diff --git a/.gitignore b/.gitignore
index bf0a94c..6b04bfa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
-/build/*
-!/build/index.html
+/build/*/*
+!/build/breakout/index.html
+!/build/paddle/index.html
 
 /target
diff --git a/Cargo.toml b/Cargo.toml
index e08b822..ad35080 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,6 +2,7 @@
 name = "breakout"
 version = "0.1.0"
 edition = "2024"
+default-run = "breakout"
 
 [dependencies]
 bevy = { version = "0.19.0", features = ["debug_glam_assert"] }
@@ -9,6 +10,9 @@ chacha20 = { version = "0.10.1", default-features = false, features = ["rng"] }
 getrandom = "0.4.3"
 rand = "0.10.2"
 
+[[bin]]
+name = "paddle"
+
 [features]
 default = ["debug"]
 debug = ["bevy/debug"]
diff --git a/Makefile b/Makefile
index d93b7c6..072a803 100644
--- a/Makefile
+++ b/Makefile
@@ -8,9 +8,12 @@ help: ## List targets in this Makefile
 
 .PHONY: build
 build:
-	cargo build --release --target wasm32-unknown-unknown --no-default-features --features wasm
-	wasm-bindgen --target web --out-dir build target/wasm32-unknown-unknown/release/breakout.wasm
+	cargo build --bin breakout --release --target wasm32-unknown-unknown --no-default-features --features wasm
+	wasm-bindgen --target web --out-dir build/breakout target/wasm32-unknown-unknown/release/breakout.wasm
+
+	cargo build --bin paddle --release --target wasm32-unknown-unknown --no-default-features --features wasm
+	wasm-bindgen --target web --out-dir build/paddle target/wasm32-unknown-unknown/release/paddle.wasm
 
 .PHONY: publish
 publish:
-	rsync --verbose --checksum --recursive --safe-links --delete --progress build/ root@lab:/www/games/breakout
+	rsync --verbose --checksum --recursive --safe-links --delete --progress build/breakout/ root@lab:/www/games/breakout
diff --git a/build/index.html b/build/breakout/index.html
similarity index 100%
rename from build/index.html
rename to build/breakout/index.html
diff --git a/build/paddle/index.html b/build/paddle/index.html
new file mode 100644
index 0000000..453547e
--- /dev/null
+++ b/build/paddle/index.html
@@ -0,0 +1,40 @@
+<html lang="en">
+	<head>
+		<meta charset="utf-8">
+		<style>
+			body {
+				height: 100vh;
+				width: 100vw;
+				display: flex;
+				align-items: center;
+				justify-content: center;
+				background-color: #222222;
+				color: white;
+			}
+			canvas {
+				background-color: black;
+			}
+			.mono {
+				font-family: monospace;
+			}
+		</style>
+		<title>Breakout</title>
+	</head>
+	<body>
+		<div>
+			<canvas id="paddle"></canvas>
+			<p style="text-align: center;">
+				Use
+				<span class="mono">⬅</span>
+				<span class="mono">➡</span>
+				to move the paddle and
+				<span class="mono">WASD</span>
+				to move the ball.
+			</p>
+		</div>
+		<script type="module">
+			import init from './paddle.js';
+			init();
+		</script>
+	</body>
+</html>
diff --git a/src/bin/paddle.rs b/src/bin/paddle.rs
new file mode 100644
index 0000000..f1c6795
--- /dev/null
+++ b/src/bin/paddle.rs
@@ -0,0 +1,156 @@
+use bevy::ecs::query::QueryData;
+use bevy::math::bounding::Aabb2d;
+use bevy::prelude::*;
+
+use breakout::debug::DebugPlugin;
+use breakout::*;
+
+const WORLD_SIZE: Vec2 = Vec2::new(480., 320.);
+const CAMERA_SCALE: f32 = 2.;
+
+fn main() {
+    App::new()
+        .insert_resource(ClearColor(Color::BLACK))
+        .add_plugins(DebugPlugin)
+        .add_plugins(DefaultPlugins.set(WindowPlugin {
+            // Until there's a reliable way to hint that a game window should
+            // float on tiling window managers, the most reliable way to achieve
+            // that is to define a fixed non-resizable window.
+            //
+            // https://github.com/rust-windowing/winit/issues/862#issuecomment-2047791401
+            primary_window: Some(Window {
+                focused: false,
+                canvas: Some("#paddle".into()),
+                resize_constraints: WindowResizeConstraints {
+                    min_width: CAMERA_SCALE * WORLD_SIZE.x,
+                    min_height: CAMERA_SCALE * WORLD_SIZE.y,
+                    max_width: CAMERA_SCALE * WORLD_SIZE.x,
+                    max_height: CAMERA_SCALE * WORLD_SIZE.y,
+                },
+                ..default()
+            }),
+            ..default()
+        }))
+        .add_systems(Startup, setup)
+        .add_systems(
+            FixedUpdate,
+            (move_paddle, move_ball, draw_trajectory).chain(),
+        )
+        .run();
+}
+
+const PADDLE_START: Vec3 = Vec3::new(WORLD_SIZE.x / 2., Paddle::SIZE.y / 2. + Paddle::GAP, 0.);
+
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<ColorMaterial>>,
+) {
+    commands.spawn((
+        Camera2d,
+        Transform::from_translation((WORLD_SIZE / 2.).extend(0.)),
+        Projection::Orthographic(OrthographicProjection {
+            scale: 1. / CAMERA_SCALE,
+            ..OrthographicProjection::default_2d()
+        }),
+    ));
+
+    commands.spawn(Ball::build(&mut meshes, &mut materials));
+
+    commands.spawn((
+        Paddle,
+        Sprite::from_color(Paddle::COLOR, Vec2::ONE),
+        Transform {
+            translation: PADDLE_START,
+            scale: Paddle::SIZE.extend(1.),
+            ..default()
+        },
+        Collider::Aabb(Aabb2d::new(Vec2::ZERO, Paddle::SIZE / 2.)),
+    ));
+}
+
+pub fn move_paddle(
+    time: Res<Time>,
+    input: Res<ButtonInput<KeyCode>>,
+    mut paddle: Single<&mut Transform, With<Paddle>>,
+) {
+    let mut v = Vec3::ZERO;
+    if input.pressed(KeyCode::ArrowLeft) {
+        v.x -= 1.;
+    }
