code
<!DOCTYPE HTML>
<html>
<head>
<style>
body {
margin: 0px;
padding: 0px;
}
</style>
</head>
<body>
<canvas id="myCanvas" width="578" height="500"></canvas>
<script>
window.requestAnimFrame = (function(callback) {
return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame ||
function(callback) {
window.setTimeout(callback, 1000 / 60);
};
})();
function drawSpring(canvas, context) {
context.beginPath();
context.moveTo(0, 0);
for(var y = 0; y < 200; y++) {
// Sine wave equation
var x = 30 * Math.sin(y / 9.05);
context.lineTo(x, y);
}
}
function drawWeight(canvas, context) {
var size = 100;
context.save();
context.fillStyle = 'red';
context.fillRect(-size / 2, 0, size, size);
context.restore();
}
function animate(canvas, theta, lastTime) {
var context = canvas.getContext('2d');
// update
var time = (new Date()).getTime();
var timeDiff = time - lastTime;
theta += timeDiff / 400;
lastTime = time;
var scale = 0.8 * (Math.sin(theta) + 1.3);
// clear
context.clearRect(0, 0, canvas.width, canvas.height);
// draw
context.save();
context.translate(canvas.width / 2, 0);
context.save();
context.scale(1, scale);
drawSpring(canvas, context);
context.restore();
context.lineWidth = 6;
context.strokeStyle = '#0096FF';
// blue-ish color
context.stroke();
context.translate(0, 200 * scale);
drawWeight(canvas, context);
context.restore();
// request new frame
requestAnimFrame(function() {
animate(canvas, theta, lastTime);
});
}
var canvas = document.getElementById('myCanvas');
var theta = 0;
var time = (new Date()).getTime();
animate(canvas, theta, time);
</script>
</body>
</html>
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