content: sub main()
      screen  = createObject("roScreen")
      port    = createObject("roMessagePort")
      timer   = createObject("roTimeSpan")
  
      screen.setMessagePort(port)
  
      width  = 1080
      height = 1080
      
      black   = &h000000FF
      white   = &hFFFFFFFF
       
      n = 16
      w = 60      
      h = 60      
      gap = 7.5   
  
      ix = (screen.getWidth()  - width)  * 0.5
      iy = (screen.getHeight() - height) * 0.5
      
      while true
          ms = timer.totalMilliseconds()
          if ms mod 1000 = 0
              for i = 0 to n
                  for j = 0 to n
                      x = ix + i * (w + gap)
                      y = iy + j * (h + gap)
                      screen.drawRect(x, y,  w, h, white)
                      if rnd(0) > 0.5
                          screen.drawRect(x + 10, y + 10,  w - 20, h - 20, black)
                      end if
                  end for
              end for     
          end if
          screen.finish()
      end while
  end sub