<!DOCTYPE html><html><head lang="en"> <meta charset="UTF-8"> <title>www.vevb.com canvas放大镜</title> <style> #copycanvas { border: 1px solid #000; display: none; } #square { width: 90px; height: 90px; background-color: #cc3; border: 1px solid #f00; opacity: 0.5; position: absolute; z-index: 999; display: none; cursor: crosshair; } </style></head><body><canvas id="canvas" width="450" height="676"></canvas><canvas id="copycanvas" width="300" height="300"></canvas><div id="square"></div><script> var canvas = document.getElementById('canvas'), //获取canvas对象 context = canvas.getContext('2d'), //获取上下文 copycanvas = document.getElementById('copycanvas'), //获取copycanvas copycontext = copycanvas.getContext('2d'), square = document.getElementById('square'), //获取透明框 squaredata = {}, //用来保存选择框数据 box = canvas.getBoundingClientRect(); //getBoundingClientRect方法可以获取元素上、下、左、右分别相对浏览器的坐标位置 //创建图像对象，并加载 image = new Image(); image.src = "3.jpg"; image.onload = function(){ context.drawImage(image,0,0,canvas.width,canvas.height); }; canvas.onmouseover = function(e){ var x = e.clientX, //获取鼠标实时坐标 y = e.clientY; createSquare(x,y); //保存透明选择框属性 }; window.onmousemove = function(e){ var x = e.clientX, y = e.clientY; //判断鼠标是否移出canvas if(x >= canvas.offsetLeft && x <= canvas.offsetLeft + canvas.width && y >= canvas.offsetTop && y <= canvas.offsetTop + canvas.height){ createSquare(x,y); }else{ hideSquare(); hideCanvas(); } } function showSquare(){ square.style.display = 'block'; } function hideSquare(){ square.style.display = 'none'; } function showCanvas(){ copycanvas.style.display = "inline"; } function hideCanvas(){ copycanvas.style.display = "none"; } function createSquare(x,y){ //控制选择框不移动出canvas x = x - 45 < canvas.offsetLeft ? canvas.offsetLeft:x - 45; y = y - 45 < canvas.offsetTop ? canvas.offsetTop:y - 45; x = x + 90 < box.right ? x:box.right - 90; y = y + 90 < box.bottom ? y:box.bottom - 90; squaredata.left = x; squaredata.top = y; moveSquare(x,y); } function moveSquare(x,y){ square.style.left = x + "px"; square.style.top = y + "px"; showCanvas(); showSquare(); copy(); } function copy(){ copycontext.drawImage( canvas, squaredata.left - box.left, squaredata.top - box.top, 90, 90, 0, 0, copycanvas.width, copycanvas.height ); }</script></body></html> 
