Improve documentation for the events

It actually needs to be completely replaced. When that finally happens,
the new bits will live here.

src/asteroids.rs

@@ -1,184 +0,0 @@
-//! 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, Lifetime, WorldSize, config::ASTEROID_LIFETIME, event::AsteroidDestroy,
-    physics::Velocity,
-};
-
-#[derive(Component, Deref, DerefMut)]
-pub struct Asteroid(AsteroidSize);
-
-#[derive(Clone, Copy, Debug)]
-pub enum AsteroidSize {
-    Small,
-    Medium,
-    Large,
-}
-
-impl AsteroidSize {
-    fn next(&self) -> Option<Self> {
-        match self {
-            AsteroidSize::Small => None,
-            AsteroidSize::Medium => Some(AsteroidSize::Small),
-            AsteroidSize::Large => Some(AsteroidSize::Medium),
-        }
-    }
-}
-
-#[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(spawn.size),
-            Collider::ball(collider_radius),
-            Sensor,
-            Transform::from_translation(spawn.pos.extend(0.0)),
-            Velocity(spawn.vel),
-            Mesh2d(mesh),
-            MeshMaterial2d(material),
-            Lifetime(Timer::from_seconds(ASTEROID_LIFETIME, TimerMode::Once)),
-        ));
-    }
-}
-
-/// Event listener for asteroid destruction events. Shrinks and multiplies
-/// asteroids until they vanish.
-///
-/// - Large -> 2x Medium
-/// - Medium -> 2x Small
-/// - Small -> (despawned)
-///
-/// The velocity of the child asteroids is scattered somewhat, as if they were
-/// explosively pushed apart.
-pub fn split_asteroids(
-    mut destroy_events: EventReader<AsteroidDestroy>,
-    mut respawn_events: EventWriter<SpawnAsteroid>,
-    mut commands: Commands,
-    query: Query<(&Transform, &Asteroid, &Velocity)>,
-) {
-    for event in destroy_events.read() {
-        if let Ok((transform, rock, velocity)) = query.get(event.0) {
-            let next_size = rock.0.next();
-            if let Some(size) = next_size {
-                let pos = transform.translation.xy();
-                let left_offset = Vec2::from_angle(0.4);
-                let right_offset = Vec2::from_angle(-0.4);
-                respawn_events.write(SpawnAsteroid {
-                    pos,
-                    vel: left_offset.rotate(velocity.0),
-                    size,
-                });
-                respawn_events.write(SpawnAsteroid {
-                    pos,
-                    vel: right_offset.rotate(velocity.0),
-                    size,
-                });
-            }
-            // Always despawn the asteroid. New ones (may) be spawned in it's
-            // place, but this one is gone.
-            commands.entity(event.0).despawn();
-        }
-    }
-}

src/event.rs

@@ -1,21 +0,0 @@
-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/events.rs

@@ -0,0 +1,36 @@
+use bevy::prelude::*;
+
+use crate::objects::AsteroidSize;
+
+/// Signals that the player's ship has been destroyed.
+///
+/// Produced by the [`fn collision_listener(...)`](`crate::physics::collision_listener`)
+/// system when the player collides with an asteroid. They are consumed by [`fn ship_impact_listener(...)`](`crate::objects::ship_impact_listener`).
+#[derive(Event)]
+pub(crate) struct ShipDestroy;
+
+/// Signals that a particular asteroid has been destroyed.
+///
+/// Produced by the [`fn collision_listener(...)`](`crate::physics::collision_listener`)
+/// system when bullets contact asteroids. It is consumed by [`fn split_asteroid(...)`](`crate::objects::spawn_asteroid`)
+/// system, which re-emits [spawn events](`SpawnAsteroid`).
+#[derive(Event)]
+pub(crate) struct AsteroidDestroy(pub Entity);
+
+/// Signals that an asteroid needs to be spawned and provides the parameters
+/// for that action.
+///
+/// Produced by the [`tick_asteroid_manager(...)`](`crate::machinery::tick_asteroid_manager`)
+/// system and consumed by the [`spawn_asteroid(...)`](`crate::objects::spawn_asteroid`) system.
+#[derive(Event)]
+pub struct SpawnAsteroid {
+    pub pos: Vec2,
+    pub vel: Vec2,
+    pub size: AsteroidSize,
+}
+
+/// Signals that a particular bullet has been destroyed (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