+    if input.pressed(KeyCode::ArrowRight) {
+        v.x += 1.;
+    }
+
+    if v == Vec3::ZERO {
+        return;
+    }
+
+    let delta = v.normalize() * Paddle::SPEED * time.delta_secs();
+    paddle.translation += delta;
+
+    let w = Paddle::SIZE.x / 2.;
+    let x = paddle
+        .translation
+        .x
+        .clamp(PADDLE_START.x - w, PADDLE_START.x + w);
+    paddle.translation.x = x;
+}
+
+#[derive(QueryData)]
+struct PaddleQuery {
+    entity: Entity,
+    transform: &'static Transform,
+    collider: &'static Collider,
+    _paddle: &'static Paddle,
+}
+
+#[derive(QueryData)]
+struct BallQuery {
+    entity: Entity,
+    transform: &'static Transform,
+    _ball: &'static Ball,
+}
+
+fn move_ball(
+    time: Res<Time>,
+    input: Res<ButtonInput<KeyCode>>,
+    mut ball: Single<&mut Transform, With<Ball>>,
+) {
+    let mut v = Vec3::ZERO;
+    if input.pressed(KeyCode::KeyW) {
+        v.y += 1.;
+    }
+    if input.pressed(KeyCode::KeyS) {
+        v.y -= 1.;
+    }
+    if input.pressed(KeyCode::KeyA) {
+        v.x -= 1.;
+    }
+    if input.pressed(KeyCode::KeyD) {
+        v.x += 1.;
+    }
+
+    if v == Vec3::ZERO {
+        return;
+    }
+
+    let delta = v.normalize() * Paddle::SPEED * time.delta_secs();
+    ball.translation += delta;
+}
+
+fn draw_trajectory(mut gizmos: Gizmos, paddle: Single<PaddleQuery>, ball: Single<BallQuery>) {
+    let ball_pos = ball.transform.translation.truncate();
+    let paddle_pos = paddle.transform.translation.truncate();
+
+    let collision_point = PADDLE_START.truncate() + Paddle::SIZE.with_x(0.) / 2.;
+
+    let velocity = collision_point - ball_pos;
+
+    let exit_v = velocity.reflect(Vec2::Y);
+
+    let destination_point = paddle_bounce(paddle_pos, collision_point, exit_v);
+
+    gizmos.line_2d(ball_pos, collision_point, LinearRgba::BLUE);
+    gizmos.ray_2d(collision_point, destination_point, LinearRgba::GREEN);
+}
diff --git a/src/debug.rs b/src/debug.rs
index 0635da9..71ace3d 100644
--- a/src/debug.rs
+++ b/src/debug.rs
@@ -2,7 +2,7 @@ use bevy::prelude::*;
 
 use crate::{Brick, GameState, WORLD_SIZE};
 
-pub(crate) struct DebugPlugin;
+pub struct DebugPlugin;
 
 impl Plugin for DebugPlugin {
     fn build(&self, app: &mut App) {
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..d956467
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,539 @@
+use bevy::ecs::query::QueryData;
+pub use bevy::math::bounding::{
+    Aabb2d, Bounded2d, BoundingCircle, BoundingVolume, IntersectsVolume,
+};
+use bevy::prelude::*;
+use bevy::sprite::Anchor;
+use core::f32::consts::PI;
+
+pub mod debug;
+
+use crate::debug::DebugPlugin;
+
+pub struct Breakout;
+
+impl Plugin for Breakout {
+    fn build(&self, app: &mut App) {
+        app.insert_resource(ClearColor(Color::BLACK))
+            .init_resource::<Level>()
+            .init_resource::<Score>()
+            .init_resource::<Lives>()
+            .add_plugins(DefaultPlugins.set(WindowPlugin {
+                // Until there's a reliable way to hint that a game window should
+                // float on tiling window managers, the most reliable way to achieve
+                // that is to define a fixed non-resizable window.
+                //
+                // https://github.com/rust-windowing/winit/issues/862#issuecomment-2047791401
+                primary_window: Some(Window {
+                    canvas: Some("#breakout".into()),
+                    resize_constraints: WindowResizeConstraints {
+                        min_width: WORLD_SIZE.x,
+                        min_height: WORLD_SIZE.y,
+                        max_width: WORLD_SIZE.x,
+                        max_height: WORLD_SIZE.y,
+                    },
+                    ..default()
+                }),
+                ..default()
+            }))
+            .add_plugins(DebugPlugin)
+            .init_state::<GameState>()
+            .add_systems(Startup, setup)
+            .add_systems(
+                FixedUpdate,
+                (
+                    (collisions, cleared_level, void_out, move_ball)
+                        .chain()
+                        .run_if(in_state(GameState::Play)),
+                    move_paddle,
+                    show_score,
+                    show_lives.run_if(resource_changed::<Lives>),
+                    serve_ball.run_if(in_state(GameState::Serve)),
+                )
+                    .chain(),
+            )
+            .add_systems(OnEnter(GameState::Build), build_level)
+            .add_systems(OnEnter(GameState::Over), reset_game);
+    }
+}
+
+const WORLD_SIZE: Vec2 = Vec2::new(480., 640.);
+
+#[derive(States, Debug, Copy, Clone, PartialEq, Eq, Hash, Default)]
+enum GameState {
+    #[default]
+    Build,
+    Serve,
+    Play,
+    Over,
+}
+
+#[derive(Resource, Debug, Copy, Clone, PartialEq, Eq, Default)]
+struct Level(u8);
+
+#[derive(Resource, Debug, Copy, Clone, PartialEq, Eq, Deref)]
+struct Lives(u8);
+
+impl Default for Lives {
+    fn default() -> Self {
+        Self(3)
+    }
+}
+
+#[derive(Resource, Debug, Copy, Clone, PartialEq, Eq, Default, Deref)]
+struct Score(u64);
+
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<ColorMaterial>>,
+) {
+    commands.spawn((
+        Camera2d,
+        Transform::from_translation((WORLD_SIZE / 2.).extend(0.)),
+    ));
+
+    commands.spawn(Ball::build(&mut meshes, &mut materials));
+
+    commands.spawn(Wall::top());
+    commands.spawn(Wall::left());
+    commands.spawn(Wall::right());
+    // There's no bottom wall because that's a void plane instead.
