let previousPixels;

​

let thresholdAmount = 50;

let leftCounter = 0;

let rightCounter = 1;

​

function setup() {

  createCanvas(640, 360);

  capture = createCapture(VIDEO);

  capture.size(640, 360);

  capture.hide();

  pixelDensity(1);

  noStroke();

  fill(0);

}

​

function copyImage(src, dst) {

  let n = src.length;

  if (!dst || dst.length != n) dst = new src.constructor(n);

  while (n--) dst[n] = src[n];

  return dst;

}

​

function draw() {

  background(243);

  frameDifference();

}

​

function frameDifference() {

  capture.loadPixels();

  let total = 0;

  if (capture.pixels.length > 0) {

    // don't forget this!

    if (!previousPixels) {

      previousPixels = copyImage(capture.pixels, previousPixels);

    } else {

      let t = thresholdAmount * 3; // 3 for r, g, b

      for (let y = 0; y < capture.height; y++) {

        for (let x = 0; x < capture.width; x++) {

          let index = 4 * (width - 1 - x + y * width);

          // calculate the differences

          let rdiff = Math.abs(

            capture.pixels[index + 0] - previousPixels[index + 0]

          );

          let gdiff = Math.abs(

            capture.pixels[index + 1] - previousPixels[index + 1]

          );

          let bdiff = Math.abs(

            capture.pixels[index + 2] - previousPixels[index + 2]

          );

          // copy the current pixels to previousPixels

          previousPixels[index + 0] = capture.pixels[index + 0];

          previousPixels[index + 1] = capture.pixels[index + 1];

          previousPixels[index + 2] = capture.pixels[index + 2];

          let diffs = rdiff + gdiff + bdiff;

          let output = 0;

          if (diffs > t) {

            output = 255;

            if (x < width / 2) {

              leftCounter++;

            } else {

              rightCounter++;

            }

          }

          capture.pixels[index] = output;

          capture.pixels[index + 1] = output;

          capture.pixels[index + 2] = output;

        }

      }

    } // finished processing one frame

    if (mouseIsPressed) capture.updatePixels();

    push();

    translate(width, 0);

    scale(-1, 1);

    image(capture, 0, 0, 640, 480);

    pop();

    print("left = " + leftCounter + " right = " + rightCounter);

    if (leftCounter > 10 && rightCounter > 10) {

      if (leftCounter > rightCounter) {

        ellipse(width / 4, height / 2, 100);

      } else {

        ellipse((3 * width) / 4, height / 2, 100);

      }

    }

    leftCounter = 0;

    rightCounter = 0;

  }

}

​