Translate scratch 2 video sensing into scratch 3 extension

- Add videoSensing extension to extension-manager

src/extension-support/extension-manager.js

@@ -9,10 +9,13 @@ const BlockType = require('./block-type');
 const Scratch3PenBlocks = require('../extensions/scratch3_pen');
 const Scratch3WeDo2Blocks = require('../extensions/scratch3_wedo2');
 const Scratch3MusicBlocks = require('../extensions/scratch3_music');
+const Scratch3VideoSensingBlocks = require('../extensions/scratch3_video_sensing');
+
 const builtinExtensions = {
     pen: Scratch3PenBlocks,
     wedo2: Scratch3WeDo2Blocks,
-    music: Scratch3MusicBlocks
+    music: Scratch3MusicBlocks,
+    videoSensing: Scratch3VideoSensingBlocks
 };
 
 /**

src/extensions/scratch3_video_sensing/debug.js

@@ -0,0 +1,7 @@
+const VideoMotion = require('./lib');
+const VideoMotionView = require('./view');
+
+module.exports = {
+    VideoMotion,
+    VideoMotionView
+};

src/extensions/scratch3_video_sensing/index.js

@@ -0,0 +1,336 @@
+const ArgumentType = require('../../extension-support/argument-type');
+const BlockType = require('../../extension-support/block-type');
+const Clone = require('../../util/clone');
+const log = require('../../util/log');
+const Timer = require('../../util/timer');
+
+const VideoMotion = require('./lib');
+
+/**
+ * Icon svg to be displayed at the left edge of each extension block, encoded as a data URI.
+ * @type {string}
+ */
+// eslint-disable-next-line max-len
+const blockIconURI = 'data:image/svg+xml;base64,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';
+
+/**
+ * Icon svg to be displayed in the category menu, encoded as a data URI.
+ * @type {string}
+ */
+// eslint-disable-next-line max-len
+const menuIconURI = 'data:image/svg+xml;base64,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';
+
+/**
+ * Class for the motion-related blocks in Scratch 3.0
+ * @param {Runtime} runtime - the runtime instantiating this block package.
+ * @constructor
+ */
+class Scratch3VideoSensingBlocks {
+    constructor (runtime) {
+        /**
+         * The runtime instantiating this block package.
+         * @type {Runtime}
+         */
+        this.runtime = runtime;
+
+        this.detect = new VideoMotion();
+
+        this._lastUpdate = null;
+
+        this._skinId = -1;
+        this._skin = null;
+        this._drawable = -1;
+
+        this._setupVideo();
+        this._setupSampleCanvas();
+        this._setupPreview();
+        this._loop();
+    }
+
+    static get INTERVAL () {
+        return 33;
+    }
+
+    static get DIMENSIONS () {
+        return [480, 360];
+    }
+
+    static get ORDER () {
+        return 1;
+    }
+
+    _setupVideo () {
+        this._video = document.createElement('video');
+        navigator.getUserMedia({
+            audio: false,
+            video: {
+                width: {min: 480, ideal: 640},
+                height: {min: 360, ideal: 480}
+            }
+        }, stream => {
+            this._video.src = window.URL.createObjectURL(stream);
+            // Hint to the stream that it should load. A standard way to do this
+            // is add the video tag to the DOM. Since this extension wants to
+            // hide the video tag and instead render a sample of the stream into
+            // the webgl rendered Scratch canvas, another hint like this one is
+            // needed.
