Bounce

Lesson 30 of 40 in Coddy's Make Games with Pygame course.

A ball bounces off the top and bottom edges. At the moment it touches one, flip the sign of vy: moving down becomes moving up by the same amount.

if ball.top <= 0 or ball.bottom >= 400:
    vy = -vy

Test with <= and >=, not ==. The ball moves 4 pixels a frame, so its bottom goes 395, 399, 403 and is never exactly 400.

The left and right edges are where points are scored, so the ball does not bounce there. For now it flies out.

Challenge

Easy

After moving the ball, flip vy when the ball's top is at 0 or less, or its bottom at 400 or more.

Try it yourself

import pygame

pygame.init()
screen = pygame.display.set_mode((600, 400))
pygame.display.set_caption("Pong")
clock = pygame.time.Clock()

ball = pygame.Rect(293, 193, 14, 14)
vx, vy = 5, 4

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

    ball.x += vx
    ball.y += vy

    screen.fill((30, 30, 46))
    pygame.draw.rect(screen, (255, 196, 0), ball)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()