js实现div转图片并保存

发布时间:2019-08-02 14:00:20发布者:Mr.Zhang阅读(430)

最近工作中遇到的需求,将div转成图片并保存。

1、准备需要用到的js插件jquery-1.8.2.js,html2canvas.min.js(将div转换为canvas),bluebird.js(用户IE支持ES6 Promise特性)

2、页面demo

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>div to img demo</title>
    <style type="text/css">
        .content{
            display: block;

            position: relative;

            width: 300px;
            height: 300px;

            background-color: #E6B246
        }
    </style>
</head>
<body>
    <div class="content" id="imgDiv">
        <div>测试</div>
    </div>
    <button id="btn">保存为图片</button>
</body>
</html>

3、遇到的问题

问题1:生成的图片模糊

解决方案:将canvas属性放大两倍,生成的时候再变回原来的1倍;

问题2:IE浏览器不支持ES6新特性,无法使用html2canvas插件生成画布

解决方案:引入bluebird.js,只需引入即可;

问题3:在执行保存时,如果直接使用html2canvas插件提供的,将生成的画布直接转换为base64的方法,将base64直接放到a标签的href属性中进行下载,当生成图片内容过多时,base64长度将超出a标签href长度限制,无法下载。

解决方案:将base64转换为Blob流

问题4:有些浏览器,比如火狐,不支持a标签直接下载

解决方案:还是使用Blob流下载

最终代码:

<script type="text/javascript">
$(document).ready(function(){
    // canvas生成图片
        $("#btn").on("click", function () {
            var getPixelRatio = function (context) { // 获取设备的PixelRatio
                var backingStore = context.backingStorePixelRatio ||
                    context.webkitBackingStorePixelRatio ||
                    context.mozBackingStorePixelRatio ||
                    context.msBackingStorePixelRatio ||
                    context.oBackingStorePixelRatio ||
                    context.backingStorePixelRatio || 0.5;
                return (window.devicePixelRatio || 0.5) / backingStore;
            };
            //生成的图片名称
            var imgName = "cs.jpg";
            var shareContent = document.getElementById("imgDiv");
            var width = shareContent.offsetWidth;
            var height = shareContent.offsetHeight;
            var canvas = document.createElement("canvas");
            var context = canvas.getContext('2d');
            var scale = getPixelRatio(context); //将canvas的容器扩大PixelRatio倍,再将画布缩放,将图像放大PixelRatio倍。
            canvas.width = width * scale;
            canvas.height = height * scale;
            canvas.style.width = width + 'px';
            canvas.style.height = height + 'px';
            context.scale(scale, scale);

            var opts = {
                scale: scale,
                canvas: canvas,
                width: width,
                height: height,
                dpi: window.devicePixelRatio
            };
            html2canvas(shareContent, opts).then(function (canvas) {
                context.imageSmoothingEnabled = false;
                context.webkitImageSmoothingEnabled = false;
                context.msImageSmoothingEnabled = false;
                context.imageSmoothingEnabled = false;
                var dataUrl = canvas.toDataURL('image/jpeg', 1.0);
                dataURIToBlob(imgName, dataUrl, callback);
            });
        });
})
    

        // edited from https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toBlob#Polyfill
       var dataURIToBlob =  function (imgName, dataURI, callback) {
            var binStr = atob(dataURI.split(',')[1]),
                len = binStr.length,
                arr = new Uint8Array(len);

            for (var i = 0; i < len; i++) {
                arr[i] = binStr.charCodeAt(i);
            }

            callback(imgName, new Blob([arr]));
        }

        var callback = function (imgName, blob) {
            var triggerDownload = $("<a>").attr("href", URL.createObjectURL(blob)).attr("download", imgName).appendTo("body").on("click", function () {
                if (navigator.msSaveBlob) {
                    return navigator.msSaveBlob(blob, imgName);
                }
            });
            triggerDownload[0].click();
            triggerDownload.remove();
        };
</script>

demo下载:div_to_img_demo

 





本文转自博客园,原文地址:https://www.cnblogs.com/bookobe/p/11285940.html