createCanvas(320, 240);

  pixelDensity(1);

}

​

function draw() {

  background(255);

  loadPixels();

  for (var y=0; y< height; y++) {

    for (var x=0; x< width; x++) {

      var index= (x+(y*width))* 4; // y is multiplied by width, then x is added for example, pixel1= 0,0 then pixel2=1,0

      pixels[index+0] = x;

          pixels[index+1] = random(255);

          pixels[index+2] = y;

          pixels[index+3] = random(255);

    }

  }

  updatePixels();

}