const pixSRP = new Float32Array(65536);

const pixRP = new Float32Array(65536);

​

const rpFlips = new Float32Array(65536);

const srpFlips = new Float32Array(65536);

​

function setup() {

  createCanvas(512, 512);

  background(0);

  randomSeed(1234567); //Random number seed value

  // Random sign flip array

  for (let i = 0; i < rpFlips.length; i++) {

    rpFlips[i] = random(-1, 1) < 0 ? -1 : 1;

  }

  // Sub-Random sign flips

  let r = 0;

  let rAdd = 0xb55988be; // additive subrandom constant

  for (let i = 0; i < srpFlips.length; i++) {

    r += rAdd;

    r &= 0xffffffff;

    srpFlips[i] = (r & 0x80000000) === 0 ? -1 : 1;

    if (srpFlips[i] > 0)

      set(256 + (i & 255), int(i / 256), color(255, 255, 255));

  }

  updatePixels();

}

​

function draw() {

  fill(0);

  square(0, 0, 255);

  fill(255);

  let x = constrain(mouseX, 0, 230);

  let y = constrain(mouseY, 0, 230);

  circle(x, y, 50);

  //loadPixels();

  getPix();

  for (let i = 0; i < pix.length; i++) {

    pixRP[i] = rpFlips[i] * pix[i];

    pixSRP[i] = srpFlips[i] * pix[i];

  }

  whtN(pixRP); //Random Projection

  whtN(pixSRP); //SubRandom Projection

  setImage(0, 0, pix);

  setImage(0, 256, pixRP);

  setImage(256, 256, pixSRP);

  updatePixels();

}

function getPix() {

  for (let y = 0, idx = 0; y < 256; y++) {

    for (let x = 0; x < 256; x++) {

      let c = get(x, y);

      pix[idx] = (red(c) + green(c) + blue(c)) * 0.3333 - 127.5;

      idx++;

    }

  }

}

function setImage(x, y, pixArray) {

  for (let yi = 0, idx = 0; yi < 256; yi++) {

    for (let xi = 0; xi < 256; xi++) {

      let c = constrain(pixArray[idx] + 127.5, 0, 255);

      idx++;

      set(x + xi, y + yi, color(c, c, c));

    }

  }

}

​

// Fast Walsh Hadamard transform, Normalized.

// Scaled so that vector length is unchanged.

function whtN(vec) {

  const n = vec.length;

  let hs = 1;

  while (hs < n) {

    let i = 0;

    while (i < n) {

      const j = i + hs;

      while (i < j) {

        var a = vec[i];

        var b = vec[i + hs];

        vec[i] = a + b;

        vec[i + hs] = a - b;

        i += 1;

      }

      i += hs;

    }

    hs += hs;

  }

  const sc = 1.0 / sqrt(n);

  for (let i = 0; i < n; i++) {

    vec[i] *= sc;

  }

}

​