html2canvas html截图插件图片放大清晰度处理方案，支撑恣意放大倍数，处理原插件图片偏移题目

Author:youzebin (2016.12.6)

插件下载地点：https://github.com/niklasvh/h…

1.起首引入html2canvas.js html2canvas 0.5.0-beta4 最新版即可

必要步骤1：修正插件的源码： (修正的处所有两处)

1. 代码第 999 行 renderWindow 的要领中 修正推断前提 增添一个options.scale存在的前提：

源码：

if (options.type === "view") {

canvas = crop(renderer.canvas, {width: renderer.canvas.width, height: renderer.canvas.height, top: 0, left: 0, x: 0, y: 0});

} else if (node === clonedWindow.document.body || node === clonedWindow.document.documentElement || options.canvas != null) {

canvas = renderer.canvas;

} else {

canvas = crop(renderer.canvas, {width: 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});

}

改成：

if (options.type === "view") {

canvas = crop(renderer.canvas, {width: renderer.canvas.width, height: renderer.canvas.height, top: 0, left: 0, x: 0, y: 0});

} else if (node === clonedWindow.document.body || node === clonedWindow.document.documentElement) {

canvas = renderer.canvas;

}else if(options.scale && options.canvas !=null){

log("放大canvas",options.canvas);

var scale = options.scale || 1;

canvas = crop(renderer.canvas, {width: bounds.width * scale, height:bounds.height * scale, top: bounds.top *scale, left: bounds.left *scale, x: 0, y: 0});

}

else {

canvas = crop(renderer.canvas, {width: 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});

}

2. 代码第 943 行 html2canvas 的要领中 修正width,height：

源码：

return renderDocument(node.ownerDocument, options, node.ownerDocument.defaultView.innerWidth, node.ownerDocument.defaultView.innerHeight, index).then(function(canvas) {

if (typeof(options.onrendered) === "function") {

log("options.onrendered is deprecated, html2canvas returns a Promise containing the canvas");

options.onrendered(canvas);

}

return canvas;

});

改成：

width = options.width != null ? options.width : node.ownerDocument.defaultView.innerWidth;

height = options.height != null ? options.height : node.ownerDocument.defaultView.innerHeight;

return renderDocument(node.ownerDocument, options, width, height, index).then(function(canvas) {

if (typeof(options.onrendered) === "function") {

log("options.onrendered is deprecated, html2canvas returns a Promise containing the canvas");

options.onrendered(canvas);

}

return canvas;

});

2.运用体式格局

var shareContent = document.getElementById("shareContent");//须要截图的包裹的(原生的)DOM 对象

var width = shareContent.offsetWidth; //猎取dom 宽度

var height = shareContent.offsetHeight; //猎取dom 高度

var canvas = document.createElement("canvas"); //建立一个canvas节点

var scale = 2; //定义恣意放大倍数 支撑小数

canvas.width = width * scale; //定义canvas 宽度 * 缩放

canvas.height = height * scale; //定义canvas高度 *缩放

canvas.getContext("2d").scale(scale,scale); //猎取context,设置scale

var opts = {

scale:scale, // 增加的scale 参数

canvas:canvas, //自定义 canvas

logging: true, //日记开关

width:width, //dom 原始宽度

height:height //dom 原始高度

};

html2canvas(shareContent, opts).then(function (canvas) {

//假如想要天生图片 引入canvas2Image.js 下载地点：

//https://github.com/hongru/canvas2image/blob/master/canvas2image.js

var img = Canvas2Image.convertToImage(canvas, canvas.width, canvas.height);

console.log(img);

});

2017.1.7 优化插件运用的体式格局，并附上demo (插件的修改照样根据上面的操纵流程)

(不好意思列位，近来发明上面插件的运用体式格局上存在截图不完全的bug，

许多人在插件的运用上存在林林总总的题目。所以决议完美这篇文章的内容)

以下我总结了一些注重事项，在代码中解释了，仅供参考。

付：完全运用的demo ,以下：

content="width=device-width,initial-scale=1,minimum-scale=1,maximum-scale=1,user-scalable=no">

html2Canvas demo

document.documentElement.style.fontSize = window.screen.width / 7.5 + 'px';

body,

html,

div,

p,

ul,

li,

a,

img,

span,

button,

header,

footer,

section {

padding: 0;

margin: 0;