+            this._track = stream.getTracks()[0];
+        }, err => {
+            // @todo Properly handle errors
+            log(err);
+        });
+    }
+
+    _setupSampleCanvas () {
+        // Create low-resolution image to sample video for analysis and preview
+        const canvas = this._sampleCanvas = document.createElement('canvas');
+        canvas.width = Scratch3VideoSensingBlocks.DIMENSIONS[0];
+        canvas.height = Scratch3VideoSensingBlocks.DIMENSIONS[1];
+        this._sampleContext = canvas.getContext('2d');
+    }
+
+    _setupPreview () {
+        if (this._skinId !== -1) return;
+        if (this._skin !== null) return;
+        if (this._drawable !== -1) return;
+        if (!this.runtime.renderer) return;
+
+        this._skinId = this.runtime.renderer.createPenSkin();
+        this._skin = this.runtime.renderer._allSkins[this._skinId];
+        this._drawable = this.runtime.renderer.createDrawable();
+        this.runtime.renderer.setDrawableOrder(
+            this._drawable,
+            Scratch3VideoSensingBlocks.ORDER
+        );
+        this.runtime.renderer.updateDrawableProperties(this._drawable, {
+            skinId: this._skinId
+        });
+    }
+
+    _loop () {
+        setTimeout(this._loop.bind(this), this.runtime.currentStepTime);
+
+        // Ensure video stream is established
+        if (!this._video) return;
+        if (!this._track) return;
+        if (typeof this._video.videoWidth !== 'number') return;
+        if (typeof this._video.videoHeight !== 'number') return;
+
+        // Bail if the camera is *still* not ready
+        const nativeWidth = this._video.videoWidth;
+        const nativeHeight = this._video.videoHeight;
+        if (nativeWidth === 0) return;
+        if (nativeHeight === 0) return;
+
+        const ctx = this._sampleContext;
+
+        // Mirror
+        ctx.scale(-1, 1);
+
+        // Generate video thumbnail for analysis
+        ctx.drawImage(
+            this._video,
+            0,
+            0,
+            nativeWidth,
+            nativeHeight,
+            Scratch3VideoSensingBlocks.DIMENSIONS[0] * -1,
+            0,
+            Scratch3VideoSensingBlocks.DIMENSIONS[0],
+            Scratch3VideoSensingBlocks.DIMENSIONS[1]
+        );
+
+        // Restore the canvas transform
+        ctx.resetTransform();
+
+        // Render to preview layer
+        if (this._skin !== null) {
+            const xOffset = Scratch3VideoSensingBlocks.DIMENSIONS[0] / 2 * -1;
+            const yOffset = Scratch3VideoSensingBlocks.DIMENSIONS[1] / 2;
+            this._skin.drawStamp(this._sampleCanvas, xOffset, yOffset);
+            this.runtime.requestRedraw();
+        }
+
+        // Add frame to detector
+        const time = Date.now();
+        if (this._lastUpdate === null) this._lastUpdate = time;
+        const offset = time - this._lastUpdate;
+        if (offset > Scratch3VideoSensingBlocks.INTERVAL) {
+            this._lastUpdate = time;
+            const data = ctx.getImageData(
+                0, 0, Scratch3VideoSensingBlocks.DIMENSIONS[0], Scratch3VideoSensingBlocks.DIMENSIONS[1]
+            );
+            this.detect.addFrame(data.data);
+        }
+    }
+
+    /**
+     * Create data for a menu in scratch-blocks format, consisting of an array of objects with text and
+     * value properties. The text is a translated string, and the value is one-indexed.
+     * @param  {object[]} info - An array of info objects each having a name property.
+     * @return {array} - An array of objects with text and value properties.
+     * @private
+     */
+    _buildMenu (info) {
+        return info.map((entry, index) => {
+            const obj = {};
+            obj.text = entry.name;
+            obj.value = String(index + 1);
+            return obj;
+        });
+    }
+
+    /**
+     * The key to load & store a target's motion-related state.
+     * @type {string}
+     */
+    static get STATE_KEY () {
+        return 'Scratch.videoSensing';
+    }
+
+    /**
+     * The default music-related state, to be used when a target has no existing music state.
+     * @type {MusicState}
+     */
+    static get DEFAULT_MOTION_STATE () {
+        return {
+            currentInstrument: 0
+        };
+    }
+
+    /**
+     * @param {Target} target - collect motion state for this target.
+     * @returns {MotionState} the mutable motion state associated with that target. This will be created if necessary.
