import pygame,sys

pygame.init()

window_size = (800,600)
sc = pygame.display.set_mode(window_size)
pygame.display.set_caption('反弹的小球')
ball_xy = [400,300]
ball_r = 20
ball_speed = [5,5]

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

    ball_xy[0] += ball_speed[0]
    ball_xy[1] += ball_speed[1]

    if ball_xy[0] - ball_r < 0 or ball_xy[0] + ball_r > window_size[0]:
        ball_speed[0] = -ball_speed[0]
    if ball_xy[1] - ball_r < 0 or ball_xy[1] + ball_r > window_size[1]:
        ball_speed[1] = -ball_speed[1]

    sc.fill('white')

    pygame.draw.circle(sc,'black',ball_xy,ball_r)
    pygame.display.flip()

    pygame.time.Clock().tick(60)

pygame.quit()
sys.exit()