@@ -1,36 +1,36 @@
-mod asteroids;
 pub mod config;
-mod event;
+mod events;
+mod machinery;
+mod objects;
 mod physics;
-mod preparation_widget;
+mod resources;
-mod ship;
+mod widgets;
-mod title_screen;
 
-use crate::asteroids::{Asteroid, AsteroidSpawner};
 use crate::config::{
     ASTEROID_SMALL_COLOR, BACKGROUND_COLOR, BULLET_COLOR, BULLET_LIFETIME, BULLET_SPEED,
     PLAYER_SHIP_COLOR, SHIP_ROTATION, SHIP_THRUST, SHIP_THRUSTER_COLOR_ACTIVE,
     SHIP_THRUSTER_COLOR_INACTIVE, WINDOW_SIZE,
 };
+use crate::machinery::AsteroidSpawner;
+use crate::objects::{Bullet, Ship};
 use crate::physics::AngularVelocity;
-use crate::ship::{Bullet, Ship};
 
 use bevy::prelude::*;
-use bevy_inspector_egui::InspectorOptions;
-use bevy_inspector_egui::prelude::ReflectInspectorOptions;
 use bevy_rapier2d::{
     plugin::{NoUserData, RapierPhysicsPlugin},
     prelude::*,
     render::RapierDebugRenderPlugin,
 };
+use machinery::Lifetime;
+use resources::{GameAssets, Lives, Score, WorldSize};
 
 pub struct AsteroidPlugin;
 
 impl Plugin for AsteroidPlugin {
     fn build(&self, app: &mut App) {
         app.add_plugins((
-            title_screen::GameMenuPlugin,
+            widgets::GameMenuPlugin,
-            preparation_widget::preparation_widget_plugin,
+            widgets::preparation_widget_plugin,
             RapierPhysicsPlugin::<NoUserData>::pixels_per_meter(10.0),
             RapierDebugRenderPlugin::default(),
         ))
@@ -45,7 +45,10 @@ impl Plugin for AsteroidPlugin {
         .insert_resource(AsteroidSpawner::new())
         .init_resource::<GameAssets>()
         .add_systems(Startup, spawn_camera)
-        .add_systems(OnEnter(GameState::Playing), (ship::spawn_player, spawn_ui))
+        .add_systems(
+            OnEnter(GameState::Playing),
+            (objects::spawn_player, widgets::spawn_ui),
+        )
         .add_systems(
             FixedUpdate,
             (
@@ -53,15 +56,15 @@ impl Plugin for AsteroidPlugin {
                 input_ship_rotation,
                 input_ship_shoot,
                 physics::wrap_entities,
-                asteroids::tick_asteroid_manager,
+                machinery::tick_asteroid_manager,
-                asteroids::spawn_asteroid.after(asteroids::tick_asteroid_manager),
+                objects::spawn_asteroid.after(machinery::tick_asteroid_manager),
-                asteroids::split_asteroids,
+                objects::split_asteroids,
-                ship::bullet_impact_listener,
+                objects::bullet_impact_listener,
-                ship::ship_impact_listener,
+                objects::ship_impact_listener,
-                collision_listener,
+                physics::collision_listener,
                 // TODO: Remove debug printing
                 debug_collision_event_printer,
-                tick_lifetimes,
+                machinery::tick_lifetimes,
             )
                 .run_if(in_state(GameState::Playing)),
         )
@@ -73,10 +76,10 @@ impl Plugin for AsteroidPlugin {
             )
                 .run_if(in_state(GameState::Playing)),
         )
-        .add_event::<asteroids::SpawnAsteroid>()
+        .add_event::<events::SpawnAsteroid>()
-        .add_event::<event::AsteroidDestroy>()
+        .add_event::<events::AsteroidDestroy>()
-        .add_event::<event::ShipDestroy>()
+        .add_event::<events::ShipDestroy>()
-        .add_event::<event::BulletDestroy>();
+        .add_event::<events::BulletDestroy>();
         app.insert_state(GameState::Playing);
     }
 }
@@ -87,69 +90,6 @@ fn debug_collision_event_printer(mut collision_events: EventReader<CollisionEven
     }
 }
 