+     * @private
+     */
+    _getMotionState (target) {
+        let motionState = target.getCustomState(Scratch3VideoSensingBlocks.STATE_KEY);
+        if (!motionState) {
+            motionState = Clone.simple(Scratch3VideoSensingBlocks.DEFAULT_MOTION_STATE);
+            target.setCustomState(Scratch3VideoSensingBlocks.STATE_KEY, motionState);
+        }
+        return motionState;
+    }
+
+    /**
+     * An array of info about each drum.
+     * @type {object[]} an array of objects.
+     * @param {string} name - the translatable name to display in the drums menu.
+     * @param {string} fileName - the name of the audio file containing the drum sound.
+     */
+    get MOTION_DIRECTION_INFO () {
+        return [
+            {
+                name: 'motion'
+            },
+            {
+                name: 'direction'
+            }
+        ];
+    }
+
+    /**
+     * An array of info about each drum.
+     * @type {object[]} an array of objects.
+     * @param {string} name - the translatable name to display in the drums menu.
+     * @param {string} fileName - the name of the audio file containing the drum sound.
+     */
+    get STAGE_SPRITE_INFO () {
+        return [
+            {
+                name: 'stage'
+            },
+            {
+                name: 'sprite'
+            }
+        ];
+    }
+
+    /**
+     * @returns {object} metadata for this extension and its blocks.
+     */
+    getInfo () {
+        return {
+            id: 'videoSensing',
+            name: 'Video Sensing',
+            menuIconURI: menuIconURI,
+            blockIconURI: blockIconURI,
+            blocks: [
+                {
+                    opcode: 'videoOn',
+                    blockType: BlockType.REPORTER,
+                    text: 'video [MOTION_DIRECTION] on [STAGE_SPRITE]',
+                    arguments: {
+                        MOTION_DIRECTION: {
+                            type: ArgumentType.NUMBER,
+                            menu: 'MOTION_DIRECTION',
+                            defaultValue: 1
+                        },
+                        STAGE_SPRITE: {
+                            type: ArgumentType.NUMBER,
+                            menu: 'STAGE_SPRITE',
+                            defaultValue: 1
+                        }
+                    }
+                }
+            ],
+            menus: {
+                MOTION_DIRECTION: this._buildMenu(this.MOTION_DIRECTION_INFO),
+                STAGE_SPRITE: this._buildMenu(this.STAGE_SPRITE_INFO)
+            }
+        };
+    }
+
+    videoOn (args, util) {
+        this.detect.analyzeFrame();
+
+        let state = this.detect;
+        if (Number(args.STAGE_SPRITE) === 2) {
+            const drawable = this.runtime.renderer._allDrawables[util.target.drawableID];
+            state = this._getMotionState(util.target);
+            this.detect.getLocalMotion(drawable, state);
+        }
+
+        if (Number(args.MOTION_DIRECTION) === 1) {
+            return state.motionAmount;
+        }
+        return state.motionDirection;
+    }
+
+    /**
+     * Check if the stack timer needs initialization.
+     * @param {object} util - utility object provided by the runtime.
+     * @return {boolean} - true if the stack timer needs to be initialized.
+     * @private
+     */
+    _stackTimerNeedsInit (util) {
+        return !util.stackFrame.timer;
+    }
+
+    /**
+     * Start the stack timer and the yield the thread if necessary.
+     * @param {object} util - utility object provided by the runtime.
+     * @param {number} duration - a duration in seconds to set the timer for.
+     * @private
+     */
+    _startStackTimer (util, duration) {
+        util.stackFrame.timer = new Timer();
+        util.stackFrame.timer.start();
+        util.stackFrame.duration = duration;
+        util.yield();
+    }
+
+    /**
+     * Check the stack timer, and if its time is not up yet, yield the thread.
+     * @param {object} util - utility object provided by the runtime.
+     * @private
+     */
+    _checkStackTimer (util) {
+        const timeElapsed = util.stackFrame.timer.timeElapsed();
+        if (timeElapsed < util.stackFrame.duration * 1000) {
+            util.yield();
+        }
+    }
+}
+
+module.exports = Scratch3VideoSensingBlocks;

src/extensions/scratch3_video_sensing/lib.js

@@ -0,0 +1,248 @@
+/**
+ * lib.js
+ *
+ * Tony Hwang and John Maloney, January 2011
+ * Michael "Z" Goddard, March 2018
+ *
+ * Video motion sensing primitives.
