HTML5镜像摄像头画布

Question

我试图采取一个网络摄像头的饲料-(景观格式)，剪出中间位(肖像格式)，并让它渲染到画布，以便它填充屏幕肖像1080‘m到1920年(为此，我缩放的位，我削减3.8)。然后，我需要翻转这个画布，以便镜像图像。我成功地剪掉了中间的部分，并把它呈现在画布上.我只是想不出怎么翻转它。

编辑

感谢所有向我指出context.scale(-1，1)的人--我的问题是，我已经在使用比例尺了.我认为我的问题与拯救环境有关，但我所做的一切都失败了吗？

<script>
       // Put event listeners into place
        window.addEventListener("DOMContentLoaded", function() {
            // Grab elements, create settings, etc.
            var canvas = document.getElementById("canvas"),
                context = canvas.getContext("2d"),
                video = document.getElementById("video"),
                videoObj = { 
                    video: {
                        mandatory: {
                            minWidth: 1280,
                            minHeight: 720,
                            /*Added by Chad*/
                            maxWidth: 1280,
                            maxHeight: 720
                        }
                    }
                },
                errBack = function(error) {
                    console.log("Video capture error: ", error.code); 
                };

            // Put video listeners into place
            if(navigator.getUserMedia) { // Standard
                navigator.getUserMedia(videoObj, function(stream) {
                    video.src = stream;
                    video.play();
                }, errBack);
            } else if(navigator.webkitGetUserMedia) { // WebKit-prefixed
                navigator.webkitGetUserMedia(videoObj, function(stream){
                    video.src = window.URL.createObjectURL(stream);
                    video.play();
                }, errBack);
            } else if(navigator.mozGetUserMedia) { // WebKit-prefixed
                navigator.mozGetUserMedia(videoObj, function(stream){
                    video.src = window.URL.createObjectURL(stream);
                    video.play();
                }, errBack);
            }

            /*
                video : video source tag
                320,0 : the shift coords
                320,180 : the canvas size
                0,0 : no shift in the canvas
                640,360 : important ! it’s the native resolution of video source
            */
            context.scale(3.8,3.8);

            function loop(){
               context.drawImage(video, 450, 0, 1080, 1920, 0, 0, 720, 1280);
               setTimeout(loop, 1000 / 30);
            }

            loop();


        }, false);
</script> 


    <video id="video" height="1080" width="1920" autoplay></video>
    <canvas id="canvas" height="1920" width="1080"></canvas>


// Put event listeners into place
window.addEventListener("DOMContentLoaded", function() {
    // Grab elements, create settings, etc.
    var canvas = document.getElementById("canvas"),
        context = canvas.getContext("2d"),
        video = document.getElementById("video"),
        videoObj = { 
            video: {
                mandatory: {
                    minWidth: 1280,
                    minHeight: 720,
                    /*Added by Chad*/
                    maxWidth: 1280,
                    maxHeight: 720
                }
            }
        },
        errBack = function(error) {
            console.log("Video capture error: ", error.code); 
        };

    // Put video listeners into place
    if(navigator.getUserMedia) { // Standard
        navigator.getUserMedia(videoObj, function(stream) {
            video.src = stream;
            video.play();
        }, errBack);
    } else if(navigator.webkitGetUserMedia) { // WebKit-prefixed
        navigator.webkitGetUserMedia(videoObj, function(stream){
            video.src = window.URL.createObjectURL(stream);
            video.play();
        }, errBack);
    } else if(navigator.mozGetUserMedia) { // WebKit-prefixed
        navigator.mozGetUserMedia(videoObj, function(stream){
            video.src = window.URL.createObjectURL(stream);
            video.play();
        }, errBack);
    }