+    commands.spawn((
+        VoidPlane(Plane2d::new(Vec2::Y)),
+        Transform::from_translation(Vec3::ZERO),
+    ));
+    commands.add_observer(on_void_out);
+
+    commands.spawn((
+        Paddle,
+        Sprite::from_color(Paddle::COLOR, Vec2::ONE),
+        Transform {
+            translation: Vec3::new(WORLD_SIZE.x / 2., Paddle::SIZE.y / 2. + Paddle::GAP, 0.),
+            scale: Paddle::SIZE.extend(1.),
+            ..default()
+        },
+        Collider::Aabb(Aabb2d::new(Vec2::ZERO, Paddle::SIZE / 2.)),
+    ));
+
+    commands.spawn((
+        ScoreText,
+        Text2d::default(),
+        TextLayout::justify(Justify::Right),
+        Anchor::BOTTOM_RIGHT,
+        Transform::from_translation(Vec3::new(WORLD_SIZE.x - 8., WORLD_SIZE.y - HUD_HEIGHT, 1.)),
+    ));
+
+    commands.add_observer(start_game);
+}
+
+#[derive(Component, Debug)]
+pub struct Ball;
+
+impl Ball {
+    pub const COLOR: Color = Color::LinearRgba(LinearRgba::GREEN);
+    pub const RADIUS: f32 = 8.;
+    pub const SPAWN_POSITION: Vec2 = Vec2::new(WORLD_SIZE.x / 2., 40.);
+    pub const SERVE_SPEED: f32 = 200.;
+    pub const MAX_SPEED: f32 = 900.;
+
+    pub fn build(
+        meshes: &mut ResMut<Assets<Mesh>>,
+        materials: &mut ResMut<Assets<ColorMaterial>>,
+    ) -> impl Bundle {
+        (
+            Ball,
+            Mesh2d(meshes.add(Circle::new(Ball::RADIUS))),
+            MeshMaterial2d(materials.add(Ball::COLOR)),
+            Transform::from_translation(Ball::SPAWN_POSITION.extend(0.)),
+            Velocity(Vec2::ZERO),
+        )
+    }
+}
+
+#[derive(Component, Debug, Copy, Clone, PartialEq, Deref, DerefMut)]
+struct Velocity(Vec2);
+
+#[derive(Component, Debug)]
+struct Wall;
+
+impl Wall {
+    const COLOR: Color = Color::LinearRgba(LinearRgba::rgb(0.5, 0.5, 0.5));
+    const THICKNESS: f32 = 4.;
+
+    const LENGTH_VERTICAL: f32 = WORLD_SIZE.y - HUD_HEIGHT;
+
+    fn top() -> impl Bundle {
+        (
+            Wall,
+            Sprite::from_color(Wall::COLOR, Vec2::ONE),
+            Transform {
+                translation: Vec3::new(
+                    WORLD_SIZE.x / 2.,
+                    WORLD_SIZE.y - Wall::THICKNESS / 2. - HUD_HEIGHT,
+                    0.,
+                ),
+                scale: Vec3::new(WORLD_SIZE.x, Wall::THICKNESS, 1.),
+                ..default()
+            },
+            Collider::Plane(Plane2d::new(Vec2::NEG_Y)),
+        )
+    }
+
+    fn left() -> impl Bundle {
+        let x = Wall::THICKNESS / 2.;
+        (
+            Wall,
+            Sprite::from_color(Wall::COLOR, Vec2::ONE),
+            Transform {
+                translation: Vec3::new(x, Self::LENGTH_VERTICAL / 2., 0.),
+                scale: Vec3::new(Wall::THICKNESS, Self::LENGTH_VERTICAL, 1.),
+                ..default()
+            },
+            Collider::Plane(Plane2d::new(Vec2::X)),
+        )
+    }
+
+    fn right() -> impl Bundle {
+        let x = WORLD_SIZE.x - Wall::THICKNESS / 2.;
+        (
+            Wall,
+            Sprite::from_color(Wall::COLOR, Vec2::ONE),
+            Transform {
+                translation: Vec3::new(x, Self::LENGTH_VERTICAL / 2., 0.),
+                scale: Vec3::new(Wall::THICKNESS, Self::LENGTH_VERTICAL, 1.),
+                ..default()
+            },
+            Collider::Plane(Plane2d::new(Vec2::NEG_X)),
+        )
+    }
+}
+
+#[derive(Component, Debug)]
+pub struct Paddle;
+
+impl Paddle {
+    pub const COLOR: Color = Color::LinearRgba(LinearRgba::rgb(0., 1., 1.));
+    pub const SIZE: Vec2 = Vec2::new(60., 10.);
+    pub const GAP: f32 = 4.;
+    pub const SPEED: f32 = WORLD_SIZE.x / 2.;
+}
+
+#[derive(Component, Debug)]
+pub enum Collider {
+    Aabb(Aabb2d),
+    Plane(Plane2d),
+}
+
+#[derive(QueryData)]
+struct ColliderData {
+    entity: Entity,
+    transform: &'static Transform,
+    collider: &'static Collider,
+    brick: Has<Brick>,
+    paddle: Has<Paddle>,
+}
+
+fn collisions(
+    mut commands: Commands,
+    ball: Single<(&Transform, &mut Velocity), With<Ball>>,
+    colliders: Query<ColliderData, Without<Ball>>,
+    mut score: ResMut<Score>,
+) {
+    let (transform, mut velocity) = ball.into_inner();
+    let circle = BoundingCircle::new(transform.translation.truncate(), Ball::RADIUS);
+
+    for object in colliders {
+        let tx = object.transform.translation.truncate();
+
+        let target = match object.collider {
+            Collider::Aabb(aabb) => aabb.translated_by(tx),
+            Collider::Plane(plane) => plane.aabb_2d(tx),
+        };
+        if !target.intersects(&circle) {
+            continue;
+        }
+
+        if object.brick {
+            commands.entity(object.entity).despawn();
+            score.0 += Brick::SCORE;
+        }
+
+        let point = target.closest_point(circle.center);
+        let normal = match object.collider {
+            Collider::Plane(plane) => plane.normal.as_vec2(),
+            Collider::Aabb(_) => {
+                let dist = circle.center - point;
+
+                if dist.x.abs() > dist.y.abs() {
+                    if dist.x < 0. { Vec2::NEG_X } else { Vec2::X }
+                } else {
+                    if dist.y < 0. { Vec2::NEG_Y } else { Vec2::Y }
+                }
+            }
+        };
+
+        // Only reflect if the current velocity has a component moving *against*
+        // the box face's normal vector. This allows the ball to exit the box
+        // without getting stuck "re-colliding" with it.
