var IceBlock = Container.expand(function () {
	var self = Container.call(this);
	var iceBlockGraphics = self.createAsset('iceBlock', 'Ice Block', .5, .5);
	self.destroyBlock = function () {
		self.destroy();
	};
});
var Player = Container.expand(function () {
	var self = Container.call(this);
	var playerGraphics = self.createAsset('player', 'Player character', .5, .5);
	self.shoot = function () {};
});
var Bullet = Container.expand(function () {
	var self = Container.call(this);
	var bulletGraphics = self.createAsset('bullet', 'Bullet', .5, .5);
	self.move = function () {};
});
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 player = self.addChild(new Player());
	var bullets = [];
	var enemies = [];
	player.x = 2048 / 2;
	player.y = 2732 / 2;
	var iceBlocks = [];
	for (var i = 0; i < 20; i++) {
		var topIceBlock = new IceBlock();
		topIceBlock.x = i * 200;
		topIceBlock.y = 0;
		iceBlocks.push(topIceBlock);
		self.addChild(topIceBlock);
		var bottomIceBlock = new IceBlock();
		bottomIceBlock.x = i * 200;
		bottomIceBlock.y = 2732 - bottomIceBlock.height;
		iceBlocks.push(bottomIceBlock);
		self.addChild(bottomIceBlock);
	}
	for (var j = 1; j < 13; j++) {
		var leftIceBlock = new IceBlock();
		leftIceBlock.x = 0;
		leftIceBlock.y = j * 200;
		iceBlocks.push(leftIceBlock);
		self.addChild(leftIceBlock);
		var rightIceBlock = new IceBlock();
		rightIceBlock.x = 2048 - rightIceBlock.width;
		rightIceBlock.y = j * 200;
		iceBlocks.push(rightIceBlock);
		self.addChild(rightIceBlock);
	}
	LK.on('tick', function () {
		for (var i = 0; i < bullets.length; i++) {
			bullets[i].move();
		}
		for (var i = 0; i < enemies.length; i++) {
			enemies[i].move();
		}
		for (var i = 0; i < bullets.length; i++) {
			for (var j = 0; j < iceBlocks.length; j++) {
				if (bullets[i].intersects(iceBlocks[j])) {
					iceBlocks[j].destroyBlock();
					iceBlocks.splice(j, 1);
					bullets[i].destroy();
					bullets.splice(i, 1);
					break;
				}
			}
		}
	});
	player.on('down', function (obj) {
		var bullet = new Bullet();
		bullet.x = player.x;
		bullet.y = player.y;
		bullets.push(bullet);
		self.addChild(bullet);
	});
	window.addEventListener('keydown', function (e) {
		switch (e.key) {
			case 'ArrowUp':
			case 'w':
				player.y -= 10;
				break;
			case 'ArrowDown':
			case 's':
				player.y += 10;
				break;
			case 'ArrowLeft':
			case 'a':
				player.x -= 10;
				break;
			case 'ArrowRight':
			case 'd':
				player.x += 10;
				break;
			default:
				break;
		}
	});
});

===================================================================
--- original.js
+++ change.js
@@ -77,20 +77,27 @@
 		bullet.y = player.y;
 		bullets.push(bullet);
 		self.addChild(bullet);
 	});
-	var dragNode = null;
-	stage.on('down', function (obj) {
-		dragNode = player;
-	});
-	stage.on('move', function (obj) {
-		var event = obj.event;
-		var pos = event.getLocalPosition(self);
-		if (dragNode) {
-			dragNode.x = pos.x;
-			dragNode.y = pos.y;
+	window.addEventListener('keydown', function (e) {
+		switch (e.key) {
+			case 'ArrowUp':
+			case 'w':
+				player.y -= 10;
+				break;
+			case 'ArrowDown':
+			case 's':
+				player.y += 10;
+				break;
+			case 'ArrowLeft':
+			case 'a':
+				player.x -= 10;
+				break;
+			case 'ArrowRight':
+			case 'd':
+				player.x += 10;
+				break;
+			default:
+				break;
 		}
 	});
-	stage.on('up', function (obj) {
-		dragNode = null;
-	});
 });