var x, y : int
x := 1
y:=1

drawline (0, 0, 0, maxy, 2)
drawline (0, maxy, maxx, maxy, 2)
drawline (maxx, maxy, maxx, 0, 2)

loop



    drawline (x * 2, maxy - x * 2, maxx - x * 2, maxy - x * 2, 2)
    drawline (maxx - x * 2, maxy - x * 2, maxx - x * 2, x * 2, 2)
    drawline (maxx - x * 2, x * 2, x * 2, x * 2, 2)
    drawline (x * 2, x * 2, x * 2, maxy - x * 2, 2)
    x := x + 2
    
    delay (500)
end loop