不显示形状的递归分形Pygame

Question

我尝试在Pygame中使用递归来编写Sierpinski地毯。代码运行良好，问题是屏幕只显示一个递归调用，而不是代码所示的8个。我很确定它会经历那些递归调用，因为我设置了时间延迟，实际上完成绘图需要时间。 我的问题是：每次有递归调用时都会显示形状的代码中缺少什么？谢谢，代码如下：

    import pygame

    white = (255, 255, 255)

    black = (0, 0, 0)

    def recursiveSquare((x, y), side, color, level):

         if level:
             (x2, y2) = (x + side, y)
             (x3, y3) = (x, y + side)
             (x4, y4) = (x + side, y + side)

             pygame.draw.polygon(screen, color, [(x, y), (x2, y2), \
                                          (x4, y4), (x3, y3)])

             recursiveSquare(((side * 0.3), (side * 0.3)), \
                   (side * 0.3), color, level - 1)
             recursiveSquare(((side * 0.3) * 4.5, (side * 0.3)), \
                   (side * 0.3), color, level - 1)
             recursiveSquare(((side * 0.3) * 8, (side * 0.3)), \
                   (side * 0.3), color, level - 1)
             recursiveSquare(((side * 0.3), (side * 0.3) * 4.5), \
                   (side * 0.3), color, level - 1)
             recursiveSquare(((side * 0.3) * 8, (side * 0.3) * 4.5),\
                   (side * 0.3), color, level - 1)
             recursiveSquare(((side * 0.3), (side * 0.3) * 8), \
                   (side * 0.3), color, level - 1)
             recursiveSquare(((side * 0.3) * 4.5, (side * 0.3) * 8),\
                   (side * 0.3), color, level - 1)
             recursiveSquare(((side * 0.3) * 8, (side * 0.3) * 8),\
                   (side * 0.3), color, level - 1)

    pygame.init()

    size = [600, 600]
    screen = pygame.display.set_mode(size)

    pygame.display.set_caption("Sierpinski Carpet")

    done = False

    clock = pygame.time.Clock()

    while not done:

         for event in pygame.event.get():

              if event.type == pygame.QUIT:

                   done = True

         screen.fill(white)

         level = 3
         recursiveSquare((200, 200), 200, negro, level)

         pygame.display.flip()

         clock.tick(20)

    pygame.quit()
    quit()