Wrap Around the Screen

Part of the The Game Loop section of Coddy's Pygame journey. Lesson 22 of 32.

In many space games, a ship or a rock that leaves one side of the screen comes back on the other. This is wrapping. The rock here drifts up and to the right, and after a few seconds it is gone for good.

Test each edge after moving. The rock's radius is 20, so let it get fully out of sight before it jumps: past 480 + 20 on the right, it comes back at -20, out of sight past the left edge, and slides in.

if pos.x > 500:
    pos.x = -20
if pos.x < -20:
    pos.x = 500

The same goes for y with the height: past 380 at the bottom it comes back at -20, and above -20 it comes back at 380.

Only the position jumps. The velocity stays, so the rock keeps drifting the same way after it wraps.

Challenge

Easy

After pos += vel * dt, wrap the rock:

Above 500, pos.x becomes -20; below -20, it becomes 500.
Above 380, pos.y becomes -20; below -20, it becomes 380.

Try it yourself

import pygame

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

pos = pygame.Vector2(240, 180)
vel = pygame.Vector2(120, -70)
dt = 0

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

    pos += vel * dt

    screen.fill((20, 20, 34))
    pygame.draw.circle(screen, (150, 150, 160), pos, 20)
    pygame.display.flip()
    dt = clock.tick(60) / 1000

pygame.quit()