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diff-cam-engine.js
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diff-cam-engine.js
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var DiffCamEngine = (function() {
var stream; // stream obtained from webcam
var video; // shows stream
var captureCanvas; // internal canvas for capturing full images from video
var captureContext; // context for capture canvas
var diffCanvas; // internal canvas for diffing downscaled captures
var diffContext; // context for diff canvas
var motionCanvas; // receives processed diff images
var motionContext; // context for motion canvas
var initSuccessCallback; // called when init succeeds
var initErrorCallback; // called when init fails
var startCompleteCallback; // called when start is complete
var captureCallback; // called when an image has been captured and diffed
var captureInterval; // interval for continuous captures
var captureIntervalTime; // time between captures, in ms
var captureWidth; // full captured image width
var captureHeight; // full captured image height
var diffWidth; // downscaled width for diff/motion
var diffHeight; // downscaled height for diff/motion
var isReadyToDiff; // has a previous capture been made to diff against?
var pixelDiffThreshold; // min for a pixel to be considered significant
var scoreThreshold; // min for an image to be considered significant
var includeMotionBox; // flag to calculate and draw motion bounding box
var includeMotionPixels; // flag to create object denoting pixels with motion
function init(options) {
// sanity check
if (!options) {
throw 'No options object provided';
}
// incoming options with defaults
video = options.video || document.createElement('video');
motionCanvas = options.motionCanvas || document.createElement('canvas');
captureIntervalTime = options.captureIntervalTime || 100;
captureWidth = options.captureWidth || 640;
captureHeight = options.captureHeight || 480;
diffWidth = options.diffWidth || 64;
diffHeight = options.diffHeight || 48;
pixelDiffThreshold = options.pixelDiffThreshold || 32;
scoreThreshold = options.scoreThreshold || 16;
includeMotionBox = options.includeMotionBox || false;
includeMotionPixels = options.includeMotionPixels || false;
// callbacks
initSuccessCallback = options.initSuccessCallback || function() {};
initErrorCallback = options.initErrorCallback || function() {};
startCompleteCallback = options.startCompleteCallback || function() {};
captureCallback = options.captureCallback || function() {};
// non-configurable
captureCanvas = document.createElement('canvas');
diffCanvas = document.createElement('canvas');
isReadyToDiff = false;
// prep video
video.autoplay = true;
// prep capture canvas
captureCanvas.width = captureWidth;
captureCanvas.height = captureHeight;
captureContext = captureCanvas.getContext('2d');
// prep diff canvas
diffCanvas.width = diffWidth;
diffCanvas.height = diffHeight;
diffContext = diffCanvas.getContext('2d');
// prep motion canvas
motionCanvas.width = diffWidth;
motionCanvas.height = diffHeight;
motionContext = motionCanvas.getContext('2d');
requestWebcam();
}
function requestWebcam() {
var constraints = {
audio: false,
video: { width: captureWidth, height: captureHeight }
};
navigator.mediaDevices.getUserMedia(constraints)
.then(initSuccess)
.catch(initError);
}
function initSuccess(requestedStream) {
stream = requestedStream;
initSuccessCallback();
}
function initError(error) {
console.log(error);
initErrorCallback();
}
function start() {
if (!stream) {
throw 'Cannot start after init fail';
}
// streaming takes a moment to start
video.addEventListener('canplay', startComplete);
video.srcObject = stream;
}
function startComplete() {
video.removeEventListener('canplay', startComplete);
captureInterval = setInterval(capture, captureIntervalTime);
startCompleteCallback();
