pygame.transform: Scale, Rotate and Flip Images

pygame.transform makes new Surfaces from old ones: bigger, smaller, rotated or mirrored. Each function returns a new Surface and leaves the original alone.

import pygame

pygame.init()
screen = pygame.display.set_mode((480, 320))
clock = pygame.time.Clock()

bat = pygame.image.load("assets/images/bat.png").convert_alpha()
big = pygame.transform.scale(bat, (96, 96))
mirrored = pygame.transform.flip(bat, True, False)
tilted = pygame.transform.rotate(bat, 30)

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

    screen.fill((40, 34, 60))
    screen.blit(bat, (30, 130))
    screen.blit(big, (110, 105))
    screen.blit(mirrored, (240, 130))
    screen.blit(tilted, (330, 120))
    pygame.display.flip()
    clock.tick(60)

pygame.quit()

From the left: the original, scaled to 96 by 96, flipped horizontally, and rotated 30 degrees.

The functions

Transforming is slow compared with blitting. Make the copies you need once, before the loop (a left-facing and a right-facing player, say), and only transform inside the loop when the result keeps changing, like a turning ship.

Rotating around the center

A rotated image is a bigger rectangle than the original (its corners stick out), so blitting it at the same top-left corner makes it wobble. Place it by the center instead, and always rotate the original:

import pygame

pygame.init()
screen = pygame.display.set_mode((480, 320))
clock = pygame.time.Clock()

original = pygame.image.load("assets/images/ship.png").convert_alpha()
center = (240, 160)
angle = 0
running = True

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

    keys = pygame.key.get_pressed()
    angle += (keys[pygame.K_LEFT] - keys[pygame.K_RIGHT]) * 4

    rotated = pygame.transform.rotate(original, angle)
    rect = rotated.get_rect(center=center)

    screen.fill((10, 12, 28))
    screen.blit(rotated, rect)
    pygame.draw.rect(screen, (80, 80, 110), rect, width=1)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()

Press Play, click the game, and turn the ship with Left and Right. The outline shows the rotated image's Rect growing and shrinking while the ship stays put.

If instead you write ship = pygame.transform.rotate(ship, 4) every frame, each rotation smears the pixels a little more and adds empty border, so after a few seconds the image is blurry and huge.

Facing left and right

Most character art faces one way. Flip it once and pick the copy by direction:

right = pygame.image.load("player.png").convert_alpha()
left = pygame.transform.flip(right, True, False)

image = left if direction < 0 else right
screen.blit(image, rect)

Pixel art

scale copies pixels without smoothing, which keeps pixel art crisp when you make it two or three times bigger. Use whole number factors (scale_by(img, 3)); a scale such as 1.5 makes some pixels wider than others. smoothscale and rotozoom blur, which suits photos and smooth art but softens pixel art.