如何旋转图像而不丢失像素数据？ （Pygame）

Question

Here's my code (Python 3.5):

import sys
import pygame
pygame.init()

screen_width = 640
screen_height = 480
screen = pygame.display.set_mode((screen_width, screen_height))
running = True

class Actor:

    def __init__(self, x, y, w, h):
        self.x = x
        self.y = y
        self.w = w
        self.h = h
        self.surface = pygame.image.load("GFX/player.bmp")

    def draw(self):
        screen.blit(self.surface, (self.x, self.y))

class Player(Actor):

    def __init__(self):
        Actor.__init__(self, 0, 0, 32, 32)
        self.directions = [False, False, False, False]
        self.speed = 0.1

    def update(self):
        if self.directions[0]:
            self.y -= self.speed
        if self.directions[1]:
            self.y += self.speed
        if self.directions[2]:
            self.x -= self.speed
        if self.directions[3]:
            self.x += self.speed

player = Player()

def rot_center(image, angle):
    orig_rect = image.get_rect()
    rot_image = pygame.transform.rotate(image, angle)
    rot_rect = orig_rect.copy()
    rot_rect.center = rot_image.get_rect().center
    rot_image = rot_image.subsurface(rot_rect).copy()
    return rot_image

def redraw():
    screen.fill((75, 0, 0))
    player.draw()
    player.update()
    pygame.display.flip()

while (running):
    for e in pygame.event.get():
        if e.type == pygame.QUIT:
            sys.exit()
        elif e.type == pygame.KEYDOWN:
            if e.key == pygame.K_ESCAPE:
                sys.exit()
            if e.key == pygame.K_w:
                player.directions[0] = True
            if e.key == pygame.K_s:
                player.directions[1] = True
            if e.key == pygame.K_a:
                player.directions[2] = True
            if e.key == pygame.K_d:
                player.directions[3] = True
        elif e.type == pygame.KEYUP:
            if e.key == pygame.K_w:
                player.directions[0] = False
            if e.key == pygame.K_s:
                player.directions[1] = False
            if e.key == pygame.K_a:
                player.directions[2] = False
            if e.key == pygame.K_d:
                player.directions[3] = False
        elif e.type == pygame.MOUSEMOTION:
            player.surface = rot_center(player.surface, pygame.mouse.get_pos()[0] / 64)

    redraw()

Pretty straightforward pygame code. I have a player with a simple image that I've created on mspaint, and I've used this function to rotate the image without causing out of memory issues. I'm rotating the image with the mouse (Considering a player that "aims" somewhere). Here's the original image:

And here's the extremely ugly result after moving the mouse a little:

I know I'd have better precision using OpenGL (Pyglet, for example), but in that case the rotation function from pygame would be completely useless. What am I missing? What am I doing wrong?

Answer 1

Keep in mind that Surfaces in Python are just grids of pixels, not mathematically perfect vector graphics. Rotating an image will cause slight destruction of quality. Continually doing so will eventually garble the image beyond recognition as you can see in your picture. Maintain a reference to the original image and never overwrite it. When you call rotate, make sure you are rotating the original picture with the cumulative angle with respect to the original, not a previously and incrementally rotated version.