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.velocity = 0;
	self.setJumpForce = function (x, y) {
		var dx = this.x - x;
		var dy = this.y - y;
		this.jumpForce = Math.sqrt(dx * dx + dy * dy) / 10;
	};
	self.update = function () {
		this.y += this.velocity;
		this.velocity += this.gravity;
		if (this.y > 2732) {
			this.y = 2732;
			this.velocity = 0;
		}
	};
});
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.velocity = -player.jumpForce;
			dragStart = null;
		}
	});
	stage.on('move', function (obj) {
		if (dragStart) {
			var pos = obj.event.getLocalPosition(self);
			player.setJumpForce(dragStart.x, dragStart.y);
		}
	});
	var platforms = [];
	var ground = self.createAsset('ground', 'Ground', 0, 1);
	ground.y = 2732;
	ground.speed = 5;
	ground.move = function () {
		this.y += this.speed;
		if (this.y > 2732) {
			this.y = 0;
		}
	};
	var player = self.addChild(new Player());
	player.x = 2048 / 2;
	player.y = ground.y - player.height;
	var firstJump = false;
	for (var i = 0; i < 5; i++) {
		var platform = new Platform();
		platform.x = Math.random() * 2048;
		platform.y = i * (2732 / 5);
		platforms.push(platform);
		self.addChild(platform);
	}
	LK.on('tick', function () {
		player.update();
		if (firstJump) {
			ground.move();
			for (var i = 0; i < platforms.length; i++) {
				platforms[i].move();
				if (platforms[i].y > 2732) {
					platforms[i].y = 0;
					platforms[i].x = Math.random() * 2048;
				}
				if (player.intersects(platforms[i]) && player.velocity > 0) {
					player.jump();
				}
			}
		}
	});
	var dragStart = null;
	stage.on('down', function (obj) {
		dragStart = obj.event.getLocalPosition(self);
	});
});

===================================================================
--- original.js
+++ change.js
@@ -3,10 +3,12 @@
 	var playerGraphics = self.createAsset('player', 'Player character', .5, .5);
 	self.gravity = 1;
 	self.jumpForce = 20;
 	self.velocity = 0;
-	self.jump = function () {
-		this.velocity = -this.jumpForce;
+	self.setJumpForce = function (x, y) {
+		var dx = this.x - x;
+		var dy = this.y - y;
+		this.jumpForce = Math.sqrt(dx * dx + dy * dy) / 10;
 	};
 	self.update = function () {
 		this.y += this.velocity;
 		this.velocity += this.gravity;
@@ -25,8 +27,20 @@
 	};
 });
 var Game = Container.expand(function () {
 	var self = Container.call(this);
+	stage.on('up', function (obj) {
+		if (dragStart) {
+			player.velocity = -player.jumpForce;
+			dragStart = null;
+		}
+	});
+	stage.on('move', function (obj) {
+		if (dragStart) {
+			var pos = obj.event.getLocalPosition(self);
+			player.setJumpForce(dragStart.x, dragStart.y);
+		}
+	});
 	var platforms = [];
 	var ground = self.createAsset('ground', 'Ground', 0, 1);
 	ground.y = 2732;
 	ground.speed = 5;
@@ -62,13 +76,9 @@
 				}
 			}
 		}
 	});
+	var dragStart = null;
 	stage.on('down', function (obj) {
-		var event = obj.event;
-		var pos = event.getLocalPosition(self);
-		if (player.intersects(pos)) {
-			player.jump();
-			firstJump = true;
-		}
+		dragStart = obj.event.getLocalPosition(self);
 	});
 });