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 demodocument.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;
}
)