+        //
+        // Put another way, if the ball is already moving in the same direction
+        // that the plane would bounce it, that's not a real collision!
+        if velocity.dot(normal) >= 0. {
+            continue;
+        }
+
+        let mut v = velocity.reflect(normal);
+
+        if object.paddle && normal == Vec2::Y {
+            v = paddle_bounce(tx, point, v);
+        }
+
+        velocity.0 = v.clamp_length_max(Ball::MAX_SPEED);
+    }
+}
+
+pub fn paddle_bounce(paddle: Vec2, collision: Vec2, velocity: Vec2) -> Vec2 {
+    let offset = (collision.x - paddle.x) / Paddle::SIZE.x;
+    let tilt = (0.).lerp(-PI / 4., offset);
+
+    const MAX_ANGLE: f32 = PI / 12.;
+    let angle = (velocity.to_angle() + tilt).clamp(MAX_ANGLE, PI - MAX_ANGLE);
+    let mag = velocity.length() * (1. + offset.abs() / 2.);
+
+    Vec2::from_angle(angle).rotate(Vec2::X * mag)
+}
+
+fn move_ball(time: Res<Time>, ball: Single<(&mut Transform, &Velocity), With<Ball>>) {
+    let (mut transform, velocity) = ball.into_inner();
+    transform.translation += velocity.extend(0.) * time.delta_secs();
+}
+
+fn move_paddle(
+    time: Res<Time>,
+    input: Res<ButtonInput<KeyCode>>,
+    mut paddle: Single<&mut Transform, With<Paddle>>,
+) {
+    let mut v = Vec3::ZERO;
+    if input.pressed(KeyCode::ArrowLeft) {
+        v.x -= 1.;
+    }
+    if input.pressed(KeyCode::ArrowRight) {
+        v.x += 1.;
+    }
+
+    if v == Vec3::ZERO {
+        return;
+    }
+
+    paddle.translation += v.normalize() * Paddle::SPEED * time.delta_secs();
+
+    let w = Paddle::SIZE.x / 2.;
+    paddle.translation.x = paddle.translation.x.clamp(w, WORLD_SIZE.x - w);
+}
+
+fn serve_ball(
+    input: Res<ButtonInput<KeyCode>>,
+    paddle: Single<&Transform, (With<Paddle>, Without<Ball>)>,
+    ball: Single<(&mut Transform, &mut Velocity), With<Ball>>,
+    mut game_state: ResMut<NextState<GameState>>,
+) {
+    let (mut transform, mut velocity) = ball.into_inner();
+    if input.pressed(KeyCode::Space) {
+        velocity.0 = Vec2::from_angle(-PI / 6.).rotate(Ball::SERVE_SPEED * Vec2::Y);
+        game_state.set(GameState::Play)
+    } else {
+        transform.translation =
+            paddle.translation + Vec3::ZERO.with_y(Paddle::SIZE.y + Ball::RADIUS);
+    }
+}
+
+#[derive(Event, Debug)]
+struct VoidOut;
+
+#[derive(Component, Debug, Deref, DerefMut)]
+struct VoidPlane(Plane2d);
+
+fn void_out(
+    mut commands: Commands,
+    ball: Single<&Transform, With<Ball>>,
+    planes: Query<(&VoidPlane, &Transform), Without<Ball>>,
+) {
+    let circle = BoundingCircle::new(ball.translation.truncate(), Ball::RADIUS);
+
+    for (plane, transform) in planes {
+        let plane = plane.aabb_2d(transform.translation.truncate());
+
+        if plane.intersects(&circle) {
+            commands.trigger(VoidOut);
+            return;
+        }
+    }
+}
+
+fn on_void_out(
+    _: On<VoidOut>,
+    mut ball: Single<&mut Velocity, With<Ball>>,
+    mut game_state: ResMut<NextState<GameState>>,
+    mut lives: ResMut<Lives>,
+) {
+    ball.0 = Vec2::ZERO;
+    lives.0 = lives.0.saturating_sub(1);
+    if lives.0 == 0 {
+        game_state.set(GameState::Over);
+    } else {
+        game_state.set(GameState::Serve)
+    }
+}
+
+#[derive(Component, Debug)]
+struct Brick;
+
+impl Brick {
+    const SCORE: u64 = 100;
+    const SIZE: Vec2 = Vec2::new(50., 20.);
+    const GAP: f32 = 10.;
+    const COLORS: [Color; 8] = [
+        Color::LinearRgba(LinearRgba::rgb(1., 0., 0.)),  // red
+        Color::LinearRgba(LinearRgba::rgb(1., 0.5, 0.)), // orange
+        Color::LinearRgba(LinearRgba::rgb(1., 1., 0.)),  // yellow
+        Color::LinearRgba(LinearRgba::rgb(0., 1., 0.)),  // green
+        Color::LinearRgba(LinearRgba::rgb(0., 1., 1.)),  // cyan
+        Color::LinearRgba(LinearRgba::rgb(0., 0., 1.)),  // blue
+        Color::LinearRgba(LinearRgba::rgb(0.5, 0., 1.)), // purple
+        Color::LinearRgba(LinearRgba::rgb(1., 0., 1.)),  // magenta
+    ];
+
+    fn build(pos: Vec2, color: Color) -> impl Bundle {
+        (
+            Brick,
+            Sprite::from_color(color, Vec2::ONE),
+            Transform {
+                translation: pos.extend(0.),
+                scale: Brick::SIZE.extend(1.),
+                ..default()
+            },
+            Collider::Aabb(Aabb2d::new(Vec2::ZERO, Brick::SIZE / 2.)),
+        )
+    }
+}
+
+fn cleared_level(
+    mut level: ResMut<Level>,
