Implement basic gun controller

The spacebar fires the gun, bullets are spawned on top of the ship with
a velocity that sends them forward (relative to the ship).

I still need a despawn mechanism, and a fire rate control. To despawn
things, I'm already planning a `Lifetime` component. For rate of fire,
an additional component will be created and attached to the player ship.

Cargo.toml

@@ -1,7 +1,10 @@
 [package]
 name = "asteroids"
-version = "0.1.0"
+version = "0.2.0"
-edition = "2021"
+edition = "2024"
 
 [dependencies]
-bevy = "0.14.2"
+bevy = { version = "0.16", features = ["dynamic_linking"] }
+bevy-inspector-egui = "0.32.0"
+bevy_rapier2d = { version = "0.31.0", features = ["debug-render-2d"] }
+rand = "0.9.2"

src/asteroids.rs

@@ -0,0 +1,129 @@
+//! This is the module containing all the rock-related things.
+//! Not... not the whole game.
+
+use bevy_rapier2d::prelude::*;
+use rand::{Rng, SeedableRng};
+use std::time::Duration;
+
+use bevy::prelude::*;
+
+use crate::{GameAssets, WorldSize, physics::Velocity};
+
+#[derive(Component, Deref, DerefMut)]
+pub struct Asteroid(AsteroidSize);
+
+pub enum AsteroidSize {
+    Small,
+    Medium,
+    Large,
+}
+
+#[derive(Resource)]
+pub struct AsteroidSpawner {
+    rng: std::sync::Mutex<rand::rngs::StdRng>,
+    timer: Timer,
+    // TODO: Configurables?
+    // - interval
+    // - density
+    // - size distribution
+}
+
+impl AsteroidSpawner {
+    pub fn new() -> Self {
+        Self {
+            rng: std::sync::Mutex::new(rand::rngs::StdRng::from_seed(crate::config::RNG_SEED)),
+            timer: Timer::new(Duration::from_secs(3), TimerMode::Repeating),
+        }
+    }
+}
+
+#[derive(Event)]
+pub struct SpawnAsteroid {
+    pos: Vec2,
+    vel: Vec2,
+    size: AsteroidSize,
+}
+
+/// Update the asteroid spawn timer and spawn any asteroids
+/// that are due this frame.
+pub fn tick_asteroid_manager(
+    mut events: EventWriter<SpawnAsteroid>,
+    mut spawner: ResMut<AsteroidSpawner>,
+    time: Res<Time>,
+    play_area: Res<WorldSize>,
+) {
+    spawner.timer.tick(time.delta());
+    if spawner.timer.just_finished() {
+        let mut rng = spawner
+            .rng
+            .lock()
+            .expect("Expected to acquire lock on the AsteroidSpawner's RNG field.");
+
+        // Use polar coordinate to decide where the asteroid will spawn
+        // Theta will be random between 0 to 2pi
+        let spawn_angle = rng.random_range(0.0..(std::f32::consts::PI * 2.0));
+        // Rho will be the radius of a circle bordering the viewport, multiplied by 1.2
+        // TODO: Use view diagonal to get a minimally sized circle around the play area
+        let spawn_distance = play_area.width.max(play_area.height) / 2.0;
+
+        // Convert polar to Cartesian, use as position
+        let pos = Vec2::new(
+            spawn_distance * spawn_angle.cos(),
+            spawn_distance * spawn_angle.sin(),
+        );
+
+        // Right now, I'm thinking I can use the opposite signs attached to the position Vec components.
+        // pos.x == -100, then vel.x = + <random>
+        // pos.x == 100, then vel.x = - <random>
+        // etc,
+        let mut vel = Vec2::new(rng.random_range(0.0..100.0), rng.random_range(0.0..100.0));
+        if pos.x > 0.0 {
+            vel.x *= -1.0;
+        }
+        if pos.y > 0.0 {
+            vel.y *= -1.0;
+        }
+
+        let size = match rng.random_range(0..=2) {
+            0 => AsteroidSize::Small,
+            1 => AsteroidSize::Medium,
+            2 => AsteroidSize::Large,
+            _ => unreachable!(),
+        };
+
+        events.write(SpawnAsteroid { pos, vel, size });
+    }
+}
+
+/// Utility function to spawn a single asteroid of a given type
+/// TODO: convert to an event listener monitoring for "spawn asteroid" events
+/// from the `fn tick_asteroid_manager(...)` system.
+pub fn spawn_asteroid(
+    mut events: EventReader<SpawnAsteroid>,
+    mut commands: Commands,
+    game_assets: Res<GameAssets>,
+) {
+    for spawn in events.read() {
+        let (mesh, material) = match spawn.size {
+            AsteroidSize::Small => game_assets.asteroid_small(),
+            AsteroidSize::Medium => game_assets.asteroid_medium(),
+            AsteroidSize::Large => game_assets.asteroid_large(),
+        };
+
+        let collider_radius = match spawn.size {
+            AsteroidSize::Small => 10.0,
+            AsteroidSize::Medium => 20.0,
+            AsteroidSize::Large => 40.0,
+        };
+
+        commands.spawn((
+            Asteroid(AsteroidSize::Small),
+            Collider::ball(collider_radius),
+            Sensor,
+            Transform::from_translation(spawn.pos.extend(0.0)),
+            Velocity(spawn.vel),
+            Mesh2d(mesh),
+            MeshMaterial2d(material),
+        ));
+    }
+}

