如何在pygame中改变圆圈的方向当撞到“墙”时？

import pygame
import sys

# 初始化pygame
pygame.init()

# 定义窗口尺寸和颜色
width, height = 800, 600
bg_color = (255, 255, 255)

# 定义圆圈初始位置和速度
circle_pos = [width // 2, height // 2]
circle_speed = [2, 2]

# 定义墙体边界
wall_left = 100
wall_right = width - 100
wall_top = 100
wall_bottom = height - 100

# 创建窗口
screen = pygame.display.set_mode((width, height))
pygame.display.set_caption("Move Circle")

# 游戏主循环
while True:
    # 填充背景色
    screen.fill(bg_color)

    # 监听事件
    for event in pygame.event.get():
        # 退出事件
        if event.type == pygame.QUIT:
            sys.exit()

    # 更新圆圈位置
    circle_pos[0] += circle_speed[0]
    circle_pos[1] += circle_speed[1]

    # 检测碰撞
    if circle_pos[0] < wall_left or circle_pos[0] > wall_right:
        circle_speed[0] = -circle_speed[0]  # 改变水平方向
    if circle_pos[1] < wall_top or circle_pos[1] > wall_bottom:
        circle_speed[1] = -circle_speed[1]  # 改变垂直方向

    # 绘制圆圈
    pygame.draw.circle(screen, (0, 0, 255), circle_pos, 50)

    # 绘制墙体
    pygame.draw.rect(screen, (0, 0, 0), (wall_left, wall_top, wall_right - wall_left, wall_bottom - wall_top), 2)

    # 更新显示
    pygame.display.flip()