+    mut ball: Single<&mut Velocity, With<Ball>>,
+    mut game_state: ResMut<NextState<GameState>>,
+    bricks: Query<(), With<Brick>>,
+) {
+    if bricks.is_empty() {
+        ball.0 = Vec2::ZERO;
+        level.0 += 1;
+        game_state.set(GameState::Build);
+    }
+}
+
+fn build_level(
+    mut commands: Commands,
+    mut game_state: ResMut<NextState<GameState>>,
+    level: Res<Level>,
+) {
+    let rows = 3 + level.0;
+
+    let half_cols = ((WORLD_SIZE.x / 2. / (Brick::SIZE.x + Brick::GAP)) - 1.).floor() as i32;
+
+    let start = Vec2::new(
+        WORLD_SIZE.x / 2.,
+        WORLD_SIZE.y - HUD_HEIGHT - Wall::THICKNESS - 3. * Brick::GAP,
+    );
+
+    for r in 0..rows {
+        let color = Brick::COLORS[(r as usize) % Brick::COLORS.len()];
+        for c in -half_cols..=half_cols {
+            let x = start.x + (c as f32) * (Brick::SIZE.x + Brick::GAP);
+            let y = start.y - (r as f32) * (Brick::SIZE.y + Brick::GAP);
+            commands.spawn(Brick::build(Vec2::new(x, y), color));
+        }
+    }
+
+    game_state.set(GameState::Serve);
+}
+
+const HUD_HEIGHT: f32 = 24.;
+
+#[derive(Component, Debug)]
+struct ScoreText;
+
+fn show_score(score: Res<Score>, mut text: Single<&mut Text2d, With<ScoreText>>) {
+    text.0 = score.to_string();
+}
+
+#[derive(Component, Debug)]
+struct LivesDot(u8);
+
+impl LivesDot {
+    const RADIUS: f32 = 5.;
+
+    fn build(
+        meshes: &mut ResMut<Assets<Mesh>>,
+        materials: &mut ResMut<Assets<ColorMaterial>>,
+        n: u8,
+    ) -> impl Bundle {
+        let x = Self::RADIUS * (2. + 3. * n as f32);
+        let y = WORLD_SIZE.y - HUD_HEIGHT / 2.;
+        (
+            LivesDot(n),
+            Mesh2d(meshes.add(Circle::new(Self::RADIUS))),
+            MeshMaterial2d(materials.add(Ball::COLOR)),
+            Transform::from_translation(Vec3::new(x, y, 1.)),
+        )
+    }
+}
+
+fn show_lives(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<ColorMaterial>>,
+    lives: Res<Lives>,
+    dots: Query<(Entity, &LivesDot)>,
+) {
+    let actual: u8 = dots.iter().len().try_into().expect("small number of lives");
+    let expected = **lives;
+
+    for (entity, dot) in dots {
+        let n = dot.0;
+        if n >= expected {
+            commands.entity(entity).despawn();
+        }
+    }
+
+    for n in actual..expected {
+        commands.spawn(LivesDot::build(&mut meshes, &mut materials, n));
+    }
+}
+
+fn reset_game(mut commands: Commands) {
+    let mut delayed = commands.delayed();
+    delayed.secs(3.).trigger(StartGame);
+}
+
+#[derive(Event, Debug)]
+struct StartGame;
+
+fn start_game(
+    _: On<StartGame>,
+    mut commands: Commands,
+    mut score: ResMut<Score>,
+    mut lives: ResMut<Lives>,
+    mut level: ResMut<Level>,
+    mut game_state: ResMut<NextState<GameState>>,
+    bricks: Query<Entity, With<Brick>>,
+) {
+    *score = Score::default();
+    *lives = Lives::default();
+    *level = Level::default();
+
+    for brick in bricks {
+        commands.entity(brick).despawn();
+    }
+
+    game_state.set(GameState::default());
+}
diff --git a/src/main.rs b/src/main.rs
index db7967e..1473b0d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,531 +1,7 @@
-use bevy::math::bounding::{Aabb2d, Bounded2d, BoundingCircle, BoundingVolume, IntersectsVolume};
 use bevy::prelude::*;
-use bevy::sprite::Anchor;
-use core::f32::consts::PI;
 
-use crate::debug::DebugPlugin;
-
-mod debug;
-
-const WORLD_SIZE: Vec2 = Vec2::new(480., 640.);
-
-#[derive(States, Debug, Copy, Clone, PartialEq, Eq, Hash, Default)]
-enum GameState {
-    #[default]
-    Build,
-    Serve,
-    Play,
-    Over,
-}
-
-#[derive(Resource, Debug, Copy, Clone, PartialEq, Eq, Default)]
-struct Level(u8);
-
-#[derive(Resource, Debug, Copy, Clone, PartialEq, Eq, Deref)]
-struct Lives(u8);
-
-impl Default for Lives {
-    fn default() -> Self {
-        Self(3)
-    }
-}
-
-#[derive(Resource, Debug, Copy, Clone, PartialEq, Eq, Default, Deref)]
-struct Score(u64);
+use breakout::Breakout;
 
 fn main() {
-    App::new()
-        .insert_resource(ClearColor(Color::BLACK))
-        .init_resource::<Level>()
-        .init_resource::<Score>()
-        .init_resource::<Lives>()
-        .add_plugins(DefaultPlugins.set(WindowPlugin {
-            // Until there's a reliable way to hint that a game window should
-            // float on tiling window managers, the most reliable way to achieve
-            // that is to define a fixed non-resizable window.