}
function stop() {
clearInterval(captureInterval);
video.src = '';
motionContext.clearRect(0, 0, diffWidth, diffHeight);
isReadyToDiff = false;
}
function capture() {
// save a full-sized copy of capture
captureContext.drawImage(video, 0, 0, captureWidth, captureHeight);
var captureImageData = captureContext.getImageData(0, 0, captureWidth, captureHeight);
// diff current capture over previous capture, leftover from last time
diffContext.globalCompositeOperation = 'difference';
diffContext.drawImage(video, 0, 0, diffWidth, diffHeight);
var diffImageData = diffContext.getImageData(0, 0, diffWidth, diffHeight);
if (isReadyToDiff) {
var diff = processDiff(diffImageData);
motionContext.putImageData(diffImageData, 0, 0);
if (diff.motionBox) {
motionContext.strokeStyle = '#fff';
motionContext.strokeRect(
diff.motionBox.x.min + 0.5,
diff.motionBox.y.min + 0.5,
diff.motionBox.x.max - diff.motionBox.x.min,
diff.motionBox.y.max - diff.motionBox.y.min
);
}
captureCallback({
imageData: captureImageData,
score: diff.score,
hasMotion: diff.score >= scoreThreshold,
motionBox: diff.motionBox,
motionPixels: diff.motionPixels,
getURL: function() {
return getCaptureUrl(this.imageData);
},
checkMotionPixel: function(x, y) {
return checkMotionPixel(this.motionPixels, x, y)
}
});
}
// draw current capture normally over diff, ready for next time
diffContext.globalCompositeOperation = 'source-over';
diffContext.drawImage(video, 0, 0, diffWidth, diffHeight);
isReadyToDiff = true;
}
function processDiff(diffImageData) {
var rgba = diffImageData.data;
// pixel adjustments are done by reference directly on diffImageData
var score = 0;
var motionPixels = includeMotionPixels ? [] : undefined;
var motionBox = undefined;
for (var i = 0; i < rgba.length; i += 4) {
var pixelDiff = rgba[i] * 0.3 + rgba[i + 1] * 0.6 + rgba[i + 2] * 0.1;
var normalized = Math.min(255, pixelDiff * (255 / pixelDiffThreshold));
rgba[i] = 0;
rgba[i + 1] = normalized;
rgba[i + 2] = 0;
if (pixelDiff >= pixelDiffThreshold) {
score++;
coords = calculateCoordinates(i / 4);
if (includeMotionBox) {
motionBox = calculateMotionBox(motionBox, coords.x, coords.y);
}
if (includeMotionPixels) {
motionPixels = calculateMotionPixels(motionPixels, coords.x, coords.y, pixelDiff);
}
}
}
return {
score: score,
motionBox: score > scoreThreshold ? motionBox : undefined,
motionPixels: motionPixels
};
}
function calculateCoordinates(pixelIndex) {
return {
x: pixelIndex % diffWidth,
y: Math.floor(pixelIndex / diffWidth)
};
}
function calculateMotionBox(currentMotionBox, x, y) {
// init motion box on demand
var motionBox = currentMotionBox || {
x: { min: coords.x, max: x },
y: { min: coords.y, max: y }
};
motionBox.x.min = Math.min(motionBox.x.min, x);
motionBox.x.max = Math.max(motionBox.x.max, x);
motionBox.y.min = Math.min(motionBox.y.min, y);
motionBox.y.max = Math.max(motionBox.y.max, y);
return motionBox;
}
function calculateMotionPixels(motionPixels, x, y, pixelDiff) {
motionPixels[x] = motionPixels[x] || [];
motionPixels[x][y] = true;
return motionPixels;
}
function getCaptureUrl(captureImageData) {
// may as well borrow captureCanvas
captureContext.putImageData(captureImageData, 0, 0);
return captureCanvas.toDataURL();
}
function checkMotionPixel(motionPixels, x, y) {
return motionPixels && motionPixels[x] && motionPixels[x][y];
}
function getPixelDiffThreshold() {
return pixelDiffThreshold;
}
function setPixelDiffThreshold(val) {
pixelDiffThreshold = val;
}
function getScoreThreshold() {
return scoreThreshold;
}
function setScoreThreshold(val) {
scoreThreshold = val;
}
return {
// public getters/setters
getPixelDiffThreshold: getPixelDiffThreshold,
setPixelDiffThreshold: setPixelDiffThreshold,
getScoreThreshold: getScoreThreshold,
setScoreThreshold: setScoreThreshold,
// public functions
init: init,
start: start,
stop: stop
};
})();