+ */
+
+const TO_DEGREE = 180 / Math.PI;
+const WIDTH = 480;
+const HEIGHT = 360;
+// chosen empirically to give a range of roughly 0-100
+const AMOUNT_SCALE = 100;
+// note 2e-4 * activePixelNum is an experimentally tuned threshold for my
+// logitech Pro 9000 webcam - TTH
+const LOCAL_AMOUNT_SCALE = AMOUNT_SCALE * 2e-4;
+const THRESHOLD = 10;
+const WINSIZE = 8;
+const LOCAL_MAX_AMOUNT = 100;
+const LOCAL_THRESHOLD = THRESHOLD / 3;
+
+const STATE_KEY = 'Scratch.videoSensing';
+
+class VideoMotion {
+    constructor () {
+        this.frameNumber = 0;
+        this.motionAmount = 0;
+        this.motionDirection = 0;
+        this.analysisDone = false;
+
+        this.curr = null;
+        this.prev = null;
+
+        this._arrays = new ArrayBuffer(WIDTH * HEIGHT * 2 * 1);
+        this._curr = new Uint8ClampedArray(this._arrays, WIDTH * HEIGHT * 0 * 1, WIDTH * HEIGHT);
+        this._prev = new Uint8ClampedArray(this._arrays, WIDTH * HEIGHT * 1 * 1, WIDTH * HEIGHT);
+    }
+
+    reset () {
+        this.prev = this.curr = null;
+        this.motionAmount = this.motionDirection = 0;
+        this.analysisDone = true;
+
+        const targets = this.runtime.targets;
+        for (let i = 0; i < targets.length; i++) {
+            targets[i].getCustomState(STATE_KEY).motionAmount = 0;
+            targets[i].getCustomState(STATE_KEY).motionDirection = 0;
+        }
+    }
+
+    addFrame (source) {
+        this.frameNumber++;
+
+        this.prev = this.curr;
+        this.curr = new Uint32Array(source.buffer.slice());
+
+        const _tmp = this._prev;
+        this._prev = this._curr;
+        this._curr = _tmp;
+        for (let i = 0; i < this.curr.length; i++) {
+            this._curr[i] = this.curr[i] & 0xff;
+        }
+
+        this.analysisDone = false;
+    }
+
+    analyzeFrame () {
+        if (!this.curr || !this.prev) {
+            this.motionAmount = this.motionDirection = -1;
+            // don't have two frames to analyze yet
+            return;
+        }
+
+        const {
+            _curr: curr,
+            _prev: prev
+        } = this;
+
+        const winStep = (WINSIZE * 2) + 1;
+        const wmax = WIDTH - WINSIZE - 1;
+        const hmax = HEIGHT - WINSIZE - 1;
+
+        let uu = 0;
+        let vv = 0;
+        let n = 0;
+
+        for (let i = WINSIZE + 1; i < hmax; i += winStep) {
+            for (let j = WINSIZE + 1; j < wmax; j += winStep) {
+                let A2 = 0;
+                let A1B2 = 0;
+                let B1 = 0;
+                let C1 = 0;
+                let C2 = 0;
+
+                let address = ((i - WINSIZE) * WIDTH) + j - WINSIZE;
+                let nextAddress = address + winStep;
+                const maxAddress = ((i + WINSIZE) * WIDTH) + j + WINSIZE;
+                for (; address <= maxAddress; address += WIDTH - winStep, nextAddress += WIDTH) {
+                    for (; address <= nextAddress; address += 1) {
+                        const gradT = ((prev[address]) - (curr[address]));
+                        const gradX = ((curr[address - 1]) - (curr[address + 1]));
+                        const gradY = ((curr[address - WIDTH]) - (curr[address + WIDTH]));
+
+                        A2 += gradX * gradX;
+                        A1B2 += gradX * gradY;
+                        B1 += gradY * gradY;
+                        C2 += gradX * gradT;
+                        C1 += gradY * gradT;
+                    }
+                }
+
+                const delta = ((A1B2 * A1B2) - (A2 * B1));
+                let u = 0;
+                let v = 0;
+                if (delta) {
+                    // system is not singular - solving by Kramer method
+                    const deltaX = -((C1 * A1B2) - (C2 * B1));
