Learn BEVY with Real Code Examples

use bevy::prelude::*;

struct Counter(i32);

fn main() {
    App::build()
        .insert_resource(WindowDescriptor {
        title: "Bevy Counter".to_string(),
        width: 400.0,
        height: 300.0,
        ..Default::default()
        })
        .insert_resource(Counter(0))
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup.system())
        .add_system(update_counter.system())
        .run();
}

fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
    commands.spawn_bundle(UiCameraBundle::default());
    commands.spawn_bundle(TextBundle {
        text: Text::with_section(
        "Count: 0",
        TextStyle {
        font: asset_server.load("fonts/FiraSans-Bold.ttf"),
        font_size: 40.0,
        color: Color::WHITE,
        },
        Default::default(),
        ),
        ..Default::default()
    }).insert(Counter(0));
}

fn update_counter(
    keyboard_input: Res<Input<KeyCode>>,
    mut query: Query<(&mut Text, &mut Counter)>
) {
    for (mut text, mut counter) in query.iter_mut() {
        if keyboard_input.just_pressed(KeyCode::Up) {
        counter.0 += 1;
        }
        if keyboard_input.just_pressed(KeyCode::Down) {
        counter.0 -= 1;
        }
        text.sections[0].value = format!("Count: {}", counter.0);
    }
}

A minimal Bevy app that displays a counter on screen and updates it with keyboard input.

use bevy::prelude::*;

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup.system())
        .add_system(move_sprite.system())
        .run();
}

struct Player;

fn setup(mut commands: Commands, asset_server: Res<AssetServer>, mut materials: ResMut<Assets<ColorMaterial>>) {
    commands.spawn_bundle(OrthographicCameraBundle::new_2d());
    commands.spawn_bundle(SpriteBundle {
        material: materials.add(asset_server.load("player.png").into()),
        ..Default::default()
    }).insert(Player);
}

fn move_sprite(keyboard_input: Res<Input<KeyCode>>, mut query: Query<&mut Transform, With<Player>>) {
    for mut transform in query.iter_mut() {
        if keyboard_input.pressed(KeyCode::Left) { transform.translation.x -= 2.0; }
        if keyboard_input.pressed(KeyCode::Right) { transform.translation.x += 2.0; }
        if keyboard_input.pressed(KeyCode::Up) { transform.translation.y += 2.0; }
        if keyboard_input.pressed(KeyCode::Down) { transform.translation.y -= 2.0; }
    }
}

Moves a sprite with arrow keys.

use bevy::prelude::*;

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup.system())
        .add_system(update_fps.system())
        .run();
}

struct FpsText;

fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
    commands.spawn_bundle(UiCameraBundle::default());
    commands.spawn_bundle(TextBundle {
        text: Text::with_section(
        "FPS: 0",
        TextStyle {
        font: asset_server.load("fonts/FiraSans-Bold.ttf"),
        font_size: 30.0,
        color: Color::WHITE,
        },
        Default::default(),
        ),
        ..Default::default()
    }).insert(FpsText);
}

fn update_fps(time: Res<Time>, mut query: Query<&mut Text, With<FpsText>>) {
    for mut text in query.iter_mut() {
        text.sections[0].value = format!("FPS: {}", (1.0 / time.delta_seconds()) as i32);
    }
}

Displays FPS on screen using Bevy UI.

use bevy::prelude::*;

struct TimerEvent(Timer);

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .insert_resource(TimerEvent(Timer::from_seconds(1.0, true)))
        .add_system(timer_system.system())
        .run();
}

fn timer_system(time: Res<Time>, mut timer: ResMut<TimerEvent>) {
    timer.0.tick(time.delta());
    if timer.0.finished() {
        println!("Timer triggered!");
    }
}

Runs a repeating timer event in Bevy.

use bevy::prelude::*;

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .add_system(mouse_position.system())
        .run();
}

fn mouse_position(windows: Res<Windows>) {
    if let Some(window) = windows.get_primary() {
        if let Some(pos) = window.cursor_position() {
        println!("Mouse: x={}, y={}", pos.x, pos.y);
        }
    }
}

Prints mouse coordinates each frame.

use bevy::prelude::*;

struct AnimationTimer(Timer);
struct SpriteSheet;

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup.system())
        .add_system(animate_sprite.system())
        .run();
}

fn setup(mut commands: Commands) {
    commands.spawn_bundle(OrthographicCameraBundle::new_2d());
    commands.spawn().insert(SpriteSheet).insert(AnimationTimer(Timer::from_seconds(0.1, true)));
}

fn animate_sprite(time: Res<Time>, mut query: Query<&mut AnimationTimer>) {
    for mut timer in query.iter_mut() {
        timer.0.tick(time.delta());
        if timer.0.finished() {
        println!("Frame advanced");
        }
    }
}

Plays frame-based sprite animation using a timer.

use bevy::prelude::*;

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .add_system(keyboard_input.system())
        .run();
}

fn keyboard_input(keyboard_input: Res<Input<KeyCode>>) {
    if keyboard_input.just_pressed(KeyCode::Space) {
        println!("Space pressed!");
    }
    if keyboard_input.just_pressed(KeyCode::Return) {
        println!("Enter pressed!");
    }
}

Detects keyboard presses and prints the key pressed.

use bevy::prelude::*;

struct Mover;

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup.system())
        .add_system(move_entity.system())
        .run();
}

fn setup(mut commands: Commands) {
    commands.spawn().insert(Mover).insert(Transform::default()).insert(GlobalTransform::default());
}

fn move_entity(time: Res<Time>, mut query: Query<&mut Transform, With<Mover>>) {
    for mut transform in query.iter_mut() {
        transform.translation.x += 50.0 * time.delta_seconds();
    }
}

Spawns an entity and moves it automatically.

use bevy::prelude::*;

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .add_system(mouse_click.system())
        .run();
}

fn mouse_click(mouse_input: Res<Input<MouseButton>>) {
    if mouse_input.just_pressed(MouseButton::Left) {
        println!("Left click!");
    }
    if mouse_input.just_pressed(MouseButton::Right) {
        println!("Right click!");
    }
}

Detects mouse clicks in a Bevy window.

use bevy::prelude::*;
use rand::prelude::*;

struct Walker;

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup.system())
        .add_system(random_move.system())
        .run();
}

fn setup(mut commands: Commands) {
    commands.spawn().insert(Walker).insert(Transform::default()).insert(GlobalTransform::default());
}

fn random_move(mut query: Query<&mut Transform, With<Walker>>) {
    let mut rng = thread_rng();
    for mut transform in query.iter_mut() {
        transform.translation.x += rng.gen_range(-1.0..1.0);
        transform.translation.y += rng.gen_range(-1.0..1.0);
    }
}

Moves an entity randomly each frame.