
height: Val::Px(65.0),
..button_style.clone()
},
background_color: NORMAL_BUTTON.into(),
..default()
},
quality_setting,
));
entity.with_children(|parent| {
parent.spawn(TextBundle::from_section(
format!("{quality_setting:?}"),
button_text_style.clone(),
));
});
if *display_quality == quality_setting {
entity.insert(SelectedOption);
}
}
});
// Display the back button to return to the settings screen
parent
.spawn((
ButtonBundle {
style: button_style,
background_color: NORMAL_BUTTON.into(),
..default()
},
MenuButtonAction::BackToSettings,
))
.with_children(|parent| {
parent.spawn(TextBundle::from_section("Back", button_text_style));
});
});
});
}
fn sound_settings_menu_setup(mut commands: Commands, volume: Res<Volume>) {
let button_style = Style {
width: Val::Px(200.0),
height: Val::Px(65.0),
margin: UiRect::all(Val::Px(20.0)),
justify_content: JustifyContent::Center,
align_items: AlignItems::Center,
..default()
};
let button_text_style = TextStyle {
font_size: 40.0,
color: TEXT_COLOR,
..default()
};
commands
.spawn((
NodeBundle {
style: Style {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
align_items: AlignItems::Center,
justify_content: JustifyContent::Center,
..default()
},
..default()
},
OnSoundSettingsMenuScreen,
))
.with_children(|parent| {
parent
.spawn(NodeBundle {
style: Style {
flex_direction: FlexDirection::Column,
align_items: AlignItems::Center,
..default()
},
background_color: Color::CRIMSON.into(),
..default()
})
.with_children(|parent| {
parent
.spawn(NodeBundle {
style: Style {
align_items: AlignItems::Center,
..default()
},
background_color: Color::CRIMSON.into(),
..default()
})
.with_children(|parent| {
parent.spawn(TextBundle::from_section(
"Volume",
button_text_style.clone(),
));
for volume_setting in [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] {
let mut entity = parent.spawn((
ButtonBundle {
style: Style {
width: Val::Px(30.0),
height: Val::Px(65.0),
..button_style.clone()
},
background_color: NORMAL_BUTTON.into(),
..default()
},
Volume(volume_setting),
));
if *volume == Volume(volume_setting) {
entity.insert(SelectedOption);
}
}
});
parent
.spawn((
ButtonBundle {
style: button_style,
background_color: NORMAL_BUTTON.into(),
..default()
},
MenuButtonAction::BackToSettings,
))
.with_children(|parent| {
parent.spawn(TextBundle::from_section("Back", button_text_style));
});
});
});
}
fn menu_action(
interaction_query: Query<
(&Interaction, &MenuButtonAction),
(Changed<Interaction>, With<Button>),
>,
mut app_exit_events: EventWriter<AppExit>,
mut menu_state: ResMut<NextState<MenuState>>,
mut game_state: ResMut<NextState<GameState>>,
) {
for (interaction, menu_button_action) in &interaction_query {
if *interaction == Interaction::Pressed {
match menu_button_action {
MenuButtonAction::Quit => {
app_exit_events.send(AppExit);
}
MenuButtonAction::Play => {
game_state.set(GameState::Game);
menu_state.set(MenuState::Disabled);
}
MenuButtonAction::Settings => menu_state.set(MenuState::Settings),
MenuButtonAction::SettingsDisplay => {
menu_state.set(MenuState::SettingsDisplay);
}
MenuButtonAction::SettingsSound => {
menu_state.set(MenuState::SettingsSound);
}
MenuButtonAction::BackToMainMenu => menu_state.set(MenuState::Main),
MenuButtonAction::BackToSettings => {
menu_state.set(MenuState::Settings);
}
}
}
}
}
}
// Generic system that takes a component as a parameter, and will despawn all entities with that component
fn despawn_screen<T: Component>(to_despawn: Query<Entity, With<T>>, mut commands: Commands) {
for entity in &to_despawn {
commands.entity(entity).despawn_recursive();
}
}
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