opencv/doc/js_tutorials/js_assets/utils.js

function Utils(errorOutputId) { // eslint-disable-line no-unused-vars
    let self = this;
    this.errorOutput = document.getElementById(errorOutputId);

    const OPENCV_URL = 'opencv.js';
    this.loadOpenCv = function(onloadCallback) {
        let script = document.createElement('script');
        script.setAttribute('async', '');
        script.setAttribute('type', 'text/javascript');
        script.addEventListener('load', () => {
            console.log(cv.getBuildInformation());
            onloadCallback();
        });
        script.addEventListener('error', () => {
            this.printError('Failed to load ' + OPENCV_URL);
        });
        script.src = OPENCV_URL;
        let node = document.getElementsByTagName('script')[0];
        node.parentNode.insertBefore(script, node);
    };

    this.loadImageToCanvas = function(url, cavansId) {
        let canvas = document.getElementById(cavansId);
        let ctx = canvas.getContext('2d');
        let img = new Image();
        img.crossOrigin = 'anonymous';
        img.onload = function() {
            canvas.width = img.width;
            canvas.height = img.height;
            ctx.drawImage(img, 0, 0, img.width, img.height);
        };
        img.src = url;
    };

    this.executeCode = function(textAreaId) {
        try {
            this.clearError();
            let code = document.getElementById(textAreaId).value;
            eval(code);
        } catch (err) {
            this.printError(err);
        }
    };

    this.clearError = function() {
        this.errorOutput.innerHTML = '';
    };

    this.printError = function(err) {
        if (typeof err === 'undefined') {
            err = '';
        } else if (typeof err === 'number') {
            if (!isNaN(err)) {
                if (typeof cv !== 'undefined') {
                    err = 'Exception: ' + cv.exceptionFromPtr(err).msg;
                }
            }
        } else if (typeof err === 'string') {
            let ptr = Number(err.split(' ')[0]);
            if (!isNaN(ptr)) {
                if (typeof cv !== 'undefined') {
                    err = 'Exception: ' + cv.exceptionFromPtr(ptr).msg;
                }
            }
        } else if (err instanceof Error) {
            err = err.stack.replace(/\n/g, '<br>');
        }
        this.errorOutput.innerHTML = err;
    };

    this.loadCode = function(scriptId, textAreaId) {
        let scriptNode = document.getElementById(scriptId);
        let textArea = document.getElementById(textAreaId);
        if (scriptNode.type !== 'text/code-snippet') {
            throw Error('Unknown code snippet type');
        }
        textArea.value = scriptNode.text.replace(/^\n/, '');
    };

    this.addFileInputHandler = function(fileInputId, canvasId) {
        let inputElement = document.getElementById(fileInputId);
        inputElement.addEventListener('change', (e) => {
            let imgUrl = URL.createObjectURL(e.target.files[0]);
            loadImageToCanvas(imgUrl, canvasId);
        }, false);
    };

    function onVideoCanPlay() {
        if (self.onCameraStartedCallback) {
            self.onCameraStartedCallback(self.stream, self.video);
        }
    };

    this.startCamera = function(resolution, callback, videoId) {
        const constraints = {
            'qvga': {width: {exact: 320}, height: {exact: 240}},
            'vga': {width: {exact: 640}, height: {exact: 480}}};
        let video = document.getElementById(videoId);
        if (!video) {
            video = document.createElement('video');
        }

        let videoConstraint = constraints[resolution];
        if (!videoConstraint) {
            videoConstraint = true;
        }

        navigator.mediaDevices.getUserMedia({video: videoConstraint, audio: false})
            .then(function(stream) {
                video.srcObject = stream;
                video.play();
                self.video = video;
                self.stream = stream;
                self.onCameraStartedCallback = callback;
                video.addEventListener('canplay', onVideoCanPlay, false);
            })
            .catch(function(err) {
                self.printError('Camera Error: ' + err.name + ' ' + err.message);
            });
    };

    this.stopCamera = function() {
        if (this.video) {
            this.video.pause();
            this.video.srcObject = null;
            this.video.removeEventListener('canplay', onVideoCanPlay);
        }
        if (this.stream) {
            this.stream.getVideoTracks()[0].stop();
        }
    };
};