-/// The collision event routing system.
-///
-/// 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>,
-    mut bullet_writer: EventWriter<event::BulletDestroy>,
-    player: Single<Entity, With<Ship>>,
-    bullets: Query<&Bullet>,
-    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.
-
-            // Option 1: Ship & Asteroid
-            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);
-                }
-            }
-
-            // Option 2: Bullet & Asteroid
-            if bullets.contains(*one) {
-                if rocks.contains(*two) {
-                    dbg!("Writing AsteroidDestroy & BulletDestroy events");
-                    asteroid_writer.write(event::AsteroidDestroy(*two));
-                    bullet_writer.write(event::BulletDestroy(*one));
-                }
-            } else if rocks.contains(*one) {
-                if bullets.contains(*two) {
-                    dbg!("Writing AsteroidDestroy & BulletDestroy events");
-                    asteroid_writer.write(event::AsteroidDestroy(*one));
-                    bullet_writer.write(event::BulletDestroy(*two));
-                }
-            }
-        }
-    }
-}
-
 #[derive(Clone, Debug, Eq, Hash, PartialEq, States)]
 pub enum GameState {
     TitleScreen, // Program is started. Present title screen and await user start
@@ -158,107 +98,6 @@ pub enum GameState {
     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(Component)]
-struct Lifetime(Timer);
-
-#[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 {
-    width: f32,
-    height: f32,
-}
-
-#[derive(Resource)]
-struct GameAssets {
-    meshes: [Handle<Mesh>; 5],
-    materials: [Handle<ColorMaterial>; 7],
-}
-
-impl GameAssets {
-    fn ship(&self) -> (Handle<Mesh>, Handle<ColorMaterial>) {
-        (self.meshes[0].clone(), self.materials[0].clone())
-    }
-
-    // The thruster mesh is actually just the ship mesh
-    fn thruster_mesh(&self) -> Handle<Mesh> {
-        self.meshes[0].clone()
-    }
-
-    // TODO: Look into parameterizing the material
-    // A shader uniform should be able to do this, but I don't know how to
-    // load those in Bevy.
-    fn thruster_mat_inactive(&self) -> Handle<ColorMaterial> {
-        self.materials[1].clone()
-    }
-
-    fn thruster_mat_active(&self) -> Handle<ColorMaterial> {
-        self.materials[2].clone()
-    }
-
-    fn asteroid_small(&self) -> (Handle<Mesh>, Handle<ColorMaterial>) {
-        (self.meshes[1].clone(), self.materials[1].clone())
-    }
-
-    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);
 }
@@ -334,7 +173,7 @@ fn input_ship_shoot(
     // For now, spawn one for each press of the spacebar.
     if keyboard_input.just_pressed(KeyCode::Space) {
         commands.spawn((
-            ship::Bullet,
+            Bullet,
             Collider::ball(0.2),
             Sensor,
             ActiveEvents::COLLISION_EVENTS,
@@ -347,19 +186,3 @@ fn input_ship_shoot(
         ));
     }
 }
-
-fn spawn_ui(mut commands: Commands, score: Res<Score>, lives: Res<Lives>) {
-    commands.spawn((
-        Text::new(format!("Score: {score:?} | Lives: {lives:?}")),
-        TextFont::from_font_size(25.0),
-    ));
-}
-
-fn tick_lifetimes(mut commands: Commands, time: Res<Time>, query: Query<(Entity, &mut Lifetime)>) {
-    for (e, mut life) in query {
-        life.0.tick(time.delta());
-        if life.0.just_finished() {
-            commands.entity(e).despawn();
-        }
-    }
-}

src/machinery.rs

@@ -0,0 +1,94 @@
+//! These are Systems that power the main game mechanics (and some misc items to support them)
+
+use rand::{Rng, SeedableRng};
+use std::time::Duration;
+
+use bevy::prelude::*;
+
+use crate::{WorldSize, events::SpawnAsteroid, objects::AsteroidSize};
+
+#[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),
+        }
+    }
+}
+
+/// 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 });
+    }
+}
+
+#[derive(Component)]
+pub struct Lifetime(pub Timer);
+
+pub fn tick_lifetimes(
+    mut commands: Commands,
+    time: Res<Time>,
+    query: Query<(Entity, &mut Lifetime)>,
+) {
+    for (e, mut life) in query {
+        life.0.tick(time.delta());
+        if life.0.just_finished() {
+            commands.entity(e).despawn();
+        }
+    }
+}

