​

function setup() {

  background (220);

  let pink = color(255, 102, 204);

  loadPixels();

  let d = pixelDensity();

  // let var = (x + y * width)*4; THIS IS THE INDEX OF PIXELS v

  let halfImage = 4 * (width * d) * ((height / 2) * d);

  for (let i = 0; i < halfImage; i += 4) { // each pixel made up of 4 positions (r, g, b, a), so it skips over 4 to skip over 1 pixel

    // in this case (r, g, b, a) = (0, 1, 2, 3)

    pixels[i + 0] = red(pink); // so 0 = r

    pixels[i + 1] = green(pink); // so 1 = g

    pixels[i + 2] = blue(pink); // so 2 = b

    pixels[i + 3] = blue(pink); // so 3 = a

// TO CLARIFY:

// red = pixels[index+0];

// green = pixels[index+1];

// blue = pixels[index+2];

// alpha = pixels[index+3];

  }

  updatePixels();

}