var mx, my, click, col : int

View.Set ("offscreenonly")

loop
    randint (col, 10, 13)
    mousewhere (mx, my, click)
    if click = 1 then
        drawline (0, 0, mx, my, col)
        drawline (0, maxy, mx, my, col)
        drawline (maxx, 0, mx, my, col)
        drawline (maxx, maxy, mx, my, col)
    end if
    View.Update
end loop