由 dawei 使用html2canvas实现浏览器截图,必须在服务器环境下才能实现。
作用
html2canvas可以通过纯JS对浏览器端经行截屏，但截图的精确度还有待提高，部分css不可识别，所以在canvas中不能完美呈现原画面样式
/*多行溢出省略就不行，只能超出隐藏了*/
.book_inf{
position: relative;
overflow : hidden;
text-overflow: ellipsis;
display: -webkit-box;
-webkit-line-clamp: 2;
-webkit-box-orient: vertical;
}
支持的浏览器
Firefox 3.5+
Google Chrome
Opera 12+
IE9+
Safari 6+
基本语法
/*参数：
* #screenshots 所需要截图的元素id，截图后要执行的函数，
* backgroundColor 配置项背景色
* canvas为截图后返回的最后一个canvas
*/
function screenshotsImg(){
html2canvas(document.querySelector("#screenshots"),{
backgroundColor: 'transparent',// 设置背景透明
}).then(canvas => {
canvasTurnImg(canvas) //保存的图片格式转换方法
});
}
可用配置项
参数名称
类型
默认值
描述
allowTaint
boolean
false
Whether to allow cross-origin images to taint the canvas---允许跨域
background
string
#fff
Canvas background color, if none is specified in DOM. Set undefined for transparent---canvas的背景颜色，如果没有设定默认白色此处被坑，我改为backgroundColor可用
height
number
null
Define the heigt of the canvas in pixels. If null, renders with full height of the window.---canvas高度设定
letterRendering
boolean
false
Whether to render each letter seperately. Necessary if letter-spacing is used.---在设置了字间距的时候有用
logging
boolean
false
Whether to log events in the console.---在console.log()中输出信息
proxy
string
undefined
Url to the proxy which is to be used for loading cross-origin images. If left empty, cross-origin images won't be loaded.---代理地址
taintTest
boolean
true
Whether to test each image if it taints the canvas before drawing them---是否在渲染前测试图片
timeout
number
0
Timeout for loading images, in milliseconds. Setting it to 0 will result in no timeout.---图片加载延迟，默认延迟为0，单位毫秒
width
number
null
Define the width of the canvas in pixels. If null, renders with full width of the window.---canvas宽度
useCORS
boolean
false
Whether to attempt to load cross-origin images as CORS served, before reverting back to proxy--跨域代理
设置图片格式
1、从canvas中直接提取图片元数据
// 图片导出为 png 格式
var type = 'png';
var imgData = canvas.toDataURL(type);
2、将mime-type改为image/octet-stream，强制让浏览器直接download
/**
* 获取mimeType
* @param {String} type the old mime-type
* @return the new mime-type
*/
var _fixType = function(type) {
type = type.toLowerCase().replace(/jpg/i, 'jpeg');
var r = type.match(/png|jpeg|bmp|gif/)[0];
return 'image/' + r;
};
// 加工image data，替换mime type
imgData = imgData.replace(_fixType(type),'image/octet-stream');
3、图片download到本地
/**
* 在本地进行文件保存
* @param {String} data
要保存到本地的图片数据
* @param {String} filename 文件名
*/
var saveFile = function(data, filename){
var save_link = document.createElementNS('http://www.w3.org/1999/xhtml', 'a');
save_link.href = data;
save_link.download = filename;
var event = document.createEvent('MouseEvents');
event.initMouseEvent('click', true, false, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
save_link.dispatchEvent(event);
};
// 下载后的文件名
var filename = 'baidufe_' + (new Date()).getTime() + '.' + type;
// download
saveFile(imgData,filename);