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<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Offset Spring</title>
<link rel="stylesheet" href="../include/style.css">
</head>
<body>
<header>
Example from <a href="http://amzn.com/1430236655?tag=html5anim-20"><em>Foundation HTML5 Animation with JavaScript</em></a>
</header>
<canvas id="canvas" width="400" height="400"></canvas>
<aside>Move mouse on canvas element.</aside>
<script src="../include/utils.js"></script>
<script src="./classes/ball.js"></script>
<script>
window.onload = function () {
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
mouse = utils.captureMouse(canvas),
ball = new Ball(),
spring = 0.03,
friction = 0.9,
springLength = 100,
vx = 0,
vy = 0;
(function drawFrame () {
window.requestAnimationFrame(drawFrame, canvas);
context.clearRect(0, 0, canvas.width, canvas.height);
var dx = ball.x - mouse.x,
dy = ball.y - mouse.y,
angle = Math.atan2(dy, dx),
targetX = mouse.x + Math.cos(angle) * springLength,
targetY = mouse.y + Math.sin(angle) * springLength;
vx += (targetX - ball.x) * spring;
vy += (targetY - ball.y) * spring;
vx *= friction;
vy *= friction;
ball.x += vx;
ball.y += vy;
context.beginPath();
context.moveTo(ball.x, ball.y);
context.lineTo(mouse.x, mouse.y);
context.stroke();
ball.draw(context);
}());
};
</script>
</body>
</html>