谷歌的“报告错误”或“反馈工具”让你选择浏览器窗口的一个区域来创建一个截图，并提交你对错误的反馈。
截图来自Jason Small，发布在一个重复的问题中。
他们是怎么做到的?谷歌的JavaScript反馈API从这里加载，反馈模块的概述将演示截图功能。
JavaScript可以读取DOM，并使用画布呈现相当准确的DOM表示。我一直在编写一个脚本，将HTML转换为画布图像。今天决定把它实现成像你描述的那样发送反馈。
该脚本允许您创建反馈表单，其中包括在客户端浏览器上创建的屏幕截图，以及表单。截图是基于DOM的，因此可能不是100%准确的真实表示，因为它不制作实际的截图，而是根据页面上可用的信息构建截图。
它不需要来自服务器的任何渲染，因为整个图像是在客户机的浏览器上创建的。HTML2Canvas脚本本身仍然处于一个非常实验性的状态，因为它不能解析我想要的CSS3属性，即使有代理可用，它也不支持加载CORS图像。
浏览器兼容性仍然非常有限(不是因为不支持更多，只是还没有时间让它更支持跨浏览器)。
想了解更多信息，请看下面的例子:
http://hertzen.com/experiments/jsfeedback/
编辑 html2canvas脚本现在可以分别在这里和一些例子。
编辑2 谷歌使用非常相似的方法(事实上，根据文档，唯一主要的区别是他们的异步遍历/绘制方法)可以在谷歌反馈团队的Elliott Sprehn的演示中找到: http://www.elliottsprehn.com/preso/fluentconf/
你的web应用现在可以使用getUserMedia()截取客户端整个桌面的“原生”截图:
来看看这个例子:
https://www.webrtc-experiment.com/Pluginfree-Screen-Sharing/
客户端将不得不使用chrome(目前)，将需要启用chrome://标志下的屏幕捕捉支持。
PoC
正如Niklas所提到的，你可以使用html2canvas库在浏览器中使用JS进行截图。我将通过提供一个使用这个库截屏的例子(“概念证明”)来扩展他的回答:
function report() { let region = document.querySelector("body"); // whole screen html2canvas(region, { onrendered: function(canvas) { let pngUrl = canvas.toDataURL(); // png in dataURL format let img = document.querySelector(".screen"); img.src = pngUrl; // here you can allow user to set bug-region // and send it with 'pngUrl' to server }, }); } .container { margin-top: 10px; border: solid 1px black; } <script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/0.4.1/html2canvas.min.js"></script> <div>Screenshot tester</div> <button onclick="report()">Take screenshot</button> <div class="container"> <img width="75%" class="screen"> </div>
在onrender中的report()函数中，在获得图像作为数据URI后，您可以将其显示给用户，并允许他通过鼠标绘制“bug区域”，然后将截图和区域坐标发送到服务器。
在这个例子中，async/await版本使用了很好的makeScreenshot()函数。
更新
简单的例子，它允许你截屏，选择区域，描述bug和发送POST请求(这里是jsfiddle)(主要函数是report())。
async function report() { let screenshot = await makeScreenshot(); // png dataUrl let img = q(".screen"); img.src = screenshot; let c = q(".bug-container"); c.classList.remove('hide') let box = await getBox(); c.classList.add('hide'); send(screenshot,box); // sed post request with bug image, region and description alert('To see POST requset with image go to: chrome console > network tab'); } // ----- Helper functions let q = s => document.querySelector(s); // query selector helper window.report = report; // bind report be visible in fiddle html async function makeScreenshot(selector="body") { return new Promise((resolve, reject) => { let node = document.querySelector(selector); html2canvas(node, { onrendered: (canvas) => { let pngUrl = canvas.toDataURL(); resolve(pngUrl); }}); }); } async function getBox(box) { return new Promise((resolve, reject) => { let b = q(".bug"); let r = q(".region"); let scr = q(".screen"); let send = q(".send"); let start=0; let sx,sy,ex,ey=-1; r.style.width=0; r.style.height=0; let drawBox= () => { r.style.left = (ex > 0 ? sx : sx+ex ) +'px'; r.style.top = (ey > 0 ? sy : sy+ey) +'px'; r.style.width = Math.abs(ex) +'px'; r.style.height = Math.abs(ey) +'px'; } //console.log({b,r, scr}); b.addEventListener("click", e=>{ if(start==0) { sx=e.pageX; sy=e.pageY; ex=0; ey=0; drawBox(); } start=(start+1)%3; }); b.addEventListener("mousemove", e=>{ //console.log(e) if(start==1) { ex=e.pageX-sx; ey=e.pageY-sy drawBox(); } }); send.addEventListener("click", e=>{ start=0; let a=100/75 //zoom out img 75% resolve({ x:Math.floor(((ex > 0 ? sx : sx+ex )-scr.offsetLeft)*a), y:Math.floor(((ey > 0 ? sy : sy+ey )-b.offsetTop)*a), width:Math.floor(Math.abs(ex)*a), height:Math.floor(Math.abs(ex)*a), desc: q('.bug-desc').value }); }); }); } function send(image,box) { let formData = new FormData(); let req = new XMLHttpRequest(); formData.append("box", JSON.stringify(box)); formData.append("screenshot", image); req.open("POST", '/upload/screenshot'); req.send(formData); } .bug-container { background: rgb(255,0,0,0.1); margin-top:20px; text-align: center; } .send { border-radius:5px; padding:10px; background: green; cursor: pointer; } .region { position: absolute; background: rgba(255,0,0,0.4); } .example { height: 100px; background: yellow; } .bug { margin-top: 10px; cursor: crosshair; } .hide { display: none; } .screen { pointer-events: none } <script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/0.4.1/html2canvas.min.js"></script> <body> <div>Screenshot tester</div> <button onclick="report()">Report bug</button> <div class="example">Lorem ipsum</div> <div class="bug-container hide"> <div>Select bug region: click once - move mouse - click again</div> <div class="bug"> <img width="75%" class="screen" > <div class="region"></div> </div> <div> <textarea class="bug-desc">Describe bug here...</textarea> </div> <div class="send">SEND BUG</div> </div> </body>
这里有一个使用getDisplayMedia的例子
document.body.innerHTML = '<video style="width: 100%; height: 100%; border: 1px black solid;"/>';
navigator.mediaDevices.getDisplayMedia()
.then( mediaStream => {
const video = document.querySelector('video');
video.srcObject = mediaStream;
video.onloadedmetadata = e => {
video.play();
video.pause();
};
})
.catch( err => console.log(`${err.name}: ${err.message}`));
同样值得一看的还有Screen Capture API文档。
使用getDisplayMedia API获取截图作为画布或Jpeg Blob / ArrayBuffer:
修复1:使用getUserMedia与chromeMediaSource仅为电子。js 修复2:抛出错误而不是返回空对象 修复3:修复演示以防止错误:getDisplayMedia必须从用户手势处理程序调用
// docs: https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices/getDisplayMedia
// see: https://www.webrtc-experiment.com/Pluginfree-Screen-Sharing/#20893521368186473
// see: https://github.com/muaz-khan/WebRTC-Experiment/blob/master/Pluginfree-Screen-Sharing/conference.js
function getDisplayMedia(options) {
if (navigator.mediaDevices && navigator.mediaDevices.getDisplayMedia) {
return navigator.mediaDevices.getDisplayMedia(options)
}
if (navigator.getDisplayMedia) {
return navigator.getDisplayMedia(options)
}
if (navigator.webkitGetDisplayMedia) {
return navigator.webkitGetDisplayMedia(options)
}
if (navigator.mozGetDisplayMedia) {
return navigator.mozGetDisplayMedia(options)
}
throw new Error('getDisplayMedia is not defined')
}
function getUserMedia(options) {
if (navigator.mediaDevices && navigator.mediaDevices.getUserMedia) {
return navigator.mediaDevices.getUserMedia(options)
}
if (navigator.getUserMedia) {
return navigator.getUserMedia(options)
}
if (navigator.webkitGetUserMedia) {
return navigator.webkitGetUserMedia(options)
}
if (navigator.mozGetUserMedia) {
return navigator.mozGetUserMedia(options)
}
throw new Error('getUserMedia is not defined')
}
async function takeScreenshotStream() {
// see: https://developer.mozilla.org/en-US/docs/Web/API/Window/screen
const width = screen.width * (window.devicePixelRatio || 1)
const height = screen.height * (window.devicePixelRatio || 1)
const errors = []
let stream
try {
stream = await getDisplayMedia({
audio: false,
// see: https://developer.mozilla.org/en-US/docs/Web/API/MediaStreamConstraints/video
video: {
width,
height,
frameRate: 1,
},
})
} catch (ex) {
errors.push(ex)
}
// for electron js
if (navigator.userAgent.indexOf('Electron') >= 0) {
try {
stream = await getUserMedia({
audio: false,
video: {
mandatory: {
chromeMediaSource: 'desktop',
// chromeMediaSourceId: source.id,
minWidth : width,
maxWidth : width,
minHeight : height,
maxHeight : height,
},
},
})
} catch (ex) {
errors.push(ex)
}
}
if (errors.length) {
console.debug(...errors)
if (!stream) {
throw errors[errors.length - 1]
}
}
return stream
}
async function takeScreenshotCanvas() {
const stream = await takeScreenshotStream()
// from: https://stackoverflow.com/a/57665309/5221762
