feat: add explosion animations on entity destruction

Spawn expanding/fading orange explosion effects when enemies or
the player are destroyed. Explosions scale from 15x15 to 50x50
over 0.4s while fading from full opacity to transparent, then
auto-despawn.

Integration points:
- Enemy killed by player bullet (bullet.rs)
- Player hit by enemy bullet (bullet.rs)
- Player collides with enemy (player.rs) - both explode
- Captured player released (player.rs)

Refs: GAL-44

src/bullet.rs

@@ -9,6 +9,7 @@ use crate::resources::{PlayerLives, PlayerRespawnTimer, Score};
 use crate::game_state::AppState;
 use crate::components::Player; // Needed for check_enemy_bullet_player_collisions
 use crate::components::Invincible; // Needed for check_enemy_bullet_player_collisions
+use crate::systems::spawn_explosion;
 
 // --- Player Bullet Systems ---
 
@@ -41,6 +42,7 @@ pub fn check_bullet_collisions(
 
             if distance < BULLET_ENEMY_COLLISION_THRESHOLD {
                 commands.entity(bullet_entity).despawn();
+                spawn_explosion(&mut commands, enemy_transform.translation);
                 commands.entity(enemy_entity).despawn();
                 // Increment score based on enemy type
                 let points = match enemy.enemy_type {
@@ -90,6 +92,7 @@ pub fn check_enemy_bullet_player_collisions(
 
             if distance < ENEMY_BULLET_PLAYER_COLLISION_THRESHOLD {
                 println!("Player hit by enemy bullet!");
+                spawn_explosion(&mut commands, player_transform.translation);
                 commands.entity(bullet_entity).despawn(); // Despawn bullet
 
                 lives.count = lives.count.saturating_sub(1);

src/components.rs

@@ -95,3 +95,8 @@ pub struct RestartMessage;
 pub struct Star {
     pub speed: f32,
 }
+
+#[derive(Component)]
+pub struct Explosion {
+    pub timer: Timer,
+}

src/constants.rs

@@ -47,3 +47,9 @@ pub const STAR_MAX_SIZE: f32 = 3.0;
 pub const STAR_MIN_SPEED: f32 = 20.0;
 pub const STAR_MAX_SPEED: f32 = 100.0;
 pub const STAR_Z_DEPTH: f32 = -10.0; // Behind all game entities
+
+// Explosion constants
+pub const EXPLOSION_DURATION: f32 = 0.4;
+pub const EXPLOSION_BASE_SIZE: Vec2 = Vec2::new(15.0, 15.0);
+pub const EXPLOSION_MAX_SIZE: Vec2 = Vec2::new(50.0, 50.0);
+pub const EXPLOSION_COLOR: Color = Color::rgba(1.0, 0.6, 0.1, 1.0);

src/main.rs

@@ -36,7 +36,7 @@ use bullet::{
     move_enemy_bullets,
 };
 use stage::check_stage_clear;
-use systems::{player_exists, player_vulnerable, setup, should_respawn_player, update_window_title};
+use systems::{player_exists, player_vulnerable, setup, should_respawn_player, update_window_title, animate_explosion};
 use starfield::scroll_starfield;
 
 fn main() {
@@ -119,6 +119,8 @@ fn main() {
         )
         // Starfield runs in all states
         .add_systems(Update, scroll_starfield)
+        // Explosion animation runs in all states
+        .add_systems(Update, animate_explosion)
         // UI and state management systems
         .add_systems(OnEnter(AppState::StartMenu), setup_start_menu_ui)
         .add_systems(OnExit(AppState::StartMenu), cleanup_start_menu_ui)

src/player.rs

@@ -9,6 +9,7 @@ use crate::constants::{
 };
 use crate::game_state::AppState;
 use crate::resources::{PlayerLives, PlayerRespawnTimer};
+use crate::systems::spawn_explosion;
 