src/objects.rs

@@ -0,0 +1,194 @@
+//! This module contains all the "things" in the game.
+//!
+//! Asteroids, the player's ship, and such.
+
+use bevy::{
+    ecs::{
+        component::Component,
+        entity::Entity,
+        event::{EventReader, EventWriter},
+        query::With,
+        system::{Commands, Query, Res, ResMut, Single},
+    },
+    math::{Vec2, Vec3, Vec3Swizzles},
+    prelude::{Deref, DerefMut},
+    render::mesh::Mesh2d,
+    sprite::MeshMaterial2d,
+    state::state::NextState,
+    time::{Timer, TimerMode},
+    transform::components::Transform,
+};
+use bevy_rapier2d::prelude::{ActiveCollisionTypes, ActiveEvents, Collider, Sensor};
+
+use crate::{
+    AngularVelocity, GameAssets, GameState, Lives,
+    config::ASTEROID_LIFETIME,
+    events::{AsteroidDestroy, BulletDestroy, ShipDestroy, SpawnAsteroid},
+    machinery::Lifetime,
+    physics::{Velocity, Wrapping},
+};
+
+#[derive(Component, Deref, DerefMut)]
+pub struct Asteroid(pub AsteroidSize);
+
+#[derive(Clone, Copy, Debug)]
+pub enum AsteroidSize {
+    Small,
+    Medium,
+    Large,
+}
+
+impl AsteroidSize {
+    pub fn next(&self) -> Option<Self> {
+        match self {
+            AsteroidSize::Small => None,
+            AsteroidSize::Medium => Some(AsteroidSize::Small),
+            AsteroidSize::Large => Some(AsteroidSize::Medium),
+        }
+    }
+}
+
+#[derive(Component)]
+pub struct Ship;
+
+#[derive(Component)]
+pub struct Bullet;
+
+/// Responds to [`SpawnAsteroid`] events, spawning as specified
+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(spawn.size),
+            Collider::ball(collider_radius),
+            Sensor,
+            Transform::from_translation(spawn.pos.extend(0.0)),
+            Velocity(spawn.vel),
+            Mesh2d(mesh),
+            MeshMaterial2d(material),
+            Lifetime(Timer::from_seconds(ASTEROID_LIFETIME, TimerMode::Once)),
+        ));
+    }
+}
+
+/// Event listener for asteroid destruction events. Shrinks and multiplies
+/// asteroids until they vanish.
+///
+/// - Large -> 2x Medium
+/// - Medium -> 2x Small
+/// - Small -> (despawned)
+///
+/// The velocity of the child asteroids is scattered somewhat, as if they were
+/// explosively pushed apart.
+pub fn split_asteroids(
+    mut destroy_events: EventReader<AsteroidDestroy>,
+    mut respawn_events: EventWriter<SpawnAsteroid>,
+    mut commands: Commands,
+    query: Query<(&Transform, &Asteroid, &Velocity)>,
+) {
+    for event in destroy_events.read() {
+        if let Ok((transform, rock, velocity)) = query.get(event.0) {
+            let next_size = rock.0.next();
+            if let Some(size) = next_size {
+                let pos = transform.translation.xy();
+                let left_offset = Vec2::from_angle(0.4);
+                let right_offset = Vec2::from_angle(-0.4);
+                respawn_events.write(SpawnAsteroid {
+                    pos,
+                    vel: left_offset.rotate(velocity.0),
+                    size,
+                });
+                respawn_events.write(SpawnAsteroid {
+                    pos,
+                    vel: right_offset.rotate(velocity.0),
+                    size,
+                });
+            }
+            // Always despawn the asteroid. New ones (may) be spawned in it's
+            // place, but this one is gone.
+            commands.entity(event.0).despawn();
+        }
+    }
+}
+
+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)),
+        ));
+}
+
+/// Watch for [`BulletDestroy`] events and despawn
+/// the associated bullet.
+pub fn bullet_impact_listener(mut commands: Commands, mut events: EventReader<BulletDestroy>) {
+    for event in events.read() {
+        commands.entity(event.0).despawn();
+    }
+}
+
+/// Watch for [`ShipDestroy`] events and update game state accordingly.
+///
+/// - Subtract a life
+/// - Check life count. If 0, go to game-over state
+/// - Clear all asteroids
+/// - Respawn player
+pub fn ship_impact_listener(
+    mut events: EventReader<ShipDestroy>,
+    mut commands: Commands,
+    mut lives: ResMut<Lives>,
+    rocks: Query<Entity, With<Asteroid>>,
+    mut player: Single<(&mut Transform, &mut Velocity), With<Ship>>,
+    mut next_state: ResMut<NextState<GameState>>,
+) {
+    for _ in events.read() {
+        // STEP 1: Decrement lives (and maybe go to game over)
+        if lives.0 == 0 {
+            // If already at 0, game is over.
+            next_state.set(GameState::GameOver);
+        } else {
+            // Decrease life count.
+            lives.0 -= 1;
+        }
+
+        // STEP 2: Clear asteroids
+        for rock in rocks {
+            commands.entity(rock).despawn();
+        }
+
+        // STEP 3: Respawn player (teleport them to the origin)
+        player.0.translation = Vec3::ZERO;
+        player.1.0 = Vec2::ZERO;
+    }
+}