src/config.rs

@@ -1,7 +1,5 @@
-/*
+//! Global constants used all over the program. Rather than leaving them scattered
- Global constants used all over the program. Rather than leaving them scattered
+//! where ever they happen to be needed, I'm concentrating them here.
-where ever they happen to be needed, I'm concentrating them here.
-*/
 
 use bevy::color::Color;
 
@@ -11,6 +9,13 @@ pub(crate) const BACKGROUND_COLOR: Color = Color::srgb(0.3, 0.3, 0.3);
 pub(crate) const PLAYER_SHIP_COLOR: Color = Color::srgb(1.0, 1.0, 1.0);
 pub(crate) const SHIP_THRUSTER_COLOR_ACTIVE: Color = Color::srgb(1.0, 0.2, 0.2);
 pub(crate) const SHIP_THRUSTER_COLOR_INACTIVE: Color = Color::srgb(0.5, 0.5, 0.5);
+pub(crate) const ASTEROID_SMALL_COLOR: Color = Color::srgb(1.0, 0., 0.);
+pub(crate) const BULLET_COLOR: Color = Color::srgb(0.0, 0.1, 0.9);
+// TODO: asteroid medium & large
 
 pub(crate) const SHIP_THRUST: f32 = 1.0;
-pub(crate) const SHIP_ROTATION: f32 = 0.1; // +/- rotation speed in... radians per frame
+pub(crate) const SHIP_ROTATION: f32 = 4.0; // +/- rotation speed in... radians per frame
+
+pub(crate) const BULLET_SPEED: f32 = 150.0;
+
+pub const RNG_SEED: [u8; 32] = *b"12345678909876543210123456789098";

src/event.rs

@@ -0,0 +1,21 @@
+use bevy::prelude::*;
+
+/// Signals that the player's ship has been destroyed.
+/// Used when the player collides with an asteroid.
+#[derive(Event)]
+pub(crate) struct ShipDestroy;
+
+/// Signals that a particular asteroid has been destroyed.
+/// Used to split (or vanish) an asteroid when a bullet strikes it.
+#[derive(Event)]
+pub(crate) struct AsteroidDestroy(pub Entity);
+
+// TODO: BulletDestroy
+// Which depends on the still-pending Bullet component creation.
+
+/// Signals that a particular bullet has been destroyed.
+/// Used to despawn the bullet after it strikes an Asteroid.
+///
+/// TODO: Maybe use it for lifetime expiration (which is also a TODO item).
+#[derive(Event)]
+pub(crate) struct BulletDestroy(pub Entity);

src/lib.rs

@@ -1,48 +1,161 @@
+mod asteroids;
 pub mod config;
+mod event;
+mod physics;
+mod preparation_widget;
+mod ship;
+mod title_screen;
 
-use crate::config::{BACKGROUND_COLOR, PLAYER_SHIP_COLOR, SHIP_ROTATION, SHIP_THRUST, WINDOW_SIZE};
+use crate::asteroids::{Asteroid, AsteroidSpawner};
+use crate::config::{
+    ASTEROID_SMALL_COLOR, BACKGROUND_COLOR, BULLET_COLOR, BULLET_SPEED, PLAYER_SHIP_COLOR,
+    SHIP_ROTATION, SHIP_THRUST, SHIP_THRUSTER_COLOR_ACTIVE, SHIP_THRUSTER_COLOR_INACTIVE,
+    WINDOW_SIZE,
+};
+use crate::physics::AngularVelocity;
+use crate::ship::Ship;
 
