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**首先看效果**

**引入下题**

HTML:

<img id="blur" src="img/back.jpg">

CSS3:

#blur{
filter:blur(10px);
-webkit-filter:blur(10px);
-moz-filter:blur(10px);
-ms-filter:blur(10px);
-o-filter:blur(10px);
}

结合CSS3毛玻璃实现微信版的发红包看完整照片效果。可以完美的兼容移动端与PC端。代码如下：

html：

<div id="content">
<!--模糊图片-->
<img id="blur" src="img/4.jpg">
<!--使用canvas绘制图片-->
<canvas id="canvas"></canvas>
<a href="javascript:reset()" rel="external nofollow"  class="button" id="button-reset">reset</a>
<a href="javascript:show()" rel="external nofollow"  class="button" id="button-show">show</a>
</div>

css3：

body,html{margin:0;padding:0;overflow:hidden}
#content{position:relative;margin:0 auto;overflow:hidden}
#blur{position:absolute;margin:0 auto;left:0;top:0;filter:blur(10px);-webkit-filter:blur(18px);-moz-filter:blur(18px);-ms-filter:blur(18px);-o-filter:blur(18px);z-index:0;display:block}
#canvas{position:absolute;margin:0 auto;left:0;top:0;z-index:1;display:block}
.button{padding:5px 10px;color:#fff;position:absolute;display:block;text-align:center;border-radius:4px;text-decoration:none;z-index:3}
#button-reset{left:10%;bottom:5%;background-color:red}
#button-show{right:10%;bottom:5%;background-color:green}

javascript：

var canWidth = window.innerWidth-20;
var canHeight = window.innerHeight-20;

var canvas=document.getElementById("canvas");
var ctx = canvas.getContext("2d");
canvas.width = canWidth;
canvas.height = canHeight;
var img = new Image();
img.src = "img/4.jpg";
var radius = 50;
var leftMargin = 0,topMargin = 0;
img.onload = function(){
//初始化父容器的宽高使窗口与canvas宽高相同
$("#content").css({"width":canvas.width + "px","height":canvas.height + "px"});

//模糊图片与canva中绘制的图片(隐藏的清楚图片)宽高相同，别忘加px，否则计算出来的只是个值，不带px
$("#blur").css("width",img.width + "px");
$("#blur").css("height",img.height + "px");

//左边距：(图片宽高 - canvas宽高) / 2;等于一边的边距宽高
leftMargin = (img.width - canvas.width)/2;
topMargin = (img.height - canvas.height)/2;

//模糊图片的上边距与左边距
$("#blur").css("top", String(-topMargin) + "px");
$("#blur").css("left", String(-leftMargin) + "px");
initCanvas();
}
function initCanvas(){
var theleft = leftMargin < 0 ? -leftMargin : 0;
var thetop = topMargin < 0 ? -topMargin : 0;
//创建圆
region = {x:Math.random() * (canvas.width-2 * radius - 2 * theleft) + radius + theleft,
y:Math.random() * (canvas.height-2 * radius - 2 * thetop) + radius + thetop, r : radius};
draw(img,region);
}
function draw(img){
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.save();
setRegion(region);
/*绘制清楚图片，如leftMargin<0那么取0，
图片宽度与canvas宽度哪个最小取哪个值*/
ctx.drawImage(img, Math.max(leftMargin,0), Math.max(topMargin,0),
Math.min(canvas.width,img.width), Math.min(canvas.height,img.height),
leftMargin < 0 ? -leftMargin : 0, topMargin < 0 ? -topMargin : 0,
Math.min(canvas.width,img.width),Math.min(canvas.height,img.height));

ctx.restore();
}
function setRegion(region){
ctx.beginPath();
ctx.arc(region.x,region.y,region.r,0,Math.PI * 2,false);
//进行裁减圆
ctx.clip();
}
function reset(){
initCanvas();
}
function show(){
var animation = setInterval(function(){
region.r += 20;
if(region.r > Math.max(canvas.width,canvas.height)){
clearInterval(animation);
}
draw(img,region);
},30);
}