最近在项目中用到了html2canvas插件,遇到的一些坑写下来,与大家共勉。
html2canvas 官方网站http://html2canvas.hertzen.com/index.html
这是一个js截屏插件,在前台利用h5的canvas 将html的内容显示在canvas上,再利用 js 将canvas转化为图片
1.vue 文件中引入 html2canvas.js
1 <remote-script src="../html2canvas.js"></remote-script>
说明:src中的路径是html2canvas.js在项目中的路径
remoteScript 标签是上篇博客定义的标签,详情见:http://www.cnblogs.com/zhuchenglin/p/7455203.html
2.在vue中使用该插件,在methods中定义一个方法,内容为:
1 setTimeout(function () { 2 html2canvas(dom,{ 3 onrendered:function (canvas) { 4 var image = new Image(); 5 image.src = canvas.toDataURL(); 6 document.getElementById('content_img').appendChild(image) 7 dom.style.display='none' 8 }, 9 }); 10 },0)
这样就可以了
说明:
在方法中如果不加 setTimeout函数的话,虽然使用console输出的dom内容正常,但是如果在vue中定义的变量中的内容在canvas中显示不出来,可能与vue的声明周期有关,这个暂时不清楚,加上setTimeout函数之后,会将此函数中的操作加到处理队列末尾
在拿到canvas后,转化为图片,直接就可以使用了。
3.关于html2canvas截出来的图片模糊的问题,我查了好多资料,试了好多方法,最终找到一篇非常有用的文章 https://segmentfault.com/a/1190000007707209
方法如下:
(1.修改插件的源码
<1.代码第999行renderWindow的方法中修改判断条件,增加一个options.scale存在的条件:
将
1 if (options.type === "view") { 2 canvas = crop(renderer.canvas, { renderer.canvas.width, height: renderer.canvas.height, top: 0, left: 0, x: 0, y: 0}); 3 } else if (node === clonedWindow.document.body || node === clonedWindow.document.documentElement || options.canvas != null) { 4 canvas = renderer.canvas; 5 } else { 6 canvas = crop(renderer.canvas, { options.width != null ? options.width : bounds.width, height: options.height != null ? options.height : bounds.height, top: bounds.top, left: bounds.left, x: 0, y: 0}); 7 8 }
修改为
1 if (options.type === "view") { 2 canvas = crop(renderer.canvas, { renderer.canvas.width, height: renderer.canvas.height, top: 0, left: 0, x: 0, y: 0}); 3 } else if (node === clonedWindow.document.body || node === clonedWindow.document.documentElement) { 4 canvas = renderer.canvas; 5 }else if(options.scale && options.canvas !=null){ 6 log("放大canvas",options.canvas); 7 var scale = options.scale || 1; 8 canvas = crop(renderer.canvas, { bounds.width * scale, height:bounds.height * scale, top: bounds.top *scale, left: bounds.left *scale, x: 0, y: 0}); 9 } 10 else { 11 canvas = crop(renderer.canvas, { options.width != null ? options.width : bounds.width, height: options.height != null ? options.height : bounds.height, top: bounds.top, left: bounds.left, x: 0, y: 0}); 12 }
2.代码第 943 行 html2canvas 的方法中 修改width,height:
将
1 return renderDocument(node.ownerDocument, options, node.ownerDocument.defaultView.innerWidth, node.ownerDocument.defaultView.innerHeight, index).then(function(canvas) { 2 if (typeof(options.onrendered) === "function") { 3 log("options.onrendered is deprecated, html2canvas returns a Promise containing the canvas"); 4 options.onrendered(canvas); 5 } 6 return canvas; 7 });
改为:
1 width = options.width != null ? options.width : node.ownerDocument.defaultView.innerWidth; 2 height = options.height != null ? options.height : node.ownerDocument.defaultView.innerHeight; 3 return renderDocument(node.ownerDocument, options, width, height, index).then(function(canvas) { 4 if (typeof(options.onrendered) === "function") { 5 log("options.onrendered is deprecated, html2canvas returns a Promise containing the canvas"); 6 options.onrendered(canvas); 7 } 8 return canvas; 9 });
然后就可以使用了,将原来的使用放式稍微还一下就可以了,使用实例如下:
在vue的方法中添加一个获取设备像素密度的方法
1 getPixelRatio(context){ 2 var backingStore = context.backingStorePixelRatio || 3 context.webkitBackingStorePixelRatio || 4 context.mozBackingStorePixelRatio || 5 context.msBackingStorePixelRatio || 6 context.oBackingStorePixelRatio || 7 context.backingStorePixelRatio || 1; 8 return (window.devicePixelRatio || 1) / backingStore; 9 },
然后将最上面的使用示例改为:
1 get_img(){ 2 let self = this; 3 setTimeout(function () { 4 var content_html = document.getElementById('content_html'); //要转化的div 5 let width = content_html.offsetWidth; 6 let height = content_html.offsetHeight; 7 let offsetTop = content_html.offsetTop; 8 let canvas = document.createElement("canvas"); 9 let context = canvas.getContext('2d'); 10 let scaleBy = self.getPixelRatio(context); 11 canvas.width = width*scaleBy; 12 canvas.height = (height+offsetTop)*scaleBy; 13 context.scale(scaleBy,scaleBy); 14 var opts = { 15 allowTaint:true,//允许加载跨域的图片 16 tainttest:true, //检测每张图片都已经加载完成 17 scale:scaleBy, // 添加的scale 参数 18 canvas:canvas, //自定义 canvas 19 logging: true, //日志开关,发布的时候记得改成false 20 width, //dom 原始宽度 21 height:height //dom 原始高度 22 }; 23 html2canvas(content_html,opts).then(function (canvas) { 24 canvas.style.width = width+"px"; 25 canvas.style.height = height+"px"; 26 var image = new Image(); 27 image.src = canvas.toDataURL(); 28 document.getElementById('content_img').appendChild(image); //将转化好的图片插入到防止图片转换的div中 29 content_html.style.display='none' 30 }); 31 }
然后在html2canvas插件加载成功后调用get_img()方法即可将比较清晰的图片插入到指定位置
注:如需转载请注明出处:http://www.cnblogs.com/zhuchenglin/p/7455336.html