-use bevy::{prelude::*, sprite::MaterialMesh2dBundle};
+use bevy::prelude::*;
-use config::{SHIP_THRUSTER_COLOR_ACTIVE, SHIP_THRUSTER_COLOR_INACTIVE};
+use bevy_inspector_egui::InspectorOptions;
+use bevy_inspector_egui::prelude::ReflectInspectorOptions;
+use bevy_rapier2d::{
+    plugin::{NoUserData, RapierPhysicsPlugin},
+    prelude::*,
+    render::RapierDebugRenderPlugin,
+};
 
 pub struct AsteroidPlugin;
 
 impl Plugin for AsteroidPlugin {
     fn build(&self, app: &mut App) {
-        app.add_systems(Startup, (spawn_camera, spawn_player))
+        app.add_plugins((
-            .insert_resource(ClearColor(BACKGROUND_COLOR))
+            title_screen::GameMenuPlugin,
-            .insert_resource(WorldSize {
+            preparation_widget::preparation_widget_plugin,
-                width: WINDOW_SIZE.x,
+            RapierPhysicsPlugin::<NoUserData>::pixels_per_meter(10.0),
-                height: WINDOW_SIZE.y,
+            RapierDebugRenderPlugin::default(),
-            })
+        ))
-            .add_systems(
+        .insert_resource(ClearColor(BACKGROUND_COLOR))
-                FixedUpdate,
+        .insert_resource(WorldSize {
-                (input_ship_thruster, input_ship_rotation, wrap_entities),
+            width: WINDOW_SIZE.x,
+            height: WINDOW_SIZE.y,
+        })
+        .insert_resource(Lives(3))
+        .register_type::<Lives>()
+        .insert_resource(Score(0))
+        .insert_resource(AsteroidSpawner::new())
+        .init_resource::<GameAssets>()
+        .add_systems(Startup, spawn_camera)
+        .add_systems(OnEnter(GameState::Playing), (ship::spawn_player, spawn_ui))
+        .add_systems(
+            FixedUpdate,
+            (
+                input_ship_thruster,
+                input_ship_rotation,
+                input_ship_shoot,
+                physics::wrap_entities,
+                asteroids::tick_asteroid_manager,
+                asteroids::spawn_asteroid.after(asteroids::tick_asteroid_manager),
+                collision_listener,
+                // TODO: Remove debug printing
+                debug_collision_event_printer,
             )
-            .add_systems(
+                .run_if(in_state(GameState::Playing)),
-                FixedPostUpdate,
+        )
-                (integrate_velocity, update_positions, apply_rotation_to_mesh),
+        .add_systems(
-            );
+            FixedPostUpdate,
+            (
+                physics::integrate_velocity,
+                physics::integrate_angular_velocity,
+            )
+                .run_if(in_state(GameState::Playing)),
+        )
+        .add_event::<asteroids::SpawnAsteroid>()
+        .add_event::<event::AsteroidDestroy>()
+        .add_event::<event::ShipDestroy>();
+        app.insert_state(GameState::Playing);
     }
 }
 
-#[derive(Component)]
+fn debug_collision_event_printer(mut collision_events: EventReader<CollisionEvent>) {
-struct Position(bevy::math::Vec2);
+    for event in collision_events.read() {
+        dbg!(event);
+    }
+}
 
-#[derive(Component)]
+/// The collision event routing system.
-struct Velocity(bevy::math::Vec2);
+///
+/// When a `CollisionEvent` occurrs, this system checks which things collided
+/// and emits secondary events accordignly.
+///
+/// | Objects | Response |
+/// |-|-|
+/// | Ship & Asteroid | emits event [`ShipDestroy`](`crate::event::ShipDestroy`) |
+/// | Asteroid & Bullet | emits event [`AsteroidDestroy`](`crate::event::AsteroidDestroy`) |
+/// | Asteroid & Asteroid | Nothing. Asteroids won't collide with each other |
+/// | Bullet & Bullet | Nothing. Bullets won't collide with each other (and probably can't under normal gameplay conditions) |
+/// | Bullet & Ship | Nothing. The player shouldn't be able to shoot themselves (and the Flying Saucer hasn't been impl.'d, so it's bullets don't count) |
+fn collision_listener(
+    mut collisions: EventReader<CollisionEvent>,
+    mut ship_writer: EventWriter<event::ShipDestroy>,
+    mut asteroid_writer: EventWriter<event::AsteroidDestroy>,
+    player: Single<Entity, With<Ship>>,
+    rocks: Query<&Asteroid>,
+) {
+    for event in collisions.read() {
+        if let CollisionEvent::Started(one, two, _flags) = event {
+            // Valid collisions are:
+            //
+            // - Ship & Asteroid
+            // - Bullet & Asteroid
+            //
+            // Asteroids don't collide with each other, bullets don't collide
+            // with each other, and bullets don't collide with the player ship.
 
