Vector2

Part of the The Game Loop section of Coddy's Pygame journey. Lesson 20 of 32.

A position is two numbers, and so is a velocity: the speed in x and the speed in y. pygame.Vector2 keeps two numbers together and does arithmetic on both at once:

pos = pygame.Vector2(240, 180)
vel = pygame.Vector2(150, 90)

pos += vel * dt

vel * dt multiplies both parts and pos += ... adds both parts, so one line moves the ball 150 pixels a second to the right and 90 down. pos.x and pos.y read or change one part, and pygame.draw.circle takes a Vector2 as its centre.

To bounce off a wall, turn one part of the velocity around. Past a side, vel.x = -vel.x sends the ball back and leaves its up and down speed alone:

if pos.x < 16 or pos.x > 464:
    vel.x = -vel.x

The ball's radius is 16, so at 16 and 464 its edge touches the window's sides.

Challenge

Medium

Replace x, y with pos = pygame.Vector2(240, 180) and vx, vy with vel = pygame.Vector2(150, 90).
Move the ball with pos += vel * dt and draw it at pos.
Turn vel.x around when pos.x is below 16 or above 464, and vel.y when pos.y is below 16 or above 344.

Try it yourself

import pygame

pygame.init()
screen = pygame.display.set_mode((480, 360))
pygame.display.set_caption("Bounce")
clock = pygame.time.Clock()

x, y = 240, 180
vx, vy = 150, 90
dt = 0

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

    x += vx * dt
    y += vy * dt

    screen.fill((30, 30, 46))
    pygame.draw.circle(screen, (80, 160, 255), (x, y), 16)
    pygame.display.flip()
    dt = clock.tick(60) / 1000

pygame.quit()