 // Helper to spawn player (used in setup and respawn)
 pub fn spawn_player_ship(commands: &mut Commands) {
@@ -116,6 +117,7 @@ pub fn handle_captured_player(
                         &mut respawn_timer,
                         &mut next_state,
                         entity,
+                        _player_pos,
                     );
                     continue; // Skip the rest of processing for this player
                 }
@@ -131,6 +133,7 @@ pub fn handle_captured_player(
                     &mut respawn_timer,
                     &mut next_state,
                     entity,
+                    transform.translation,
                 );
             }
         }
@@ -144,11 +147,15 @@ fn lose_life_and_respawn(
     respawn_timer: &mut ResMut<PlayerRespawnTimer>,
     next_state: &mut ResMut<NextState<AppState>>,
     player_entity: Entity,
+    player_position: Vec3,
 ) {
     // Lose a life
     lives.count = lives.count.saturating_sub(1);
     println!("Lives remaining: {}", lives.count);
 
+    // Spawn explosion at player position before destroying
+    spawn_explosion(commands, player_position);
+
     // Destroy player
     commands.entity(player_entity).despawn();
 
@@ -218,11 +225,13 @@ pub fn check_player_enemy_collisions(
 
             if distance < PLAYER_ENEMY_COLLISION_THRESHOLD {
                 println!("Player hit by enemy!");
+                spawn_explosion(&mut commands, enemy_transform.translation);
                 commands.entity(enemy_entity).despawn(); // Despawn enemy
 
                 lives.count = lives.count.saturating_sub(1); // Decrement lives safely
                 println!("Lives remaining: {}", lives.count);
 
+                spawn_explosion(&mut commands, player_transform.translation);
                 commands.entity(player_entity).despawn(); // Despawn player
 
                 if lives.count > 0 {

src/systems.rs

@@ -1,6 +1,7 @@
 use bevy::prelude::*;
 
-use crate::components::{Invincible, Player};
+use crate::components::{Explosion, Invincible, Player};
+use crate::constants::{EXPLOSION_BASE_SIZE, EXPLOSION_COLOR, EXPLOSION_DURATION, EXPLOSION_MAX_SIZE};
 use crate::resources::{CurrentStage, PlayerLives, Score};
 use crate::player::spawn_player_ship;
 use crate::starfield::spawn_starfield;
@@ -45,3 +46,52 @@ pub fn update_window_title(
         );
     }
 }
+
+// --- Explosion Systems ---
+
+pub fn spawn_explosion(commands: &mut Commands, position: Vec3) {
+    commands.spawn((
+        SpriteBundle {
+            sprite: Sprite {
+                color: EXPLOSION_COLOR,
+                custom_size: Some(EXPLOSION_BASE_SIZE),
+                ..default()
+            },
+            transform: Transform {
+                translation: position,
+                ..default()
+            },
+            ..default()
+        },
+        Explosion {
+            timer: Timer::new(std::time::Duration::from_secs_f32(EXPLOSION_DURATION), TimerMode::Once),
+        },
+    ));
+}
+
+pub fn animate_explosion(
+    mut commands: Commands,
+    time: Res<Time>,
+    mut query: Query<(Entity, &mut Explosion, &mut Sprite)>,
+) {
+    for (entity, mut explosion, mut sprite) in query.iter_mut() {
+        explosion.timer.tick(time.delta());
+
+        let progress = explosion.timer.elapsed_secs() / EXPLOSION_DURATION;
+        let clamped_progress = progress.min(1.0);
+
+        // Scale from base to max size
+        let scale_x = EXPLOSION_BASE_SIZE.x + (EXPLOSION_MAX_SIZE.x - EXPLOSION_BASE_SIZE.x) * clamped_progress;
+        let scale_y = EXPLOSION_BASE_SIZE.y + (EXPLOSION_MAX_SIZE.y - EXPLOSION_BASE_SIZE.y) * clamped_progress;
+        sprite.custom_size = Some(Vec2::new(scale_x, scale_y));
+
+        // Fade alpha from 1.0 to 0.0
+        let alpha = 1.0 - clamped_progress;
+        let base = EXPLOSION_COLOR;
+        sprite.color = Color::rgba(base.r(), base.g(), base.b(), alpha);
+
+        if explosion.timer.finished() {
+            commands.entity(entity).despawn();
+        }
+    }
+}