-#[derive(Component)]
+            // Option 1: Ship & Asteroid
-struct Rotation(f32);
+            if *one == *player {
+                if rocks.contains(*two) {
+                    // player-asteroid collision
+                    dbg!("Writing ShipDestroy event");
+                    ship_writer.write(event::ShipDestroy);
+                } // else, we don't care
+            } else if *two == *player {
+                if rocks.contains(*one) {
+                    dbg!("Writing ShipDestroy event");
+                    ship_writer.write(event::ShipDestroy);
+                }
+            }
 
-#[derive(Component)]
+            // TODO: Bullet-asteroid collisions
-struct Ship;
+        }
+    }
+}
 
-// Data component to store color properties attached to an entity
+#[derive(Clone, Debug, Eq, Hash, PartialEq, States)]
-// This was easier (and imo better) than holding global consts with
+pub enum GameState {
-// UUID assets.
+    TitleScreen, // Program is started. Present title screen and await user start
-#[derive(Component)]
+    GetReady,    // Short timer to let the player get ready after pressing start
-struct ThrusterColors(Handle<ColorMaterial>, Handle<ColorMaterial>);
+    Playing,     // Player has started the game. Run the main loop
+    GameOver,    // Game has ended. Present game over dialogue and await user restart
+}
+
+#[derive(Resource, Debug, Deref, Clone, Copy)]
+struct Score(i32);
+
+impl From<Score> for String {
+    fn from(value: Score) -> Self {
+        value.to_string()
+    }
+}
+
+#[derive(InspectorOptions, Reflect, Resource, Debug, Deref, Clone, Copy)]
+#[reflect(Resource, InspectorOptions)]
+struct Lives(i32);
+
+impl From<Lives> for String {
+    fn from(value: Lives) -> Self {
+        value.to_string()
+    }
+}
 
 #[derive(Resource)]
 struct WorldSize {
@@ -50,51 +163,81 @@ struct WorldSize {
     height: f32,
 }
 
-fn spawn_camera(mut commands: Commands) {
+#[derive(Resource)]
-    commands.spawn(Camera2dBundle::default());
+struct GameAssets {
+    meshes: [Handle<Mesh>; 5],
+    materials: [Handle<ColorMaterial>; 7],
 }
 
-fn spawn_player(
+impl GameAssets {
-    mut commands: Commands,
+    fn ship(&self) -> (Handle<Mesh>, Handle<ColorMaterial>) {
-    mut meshes: ResMut<Assets<Mesh>>,
+        (self.meshes[0].clone(), self.materials[0].clone())
-    mut materials: ResMut<Assets<ColorMaterial>>,
+    }
-) {
-    let triangle = Triangle2d::new(
-        Vec2::new(0.5, 0.0),
-        Vec2::new(-0.5, 0.45),
-        Vec2::new(-0.5, -0.45),
-    );
-    let thruster_firing_id = materials.add(SHIP_THRUSTER_COLOR_ACTIVE);
-    let thruster_stopped_id = materials.add(SHIP_THRUSTER_COLOR_INACTIVE);
 
-    let ship_mesh = MaterialMesh2dBundle {
+    // The thruster mesh is actually just the ship mesh
-        mesh: meshes.add(triangle).into(),
+    fn thruster_mesh(&self) -> Handle<Mesh> {
-        material: materials.add(PLAYER_SHIP_COLOR),
+        self.meshes[0].clone()
-        transform: Transform::default().with_scale(Vec3::new(20.0, 20.0, 20.0)),
+    }
-        ..default()
-    };
 
-    let thruster_mesh = MaterialMesh2dBundle {
+    // TODO: Look into parameterizing the material
-        mesh: meshes.add(triangle).into(),
+    // A shader uniform should be able to do this, but I don't know how to
-        material: materials.add(PLAYER_SHIP_COLOR),
+    // load those in Bevy.
-        transform: Transform::default()
+    fn thruster_mat_inactive(&self) -> Handle<ColorMaterial> {
-            .with_scale(Vec3::splat(0.5))
+        self.materials[1].clone()
-            .with_translation(Vec3::new(-0.5, 0.0, -0.1)),
+    }
-        ..default()
-    };
 
