canvas+javascript实现淘宝商品放大镜效果 

<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
    <title>jQuery之家</title>
    <style type="text/css">
        *{margin:0;padding:0;}
        body{font-size: 14px;}
        canvas{
            display:none;
            background-color: #ffff91;
        }
        #square{
            width:80px;
            height: 80px;
            background-color: rgba(117,240,255,0.5);
            position:absolute;
            z-index: 999;
            cursor:crosshair;
            display:none;
        }
    </style>
    <script>
        onload=function(){
            var canvas=document.getElementById("canvas");//获取画布
            var ctx=canvas.getContext("2d");//获取画笔
            var img=document.getElementsByTagName("img")[0];//获取图片
            var square=document.getElementById("square");//获取选择框
            var squareData={};//存选择框信息
            var imgPosition=img.getBoundingClientRect();//获取图片的位置
            var p=img.naturalWidth/img.width;//原始图片与缩小后图片的比例
           // var even;
            //鼠标移入
            img.onmouseove=function(e){
                var even=e||event;//兼容火狐浏览器
                var x=even.clientX,
                    y=even.clientY;
                createSquare(x,y);
            };
            window.onmousemove=function(e){
                var even=e||event;
                var x=even.clientX;
                var y=even.clientY;
                //使选择框限制在图片内部
                if(x>=img.offsetLeft&&x<=img.offsetLeft+img.width&&y>=img.offsetTop&&y<=img.offsetTop+img.height){
                     createSquare(x,y);
                }else{
                    hideSquare();
                    hideCanvas();
                }
            };
            function createSquare(x,y){
                x=x-40<img.offsetLeft?img.offsetLeft:x-40;
                y=y-40<img.offsetTop?img.offsetTop:y-40;
                x=x+80<imgPosition.right?x:imgPosition.right-80;
                y=y+80<imgPosition.bottom?y:imgPosition.bottom-80;
                //将选择框左上角的位置存到squareData
                squareData.left=x;
                squareData.top=y;
                moveSquare(x,y);
            }
            function moveSquare(x,y){
                //设置选择框偏移位置
                square.style.left=x+"px";
                square.style.top=y+"px";
                showCanvas();
                showSquare();
                draw();
            }
            function showCanvas(){
                canvas.style.display="inline";
            }
            function hideCanvas(){
                canvas.style.display="none";
            }
            function showSquare(){
                square.style.display="inline";
            }
            function hideSquare(){
                square.style.display="none";
            }
            //将放大后的图片画到canvas中
            function draw(){
                console.log(squareData.left-imgPosition.left);
                ctx.drawImage(img,(squareData.left-imgPosition.left)*p,p*(squareData.top-imgPosition.top),p*80,p*80,0,0,canvas.width,canvas.height);
            }
        }
    </script>
</head>
<body>
<img src="img/N7ETzFO.jpg" alt="" width="300px">
<canvas id="canvas" width="300px" height="225px"></canvas>
<div id="square"></div>
</body>
</html>

canvas 绘制图片是根据原始图片的尺寸进行绘制，而不是根据利用属性或样式放大缩小后的图片，所以要乘以原始图片与现在图片的比例。

posted @ 2018-08-21 17:41  牛坤  阅读(740)  评论(0)    收藏  举报