+                    const deltaY = -((A1B2 * C2) - (A2 * C1));
+                    const Idelta = 8 / delta;
+                    u = deltaX * Idelta;
+                    v = deltaY * Idelta;
+                } else {
+                    // singular system - find optical flow in gradient direction
+                    const Norm = ((A1B2 + A2) * (A1B2 + A2)) + ((B1 + A1B2) * (B1 + A1B2));
+                    if (Norm) {
+                        const IGradNorm = 8 / Norm;
+                        const temp = -(C1 + C2) * IGradNorm;
+                        u = (A1B2 + A2) * temp;
+                        v = (B1 + A1B2) * temp;
+                    }
+                }
+
+                if (-winStep < u && u < winStep && -winStep < v && v < winStep) {
+                    uu += u;
+                    vv += v;
+                    n++;
+                }
+            }
+        }
+
+        uu /= n;
+        vv /= n;
+        this.motionAmount = Math.round(AMOUNT_SCALE * Math.hypot(uu, vv));
+        if (this.motionAmount > THRESHOLD) {
+            // Scratch direction
+            this.motionDirection = (((Math.atan2(vv, uu) * TO_DEGREE) + 270) % 360) - 180;
+        }
+        this.analysisDone = true;
+    }
+
+    getLocalMotion (drawable, state) {
+        if (!this.curr || !this.prev) {
+            state.motionAmount = state.motionDirection = -1;
+            // don't have two frames to analyze yet
+            return;
+        }
+        if (state.motionFrameNumber !== this.frameNumber) {
+            const {
+                _prev: prev,
+                _curr: curr
+            } = this;
+
+            const boundingRect = drawable.getFastBounds();
+            const xmin = Math.floor(boundingRect.left + (WIDTH / 2));
+            const xmax = Math.floor(boundingRect.right + (WIDTH / 2));
+            const ymin = Math.floor((HEIGHT / 2) - boundingRect.top);
+            const ymax = Math.floor((HEIGHT / 2) - boundingRect.bottom);
+
+            let A2 = 0;
+            let A1B2 = 0;
+            let B1 = 0;
+            let C1 = 0;
+            let C2 = 0;
+            let scaleFactor = 0;
+
+            const position = [0, 0, 0];
+
+            for (let i = ymin; i < ymax; i++) {
+                for (let j = xmin; j < xmax; j++) {
+                    position[0] = j - (WIDTH / 2);
+                    position[1] = (HEIGHT / 2) - i;
+                    if (
+                        j > 0 && (j < WIDTH - 1) &&
+                        i > 0 && (i < HEIGHT - 1) &&
+                        drawable.isTouching(position)
+                    ) {
+                        const address = (i * WIDTH) + j;
+                        const gradT = ((prev[address]) - (curr[address]));
+                        const gradX = ((curr[address - 1]) - (curr[address + 1]));
+                        const gradY = ((curr[address - WIDTH]) - (curr[address + WIDTH]));
+
+                        A2 += gradX * gradX;
+                        A1B2 += gradX * gradY;
+                        B1 += gradY * gradY;
+                        C2 += gradX * gradT;
+                        C1 += gradY * gradT;
+                        scaleFactor++;
+                    }
+                }
+            }
+
+            const delta = ((A1B2 * A1B2) - (A2 * B1));
+            let u = 0;
+            let v = 0;
+            if (delta) {
+                // system is not singular - solving by Kramer method
+                const deltaX = -((C1 * A1B2) - (C2 * B1));
+                const deltaY = -((A1B2 * C2) - (A2 * C1));
+                const Idelta = 8 / delta;
+                u = deltaX * Idelta;
+                v = deltaY * Idelta;
+            } else {
+                // singular system - find optical flow in gradient direction
