mengerSponge2d.pde

void Menger(PVector centerPosition, float sideWidth)
{
  rect(centerPosition.x - sideWidth / 6, centerPosition.y - sideWidth / 6,
       sideWidth/3, sideWidth/3);
  if(sideWidth < 3) return;
  for(int i=-1; i<2; i++)
  {
    for(int j=-1; j<2; j++)
    {
      if(i==0 && j==0) continue;
      Menger(
        new PVector(centerPosition.x + j * sideWidth / 3,
                    centerPosition.y + i * sideWidth / 3),
        sideWidth / 3
      );
    }
  }
}

void setup()
{
  size(800, 800);
  background(0);
  fill(255);
  noStroke();
  rect(0, 0, width, height);
  fill(100);
  Menger(new PVector(width/2, height/2), width);
}