如何在pygame中让一个矩形一个接一个地出现？

import pygame
import time

pygame.init()

# 设置窗口大小和背景颜色
width, height = 800, 600
bg_color = (255, 255, 255)

screen = pygame.display.set_mode((width, height))
pygame.display.set_caption("Rectangles")

clock = pygame.time.Clock()

rectangles = []  # 存储矩形的列表

def draw_rectangles():
    for rect in rectangles:
        pygame.draw.rect(screen, (0, 0, 0), rect)

def game_loop():
    running = True
    while running:
        screen.fill(bg_color)
        
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                running = False
        
        # 创建一个矩形并添加到列表中
        rect = pygame.Rect(100, 100, 50, 50)
        rectangles.append(rect)
        
        draw_rectangles()
        pygame.display.flip()
        
        # 延迟一段时间
        time.sleep(0.5)
        
        # 移除最早创建的矩形
        rectangles.pop(0)
        
        clock.tick(60)

    pygame.quit()

game_loop()