+                const Norm = ((A1B2 + A2) * (A1B2 + A2)) + ((B1 + A1B2) * (B1 + A1B2));
+                if (Norm) {
+                    const IGradNorm = 8 / Norm;
+                    const temp = -(C1 + C2) * IGradNorm;
+                    u = (A1B2 + A2) * temp;
+                    v = (B1 + A1B2) * temp;
+                }
+            }
+
+            let activePixelNum = 0;
+            if (scaleFactor) {
+                // store the area of the sprite in pixels
+                activePixelNum = scaleFactor;
+                scaleFactor /= (2 * WINSIZE * 2 * WINSIZE);
+
+                u = u / scaleFactor;
+                v = v / scaleFactor;
+            }
+
+            state.motionAmount = Math.round(LOCAL_AMOUNT_SCALE * activePixelNum * Math.hypot(u, v));
+            if (state.motionAmount > LOCAL_MAX_AMOUNT) {
+                // clip all magnitudes greater than 100
+                state.motionAmount = LOCAL_MAX_AMOUNT;
+            }
+            if (state.motionAmount > LOCAL_THRESHOLD) {
+                // Scratch direction
+                state.motionDirection = (((Math.atan2(v, u) * TO_DEGREE) + 270) % 360) - 180;
+            }
+            state.motionFrameNumber = this.frameNumber;
+        }
+    }
+}
+
+module.exports = VideoMotion;

src/extensions/scratch3_video_sensing/view.js

@@ -0,0 +1,263 @@
+const WIDTH = 480;
+const HEIGHT = 360;
+const WINSIZE = 8;
+const AMOUNT_SCALE = 100;
+const THRESHOLD = 10;
+
+const OUTPUT = {
+    INPUT: -1,
+    XYT: 0,
+    XYT_CELL: 1,
+    XY: 2,
+    XY_CELL: 3,
+    T: 4,
+    T_CELL: 5,
+    C: 6,
+    AB: 7,
+    UV: 8
+};
+
+class VideoMotionView {
+    constructor (motion, output = OUTPUT.XYT) {
+        this.motion = motion;
+
+        const canvas = this.canvas = document.createElement('canvas');
+        canvas.width = WIDTH;
+        canvas.height = HEIGHT;
+        this.context = canvas.getContext('2d');
+
+        this.output = output;
+        this.buffer = new Uint32Array(WIDTH * HEIGHT);
+    }
+
+    static get OUTPUT () {
+        return OUTPUT;
+    }
+
+    _eachAddress (xStart, yStart, xStop, yStop, fn) {
+        for (let i = yStart; i < yStop; i++) {
+            for (let j = xStart; j < xStop; j++) {
+                const address = (i * WIDTH) + j;
+                fn(address, j, i);
+            }
+        }
+    }
+
+    _eachCell (xStart, yStart, xStop, yStop, xStep, yStep, fn) {
+        const xStep2 = (xStep / 2) | 0;
+        const yStep2 = (yStep / 2) | 0;
+        for (let i = yStart; i < yStop; i += yStep) {
+            for (let j = xStart; j < xStop; j += xStep) {
+                fn(
+                    _fn => this._eachAddress(j - xStep2 - 1, i - yStep2 - 1, j + xStep2, i + yStep2, _fn),
+                    j - xStep2 - 1,
+                    i - yStep2 - 1,
+                    j + xStep2,
+                    i + yStep2
+                );
+            }
+        }
+    }
+
+    _grads (address) {
+        const {curr, prev} = this.motion;
+        const gradX = (curr[address - 1] & 0xff) - (curr[address + 1] & 0xff);
+        const gradY = (curr[address - WIDTH] & 0xff) - (curr[address + WIDTH] & 0xff);
+        const gradT = (prev[address] & 0xff) - (curr[address] & 0xff);
+        return {gradX, gradY, gradT};
+    }
+
+    draw () {
+        if (!(this.motion.prev && this.motion.curr)) {
+            return;
+        }
+
+        const {buffer} = this;
+
+        if (this.output === OUTPUT.INPUT) {
+            const {curr} = this.motion;
+            this._eachAddress(1, 1, WIDTH - 1, HEIGHT - 1, address => {
+                buffer[address] = curr[address];
+            });
+        }
+        if (this.output === OUTPUT.XYT) {