src/physics.rs

@@ -1,9 +1,13 @@
 //! Custom physics items
 //! TODO: Refactor in terms of Rapier2D, *or* implement colliders and remove it.
 
-use crate::WorldSize;
+use crate::{
+    WorldSize, events,
+    objects::{Asteroid, Bullet, Ship},
+};
 
 use bevy::prelude::*;
+use bevy_rapier2d::pipeline::CollisionEvent;
 
 #[derive(Clone, Component)]
 pub(crate) struct Velocity(pub(crate) bevy::math::Vec2);
@@ -57,3 +61,66 @@ pub(crate) fn wrap_entities(
         }
     }
 }
+
+/// The collision event routing system.
+///
+/// When a `CollisionEvent` occurrs, this system checks which things collided
+/// and emits secondary events accordignly.
+///
+/// | Objects | Response |
+/// |-|-|
+/// | Ship & Asteroid | emits event [`ShipDestroy`](`crate::events::ShipDestroy`) |
+/// | Asteroid & Bullet | emits event [`AsteroidDestroy`](`crate::events::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) |
+pub fn collision_listener(
+    mut collisions: EventReader<CollisionEvent>,
+    mut ship_writer: EventWriter<events::ShipDestroy>,
+    mut asteroid_writer: EventWriter<events::AsteroidDestroy>,
+    mut bullet_writer: EventWriter<events::BulletDestroy>,
+    player: Single<Entity, With<Ship>>,
+    bullets: Query<&Bullet>,
+    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.
+
+            // Option 1: Ship & Asteroid
+            if *one == *player {
+                if rocks.contains(*two) {
+                    // player-asteroid collision
+                    dbg!("Writing ShipDestroy event");
+                    ship_writer.write(events::ShipDestroy);
+                } // else, we don't care
+            } else if *two == *player {
+                if rocks.contains(*one) {
+                    dbg!("Writing ShipDestroy event");
+                    ship_writer.write(events::ShipDestroy);
+                }
+            }
+
+            // Option 2: Bullet & Asteroid
+            if bullets.contains(*one) {
+                if rocks.contains(*two) {
+                    dbg!("Writing AsteroidDestroy & BulletDestroy events");
+                    asteroid_writer.write(events::AsteroidDestroy(*two));
+                    bullet_writer.write(events::BulletDestroy(*one));
+                }
+            } else if rocks.contains(*one) {
+                if bullets.contains(*two) {
+                    dbg!("Writing AsteroidDestroy & BulletDestroy events");
+                    asteroid_writer.write(events::AsteroidDestroy(*one));
+                    bullet_writer.write(events::BulletDestroy(*two));
+                }
+            }
+        }
+    }
+}

