Rotation in pygame

I've been looking for solutions on how to make my image rotate around a single point but from what I've found nothing has really worked.

What I know

I can rotate using pygame.transform.rotate(surface, angle)
I need to constantly reset the center so the image does not rotate on its rotated self.
Need to update image to eliminate distortion

At first the image looks like this

Then when I rotate it a couple times it looks like this

Here's my code

import pygame


class pyGameSetup:

def __init__(self, title, width, height):

    # initialize pygame library
    pygame.init()

    # set up specific display properties
    self.game_display = pygame.display.set_mode((width, height))
    pygame.display.set_caption(title)

    # update display
    pygame.display.update()

    # create new global variables for the class
    # game state
    self.running = True

    # colors, only main
    # TODO: implement more color RGB values, if updated, update corresponding method
    self.white = (255, 255, 255)
    self.black = (0, 0, 0)
    self.grey = (128, 128, 128)
    self.pink = (255, 102, 178)
    self.blue = (0, 0, 255)
    self.red = (255, 0, 0)
    self.green = (0, 255, 0)
    self.purple = (127, 0, 255)
    self.yellow = (255, 255, 0)
    self.teal = (0, 204, 204)
    self.orange = (255, 128, 0)

    # player coordinates and properties
    self.player_x = int(width / 2)
    self.player_y = int(height / 2)
    self.player_width = 100
    self.player_height = 50
    self.player_speed_x = 0
    self.player_speed_y = 0
    self.move_speed = 5

    # FPS controllers (note start speed should always be 60 / 5 so, 1 / 300
    self.clock = pygame.time.Clock()
    self.fps = 60

    # screen values
    self.width = width
    self.height = height

    # rotation for car
    self.angle = 200

    # car image
    self.car1 = pygame.image.load("Images\\Car1.png")
    self.update_size()
    self.car_rect = self.car1.get_rect()
    self.car_rect.center = (self.player_x, self.player_y)


def exit(self):
    pygame.quit()
    self.running = False
    quit()

def game_loop(self):
    while self.running:
        for event in pygame.event.get():
            self.event_handler(event)

        # update player position
        # self.player_x += self.player_speed_x
        self.angle = self.player_speed_x
        self.player_y += self.player_speed_y

        # check to make sure it's in bounds
        self.check_valid_move()

        # reprint canvas
        self.game_display.fill(self.white)

        # update angle
        self.update_angle()

        # print player
        self.game_display.blit(self.car1, (self.player_x, self.player_y, self.player_width,
                                           self.player_height))

        # update display
        pygame.display.update()

        # FPS
        self.clock.tick(self.fps)

def event_handler(self, e):
    if e.type == pygame.QUIT:
        self.exit()
    if e.type == pygame.KEYDOWN:
            if e.key == pygame.K_LEFT:
                self.player_speed_x = -self.move_speed
            if e.key == pygame.K_RIGHT:
                self.player_speed_x = self.move_speed
            if e.key == pygame.K_UP:
                self.player_speed_y = -self.move_speed
            if e.key == pygame.K_DOWN:
                self.player_speed_y = self.move_speed
    if e.type == pygame.KEYUP:
            if e.key == pygame.K_LEFT:
                self.player_speed_x = 0
            if e.key == pygame.K_RIGHT:
                self.player_speed_x = 0
            if e.key == pygame.K_UP:
                self.player_speed_y = 0
            if e.key == pygame.K_DOWN:
                self.player_speed_y = 0

def check_valid_move(self):
    if self.player_x <= 0:
        self.player_x = 0
    if self.player_x >= self.width - self.player_width:
        self.player_x = self.width - self.player_width
    if self.player_y <= 0:
        self.player_y = 0
    if self.player_y >= self.height - self.player_height:
        self.player_y = self.height - self.player_height

def update_size(self):
    self.car1 = pygame.transform.scale(self.car1, (self.player_width, self.player_height))
    self.car1 = pygame.transform.rotate(self.car1, -90)

def update_angle(self):
    old_center = self.car_rect.center
    self.car1 = pygame.transform.rotate(self.car1, self.angle)
    self.car_rect.center = old_center

x = pyGameSetup('Game', 800, 600)
x.game_loop()

The error is in update_angle where I honestly am completely lost and do not even know what it's doing. Thanks in advance.

回答1:

Your problem is that you are rotating a rotated image. Thus, the image is looking skewed, which would be expected. Instead, have two variables, one for the original variable, one for the most recent rotation.

So instead of:

car1 = original_image_rect
car1 = pygame.transform.rotate(car1, 10)
car1 = pygame.transform.rotate(car1, 10)
...

You would do:

car1 = original_image_rect
car2 = pygame.transform.rotate(car1, 10)
car2 = pygame.transform.rotate(car1, 20)
...

回答2:

This result seems to be pretty normal for the image of low resolution rotated several times without antialiasing. What you should do is:

Use the source image exactly 2x bigger, if possible. Rotate it FIRST and then scale down exactly 2x - if possible, during blit, so you don't need to scale it as a separate step.
Don't rotate rotated image. I.e. don't rotate it 3 times by 5 degrees, but every time copy the original image and rotate it by 5, 10, 15 degrees. This way you will keed distortion to the minimum and also won't have to re-assign the center.