html5 spring demo

<!DOCTYPE HTML>

<html lang="en-US">

<head>

    <meta charset="UTF-8">

    <title>Follow Mouse</title>

    <script type="text/javascript" src="utils.js"></script>

    <script type="text/javascript" src="ball.js"></script>

    <style type="text/css">

        body{background-color: silver;}

        #canvas{background-color: white;}

    </style>

</head>

<body>

    <canvas id="canvas" width="400" height="400"></canvas>

    <textarea name="" id="log" cols="30" rows="10"></textarea>

    <script type="text/javascript">

        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,

                gravity=2,

                vx=0,

                vy=0;

                (function drawFrame(){

                    window.requestAnimationFrame(drawFrame,canvas);

                    context.clearRect(0,0,canvas.width,canvas.height);

                    var dx=mouse.x-ball.x,

                        dy=mouse.y-ball.y,

                        ax=dx*spring,

                        ay=dy*spring;

                    vx+=ax;

                    vy+=ay;

                    vy+=gravity;

                    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>

utils.js 文件 https://gist.github.com/King-fly/6034511/raw/2e28359afdfb45800948f0e6bd31aa958ba7f5cb/html5+utilsball.js 文件 https://gist.github.com/King-fly/6034525/raw/4664959f6e33196b9b4520136cc67573e07c8282/ball.js

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