var Player = Container.expand(function () {
	var self = Container.call(this);
	var playerGraphics = self.createAsset('player', 'Player character', .5, .5);
	self.gravity = 1;
	self.jumpForce = 20;
	self.velocityX = 0;
	self.velocityY = 0;
	self.setJumpForce = function (x, y) {
		this.jumpForceX = x / 12.5;
		this.jumpForceY = y / 12.5;
	};
	self.jumping = false;
	self.onPlatform = false;
	self.update = function () {
		this.x += this.velocityX;
		this.y += this.velocityY;
		this.velocityY += this.gravity;
		this.velocityX *= 0.98;
		this.velocityY *= 0.98;
		if (this.y > 2732) {
			this.y = 2732;
			this.velocityY = 0;
		}
		if (this.x < 0 || this.x > 2048) {
			this.velocityX *= -1;
		}
		if (this.velocityY >= 0) {
			this.jumping = false;
		} else if (this.velocityY < 0) {
			this.jumping = true;
		}
	};
});
var Platform = Container.expand(function () {
	var self = Container.call(this);
	var platformGraphics = self.createAsset('platform', 'Platform', .5, .5);
	self.speed = 5;
	self.move = function () {
		this.y += this.speed;
	};
});
var Game = Container.expand(function () {
	var self = Container.call(this);
	stage.on('up', function (obj) {
		if (dragStart && player.onPlatform) {
			var pos = obj.event.getLocalPosition(self);
			player.setJumpForce(dragStart.x - pos.x, dragStart.y - pos.y);
			player.velocityX = player.jumpForceX;
			player.velocityY = player.jumpForceY;
			dragStart = null;
		}
	});
	stage.on('move', function (obj) {
		if (dragStart) {
			var pos = obj.event.getLocalPosition(self);
		}
	});
	var platforms = [];
	var player = self.addChild(new Player());
	player.x = 2048 / 2;
	player.y = 2732 - player.height;
	var firstJump = false;
	for (var i = 0; i < 6; i++) {
		var platform = new Platform();
		if (i == 0) {
			platform.x = player.x;
			platform.y = player.y + player.height;
		} else {
			platform.x = Math.random() * 2048;
			platform.y = i * (2732 / 6);
		}
		platforms.push(platform);
		self.addChild(platform);
	}
	LK.on('tick', function () {
		player.update();
		for (var i = 0; i < platforms.length; i++) {
			if (player.intersects(platforms[i]) && !player.jumping && player.y + player.height / 2 < platforms[i].y) {
				player.y = platforms[i].y - player.height;
				player.velocityY = 0;
				player.velocityX *= 0.8;
				player.onPlatform = true;
			} else {
				player.onPlatform = false;
			}
		}
	});
	var dragStart = null;
	stage.on('down', function (obj) {
		dragStart = obj.event.getLocalPosition(self);
	});
});

===================================================================
--- original.js
+++ change.js
@@ -9,8 +9,9 @@
 		this.jumpForceX = x / 12.5;
 		this.jumpForceY = y / 12.5;
 	};
 	self.jumping = false;
+	self.onPlatform = false;
 	self.update = function () {
 		this.x += this.velocityX;
 		this.y += this.velocityY;
 		this.velocityY += this.gravity;
@@ -40,9 +41,9 @@
 });
 var Game = Container.expand(function () {
 	var self = Container.call(this);
 	stage.on('up', function (obj) {
-		if (dragStart && !player.jumping) {
+		if (dragStart && player.onPlatform) {
 			var pos = obj.event.getLocalPosition(self);
 			player.setJumpForce(dragStart.x - pos.x, dragStart.y - pos.y);
 			player.velocityX = player.jumpForceX;
 			player.velocityY = player.jumpForceY;
@@ -77,8 +78,11 @@
 			if (player.intersects(platforms[i]) && !player.jumping && player.y + player.height / 2 < platforms[i].y) {
 				player.y = platforms[i].y - player.height;
 				player.velocityY = 0;
 				player.velocityX *= 0.8;
+				player.onPlatform = true;
+			} else {
+				player.onPlatform = false;
 			}
 		}
 	});
 	var dragStart = null;