Pygame问题:我的玩家图像不能随着滚动移动

import pygame

# 初始化Pygame
pygame.init()

# 创建屏幕
screen = pygame.display.set_mode((800, 600))

# 加载玩家图像
player_image = pygame.image.load("player.png").convert_alpha()

# 创建玩家对象
player_rect = player_image.get_rect()
player_rect.x = 400
player_rect.y = 300

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

    # 检测按键状态
    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT]:
        player_rect.x -= 5
    if keys[pygame.K_RIGHT]:
        player_rect.x += 5
    if keys[pygame.K_UP]:
        player_rect.y -= 5
    if keys[pygame.K_DOWN]:
        player_rect.y += 5

    # 绘制背景
    screen.fill((255, 255, 255))

    # 绘制玩家图像
    screen.blit(player_image, player_rect)

    # 更新屏幕
    pygame.display.flip()

# 退出游戏
pygame.quit()