相机在pygame中不能移动

import pygame

# 初始化pygame
pygame.init()

# 设置游戏窗口大小
screen_width = 800
screen_height = 600
screen = pygame.display.set_mode((screen_width, screen_height))

# 定义相机对象
class Camera:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def move(self, dx, dy):
        self.x += dx
        self.y += dy

# 创建相机对象
camera = Camera(0, 0)

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

    # 获取玩家输入
    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT]:
        camera.move(-1, 0)
    if keys[pygame.K_RIGHT]:
        camera.move(1, 0)
    if keys[pygame.K_UP]:
        camera.move(0, -1)
    if keys[pygame.K_DOWN]:
        camera.move(0, 1)

    # 绘制对象
    # 根据相机的位置调整绘制对象的坐标
    object_x = 100 - camera.x
    object_y = 100 - camera.y
    pygame.draw.rect(screen, (255, 0, 0), pygame.Rect(object_x, object_y, 50, 50))

    # 更新屏幕
    pygame.display.flip()

# 退出游戏
pygame.quit()