-    let thruster = commands.spawn(thruster_mesh).id();
+    fn thruster_mat_active(&self) -> Handle<ColorMaterial> {
+        self.materials[2].clone()
+    }
 
-    let mut ship_id = commands.spawn((
+    fn asteroid_small(&self) -> (Handle<Mesh>, Handle<ColorMaterial>) {
-        Ship,
+        (self.meshes[1].clone(), self.materials[1].clone())
-        Position(Vec2::default()),
+    }
-        Velocity(Vec2::ZERO),
-        Rotation(0.0),
-        ship_mesh,
-        ThrusterColors(thruster_firing_id, thruster_stopped_id),
-    ));
 
-    ship_id.add_child(thruster);
+    fn asteroid_medium(&self) -> (Handle<Mesh>, Handle<ColorMaterial>) {
+        (self.meshes[2].clone(), self.materials[2].clone())
+    }
+
+    fn asteroid_large(&self) -> (Handle<Mesh>, Handle<ColorMaterial>) {
+        (self.meshes[3].clone(), self.materials[3].clone())
+    }
+
+    fn bullet(&self) -> (Handle<Mesh>, Handle<ColorMaterial>) {
+        (self.meshes[4].clone(), self.materials[6].clone())
+    }
+}
+
+impl FromWorld for GameAssets {
+    fn from_world(world: &mut World) -> Self {
+        let mut world_meshes = world.resource_mut::<Assets<Mesh>>();
+        let meshes = [
+            world_meshes.add(Triangle2d::new(
+                Vec2::new(0.5, 0.0),
+                Vec2::new(-0.5, 0.45),
+                Vec2::new(-0.5, -0.45),
+            )),
+            world_meshes.add(Circle::new(10.0)),
+            world_meshes.add(Circle::new(20.0)),
+            world_meshes.add(Circle::new(40.0)),
+            world_meshes.add(Circle::new(0.2)),
+        ];
+        let mut world_materials = world.resource_mut::<Assets<ColorMaterial>>();
+        let materials = [
+            world_materials.add(PLAYER_SHIP_COLOR),
+            world_materials.add(SHIP_THRUSTER_COLOR_INACTIVE),
+            world_materials.add(SHIP_THRUSTER_COLOR_ACTIVE),
+            world_materials.add(ASTEROID_SMALL_COLOR),
+            // TODO: asteroid medium and large colors
+            world_materials.add(ASTEROID_SMALL_COLOR),
+            world_materials.add(ASTEROID_SMALL_COLOR),
+            world_materials.add(BULLET_COLOR),
+        ];
+        GameAssets { meshes, materials }
+    }
+}
+
+fn spawn_camera(mut commands: Commands) {
+    commands.spawn(Camera2d);
 }
 
 /*
@@ -102,10 +245,14 @@ fn spawn_player(
 */
 fn input_ship_thruster(
     keyboard_input: Res<ButtonInput<KeyCode>>,
-    mut query: Query<(&mut Velocity, &Rotation, &mut Children, &ThrusterColors), With<Ship>>,
+    mut query: Query<(&mut physics::Velocity, &Transform, &mut Children), With<Ship>>,
     mut commands: Commands,
+    game_assets: Res<GameAssets>,
 ) {
-    let Ok((mut velocity, rotation, children, colors)) = query.get_single_mut() else {
+    // TODO: Maybe change for a Single<Ship>> so this only runs for the one ship
+    // buuut... that would silently do nothing if there are 0 or >1 ships, and
+    // I might want to crash on purpose in that case.
+    let Ok((mut velocity, transform, children)) = query.single_mut() else {
         let count = query.iter().count();
         panic!("There should be exactly one player ship! Instead, there seems to be {count}.");
     };
@@ -115,10 +262,14 @@ fn input_ship_thruster(
         .expect("Couldn't find first child, which should be the thruster");
 
     if keyboard_input.pressed(KeyCode::KeyW) {
-        velocity.0 += Vec2::from_angle(rotation.0) * SHIP_THRUST;
+        velocity.0 += (transform.rotation * Vec3::X).xy() * SHIP_THRUST;
-        commands.entity(*thrusters).insert(colors.0.clone());
+        commands
+            .entity(*thrusters)
+            .insert(MeshMaterial2d(game_assets.thruster_mat_active()));
     } else {
-        commands.entity(*thrusters).insert(colors.1.clone());
+        commands
+            .entity(*thrusters)
+            .insert(MeshMaterial2d(game_assets.thruster_mat_inactive()));
     }
 }
 
