Spin from the Original

Part of the Sprites and Images section of Coddy's Pygame journey. Lesson 9 of 36.

A spike ball that spins all the time turns a little every frame. There is a tempting way to write it, and it breaks:

ball = pygame.transform.rotate(ball, 2)  # wrong

Each frame turns the last turned picture. Every rotation adds a see-through border, so the Surface grows about 3 percent a frame: twice the size after half a second, nearly 1,800 pixels wide after two. The pixels also smear a bit more with each turn. The game soon slows to a crawl.

Keep the original and the angle instead, and make the turned picture from the original every frame:

angle += 2
spun = pygame.transform.rotate(ball, angle)
screen.blit(spun, spun.get_rect(center=(320, 240)))

Now spun is one rotation away from the file, whatever the angle: never bigger than 67 by 67 pixels and never blurrier than one turn. The same rule holds for every transform: work from the original, not from the last copy.

Challenge

Medium

Before the loop, make angle = 0.
Each frame, add 2 to angle.
Rotate the original ball by angle and draw the result with its centre at (320, 240). Never change ball itself.

Try it yourself

import pygame

pygame.init()
screen = pygame.display.set_mode((640, 480))
pygame.display.set_caption("Spinning Spikes")
clock = pygame.time.Clock()

ball = pygame.image.load("assets/images/spike_ball.png").convert_alpha()

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

    screen.fill((20, 22, 40))
    screen.blit(ball, ball.get_rect(center=(320, 240)))
    pygame.display.flip()
    clock.tick(60)

pygame.quit()