const video = document.createElement('video')
const result = await new Promise((resolve, reject) => {
video.onloadedmetadata = () => {
video.play()
video.pause()
// from: https://github.com/kasprownik/electron-screencapture/blob/master/index.js
const canvas = document.createElement('canvas')
canvas.width = video.videoWidth
canvas.height = video.videoHeight
const context = canvas.getContext('2d')
// see: https://developer.mozilla.org/en-US/docs/Web/API/HTMLVideoElement
context.drawImage(video, 0, 0, video.videoWidth, video.videoHeight)
resolve(canvas)
}
video.srcObject = stream
})
stream.getTracks().forEach(function (track) {
track.stop()
})
if (result == null) {
throw new Error('Cannot take canvas screenshot')
}
return result
}
// from: https://stackoverflow.com/a/46182044/5221762
function getJpegBlob(canvas) {
return new Promise((resolve, reject) => {
// docs: https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toBlob
canvas.toBlob(blob => resolve(blob), 'image/jpeg', 0.95)
})
}
async function getJpegBytes(canvas) {
const blob = await getJpegBlob(canvas)
return new Promise((resolve, reject) => {
const fileReader = new FileReader()
fileReader.addEventListener('loadend', function () {
if (this.error) {
reject(this.error)
return
}
resolve(this.result)
})
fileReader.readAsArrayBuffer(blob)
})
}
async function takeScreenshotJpegBlob() {
const canvas = await takeScreenshotCanvas()
return getJpegBlob(canvas)
}
async function takeScreenshotJpegBytes() {
const canvas = await takeScreenshotCanvas()
return getJpegBytes(canvas)
}
function blobToCanvas(blob, maxWidth, maxHeight) {
return new Promise((resolve, reject) => {
const img = new Image()
img.onload = function () {
const canvas = document.createElement('canvas')
const scale = Math.min(
1,
maxWidth ? maxWidth / img.width : 1,
maxHeight ? maxHeight / img.height : 1,
)
canvas.width = img.width * scale
canvas.height = img.height * scale
const ctx = canvas.getContext('2d')
ctx.drawImage(img, 0, 0, img.width, img.height, 0, 0, canvas.width, canvas.height)
resolve(canvas)
}
img.onerror = () => {
reject(new Error('Error load blob to Image'))
}
img.src = URL.createObjectURL(blob)
})
}
演示:
document.body.onclick = async () => {
// take the screenshot
var screenshotJpegBlob = await takeScreenshotJpegBlob()
// show preview with max size 300 x 300 px
var previewCanvas = await blobToCanvas(screenshotJpegBlob, 300, 300)
previewCanvas.style.position = 'fixed'
document.body.appendChild(previewCanvas)
// send it to the server
var formdata = new FormData()
formdata.append("screenshot", screenshotJpegBlob)
await fetch('https://your-web-site.com/', {
method: 'POST',
body: formdata,
'Content-Type' : "multipart/form-data",
})
}
// and click on the page
这是一个完整的截图示例，可以在2021年使用chrome浏览器。最终结果是一个准备传输的blob。流程是:请求媒体>抓取帧>绘制到画布>传输到blob。如果你想更有效地使用内存探索OffscreenCanvas或者ImageBitmapRenderingContext
https://jsfiddle.net/v24hyd3q/1/
// Request media
navigator.mediaDevices.getDisplayMedia().then(stream =>
{
// Grab frame from stream
let track = stream.getVideoTracks()[0];
let capture = new ImageCapture(track);
capture.grabFrame().then(bitmap =>
{
// Stop sharing
track.stop();
// Draw the bitmap to canvas
canvas.width = bitmap.width;
canvas.height = bitmap.height;
canvas.getContext('2d').drawImage(bitmap, 0, 0);
// Grab blob from canvas
canvas.toBlob(blob => {
// Do things with blob here
console.log('output blob:', blob);
});
});
})
.catch(e => console.log(e));
你可以试试我的新JS库:截图. JS。
它可以拍摄真实的屏幕截图。
你加载脚本:
<script src="https://raw.githubusercontent.com/amiad/screenshot.js/master/screenshot.js"></script>
并截屏:
new Screenshot({success: img => {
// callback function
myimage = img;
}});
您可以在项目页面中阅读更多选项。
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