void draw(){
          rotate( 15 * pos );
          
          fill(0, 10);
          rect(0, 0, width, height);
          
          fill(255, 0, 0);
          rect( pos, pos, 20, 20 );
          
          pos += dir;
          
          if ( pos > width ) {
                  dir = -1;
          } else if ( pos + 20 < 0 ) {
                  dir = 1;
          }
  }
  </script>
  <!--