-            //
-            // https://github.com/rust-windowing/winit/issues/862#issuecomment-2047791401
-            primary_window: Some(Window {
-                canvas: Some("#breakout".into()),
-                resize_constraints: WindowResizeConstraints {
-                    min_width: WORLD_SIZE.x,
-                    min_height: WORLD_SIZE.y,
-                    max_width: WORLD_SIZE.x,
-                    max_height: WORLD_SIZE.y,
-                },
-                ..default()
-            }),
-            ..default()
-        }))
-        .add_plugins(DebugPlugin)
-        .init_state::<GameState>()
-        .add_systems(Startup, setup)
-        .add_systems(
-            FixedUpdate,
-            (
-                (collisions, cleared_level, void_out, move_ball)
-                    .chain()
-                    .run_if(in_state(GameState::Play)),
-                move_paddle,
-                show_score,
-                show_lives.run_if(resource_changed::<Lives>),
-                serve_ball.run_if(in_state(GameState::Serve)),
-            )
-                .chain(),
-        )
-        .add_systems(OnEnter(GameState::Build), build_level)
-        .add_systems(OnEnter(GameState::Over), reset_game)
-        .run();
-}
-
-fn setup(
-    mut commands: Commands,
-    mut meshes: ResMut<Assets<Mesh>>,
-    mut materials: ResMut<Assets<ColorMaterial>>,
-) {
-    commands.spawn((
-        Camera2d,
-        Transform::from_translation((WORLD_SIZE / 2.).extend(0.)),
-    ));
-
-    commands.spawn(Ball::build(&mut meshes, &mut materials));
-
-    commands.spawn(Wall::top());
-    commands.spawn(Wall::left());
-    commands.spawn(Wall::right());
-    // There's no bottom wall because that's a void plane instead.
-    commands.spawn((
-        VoidPlane(Plane2d::new(Vec2::Y)),
-        Transform::from_translation(Vec3::ZERO),
-    ));
-    commands.add_observer(on_void_out);
-
-    commands.spawn((
-        Paddle,
-        Sprite::from_color(Paddle::COLOR, Vec2::ONE),
-        Transform {
-            translation: Vec3::new(WORLD_SIZE.x / 2., Paddle::SIZE.y / 2. + Paddle::GAP, 0.),
-            scale: Paddle::SIZE.extend(1.),
-            ..default()
-        },
-        Collider::Aabb(Aabb2d::new(Vec2::ZERO, Paddle::SIZE / 2.)),
-    ));
-
-    commands.spawn((
-        ScoreText,
-        Text2d::default(),
-        TextLayout::justify(Justify::Right),
-        Anchor::BOTTOM_RIGHT,
-        Transform::from_translation(Vec3::new(WORLD_SIZE.x - 8., WORLD_SIZE.y - HUD_HEIGHT, 1.)),
-    ));
-
-    commands.add_observer(start_game);
-}
-
-#[derive(Component, Debug)]
-struct Ball;
-
-impl Ball {
-    const COLOR: Color = Color::LinearRgba(LinearRgba::GREEN);
-    const RADIUS: f32 = 8.;
-    const SPAWN_POSITION: Vec2 = Vec2::new(WORLD_SIZE.x / 2., 40.);
-    const SERVE_SPEED: f32 = 200.;
-    const MAX_SPEED: f32 = 900.;
-
-    fn build(
-        meshes: &mut ResMut<Assets<Mesh>>,
-        materials: &mut ResMut<Assets<ColorMaterial>>,
-    ) -> impl Bundle {
-        (
-            Ball,
-            Mesh2d(meshes.add(Circle::new(Ball::RADIUS))),
-            MeshMaterial2d(materials.add(Ball::COLOR)),
-            Transform::from_translation(Ball::SPAWN_POSITION.extend(0.)),
-            Velocity(Vec2::ZERO),
-        )
-    }
-}
-
-#[derive(Component, Debug, Copy, Clone, PartialEq, Deref, DerefMut)]
-struct Velocity(Vec2);
-
-#[derive(Component, Debug)]
-struct Wall;
-
-impl Wall {
-    const COLOR: Color = Color::LinearRgba(LinearRgba::rgb(0.5, 0.5, 0.5));
-    const THICKNESS: f32 = 4.;
-
-    const LENGTH_VERTICAL: f32 = WORLD_SIZE.y - HUD_HEIGHT;
-
-    fn top() -> impl Bundle {
-        (
-            Wall,
-            Sprite::from_color(Wall::COLOR, Vec2::ONE),
-            Transform {
-                translation: Vec3::new(
-                    WORLD_SIZE.x / 2.,
-                    WORLD_SIZE.y - Wall::THICKNESS / 2. - HUD_HEIGHT,
-                    0.,
-                ),
-                scale: Vec3::new(WORLD_SIZE.x, Wall::THICKNESS, 1.),
-                ..default()
-            },
-            Collider::Plane(Plane2d::new(Vec2::NEG_Y)),
-        )
-    }
-
-    fn left() -> impl Bundle {
-        let x = Wall::THICKNESS / 2.;
-        (
-            Wall,
-            Sprite::from_color(Wall::COLOR, Vec2::ONE),
-            Transform {
-                translation: Vec3::new(x, Self::LENGTH_VERTICAL / 2., 0.),
-                scale: Vec3::new(Wall::THICKNESS, Self::LENGTH_VERTICAL, 1.),
-                ..default()
-            },
-            Collider::Plane(Plane2d::new(Vec2::X)),
-        )
-    }
-
-    fn right() -> impl Bundle {
-        let x = WORLD_SIZE.x - Wall::THICKNESS / 2.;
-        (
-            Wall,
-            Sprite::from_color(Wall::COLOR, Vec2::ONE),
-            Transform {
-                translation: Vec3::new(x, Self::LENGTH_VERTICAL / 2., 0.),