@@ -128,62 +279,54 @@ fn input_ship_thruster(
 */
 fn input_ship_rotation(
     keyboard_input: Res<ButtonInput<KeyCode>>,
-    mut query: Query<&mut Rotation, With<Ship>>,
+    mut query: Query<&mut AngularVelocity, With<Ship>>,
 ) {
-    let Ok(mut rotation) = query.get_single_mut() else {
+    let Ok(mut angular_vel) = query.single_mut() else {
         let count = query.iter().count();
         panic!("There should be exactly one player ship! Instead, there seems to be {count}.");
     };
 
     if keyboard_input.pressed(KeyCode::KeyA) {
-        rotation.0 += SHIP_ROTATION;
+        angular_vel.0 = SHIP_ROTATION;
     } else if keyboard_input.pressed(KeyCode::KeyD) {
-        rotation.0 -= SHIP_ROTATION;
+        angular_vel.0 = -SHIP_ROTATION;
+    } else {
+        angular_vel.0 = 0.0;
     }
 }
 
-/*
+fn input_ship_shoot(
- Add velocity to position
+    keyboard_input: Res<ButtonInput<KeyCode>>,
-*/
+    ship: Single<(&Transform, &physics::Velocity), With<Ship>>,
-fn integrate_velocity(mut query: Query<(&mut Position, &Velocity)>, time: Res<Time>) {
+    game_assets: Res<GameAssets>,
-    for (mut position, velocity) in &mut query {
+    mut commands: Commands,
-        position.0 += velocity.0 * time.delta_seconds();
+) {
+    let (ship_pos, ship_vel) = *ship;
+
+    // Derive bullet velocity, add to the ship's velocity
+    let bullet_vel = (ship_pos.rotation * Vec3::X).xy() * BULLET_SPEED;
+    let bullet_vel = bullet_vel + ship_vel.0;
+
+    // TODO: create a timer for the gun fire rate.
+    // For now, spawn one for each press of the spacebar.
+    if keyboard_input.just_pressed(KeyCode::Space) {
+        commands.spawn((
+            ship::Bullet,
+            Collider::ball(0.2),
+            Sensor,
+            ActiveEvents::COLLISION_EVENTS,
+            ActiveCollisionTypes::STATIC_STATIC,
+            physics::Velocity(bullet_vel),
+            Mesh2d(game_assets.bullet().0),
+            MeshMaterial2d(game_assets.bullet().1),
+            ship_pos.clone(), // clone ship transform
+        ));
     }
 }
 
-fn update_positions(mut query: Query<(&mut Transform, &Position)>) {
+fn spawn_ui(mut commands: Commands, score: Res<Score>, lives: Res<Lives>) {
-    for (mut transform, position) in &mut query {
+    commands.spawn((
-        transform.translation.x = position.0.x;
+        Text::new(format!("Score: {score:?} | Lives: {lives:?}")),
-        transform.translation.y = position.0.y;
+        TextFont::from_font_size(25.0),
-    }
+    ));
-}
-
-/*
- Assigns the rotation to the transform by copying it from the Rotation component.
-*/
-fn apply_rotation_to_mesh(mut query: Query<(&mut Transform, &Rotation)>) {
-    for (mut transform, rotation) in &mut query {
-        transform.rotation = Quat::from_rotation_z(rotation.0);
-    }
-}
-
-fn wrap_entities(mut query: Query<&mut Position>, world_size: Res<WorldSize>) {
-    let right = world_size.width / 2.0;
-    let left = -right;
-    let top = world_size.height / 2.0;
-    let bottom = -top;
-
-    for mut pos in query.iter_mut() {
-        if pos.0.x > right {
-            pos.0.x = left;
-        } else if pos.0.x < left {
-            pos.0.x = right;
-        }
-
-        if pos.0.y > top {
-            pos.0.y = bottom;
-        } else if pos.0.y < bottom {
-            pos.0.y = top;
-        }
-    }
 }

src/main.rs

@@ -1,6 +1,7 @@
 use bevy::{prelude::*, window::WindowResolution};
 