+            this._eachAddress(1, 1, WIDTH - 1, HEIGHT - 1, address => {
+                const {gradX, gradY, gradT} = this._grads(address);
+                const over1 = gradT / 0xcf;
+                buffer[address] =
+                    (0xff << 24) +
+                    (Math.floor((((gradY * over1) & 0xff) + 0xff) / 2) << 8) +
+                    Math.floor((((gradX * over1) & 0xff) + 0xff) / 2);
+            });
+        }
+        if (this.output === OUTPUT.XYT_CELL) {
+            const winStep = (WINSIZE * 2) + 1;
+            const wmax = WIDTH - WINSIZE - 1;
+            const hmax = HEIGHT - WINSIZE - 1;
+
+            this._eachCell(WINSIZE + 1, WINSIZE + 1, wmax, hmax, winStep, winStep, eachAddress => {
+                let C1 = 0;
+                let C2 = 0;
+                let n = 0;
+
+                eachAddress(address => {
+                    const {gradX, gradY, gradT} = this._grads(address);
+                    C2 += (Math.max(Math.min(gradX / 0x0f, 1), -1)) * (gradT / 0xff);
+                    C1 += (Math.max(Math.min(gradY / 0x0f, 1), -1)) * (gradT / 0xff);
+                    n += 1;
+                });
+
+                C1 /= n;
+                C2 /= n;
+                C1 = Math.log(C1 + (1 * Math.sign(C1))) / Math.log(2);
+                C2 = Math.log(C2 + (1 * Math.sign(C2))) / Math.log(2);
+
+                eachAddress(address => {
+                    buffer[address] = (0xff << 24) +
+                        (((((C1 * 0x7f) | 0) + 0x80) << 8) & 0xff00) +
+                        (((((C2 * 0x7f) | 0) + 0x80) << 0) & 0xff);
+                });
+            });
+        }
+        if (this.output === OUTPUT.XY) {
+            this._eachAddress(1, 1, WIDTH - 1, HEIGHT - 1, address => {
+                const {gradX, gradY} = this._grads(address);
+                buffer[address] = (0xff << 24) + (((gradY + 0xff) / 2) << 8) + ((gradX + 0xff) / 2);
+            });
+        }
+        if (this.output === OUTPUT.XY_CELL) {
+            const winStep = (WINSIZE * 2) + 1;
+            const wmax = WIDTH - WINSIZE - 1;
+            const hmax = HEIGHT - WINSIZE - 1;
+
+            this._eachCell(WINSIZE + 1, WINSIZE + 1, wmax, hmax, winStep, winStep, eachAddress => {
+                let C1 = 0;
+                let C2 = 0;
+                let n = 0;
+
+                eachAddress(address => {
+                    const {gradX, gradY} = this._grads(address);
+                    C2 += Math.max(Math.min(gradX / 0x1f, 1), -1);
+                    C1 += Math.max(Math.min(gradY / 0x1f, 1), -1);
+                    n += 1;
+                });
+
+                C1 /= n;
+                C2 /= n;
+                C1 = Math.log(C1 + (1 * Math.sign(C1))) / Math.log(2);
+                C2 = Math.log(C2 + (1 * Math.sign(C2))) / Math.log(2);
+
+                eachAddress(address => {
+                    buffer[address] = (0xff << 24) +
+                        (((((C1 * 0x7f) | 0) + 0x80) << 8) & 0xff00) +
+                        (((((C2 * 0x7f) | 0) + 0x80) << 0) & 0xff);
+                });
+            });
+        } else if (this.output === OUTPUT.T) {
+            this._eachAddress(1, 1, WIDTH - 1, HEIGHT - 1, address => {
+                const {gradT} = this._grads(address);
+                buffer[address] = (0xff << 24) + ((gradT + 0xff) / 2 << 16);
+            });
+        }
+        if (this.output === OUTPUT.T_CELL) {
+            const winStep = (WINSIZE * 2) + 1;
+            const wmax = WIDTH - WINSIZE - 1;
+            const hmax = HEIGHT - WINSIZE - 1;
+
+            this._eachCell(WINSIZE + 1, WINSIZE + 1, wmax, hmax, winStep, winStep, eachAddress => {
+                let T = 0;
+                let n = 0;
+
+                eachAddress(address => {
