HTML5调用手机前置摄像头或后置摄像头拍照，canvas显示,经过Android测试

最近刚好有些时间，打算写一个完善一点的demo出来，处理一下兼容性和拍摄视频上传 ps：预计需要下周完成 2019-8-24

HTML5可以通过调用navigator.getUserMedia来获取手机设备摄像头，兼容性写法如下

window.navigator.getUserMedia = navigator.getUserMedia || navigator.webKitGetUserMedia || navigator.mozGetUserMedia || navigator.msGetUserMedia;

但是navigator.getUserMediau已经从 Web 标准中删除，虽然部分浏览器可以使用，生产环境中还是要做好兼容。新的API更替为MediaDevices.getUserMedia。MediaDevices.getUserMedia可以通过video的facingMode属性指定调用手机的前置或后置摄像头

video:{ 'facingMode': "user" }//调用前置摄像头
video: { facingMode: { exact: "environment" } }//后置

注意，以下HTML需要在HTTPS下访问方可正常工作

具体代码：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width,initial-scale=1.0,maximum-scale=1.0,minimum-scale=1.0,user-scalable=no">
    <title>Document1</title>
    <style type='text/css'>
        * { margin: 0; padding: 0; }

        html, body { height: 100%; }

        .flex { display: flex; }

        .flex-row { flex-direction: row; justify-content: space-around; align-items: center; }

        .flex-column { flex-direction: column; justify-content: flex-start; align-items: center; }

        body { overflow: auto; background: #fff; }

        .title { width: 920px; padding: 30px; align-items: flex-end; }

        .title h1 { padding-bottom: 20px; font-size: 38px; color: #ffffff; text-shadow: 0 1px 3px #222222; }

        .title p { font-size: 18px; color: #f5f5f5; text-shadow: 0 1px 3px #565656; }

        .wrap { width: 1220px; }

        .wrap .reference { position: relative; padding: 10px; background-color: rgba(255, 255, 255, 0); border-radius: 10px; box-shadow: 0 0 20px #a1a19f; }

        .wrap .reference img.face { display: block; width: 320px; height: auto; border-radius: 10px; }

        .wrap .reference img.toggle { position: absolute; right: 10px; top: 10px; width: 50px; height: 50px; }

        .wrap .scan video { background-color: rgba(0, 0, 0, .8); border-radius: 10px; }

        .wrap .control { justify-content: space-around; height: 456px; padding: 0 20px; }

        .wrap .control p { width: 160px; height: 60px; background-color: #f9f9f9; text-align: center; line-height: 60px; color: #ffffff; font-size: 24px; border-radius: 8px; cursor: pointer; box-shadow: -8px -8px 150px -8px #b2b3b5 inset, 0 0 5px #222222; text-shadow: 0 0 1px #222222; transition: .5s; }

        .wrap .control p:hover { box-shadow: -8px -8px 150px -8px #50c4f1 inset, 0 0 5px #ffffff; }

        .wrap .scan { position: relative; overflow: hidden; }

        .wrap .scan .strainer { position: absolute; top: 10px; width: 320px; z-index: 999; height: 3px; }

        .wrap .scan .capture { width: 320px; height: 456px; }

        .wrap .scan .strainer.on { background: linear-gradient(to left, transparent, #0bffb2, transparent); animation: scan 1s linear infinite; }

        @keyframes scan {
            0% { top: 10px; }
            50% { top: 456px; }
            100% { top: 10px; }
        }

    </style>
    <script type="text/javascript" src="vconsole.min.js"></script>
</head>
<body>
    <div class="title flex flex-column">
</div>
<div class="wrap flex flex-row">
    <div class="control flex flex-column">
        <p class="open">开启摄像头</p>
        <p class="recognition">显示到Canvas</p>
        <p class="close">关闭摄像头</p>
    </div>
    <div class="scan reference">
        <div class="strainer"></div>
        <video class="capture" width="320" height="456" src=""></video>
    </div>

</div>

    <script type="text/javascript">
        var buffer;
        var oCapture = document.querySelector(".capture"),
        open = document.querySelector(".open"),
        recognition = document.querySelector(".recognition"),
        close = document.querySelector(".close");
        var control = document.querySelector(".control");

        window.navigator.getUserMedia = navigator.getUserMedia || navigator.webKitGetUserMedia || navigator.mozGetUserMedia || navigator.msGetUserMedia;
        
        function invokingCarera(){
            if(navigator.mediaDevices&&navigator.mediaDevices.getUserMedia){
                navigator.mediaDevices.getUserMedia({
                    'audio':true,
                    'video':{ 'facingMode': "user" }//调用前置摄像头，后置摄像头使用video: { facingMode: { exact: "environment" } }
                })
                .then(function(mediaStream) {console.log(555);getVideoStream(mediaStream)})
                .catch(function(error) { console.log(666);console.log(error) })
            }else if(navigator.getUserMedia){
                navigator.getUserMedia({
                    'video':true,
                    'audio':true
                },getVideoStream,getFail)
            }else{
                alert('不支持摄像头调用！')
            }
        }
        //调用成功
        function getVideoStream(stream){
            buffer = stream;
            if(oCapture.mozSrcObject !== undefined){
                oCapture.mozSrcObject = buffer;
            }else{
                oCapture.src = window.URL && window.URL.createObjectURL(buffer);                
            }
            oCapture.play();
        }
        function getFail(){

        }
        recognition.onclick = function(){

        }
        control.addEventListener('click',function(e){
            e = e || window.event;
            var className = e.target.className;
            switch(className){
                case 'open':
                invokingCarera();
                break;
                case 'close':
                closeCamera();
                break;
                case 'recognition':
                screenShot();
                break;
                default:
                break;
            }
        })
        function closeCamera(){
            buffer&&buffer.getTracks()[1].stop();//关闭摄像头
        }        
        window.requestAnimFrame = (function(){
          return  window.requestAnimationFrame       ||
                  window.webkitRequestAnimationFrame ||
                  window.mozRequestAnimationFrame    ||
                  function( callback ){
                    window.setTimeout(callback, 1000 / 60);
                  };
        })();
        function screenShot(){
            var canvas = document.createElement('canvas');
            canvas.width=320,canvas.height = 456;
            document.querySelector(".wrap").appendChild(canvas);
            var ctx =  canvas.getContext('2d');
            function drawVideo(){
                ctx.drawImage(oCapture,0,0,320,456);
                ctx.font = "30px sans-serif";
                ctx.fillStyle = "blue";
                ctx.fillText("请眨眼", 50, 50);
                requestAnimationFrame(drawVideo);
            }
            window.requestAnimationFrame(drawVideo);
        }
    </script>
</body>
</html>