-use asteroids::{config::WINDOW_SIZE, AsteroidPlugin};
+use asteroids::{AsteroidPlugin, config::WINDOW_SIZE};
+use bevy_inspector_egui::{bevy_egui::EguiPlugin, quick::WorldInspectorPlugin};
 
 fn main() {
     App::new()
@@ -12,5 +13,7 @@ fn main() {
             ..default()
         }))
         .add_plugins(AsteroidPlugin)
+        .add_plugins(EguiPlugin::default())
+        .add_plugins(WorldInspectorPlugin::new())
         .run();
 }

src/physics.rs

@@ -0,0 +1,59 @@
+//! Custom physics items
+//! TODO: Refactor in terms of Rapier2D, *or* implement colliders and remove it.
+
+use crate::WorldSize;
+
+use bevy::prelude::*;
+
+#[derive(Clone, Component)]
+pub(crate) struct Velocity(pub(crate) bevy::math::Vec2);
+
+#[derive(Component)]
+pub(crate) struct AngularVelocity(pub(crate) f32);
+
+/// Marker for any entity that should wrap on screen edges
+#[derive(Component)]
+pub(crate) struct Wrapping;
+
+/// Integrate linear velocity and update the entity's transform.
+pub(crate) fn integrate_velocity(mut query: Query<(&mut Transform, &Velocity)>, time: Res<Time>) {
+    for (mut transform, velocity) in &mut query {
+        let delta = velocity.0 * time.delta_secs();
+        transform.translation += delta.extend(0.0);
+    }
+}
+
+/// Integrate angular velocity and update the entity's transform.
+pub(crate) fn integrate_angular_velocity(
+    mut objects: Query<(&mut Transform, &AngularVelocity)>,
+    time: Res<Time>,
+) {
+    for (mut transform, ang_vel) in &mut objects {
+        let delta = ang_vel.0 * time.delta_secs();
+        transform.rotate_z(delta);
+    }
+}
+
+pub(crate) fn wrap_entities(
+    mut query: Query<&mut Transform, With<Wrapping>>,
+    world_size: Res<WorldSize>,
+) {
+    let right = world_size.width / 2.0;
+    let left = -right;
+    let top = world_size.height / 2.0;
+    let bottom = -top;
+
+    for mut pos in query.iter_mut() {
+        if pos.translation.x > right {
+            pos.translation.x = left;
+        } else if pos.translation.x < left {
+            pos.translation.x = right;
+        }
+
+        if pos.translation.y > top {
+            pos.translation.y = bottom;
+        } else if pos.translation.y < bottom {
+            pos.translation.y = top;
+        }
+    }
+}

src/preparation_widget.rs

@@ -0,0 +1,99 @@
+use crate::GameState;
+
+use bevy::{
+    color::palettes::css::{BLACK, GREEN, LIGHT_BLUE, RED},
+    prelude::*,
+};
+
+pub fn preparation_widget_plugin(app: &mut App) {
+    app.add_systems(OnEnter(GameState::GetReady), spawn_get_ready)
+        .add_systems(OnExit(GameState::GetReady), despawn_get_ready)
+        .add_systems(
+            Update,
+            (animate_get_ready_widget).run_if(in_state(GameState::GetReady)),
+        )
+        .insert_resource(ReadySetGoTimer(Timer::from_seconds(3.0, TimerMode::Once)));
+}
+
+/// Marker component for things on the get-ready indicator
+#[derive(Component)]
+struct OnReadySetGo;
+
+/// Newtype wrapper for `Timer`. Used to count down during the "get ready" phase.
+#[derive(Deref, DerefMut, Resource)]
+struct ReadySetGoTimer(Timer);
+
+/// Marker for the counter text segment
+#[derive(Component)]
+struct CountdownText;
+
+/// Marker for the counter bar segment
+#[derive(Component)]
+struct CountdownBar;
+
+fn spawn_get_ready(mut commands: Commands) {
+    commands.spawn((
+        OnReadySetGo, // marker, so this can be de-spawned properly
+        Node {
+            align_self: AlignSelf::Center,
+            justify_self: JustifySelf::Center,
+            align_items: AlignItems::Center,
+            justify_content: JustifyContent::Center,
+            flex_direction: FlexDirection::Column,
+            width: Val::Percent(30.),
+            height: Val::Percent(30.),
+            ..default()
+        },
+        BackgroundColor(LIGHT_BLUE.into()),
+        children![
+            (Text::new("Get Ready!"), TextColor(BLACK.into())),
+            (
+                CountdownBar,
+                Node {
+                    width: Val::Percent(90.0),
+                    height: Val::Percent(10.),
+                    ..default()
+                },
+                BackgroundColor(GREEN.into()),
+            ),
+            (
+                CountdownText,
+                Text::new("<uninit timer>"),
+                TextColor(RED.into()),
+            )
+        ],
+    ));
+}
+
+// TODO: Replace this with a generic somewhere else in the crate
+// want: `despawn_screen::<OnReadySetGo>>()`
+fn despawn_get_ready(mut commands: Commands, to_despawn: Query<Entity, With<OnReadySetGo>>) {
+    for entity in to_despawn {
+        commands.entity(entity).despawn();
+    }
+}
+
+fn animate_get_ready_widget(
+    mut text_segment: Single<&mut Text, With<CountdownText>>,
+    mut bar_segment: Single<&mut Node, With<CountdownBar>>,
+    time: Res<Time>,
+    mut timer: ResMut<ReadySetGoTimer>,
+    mut game_state: ResMut<NextState<GameState>>,
+) {
+    // Advance the timer, read the remaining time and write it onto the label.
+    timer.tick(time.delta());
+
+    // Add one to the visual value so the countdown starts at 3 and stops at 1.
+    // Otherwise it starts at 2 and disappears after showing 0.
+    // That feels wrong even though it's functionally identical.
+    let tval = timer.0.remaining().as_secs() + 1;
+    **text_segment = format!("{tval}").into();
+
+    // Shrink the progress bar Node
+    bar_segment.width = Val::Percent(100.0 * (1.0 - timer.fraction()));
+
+    // If the timer has expired, change state to playing.
+    if timer.finished() {
+        game_state.set(GameState::Playing);
+    }
+}