+                    const {gradT} = this._grads(address);
+                    T += gradT / 0xff;
+                    n += 1;
+                });
+
+                T /= n;
+
+                eachAddress(address => {
+                    buffer[address] = (0xff << 24) +
+                        (((((T * 0x7f) | 0) + 0x80) << 16) & 0xff0000);
+                });
+            });
+        } else if (this.output === OUTPUT.C) {
+            this._eachAddress(1, 1, WIDTH - 1, HEIGHT - 1, address => {
+                const {gradX, gradY, gradT} = this._grads(address);
+                buffer[address] =
+                    (0xff << 24) +
+                    ((gradY * gradT) << 8) +
+                    (gradX * gradT);
+            });
+        } else if (this.output === OUTPUT.AB) {
+            this._eachAddress(1, 1, WIDTH - 1, HEIGHT - 1, address => {
+                const {gradX, gradY} = this._grads(address);
+                buffer[address] =
+                    (0xff << 24) +
+                    ((gradX * gradY) << 16) +
+                    ((gradY * gradY) << 8) +
+                    (gradX * gradX);
+            });
+        } else if (this.output === OUTPUT.UV) {
+            const winStep = (WINSIZE * 2) + 1;
+            const wmax = WIDTH - WINSIZE - 1;
+            const hmax = HEIGHT - WINSIZE - 1;
+
+            this._eachCell(WINSIZE + 1, WINSIZE + 1, wmax, hmax, winStep, winStep, eachAddress => {
+                let A2 = 0;
+                let A1B2 = 0;
+                let B1 = 0;
+                let C2 = 0;
+                let C1 = 0;
+
+                eachAddress(address => {
+                    const {gradX, gradY, gradT} = this._grads(address);
+                    A2 += gradX * gradX;
+                    A1B2 += gradX * gradY;
+                    B1 += gradY * gradY;
+                    C2 += gradX * gradT;
+                    C1 += gradY * gradT;
+                });
+
+                const delta = ((A1B2 * A1B2) - (A2 * B1));
+                let u = 0;
+                let v = 0;
+                if (delta) {
+                    /* system is not singular - solving by Kramer method */
+                    const deltaX = -((C1 * A1B2) - (C2 * B1));
+                    const deltaY = -((A1B2 * C2) - (A2 * C1));
+                    const Idelta = 8 / delta;
+                    u = deltaX * Idelta;
+                    v = deltaY * Idelta;
+                } else {
+                    /* singular system - find optical flow in gradient direction */
+                    const Norm = ((A1B2 + A2) * (A1B2 + A2)) + ((B1 + A1B2) * (B1 + A1B2));
+                    if (Norm) {
+                        const IGradNorm = 8 / Norm;
+                        const temp = -(C1 + C2) * IGradNorm;
+                        u = (A1B2 + A2) * temp;
+                        v = (B1 + A1B2) * temp;
+                    }
+                }
+
+                const inRange = (-winStep < u && u < winStep && -winStep < v && v < winStep);
+                const hypot = Math.hypot(u, v);
+                const amount = AMOUNT_SCALE * hypot;
+                eachAddress(address => {
+                    buffer[address] =
+                        (0xff << 24) +
+                        (inRange && amount > THRESHOLD ?
+                            (((((v / winStep) + 1) / 2 * 0xff) << 8) & 0xff00) +
+                            (((((u / winStep) + 1) / 2 * 0xff) << 0) & 0xff) :
+                            0x8080
+                        );
+                });
+            });
+        }
+
+        const data = new ImageData(new Uint8ClampedArray(this.buffer.buffer), WIDTH, HEIGHT);
+        this.context.putImageData(data, 0, 0);
+    }
+}
+
+module.exports = VideoMotionView;