HTML5 canvas做的一个图片局部放大的效果

看到老外做HTML5的越来越多了,今天看到一个其中用HTML5做的效果不错,
是在canvas上画的圈,做放大器,并且监视了鼠标的相关事件,代码如下:
HTML部分

    
        
        
        
        
        
    
    
        

            
        
        

            
HTML5 canvas - Image zoomer
            [url=http://www.script-tutorials.com/html5-canvas-image-zoomer/]Back to original tutorial on Script Tutorials[/url]
        
    

CSS部分:

*{
    margin:0;
    padding:0;
}

body {
    background-color:#bababa;
    color:#fff;
    font:14px/1.3 Arial,sans-serif;
}

footer {
    background-color:#212121;
    bottom:0;
    box-shadow: 0 -1px 2px #111111;
    display:block;
    height:70px;
    left:0;
    position:fixed;
    width:100%;
    z-index:100;
}

footer h2{
    font-size:22px;
    font-weight:normal;
    left:50%;
    margin-left:-400px;
    padding:22px 0;
    position:absolute;
    width:540px;
}

footer a.stuts,a.stuts:visited{
    border:none;
    text-decoration:none;
    color:#fcfcfc;
    font-size:14px;
    left:50%;
    line-height:31px;
    margin:23px 0 0 110px;
    position:absolute;
    top:0;
}

footer .stuts span {
    font-size:22px;
    font-weight:bold;
    margin-left:5px;
}

.container {
    color:#000;
    margin:20px auto;
    position:relative;
    width:800px;
}

#panel {
    border:1px #000 solid;
    box-shadow:4px 6px 6px #444444;
    cursor:crosshair;
}

script.js

// variables
var canvas, ctx;
var image;
var iMouseX, iMouseY = 1;
var bMouseDown = false;
var iZoomRadius = 100;
var iZoomPower = 2;

// drawing functions
function clear() { // clear canvas function
    ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
}

function drawScene() { // main drawScene function
    clear(); // clear canvas

    if (bMouseDown) { // drawing zoom area
        ctx.drawImage(image, 0 - iMouseX * (iZoomPower - 1), 0 - iMouseY * (iZoomPower - 1), ctx.canvas.width * iZoomPower, ctx.canvas.height * iZoomPower);
        ctx.globalCompositeOperation = 'destination-atop';

        var oGrd = ctx.createRadialGradient(iMouseX, iMouseY, 0, iMouseX, iMouseY, iZoomRadius);
        oGrd.addColorStop(0.8, "rgba(0, 0, 0, 1.0)");
        oGrd.addColorStop(1.0, "rgba(0, 0, 0, 0.1)");
        ctx.fillStyle = oGrd;
        ctx.beginPath();
        ctx.arc(iMouseX, iMouseY, iZoomRadius, 0, Math.PI*2, true);
        ctx.closePath();
        ctx.fill();
    }

    // draw source image
    ctx.drawImage(image, 0, 0, ctx.canvas.width, ctx.canvas.height);
}

$(function(){
    // loading source image
    image = new Image();
    image.onload = function () {
    }
    image.src = 'images/image.jpg';

    // creating canvas object
    canvas = document.getElementById('panel');
    ctx = canvas.getContext('2d');

    $('#panel').mousemove(function(e) { // mouse move handler
        var canvasOffset = $(canvas).offset();
        iMouseX = Math.floor(e.pageX - canvasOffset.left);
        iMouseY = Math.floor(e.pageY - canvasOffset.top);
    });

    $('#panel').mousedown(function(e) { // binding mousedown event
        bMouseDown = true;
    });

    $('#panel').mouseup(function(e) { // binding mouseup event
        bMouseDown = false;
    });

    setInterval(drawScene, 30); // loop drawScene
});

一个在线效果在:
http://www.script-tutorials.com/demos/167/index.html
要用chrome,firefox,safri等浏览器看