1、原理：先创建一张img图片，用filter滤镜制作毛玻璃效果。
2、利用绝对定位，使canvas刚好盖在img上面。
3、利用canvas原生clip函数剪辑一个圆形。
地址：http://sandbox.runjs.cn/show/c3mlltak
源代码：
<!DOCTYPE html>
<html lang="en">
<head>
<!--Designer:[han.jackson] Developer:[zengxiangliang] date:20160412-->
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title></title>
<meta name="keywords" content="keywords"/>
<meta name="description" content="description"/>
<meta name="robots" content="all"/>
<meta name="viewport"
content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0"/>
<meta name="format-detection" content="telephone=no"/>
<meta name="format-detection" content="email=no"/>
<style>
*{
margin: 0;
padding: 0;
}
html,body,.container,.bgimg{
width:100%;
height:100%;
}
.container{
position: relative;
}
.bgimg{
position: absolute;
top:0;
left:0;
-webkit-filter: blur(15px);
-moz-filter: blur(15px);
}
#canvas{
position: absolute;
top:0;
left:0;
}
.button{
position: absolute;
bottom:10%;
border-radius: 5px;
font-size:20px;
padding:5px 10px;
text-decoration: none;
color:#fff;
}
.reset{
left:20%;
background-color: #07C4EC;
}
.show{
right:20%;
background-color: #EC9807;
}
</style>
</head>
<body>
<div class="container">
<img class="bgimg" src="data:images/p43.jpg" alt=""/>
<canvas id="canvas">您的浏览器不支持canvas</canvas>
<a class="button reset" href="javascript:;">reset</a>
<a class="button show" href="javascript:;">show</a>
</div>
<script>
;
(function () {
window.addEventListener('load', winEventLoad, false);
window.addEventListener('resize', canvasApp, false);
function winEventLoad() {
canvasApp();
}
function canvasApp(){
if(!!!document.getElementById('canvas').getContext('2d')){return}
var myCanvas = document.getElementById('canvas');
var ctx = myCanvas.getContext('2d');
var ww = document.documentElement.clientWidth;
var wh = document.documentElement.clientHeight;
var radius = 40; var t;
var requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame || window.msRequestAnimationFrame; var cancelAnimationFrame = window.cancelAnimationFrame || window.mozCancelAnimationFrame; myCanvas.width = ww;
myCanvas.height = wh; var options = {
x:Math.random()*(canvas.width-radius*2)+radius,
y:Math.random()*(canvas.height-radius*2)+radius,
r:radius
}; var img = new Image();
img.src = 'images/p43.jpg';
img.onload = function () {
initCanvas();
};
function setClippingRegion(options){
ctx.beginPath();
ctx.arc(options.x, options.y, options.r, 0, Math.PI * 2, false);
ctx.closePath();
ctx.clip();
}
function draw(options) {
ctx.clearRect(0, 0, canvas.width, canvas.height); ctx.save();
setClippingRegion(options);
ctx.drawImage(img,0,0,canvas.width, canvas.height);
ctx.restore();
}
function initCanvas(){
draw(options);
}
function show(){
var diagonal = Math.max(canvas.width,canvas.height)*2;
(function showloop(){
options.r += 20;
t = requestAnimationFrame(showloop);
if(options.r>diagonal){
cancelAnimationFrame(t);
}
draw(options);
}());
}
function reset(){
cancelAnimationFrame(t);
options = {
x:Math.random()*(canvas.width-radius*2)+radius,
y:Math.random()*(canvas.height-radius*2)+radius,
r:radius
};
options.r = 0;
(function resetloop(){
options.r += 2;
var t = requestAnimationFrame(resetloop);
if(options.r >= radius){
cancelAnimationFrame(t);
}
draw(options);
})();
}
document.querySelector('.show').addEventListener('click',show,false);
document.querySelector('.reset').addEventListener('click',reset,false);
}
}())
</script>
</body>
</html>