-                scale: Vec3::new(Wall::THICKNESS, Self::LENGTH_VERTICAL, 1.),
-                ..default()
-            },
-            Collider::Plane(Plane2d::new(Vec2::NEG_X)),
-        )
-    }
-}
-
-#[derive(Component, Debug)]
-struct Paddle;
-
-impl Paddle {
-    const COLOR: Color = Color::LinearRgba(LinearRgba::rgb(0., 1., 1.));
-    const SIZE: Vec2 = Vec2::new(60., 10.);
-    const GAP: f32 = 4.;
-    const SPEED: f32 = WORLD_SIZE.x / 2.;
-}
-
-#[derive(Component, Debug)]
-enum Collider {
-    Aabb(Aabb2d),
-    Plane(Plane2d),
-}
-
-fn collisions(
-    mut commands: Commands,
-    ball: Single<(&Transform, &mut Velocity), With<Ball>>,
-    colliders: Query<
-        (
-            Entity,
-            &Transform,
-            &Collider,
-            Option<&Brick>,
-            Option<&Paddle>,
-        ),
-        Without<Ball>,
-    >,
-    mut score: ResMut<Score>,
-) {
-    let (transform, mut velocity) = ball.into_inner();
-    let circle = BoundingCircle::new(transform.translation.truncate(), Ball::RADIUS);
-
-    for (entity, transform, collider, brick, paddle) in colliders {
-        let tx = transform.translation.truncate();
-
-        let target = match collider {
-            Collider::Aabb(aabb) => aabb.translated_by(tx),
-            Collider::Plane(plane) => plane.aabb_2d(tx),
-        };
-        if !target.intersects(&circle) {
-            continue;
-        }
-
-        if brick.is_some() {
-            commands.entity(entity).despawn();
-            score.0 += Brick::SCORE;
-        }
-
-        let point = target.closest_point(circle.center);
-        let normal = match collider {
-            Collider::Plane(plane) => plane.normal.as_vec2(),
-            Collider::Aabb(_) => {
-                let dist = circle.center - point;
-
-                if dist.x.abs() > dist.y.abs() {
-                    if dist.x < 0. { Vec2::NEG_X } else { Vec2::X }
-                } else if dist.y < 0. {
-                    Vec2::NEG_Y
-                } else {
-                    Vec2::Y
-                }
-            }
-        };
-
-        // Only reflect if the current velocity has a component moving *against*
-        // the box face's normal vector. This allows the ball to exit the box
-        // without getting stuck "re-colliding" with it.
-        //
-        // Put another way, if the ball is already moving in the same direction
-        // that the plane would bounce it, that's not a real collision!
-        if velocity.dot(normal) >= 0. {
-            continue;
-        }
-
-        let mut v = velocity.reflect(normal);
-
-        if paddle.is_some() && normal == Vec2::Y {
-            let offset = (point.x - tx.x) / Paddle::SIZE.x;
-            let tilt = (0.).lerp(-PI / 4., offset);
-
-            let angle = (v.to_angle() + tilt).clamp(PI / 6., 5. * PI / 6.);
-            let mag = v.length() * (1. + offset.abs() / 2.);
-
-            v = Vec2::from_angle(angle).rotate(Vec2::X * mag);
-        }
-
-        velocity.0 = v.clamp_length_max(Ball::MAX_SPEED);
-    }
-}
-
-fn move_ball(time: Res<Time>, ball: Single<(&mut Transform, &Velocity), With<Ball>>) {
-    let (mut transform, velocity) = ball.into_inner();
-    transform.translation += velocity.extend(0.) * time.delta_secs();
-}
-
-fn move_paddle(
-    time: Res<Time>,
-    input: Res<ButtonInput<KeyCode>>,
-    mut paddle: Single<&mut Transform, With<Paddle>>,
-) {
-    let mut v = Vec3::ZERO;
-    if input.pressed(KeyCode::ArrowLeft) {
-        v.x -= 1.;
-    }
-    if input.pressed(KeyCode::ArrowRight) {
-        v.x += 1.;
-    }
-
-    if v == Vec3::ZERO {
-        return;
-    }
-
-    paddle.translation += v.normalize() * Paddle::SPEED * time.delta_secs();
-
-    let w = Paddle::SIZE.x / 2.;
-    paddle.translation.x = paddle.translation.x.clamp(w, WORLD_SIZE.x - w);
-}
-
-fn serve_ball(
-    input: Res<ButtonInput<KeyCode>>,
-    paddle: Single<&Transform, (With<Paddle>, Without<Ball>)>,
-    ball: Single<(&mut Transform, &mut Velocity), With<Ball>>,
-    mut game_state: ResMut<NextState<GameState>>,
-) {
-    let (mut transform, mut velocity) = ball.into_inner();
-    if input.pressed(KeyCode::Space) {
-        velocity.0 = Vec2::from_angle(-PI / 6.).rotate(Ball::SERVE_SPEED * Vec2::Y);
-        game_state.set(GameState::Play)
-    } else {
-        transform.translation =
-            paddle.translation + Vec3::ZERO.with_y(Paddle::SIZE.y + Ball::RADIUS);
-    }
-}
-
-#[derive(Event, Debug)]
-struct VoidOut;
-
-#[derive(Component, Debug, Deref, DerefMut)]
-struct VoidPlane(Plane2d);
-
-fn void_out(
-    mut commands: Commands,
-    ball: Single<&Transform, With<Ball>>,
-    planes: Query<(&VoidPlane, &Transform), Without<Ball>>,
-) {
-    let circle = BoundingCircle::new(ball.translation.truncate(), Ball::RADIUS);
-
-    for (plane, transform) in planes {
-        let plane = plane.aabb_2d(transform.translation.truncate());