src/ship.rs

@@ -0,0 +1,37 @@
+use crate::{
+    AngularVelocity, GameAssets,
+    physics::{Velocity, Wrapping},
+};
+
+use bevy::prelude::*;
+use bevy_rapier2d::prelude::*;
+
+#[derive(Component)]
+pub struct Ship;
+
+#[derive(Component)]
+pub struct Bullet;
+
+pub fn spawn_player(mut commands: Commands, game_assets: Res<GameAssets>) {
+    commands
+        .spawn((
+            Collider::ball(0.7),
+            Sensor,
+            ActiveEvents::COLLISION_EVENTS,
+            ActiveCollisionTypes::STATIC_STATIC,
+            Ship,
+            Wrapping,
+            Velocity(Vec2::ZERO),
+            AngularVelocity(0.0),
+            Mesh2d(game_assets.ship().0),
+            MeshMaterial2d(game_assets.ship().1),
+            Transform::default().with_scale(Vec3::new(20.0, 20.0, 20.0)),
+        ))
+        .with_child((
+            Mesh2d(game_assets.thruster_mesh()),
+            MeshMaterial2d(game_assets.thruster_mat_inactive()),
+            Transform::default()
+                .with_scale(Vec3::splat(0.5))
+                .with_translation(Vec3::new(-0.5, 0.0, -0.1)),
+        ));
+}

src/title_screen.rs

@@ -0,0 +1,54 @@
+use crate::GameState;
+
+use bevy::prelude::*;
+
+pub struct GameMenuPlugin;
+
+impl Plugin for GameMenuPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_systems(OnEnter(GameState::TitleScreen), spawn_menu)
+            .add_systems(OnExit(GameState::TitleScreen), despawn_menu)
+            .add_systems(
+                Update,
+                handle_spacebar.run_if(in_state(GameState::TitleScreen)),
+            );
+    }
+}
+
+// Marker component for the title screen UI entity.
+// This way, a query for the TitleUI can be used to despawn the title screen
+#[derive(Component)]
+struct TitleUI;
+
+fn spawn_menu(mut commands: Commands) {
+    commands
+        .spawn((
+            TitleUI,
+            Node {
+                flex_direction: FlexDirection::Column,
+                ..Default::default()
+            },
+        ))
+        .with_children(|cmds| {
+            cmds.spawn((
+                Text::new("Robert's Bad Asteroids Game"),
+                TextFont::from_font_size(50.0),
+            ));
+            cmds.spawn((
+                Text::new("Press space to begin"),
+                TextFont::from_font_size(40.0),
+            ));
+        });
+}
+
+fn despawn_menu(mut commands: Commands, to_despawn: Query<Entity, With<TitleUI>>) {
+    for entity in &to_despawn {
+        commands.entity(entity).despawn();
+    }
+}
+
+fn handle_spacebar(input: Res<ButtonInput<KeyCode>>, mut game_state: ResMut<NextState<GameState>>) {
+    if input.just_pressed(KeyCode::Space) {
+        game_state.set(GameState::GetReady);
+    }
+}