    /*
        video : video source tag
        320,0 : the shift coords
        320,180 : the canvas size
        0,0 : no shift in the canvas
        640,360 : important ! it’s the native resolution of video source
    */




    context.scale(-3.8,3.8);
    context.translate(-720,0);
    function loop(){
       context.drawImage(video, 450, 0, 1080, 1920, 0, 0, 720, 1280);
       setTimeout(loop, 1000 / 30);
    }

    loop();


}, false);

Answer 1

您不应该使用ctx.scale和ctx.translate方法进行裁剪。

相反，在加载视频时，计算裁剪位置，然后在绘图循环的调用中应用这些计算的位置。

完成后，可以很容易地按照@Mahout的建议应用context.scale(-1, 1);。

请注意，在应用context.translate(canvas.width, 0);之前还需要使用scale()。

我重构了您的代码，因为您请求视频授权的方式是out of date (就像关于它的铬一样)。

我也更改了您的循环，以便只在视频加载时调用它，不需要尝试绘制任何尚不存在的内容，我用requestAnimationFrame方法更改了您的requestAnimationFrame，该方法在大约30 has时触发。

​

// Put event listeners into place
window.addEventListener("DOMContentLoaded", function() {
    // Grab elements, create settings, etc.
    var canvas = document.getElementById("canvas"),
        context = canvas.getContext("2d"),
        // we don't need to append the video to the document
        video = document.createElement("video"),
        videoObj = 
        navigator.getUserMedia || navigator.mozGetUserMedia ? // our browser is up to date with specs ?
        { 
        video: {
            width: { min: 1280,  max: 1280 },
            height: { min: 720,  max: 720 },
            require: ['width', 'height']
            }
        }:
        {
        video: {
            mandatory: {
                minWidth: 1280,
                minHeight: 720,
                maxWidth: 1280,
                maxHeight: 720
            }
        }
    },
    errBack = function(error) {
        console.log("Video capture error: ", error.code); 
    };
    // create a crop object that will be calculated on load of the video
    var crop;
    // create a variable that will enable us to stop the loop.
    var raf;
    
    navigator.getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia;
    // Put video listeners into place
        navigator.getUserMedia(videoObj, function(stream) {
            video.srcObject = stream;
            video.onplaying = function(){
                var croppedWidth = ( Math.min(video.videoHeight, canvas.height) / Math.max(video.videoHeight,canvas.height)) * Math.min(video.videoWidth, canvas.width),
                croppedX = ( video.videoWidth - croppedWidth) / 2;
                crop = {w:croppedWidth, h:video.videoHeight, x:croppedX, y:0};
                // call our loop only when the video is playing
                raf = requestAnimationFrame(loop);
                };
            video.onpause = function(){
                // stop the loop
                cancelAnimationFrame(raf);
                }
            video.play();
        }, errBack);

    function loop(){
       context.drawImage(video, crop.x, crop.y, crop.w, crop.h, 0, 0, canvas.width, canvas.height);
       raf = requestAnimationFrame(loop);
    }
// now that our video is drawn correctly, we can do...
context.translate(canvas.width, 0);
context.scale(-1,1);

}, false);

body,html{margin:0}
canvas{ border:1px solid;}

<canvas id="canvas" height="1920" width="1080"></canvas>

​

for chrome

Answer 2

对于水平翻转，可以使用context.scale(-1, 1);。

来自http://www.html5canvastutorials.com/advanced/html5-canvas-mirror-transform-tutorial/

编辑

作为最后的手段，可以使用这个CSS。

#canvas {
        -moz-transform: scaleX(-1);
        -o-transform: scaleX(-1);
        -webkit-transform: scaleX(-1);
        transform: scaleX(-1);
        filter: FlipH;
        -ms-filter: "FlipH";
}

如果需要，所有这些都可以用javascript动态应用。未经测试，但希望能工作！

Answer 3

快速回答(试过和测试)：

let context = document.getElementById("canvas").getContext("2d");
context.translate(width, 0)
context.scale(-1, 1)
context.drawImage(image, 0, 0, width, height)