-
-        if plane.intersects(&circle) {
-            commands.trigger(VoidOut);
-            return;
-        }
-    }
-}
-
-fn on_void_out(
-    _: On<VoidOut>,
-    mut ball: Single<&mut Velocity, With<Ball>>,
-    mut game_state: ResMut<NextState<GameState>>,
-    mut lives: ResMut<Lives>,
-) {
-    ball.0 = Vec2::ZERO;
-    lives.0 = lives.0.saturating_sub(1);
-    if lives.0 == 0 {
-        game_state.set(GameState::Over);
-    } else {
-        game_state.set(GameState::Serve)
-    }
-}
-
-#[derive(Component, Debug)]
-struct Brick;
-
-impl Brick {
-    const SCORE: u64 = 100;
-    const SIZE: Vec2 = Vec2::new(50., 20.);
-    const GAP: f32 = 10.;
-    const COLORS: [Color; 8] = [
-        Color::LinearRgba(LinearRgba::rgb(1., 0., 0.)),  // red
-        Color::LinearRgba(LinearRgba::rgb(1., 0.5, 0.)), // orange
-        Color::LinearRgba(LinearRgba::rgb(1., 1., 0.)),  // yellow
-        Color::LinearRgba(LinearRgba::rgb(0., 1., 0.)),  // green
-        Color::LinearRgba(LinearRgba::rgb(0., 1., 1.)),  // cyan
-        Color::LinearRgba(LinearRgba::rgb(0., 0., 1.)),  // blue
-        Color::LinearRgba(LinearRgba::rgb(0.5, 0., 1.)), // purple
-        Color::LinearRgba(LinearRgba::rgb(1., 0., 1.)),  // magenta
-    ];
-
-    fn build(pos: Vec2, color: Color) -> impl Bundle {
-        (
-            Brick,
-            Sprite::from_color(color, Vec2::ONE),
-            Transform {
-                translation: pos.extend(0.),
-                scale: Brick::SIZE.extend(1.),
-                ..default()
-            },
-            Collider::Aabb(Aabb2d::new(Vec2::ZERO, Brick::SIZE / 2.)),
-        )
-    }
-}
-
-fn cleared_level(
-    mut level: ResMut<Level>,
-    mut ball: Single<&mut Velocity, With<Ball>>,
-    mut game_state: ResMut<NextState<GameState>>,
-    bricks: Query<(), With<Brick>>,
-) {
-    if bricks.is_empty() {
-        ball.0 = Vec2::ZERO;
-        level.0 += 1;
-        game_state.set(GameState::Build);
-    }
-}
-
-fn build_level(
-    mut commands: Commands,
-    mut game_state: ResMut<NextState<GameState>>,
-    level: Res<Level>,
-) {
-    let rows = 3 + level.0;
-
-    let half_cols = ((WORLD_SIZE.x / 2. / (Brick::SIZE.x + Brick::GAP)) - 1.).floor() as i32;
-
-    let start = Vec2::new(
-        WORLD_SIZE.x / 2.,
-        WORLD_SIZE.y - HUD_HEIGHT - Wall::THICKNESS - 3. * Brick::GAP,
-    );
-
-    for r in 0..rows {
-        let color = Brick::COLORS[(r as usize) % Brick::COLORS.len()];
-        for c in -half_cols..=half_cols {
-            let x = start.x + (c as f32) * (Brick::SIZE.x + Brick::GAP);
-            let y = start.y - (r as f32) * (Brick::SIZE.y + Brick::GAP);
-            commands.spawn(Brick::build(Vec2::new(x, y), color));
-        }
-    }
-
-    game_state.set(GameState::Serve);
-}
-
-const HUD_HEIGHT: f32 = 24.;
-
-#[derive(Component, Debug)]
-struct ScoreText;
-
-fn show_score(score: Res<Score>, mut text: Single<&mut Text2d, With<ScoreText>>) {
-    text.0 = score.to_string();
-}
-
-#[derive(Component, Debug)]
-struct LivesDot(u8);
-
-impl LivesDot {
-    const RADIUS: f32 = 5.;
-
-    fn build(
-        meshes: &mut ResMut<Assets<Mesh>>,
-        materials: &mut ResMut<Assets<ColorMaterial>>,
-        n: u8,
-    ) -> impl Bundle {
-        let x = Self::RADIUS * (2. + 3. * n as f32);
-        let y = WORLD_SIZE.y - HUD_HEIGHT / 2.;
-        (
-            LivesDot(n),
-            Mesh2d(meshes.add(Circle::new(Self::RADIUS))),
-            MeshMaterial2d(materials.add(Ball::COLOR)),
-            Transform::from_translation(Vec3::new(x, y, 1.)),
-        )
-    }
-}
-
-fn show_lives(
-    mut commands: Commands,
-    mut meshes: ResMut<Assets<Mesh>>,
-    mut materials: ResMut<Assets<ColorMaterial>>,
-    lives: Res<Lives>,
-    dots: Query<(Entity, &LivesDot)>,
-) {
-    let actual: u8 = dots.iter().len().try_into().expect("small number of lives");
-    let expected = **lives;
-
-    for (entity, dot) in dots {
-        let n = dot.0;
-        if n >= expected {
-            commands.entity(entity).despawn();
-        }
-    }
-
-    for n in actual..expected {
-        commands.spawn(LivesDot::build(&mut meshes, &mut materials, n));
-    }
-}
-
-fn reset_game(mut commands: Commands) {
-    let mut delayed = commands.delayed();
-    delayed.secs(3.).trigger(StartGame);
-}
-
-#[derive(Event, Debug)]
-struct StartGame;
-
-fn start_game(
-    _: On<StartGame>,
-    mut commands: Commands,
-    mut score: ResMut<Score>,
-    mut lives: ResMut<Lives>,
-    mut level: ResMut<Level>,
-    mut game_state: ResMut<NextState<GameState>>,
-    bricks: Query<Entity, With<Brick>>,
-) {
-    *score = Score::default();
-    *lives = Lives::default();
-    *level = Level::default();
-
-    for brick in bricks {
-        commands.entity(brick).despawn();
-    }
-
-    game_state.set(GameState::default());
+    App::new().add_plugins(Breakout).run();
 }