PyGame のボール バウンス シナリオでボールが上部の壁を貫通する問題を解決するにはどうすればよいですか?

<code class="python">import pygame

# Initialize PyGame
pygame.init()

# Set screen dimensions
screenWidth = 1200
screenHeight = 700

# Create the game window
window = pygame.display.set_mode((screenWidth, screenHeight))
pygame.display.set_caption('Atari Breakout')

# Define the ball's initial position and radius
box = Circle(600, 300, 10)

# Define the boundary bounds
bounds = pygame.Rect(450, 200, 300, 200)

# Main game loop
run = True
clock = pygame.time.Clock()

while run:

    # Set the frame rate
    clock.tick(60)

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    # Check for key presses (spacebar to start the ball's movement)
    keys = pygame.key.get_pressed()
    if keys[pygame.K_SPACE]:
        start = True

    # Move the ball and adjust its velocity when it hits the boundaries
    if start:
        box.y -= box.vel_y
        box.x += box.vel_x

        if box.x - box.radius < bounds.left or box.x + box.radius > bounds.right:
            box.vel_x *= -1
        if box.y - box.radius < bounds.top or box.y + box.radius > bounds.bottom:
            box.vel_y *= -1

    # Render the game window
    window.fill((0, 0, 0))
    pygame.draw.rect(window, (255, 0, 0), bounds, 1)
    pygame.draw.circle(window, (44, 176, 55), (box.x, box.y), box.radius)
    pygame.display.update()

# Quit PyGame
pygame.quit()</code>