使用pygame移动矩形会一直闪烁

import pygame

# 初始化pygame
pygame.init()

# 设置屏幕尺寸
screen_width = 800
screen_height = 600
screen = pygame.display.set_mode((screen_width, screen_height))

# 设置矩形初始位置和速度
rect_x = 0
rect_y = 0
rect_speed = 5

# 游戏主循环
running = True
while running:
    # 处理事件
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    # 移动矩形
    rect_x += rect_speed
    rect_y += rect_speed

    # 清空屏幕
    screen.fill((0, 0, 0))

    # 绘制矩形
    pygame.draw.rect(screen, (255, 255, 255), (rect_x, rect_y, 50, 50))

    # 更新屏幕
    pygame.display.flip()

    # 控制帧率
    pygame.time.Clock().tick(60)

# 退出游戏
pygame.quit()