demo4.html

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <title>rainyday.js demo #4</title>
        <style media="screen">
            body {
                overflow: hidden;
                height: 100%;
                margin: 0;
                padding: 0;
            }

            img {
                width: 100%;
                height: 100%;
            }
        </style>
        <script src="rainyday.js"></script>
        <script>
            function run() {
                var image = document.getElementById('background');
                image.onload = function() {
                    var engine = new RainyDay({
                        image: this,
                        gravityAngle: Math.PI / 9
                    });
                    engine.trail = engine.TRAIL_SMUDGE;
                    engine.rain([ [1, 0, 1000], [3, 3, 1] ], 100);
                };
                image.crossOrigin = 'anonymous';
                image.src = 'http://i.imgur.com/VuX2Nf0.jpg';
            }
        </script>
    </head>
    <body onload="run();">
        <img id="background" alt="background" src="" />
    </body>
</html>