src/resources.rs

@@ -0,0 +1,121 @@
+//! All the resources for the game
+
+use bevy::{
+    asset::{Assets, Handle},
+    ecs::{
+        resource::Resource,
+        world::{FromWorld, World},
+    },
+    math::{
+        Vec2,
+        primitives::{Circle, Triangle2d},
+    },
+    prelude::{Deref, Reflect, ReflectResource},
+    render::mesh::Mesh,
+    sprite::ColorMaterial,
+};
+use bevy_inspector_egui::InspectorOptions;
+use bevy_inspector_egui::inspector_options::ReflectInspectorOptions;
+
+use crate::{
+    ASTEROID_SMALL_COLOR, BULLET_COLOR, PLAYER_SHIP_COLOR, SHIP_THRUSTER_COLOR_ACTIVE,
+    SHIP_THRUSTER_COLOR_INACTIVE,
+};
+
+#[derive(Resource, Debug, Deref, Clone, Copy)]
+pub struct Score(pub 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)]
+pub struct Lives(pub i32);
+
+impl From<Lives> for String {
+    fn from(value: Lives) -> Self {
+        value.to_string()
+    }
+}
+
+#[derive(Resource)]
+pub struct WorldSize {
+    pub width: f32,
+    pub height: f32,
+}
+
+#[derive(Resource)]
+pub struct GameAssets {
+    meshes: [Handle<Mesh>; 5],
+    materials: [Handle<ColorMaterial>; 7],
+}
+
+impl GameAssets {
+    pub fn ship(&self) -> (Handle<Mesh>, Handle<ColorMaterial>) {
+        (self.meshes[0].clone(), self.materials[0].clone())
+    }
+
+    // The thruster mesh is actually just the ship mesh
+    pub fn thruster_mesh(&self) -> Handle<Mesh> {
+        self.meshes[0].clone()
+    }
+
+    // TODO: Look into parameterizing the material
+    // A shader uniform should be able to do this, but I don't know how to
+    // load those in Bevy.
+    pub fn thruster_mat_inactive(&self) -> Handle<ColorMaterial> {
+        self.materials[1].clone()
+    }
+
+    pub fn thruster_mat_active(&self) -> Handle<ColorMaterial> {
+        self.materials[2].clone()
+    }
+
+    pub fn asteroid_small(&self) -> (Handle<Mesh>, Handle<ColorMaterial>) {
+        (self.meshes[1].clone(), self.materials[1].clone())
+    }
+
+    pub fn asteroid_medium(&self) -> (Handle<Mesh>, Handle<ColorMaterial>) {
+        (self.meshes[2].clone(), self.materials[2].clone())
+    }
+
+    pub fn asteroid_large(&self) -> (Handle<Mesh>, Handle<ColorMaterial>) {
+        (self.meshes[3].clone(), self.materials[3].clone())
+    }
+
+    pub 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 }
+    }
+}

src/ship.rs

@@ -1,82 +0,0 @@
-use crate::{
-    AngularVelocity, GameAssets, GameState, Lives,
-    asteroids::Asteroid,
-    event::{BulletDestroy, ShipDestroy},
-    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)),
-        ));
-}
-
-/// Watch for [`BulletDestroy`] events and despawn
-/// the associated bullet.
-pub fn bullet_impact_listener(mut commands: Commands, mut events: EventReader<BulletDestroy>) {
-    for event in events.read() {
-        commands.entity(event.0).despawn();
-    }
-}
-
-/// Watch for [`ShipDestroy`] events and update game state accordingly.
-///
-/// - Subtract a life
-/// - Check life count. If 0, go to game-over state
-/// - Clear all asteroids
-/// - Respawn player
-pub fn ship_impact_listener(
-    mut events: EventReader<ShipDestroy>,
-    mut commands: Commands,
-    mut lives: ResMut<Lives>,
-    rocks: Query<Entity, With<Asteroid>>,
-    mut player: Single<(&mut Transform, &mut Velocity), With<Ship>>,
-    mut next_state: ResMut<NextState<GameState>>,
-) {
-    for _ in events.read() {
-        // STEP 1: Decrement lives (and maybe go to game over)
-        if lives.0 == 0 {
-            // If already at 0, game is over.
-            next_state.set(GameState::GameOver);
-        } else {
-            // Decrease life count.
-            lives.0 -= 1;
-        }
-
-        // STEP 2: Clear asteroids
-        for rock in rocks {
-            commands.entity(rock).despawn();
-        }
-
-        // STEP 3: Respawn player (teleport them to the origin)
-        player.0.translation = Vec3::ZERO;
-        player.1.0 = Vec2::ZERO;
-    }
-}

src/title_screen.rs

@@ -1,54 +0,0 @@
-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);
-    }
-}

src/widgets.rs

@@ -1,10 +1,20 @@
-use crate::GameState;
+use crate::{
+    GameState,
+    resources::{Lives, Score},
+};
 
 use bevy::{
     color::palettes::css::{BLACK, GREEN, LIGHT_BLUE, RED},
     prelude::*,
 };
 
+pub fn spawn_ui(mut commands: Commands, score: Res<Score>, lives: Res<Lives>) {
+    commands.spawn((
+        Text::new(format!("Score: {score:?} | Lives: {lives:?}")),
+        TextFont::from_font_size(25.0),
+    ));
+}
+
 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)
@@ -97,3 +107,54 @@ fn animate_get_ready_widget(
         game_state.set(GameState::Playing);
     }
 }
+
+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);
+    }
+}