var Snowflake = Container.expand(function () {
	var self = Container.call(this);
	var snowflakeGraphics = self.createAsset('snowflake', 'Snowflake', .5, .5);
	snowflakeGraphics.width = 10;
	snowflakeGraphics.height = 10;
	self.speed = Math.random() * 4 + 2;
	self.move = function () {
		self.y += self.speed;
		self.x += Math.sin(self.y / 100) * 5;
		if (self.y > 2800) {
			self.y = -10;
		}
	};
});
var FloorTile = Container.expand(function () {
	var self = Container.call(this);
	var floorTileGraphics = self.createAsset('floorTile', 'Floor Tile', .5, .5);
	floorTileGraphics.width = 200;
	floorTileGraphics.height = 200;
});
var IceBlock = Container.expand(function () {
	var self = Container.call(this);
	var iceBlockGraphics = self.createAsset('iceBlock', 'Ice Block', .5, .5);
});
var Player = Container.expand(function () {
	var self = Container.call(this);
	var playerGraphics = self.createAsset('player', 'Player character', .5, .5);
	self.velocity = {
		x: 0,
		y: 0
	};
	self.shoot = function () {};
	self.move = function () {
		self.x += self.velocity.x;
		self.y += self.velocity.y;
		self.velocity.x *= 0.95;
		self.velocity.y *= 0.95;
	};
});
var Bullet = Container.expand(function () {
	var self = Container.call(this);
	var bulletGraphics = self.createAsset('bullet', 'Bullet', .5, .5);
	self.direction = {
		x: 0,
		y: 0
	};
	self.speed = 10;
	self.move = function () {
		self.x += self.direction.x * self.speed;
		self.y += self.direction.y * self.speed;
	};
});
var Enemy = Container.expand(function () {
	var self = Container.call(this);
	var enemyGraphics = self.createAsset('enemy', 'Enemy character', .5, .5);
	self.move = function () {};
});
var Game = Container.expand(function () {
	var self = Container.call(this);
	var iceBlocks = [];
	var blockSize = 200;
	var worldWidth = blockSize * 11;
	var worldHeight = blockSize * 15;
	console.log('Game world size:', worldWidth, 'x', worldHeight);
	console.log('LK.stageContainer.height:', LK.stageContainer.height);
	for (var i = 0; i < worldWidth / blockSize; i++) {
		for (var j = 0; j < worldHeight / blockSize; j++) {
			if (i === 0 || i === worldWidth / blockSize - 1 || j === 0 || j === worldHeight / blockSize - 1) {
				var iceBlock = new IceBlock();
				iceBlock.x = i * blockSize;
				iceBlock.y = j * blockSize;
				self.addChild(iceBlock);
			} else {
				var floorTile = new FloorTile();
				floorTile.x = i * blockSize;
				floorTile.y = j * blockSize;
				self.addChild(floorTile);
			}
		}
	}
	var player = self.addChild(new Player());
	var arrowUp = self.createAsset('arrowUp', 'Arrow Up', .5, .5);
	arrowUp.rotation = -Math.PI / 2;
	arrowUp.on('down', function () {
		player.velocity.y -= 5;
	});
	var arrowDown = self.createAsset('arrowDown', 'Arrow Down', .5, .5);
	arrowDown.rotation = Math.PI / 2;
	arrowDown.on('down', function () {
		player.velocity.y += 5;
	});
	var arrowLeft = self.createAsset('arrowLeft', 'Arrow Left', .5, .5);
	arrowLeft.rotation = Math.PI;
	arrowLeft.on('down', function () {
		player.velocity.x -= 5;
	});
	var arrowRight = self.createAsset('arrowRight', 'Arrow Right', .5, .5);
	arrowRight.on('down', function () {
		player.velocity.x += 5;
	});
	var arrowKeysCenter = LK.stageContainer.width;
	arrowUp.x = arrowKeysCenter;
	arrowUp.y = LK.stageContainer.height + 50;
	arrowDown.x = arrowKeysCenter;
	arrowDown.y = LK.stageContainer.height + 200;
	arrowLeft.x = arrowKeysCenter - 100;
	arrowLeft.y = LK.stageContainer.height + 125;
	arrowRight.x = arrowKeysCenter + 100;
	arrowRight.y = LK.stageContainer.height + 125;
	LK.gui.addChild(arrowUp);
	LK.gui.addChild(arrowDown);
	LK.gui.addChild(arrowLeft);
	LK.gui.addChild(arrowRight);
	var bullets = [];
	var enemies = [];
	var enemySpawnInterval = LK.setInterval(function () {
		var enemy = new Enemy();
		enemy.x = Math.random() * worldWidth;
		enemy.y = Math.random() * worldHeight;
		enemies.push(enemy);
		self.addChild(enemy);
	}, 2000);
	var snowflakes = [];
	for (var i = 0; i < 10; i++) {
		var snowflake = new Snowflake();
		snowflake.x = Math.random() * 1800;
		snowflake.y = Math.random() * LK.stageContainer.height;
		snowflakes.push(snowflake);
		self.addChild(snowflake);
	}
	player.x = 330;
	player.y = 300;
	LK.on('tick', function () {
		player.move();
		for (var i = 0; i < bullets.length; i++) {
			bullets[i].move();
			if (bullets[i].x < 0 || bullets[i].x > worldWidth || bullets[i].y < 0 || bullets[i].y > worldHeight) {
				bullets[i].destroy();
				bullets.splice(i, 1);
				continue;
			}
			for (var j = 0; j < enemies.length; j++) {
				if (bullets[i].intersects(enemies[j])) {
					enemies[j].destroy();
					enemies.splice(j, 1);
					break;
				}
			}
		}
		for (var i = 0; i < enemies.length; i++) {
			enemies[i].move();
		}
		for (var i = 0; i < snowflakes.length; i++) {
			snowflakes[i].move();
		}
	});
	stage.on('down', function (obj) {
		var bullet = new Bullet();
		bullet.x = player.x;
		bullet.y = player.y;
		var pos = obj.event.getLocalPosition(self);
		var dx = pos.x - player.x;
		var dy = pos.y - player.y;
		var magnitude = Math.sqrt(dx * dx + dy * dy);
		bullet.direction.x = dx / magnitude;
		bullet.direction.y = dy / magnitude;
		bullets.push(bullet);
		self.addChild(bullet);
		player.x -= bullet.direction.x * 10;
		player.y -= bullet.direction.y * 10;
		var recoilFrames = 10;
		LK.on('tick', function recoilTick() {
			if (recoilFrames-- <= 0) {
				return;
			}
			player.x += bullet.direction.x;
			player.y += bullet.direction.y;
		});
	});
});

===================================================================
--- original.js
+++ change.js
@@ -133,8 +133,13 @@
 	LK.on('tick', function () {
 		player.move();
 		for (var i = 0; i < bullets.length; i++) {
 			bullets[i].move();
+			if (bullets[i].x < 0 || bullets[i].x > worldWidth || bullets[i].y < 0 || bullets[i].y > worldHeight) {
+				bullets[i].destroy();
+				bullets.splice(i, 1);
+				continue;
+			}
 			for (var j = 0; j < enemies.length; j++) {
 				if (bullets[i].intersects(enemies[j])) {
 					enemies[j].destroy();
 					enemies.splice(j, 1);