Pygame:我如何解决PyGame上随机生成的平台在屏幕的错误部分以错误的方向移动的问题？

import pygame
import random

# 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))

# 平台类
class Platform(pygame.sprite.Sprite):
    def __init__(self):
        super().__init__()
        self.image = pygame.Surface((100, 20))
        self.image.fill((255, 255, 255))
        self.rect = self.image.get_rect()
        self.rect.x = random.randint(0, screen_width - self.rect.width)
        self.rect.y = random.randint(0, screen_height - self.rect.height)
        self.direction = random.choice([-1, 1])  # 随机选择移动方向

    def update(self):
        self.rect.x += self.direction
        if self.rect.left < 0 and self.direction == -1:
            self.direction = 1
        elif self.rect.right > screen_width and self.direction == 1:
            self.direction = -1

# 创建平台组
platforms = pygame.sprite.Group()

# 生成平台
for _ in range(10):
    platform = Platform()
    platforms.add(platform)

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

    # 更新平台位置
    platforms.update()

    # 绘制屏幕
    screen.fill((0, 0, 0))
    platforms.draw(screen)
    pygame.display.flip()

# 退出游戏
pygame.quit()