主要采用了canvas内渲染canvas的技术，还有利用比例来放大图片
比例：放大镜宽度/画布宽度=原图宽度/渲染图宽度
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>放大镜效果canvas实现</title><style>*{ margin: 0; padding: 0;}#canvas{ position: absolute; left: 50%; top: 50%; -webkit-transform: translate3d(-50%,-50%,0); transform: translate3d(-50%,-50%,0); cursor:none;}</style></head><body> <canvas id="canvas"></canvas> <canvas id="zoom" style="display:none"></canvas> <script> var cvs=document.querySelector("#canvas"); var zm=document.querySelector("#zoom"); var ctx=cvs.getContext("2d"); var ztx=zm.getContext("2d"); var img=new Image(); var scale=3; var magR=150; img.src="data:images/loli.jpg"; img.onload=function(){ cvs.width=img.width/scale; cvs.height=img.height/scale; zm.width=img.width; zm.height=img.height; ctx.drawImage(img,0,0,cvs.width,cvs.height); ztx.drawImage(img,0,0,zm.width,zm.height); cvs.onmousemove=function(e){ var x=e.clientX-getBox(cvs).left; var y=e.clientY-getBox(cvs).top; var w=h=magR*2; var sx=x*scale-magR; var sy=y*scale-magR; var dx=x-magR; var dy=y-magR; ctx.drawImage(img,0,0,cvs.width,cvs.height); ctx.save(); ctx.lineWidth=2; ctx.strokeStyle="#000"; ctx.beginPath(); ctx.arc(x,y,magR,0,Math.PI*2,false); ctx.stroke(); ctx.clip(); ctx.drawImage(zm,sx,sy,w,h,dx,dy,w,h); ctx.restore();} cvs.onmouseout=function(){ ctx.clearRect(0,0,cvs.width,cvs.height); ctx.drawImage(img,0,0,cvs.width,cvs.height);} function getBox(canvas){ return canvas.getBoundingClientRect();}}</script></body></html>
演示地址 zoom