}

*, :before, :after {

-webkit-tap-highlight-color: transparent;

-webkit-user-select: none;

outline: none;

box-sizing: border-box;

-webkit-box-sizing: border-box;

}

::-webkit-scrollbar {

width: 0;

opacity: 0;

}

button{

font-family: simsun,"microsoft yahei", arial, "Helvetica Neue", Helvetica, STHeiTi, sans-serif;

}

body {

font-family: "microsoft yahei", arial, "Helvetica Neue", Helvetica, STHeiTi, sans-serif;

color: #000;

background-color: #f5f5f5;

-webkit-overflow-scrolling: touch;

}

.share-container {

padding-top: 0.72rem;

width: 2.35rem;

margin: 0 auto;

}

.share-content {

padding-top: 0.72rem;

height:3rem;

background-color: blue;

border-radius: 5px;

width: 100%;

}

.text{

font-size: 0.36rem;

color: #f2f2f2;

}

.btn-share {

width: 64%;

height: 0.89rem;

background-color: #3baaff;

border-radius: 0.89rem;

border: 1px solid #3baaff;

color: white;

font-size: 0.36rem;

margin: 0.75rem 0 0.67rem;

}

.btn-share:active{

background-color: #1b96c8;

}

截 图

//定义查找元素要领

function $(selector) {

return document.querySelector(selector);

}

var main = {

init:function(){

main.setListener();

},

//设置监听事宜

setListener:function(){

var btnShare = document.getElementById("btnShare");

btnShare.onclick = function(){

main.html2Canvas();

}

},

//猎取像素密度

getPixelRatio:function(context){

var backingStore = context.backingStorePixelRatio ||

context.webkitBackingStorePixelRatio ||

context.mozBackingStorePixelRatio ||

context.msBackingStorePixelRatio ||

context.oBackingStorePixelRatio ||

context.backingStorePixelRatio || 1;

return (window.devicePixelRatio || 1) / backingStore;

},

//绘制dom 元素，天生截图canvas

html2Canvas: function () {

var shareContent = $("#shareContent");// 须要绘制的部份的 (原生)dom 对象 ，注重容器的宽度不要运用百分比，运用牢固宽度，防止缩放题目

var width = shareContent.offsetWidth; // 猎取(原生)dom 宽度

var height = shareContent.offsetHeight; // 猎取(原生)dom 高

var offsetTop = shareContent.offsetTop; //元素间隔顶部的偏移量

var canvas = document.createElement('canvas'); //建立canvas 对象

var context = canvas.getContext('2d');

var scaleBy = main.getPixelRatio(context); //猎取像素密度的要领 (也能够采纳自定义缩放比例)

canvas.width = width * scaleBy; //这里 因为绘制的dom 为牢固宽度，居中，所以没有偏移

canvas.height = (height + offsetTop) * scaleBy; // 注重高度题目，因为顶部有个间隔所以要加上顶部的间隔，处理图象高度偏移题目

context.scale(scaleBy, scaleBy);

var opts = {

allowTaint:true,//许可加载跨域的图片

tainttest:true, //检测每张图片都已加载完成

scale:scaleBy, // 增加的scale 参数

canvas:canvas, //自定义 canvas

logging: true, //日记开关，宣布的时刻记得改成false

width:width, //dom 原始宽度

height:height //dom 原始高度

};

html2canvas(shareContent, opts).then(function (canvas) {

console.log("html2canvas");

var body = document.getElementsByTagName("body");

body[0].appendChild(canvas);

});

}

};

//末了运转代码

main.init();

运转上面的demo 前有以下 注重点：

前面的内容没看过,没下载过html2canvas.js 没根据插件悛改申明操纵的先改好再说

注重元素的款式的运用：

外层元素width 不能运用百分比 ,防止致使图片与笔墨间缩放比例题目

毛病运用体式格局如

.container {

width:50%;

margin: 0 auto;

}

须要改成如：

.container {

width:300px;

margin: 0 auto;

}