已经存在一个canvas画布：
1.先将画布canvas复制到一个new的image中 2.使用鼠标放到image上实现局部放大的效果
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<!DOCTYPE HTML>
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<html>
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<head>
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<style type="text/css">
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#magnifier{
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width:520px;
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height:320px;
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position:absolute;
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top:100px;
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left:650px;
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}
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#img{
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width:520px;
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height:320px;
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padding:1px;
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border:1px solid #ccc;
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}
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#Browser{
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border:1px solid #ccc;
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z-index:100;
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position:absolute;
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background:#ccc;
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}
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#mag{
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border:1px solid #ccc;
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overflow:hidden;
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z-index:100;
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}
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</style>
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<script type="text/javascript">
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function getEventObject(W3CEvent) { //事件标准化函数
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return W3CEvent || window.event;
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}
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function getPointerPosition(e) { //兼容浏览器的鼠标x,y获得函数
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e = e || getEventObject(e);
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var x = e.pageX || (e.clientX + (document.documentElement.scrollLeft || document.body.scrollLeft));
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var y = e.pageY || (e.clientY + (document.documentElement.scrollTop || document.body.scrollTop));
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return { 'x':x,'y':y };
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}
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function setOpacity(elem,level) { //兼容浏览器设置透明值
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if(elem.filters) {
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elem.style.filter = 'alpha(opacity=' + level * 100 + ')';
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} else {
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elem.style.opacity = level;
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}
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}
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function css(elem,prop) { //css设置函数,可以方便设置css值,并且兼容设置透明值
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for(var i in prop) {
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if(i == 'opacity') {
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setOpacity(elem,prop[i]);
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} else {
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elem.style[i] = prop[i];
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}
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}
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return elem;
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}
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var magnifier = {
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m : null,
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init:function(magni){
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var m = this.m = magni || {
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cont : null, //装载原始图像的div
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img : null, //放大的图像
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mag : null, //放大框
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scale : 15 //比例值,设置的值越大放大越大,但是这里有个问题就是如果不可以整除时,会产生些很小的白边,目前不知道如何解决
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}
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css(m.img,{
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'position' : 'absolute',
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'width' : (m.cont.clientWidth * m.scale) + 'px', //原始图像的宽*比例值
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'height' : (m.cont.clientHeight * m.scale) + 'px' //原始图像的高*比例值
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})
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css(m.mag,{
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'display' : 'none',
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'width' : m.cont.clientWidth + 'px', //m.cont为原始图像,与原始图像等宽
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'height' : m.cont.clientHeight + 'px',
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'position' : 'absolute',
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'left' : m.cont.offsetLeft - m.cont.offsetWidth - 5 + 'px', //放大框的位置为原始图像的左边距离5px
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'top' : m.cont.offsetTop + 'px'
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})
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var borderWid = m.cont.getElementsByTagName('div')[0].offsetWidth - m.cont.getElementsByTagName('div')[0].clientWidth; //获取border的宽
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css(m.cont.getElementsByTagName('div')[0],{ //m.cont.getElementsByTagName('div')[0]为浏览框
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'display' : 'none', //开始设置为不可见
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'width' : m.cont.clientWidth / m.scale - borderWid + 'px', //原始图片的宽/比例值 - border的宽度
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'height' : m.cont.clientHeight / m.scale - borderWid + 'px', //原始图片的高/比例值 - border的宽度
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'opacity' : 0.5 //设置透明度
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})
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var canvas = document.getElementById('myCanvas');
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var url = canvas.toDataURL();
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var myimg=document.getElementById('img');
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//m.img.src = m.cont.getElementsByTagName('img')[0].src; //让原始图像的src值给予放大图像
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m.img.src =url;
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m.cont.style.cursor = 'crosshair';
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m.cont.onmouseover = magnifier.start;
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},
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start:function(e){
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if(document.all){ //只在IE下执行,主要避免IE6的select无法覆盖
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magnifier.createIframe(magnifier.m.img);
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}
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this.onmousemove = magnifier.move; //this指向m.cont
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this.onmouseout = magnifier.end;
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},
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move:function(e){
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var pos = getPointerPosition(e); //事件标准化
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this.getElementsByTagName('div')[0].style.display = '';
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css(this.getElementsByTagName('div')[0],{
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'top' : Math.min(Math.max(pos.y - this.offsetTop - parseInt(this.getElementsByTagName('div')[0].style.height) / 2,0),this.clientHeight - this.getElementsByTagName('div')[0].offsetHeight) + 'px',
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'left' : Math.min(Math.max(pos.x - this.offsetLeft - parseInt(this.getElementsByTagName('div')[0].style.width) / 2,0),this.clientWidth - this.getElementsByTagName('div')[0].offsetWidth) + 'px'
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//left=鼠标x - this.offsetLeft - 浏览框宽/2,Math.max和Math.min让浏览框不会超出图像
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})
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magnifier.m.mag.style.display = '';
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css(magnifier.m.img,{
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'top' : - (parseInt(this.getElementsByTagName('div')[0].style.top) * magnifier.m.scale) + 'px',
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'left' : - (parseInt(this.getElementsByTagName('div')[0].style.left) * magnifier.m.scale) + 'px'
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})
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},
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end:function(e){
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this.getElementsByTagName('div')[0].style.display = 'none';
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magnifier.removeIframe(magnifier.m.img); //销毁iframe
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magnifier.m.mag.style.display = 'none';
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},
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createIframe:function(elem){
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var layer = document.createElement('iframe');
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layer.tabIndex = '-1';
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layer.src = 'javascript:false;';
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elem.parentNode.appendChild(layer);
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layer.style.width = elem.offsetWidth + 'px';
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layer.style.height = elem.offsetHeight + 'px';
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},
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removeIframe:function(elem){
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var layers = elem.parentNode.getElementsByTagName('iframe');
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while(layers.length >0){
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layers[0].parentNode.removeChild(layers[0]);
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}
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}
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}
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window.onload = function(){
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magnifier.init({
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cont : document.getElementById('magnifier'),
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img : document.getElementById('magnifierImg'),
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mag : document.getElementById('mag'),
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scale : 3
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});
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}
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</script>
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</head>
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<body>
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<canvas id="myCanvas" width="200" height="100" style="border:1px solid #c3c3c3; display:none;">
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Your browser does not support the canvas element.
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</canvas>
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<input type="button" name="button" value="button" onclick="convertCanvasToImage()"/>
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<div id="magnifier">
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<img src=" " id="img" />
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<div id="Browser"></div>
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</div>
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<div id="mag"><img id="magnifierImg" /></div>
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<script type="text/javascript">
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var c=document.getElementById("myCanvas");
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var cxt=c.getContext("2d");
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cxt.moveTo(10,10);
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cxt.lineTo(150,50);
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cxt.lineTo(10,50);
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cxt.stroke();
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</script>
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<script type="text/javascript">
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function convertCanvasToImage() {
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var canvas = document.getElementById('myCanvas');
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var url = canvas.toDataURL();
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var myimg=document.getElementById('img');
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myimg.src = url;
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}
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</script>
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</body>
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</html>
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