/**** 
* Classes
****/
// Missile class
// Alien class
// Explosion class
var Explosion = Container.expand(function () {
	var self = Container.call(this);
	self.particles = [];
	for (var i = 0; i < 10; i++) {
		var particle = self.attachAsset('alien', {
			anchorX: 0.5,
			anchorY: 0.5,
			scaleX: 0.2,
			scaleY: 0.2,
			alpha: 0.8
		});
		particle.vx = (Math.random() - 0.5) * 10;
		particle.vy = (Math.random() - 0.5) * 10;
		self.particles.push(particle);
	}
	self.update = function () {
		for (var i = self.particles.length - 1; i >= 0; i--) {
			var p = self.particles[i];
			p.x += p.vx;
			p.y += p.vy;
			p.alpha -= 0.02;
			if (p.alpha <= 0) {
				p.destroy();
				self.particles.splice(i, 1);
			}
		}
	};
});
var Alien = Container.expand(function () {
	var self = Container.call(this);
	var alienGraphics = self.attachAsset('alien', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.baseSpeed = 2;
	self.speedMultiplier = 1;
	self.move = function () {
		var dy = earth.y - self.y;
		var dx = earth.x - self.x;
		var angle = Math.atan2(dy, dx);
		var speed = self.baseSpeed * self.speedMultiplier;
		self.x += speed * Math.cos(angle);
		self.y += speed * Math.sin(angle);
	};
});
// Shield class
var Shield = Container.expand(function () {
	var self = Container.call(this);
	self.attachAsset('shield', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.orbitRadius = 200;
	self.orbitSpeed = 0.04;
	self.orbitAngle = 0;
	self.update = function () {
		self.orbitAngle += self.orbitSpeed;
		self.x = earth.x + self.orbitRadius * Math.cos(self.orbitAngle);
		self.y = earth.y + self.orbitRadius * Math.sin(self.orbitAngle);
		var angleToEarth = Math.atan2(earth.y - self.y, earth.x - self.x);
		self.rotation = angleToEarth + Math.PI / 2;
	};
});

/**** 
* Initialize Game
****/
var game = new LK.Game({
	backgroundColor: 0x000000 // Init game with black background
});

/**** 
* Game Code
****/
// Game variables
// Initialize assets used in the game.
var aliens = [];
var earth;
var scoreTxt;
var spawnAlienInterval = 120; // Frames until a new alien spawns
var spawnAlienIntervalDecrement = 0.98; // Multiplier to decrease spawn interval
var nextAlienSpawn = spawnAlienInterval;
// Initialize Earth
function initEarth() {
	earth = game.addChild(LK.getAsset('earth', {
		anchorX: 0.5,
		anchorY: 0.5,
		x: game.width / 2,
		y: game.height / 2
	}));
	window.shield = game.addChild(new Shield());
	window.shield.x = earth.x;
	window.shield.y = earth.y - window.shield.orbitRadius;
}
// Initialize score display
function initScore() {
	scoreTxt = new Text2('0', {
		size: 150,
		fill: "#ffffff"
	});
	scoreTxt.anchor.set(0.5, 0);
	LK.gui.top.addChild(scoreTxt);
}
// Spawn an alien
function spawnAlien() {
	var alien = new Alien();
	var side = Math.floor(Math.random() * 4);
	switch (side) {
		case 0:
			// top
			alien.x = Math.random() * game.width;
			alien.y = -alien.height;
			break;
		case 1:
			// right
			alien.x = game.width + alien.width;
			alien.y = Math.random() * game.height;
			break;
		case 2:
			// bottom
			alien.x = Math.random() * game.width;
			alien.y = game.height + alien.height;
			break;
		case 3:
			// left
			alien.x = -alien.width;
			alien.y = Math.random() * game.height;
			break;
	}
	aliens.push(alien);
	game.addChild(alien);
}
// Check for collisions
function checkCollisions() {
	for (var i = 0; i < aliens.length; i++) {
		if (window.shield.intersects(aliens[i])) {
			var explosion = new Explosion();
			explosion.x = aliens[i].x;
			explosion.y = aliens[i].y;
			game.addChild(explosion);
			aliens[i].destroy();
			LK.setScore(LK.getScore() + 1);
			scoreTxt.setText(LK.getScore().toString());
			aliens.splice(i, 1);
		}
	}
}
// Game over check
function checkGameOver() {
	for (var i = 0; i < aliens.length; i++) {
		if (aliens[i].intersects(earth)) {
			LK.effects.flashScreen(0xff0000, 1000);
			LK.showGameOver();
			break;
		}
	}
}
// Touch event to move shield
game.on('down', function (obj) {
	window.shield.orbitSpeed *= -1;
});
// Game tick event
LK.on('tick', function () {
	// Update explosions
	game.children.forEach(function (child) {
		if (child instanceof Explosion) {
			child.update();
		}
	});
	// Move aliens
	for (var j = aliens.length - 1; j >= 0; j--) {
		aliens[j].move();
		if (aliens[j].y > game.height + aliens[j].height) {
			aliens[j].destroy();
			aliens.splice(j, 1);
		}
	}
	// Spawn aliens and update spawn interval
	nextAlienSpawn--;
	if (nextAlienSpawn <= 0) {
		spawnAlien();
		nextAlienSpawn = spawnAlienInterval;
		spawnAlienInterval *= spawnAlienIntervalDecrement;
	}
	// Increase alien speed progressively
	for (var i = 0; i < aliens.length; i++) {
		aliens[i].speedMultiplier += 0.01;
	}
	// Update shield position
	window.shield.update();
	// Check for collisions and game over
	checkCollisions();
	checkGameOver();
});
// Initialize game elements
initEarth();
initScore();

===================================================================
--- original.js
+++ change.js
@@ -29,11 +29,8 @@
 				p.destroy();
 				self.particles.splice(i, 1);
 			}
 		}
-		if (self.particles.length === 0) {
-			self.destroy();
-		}
 	};
 });
 var Alien = Container.expand(function () {
 	var self = Container.call(this);
@@ -169,8 +166,14 @@
 	window.shield.orbitSpeed *= -1;
 });
 // Game tick event
 LK.on('tick', function () {
+	// Update explosions
+	game.children.forEach(function (child) {
+		if (child instanceof Explosion) {
+			child.update();
+		}
+	});
 	// Move aliens
 	for (var j = aliens.length - 1; j >= 0; j--) {
 		aliens[j].move();
 		if (aliens[j].y > game.height + aliens[j].height) {