Rotating an image while preserving the center in pygame

Question

I have a sprite that i want to rotate when i hit he left and right arrow but when i rotate it it moves a little bit. my code is shown bellow

class Ship(pygame.sprite.Sprite):
    def __init__(self,color):
        super().__init__()
        self.image=pygame.image.load("ship.png")
        self.colorlayer=pygame.image.load("shipcolor.png")
        self.rect = self.image.get_rect()
        self.x=400
        self.y=300
        self.angle_delta = 0

    def drawsprite(self,surface):
        old_image_center = self.rect.center
        new_image = pygame.image.load("ship.png")
        new_colorlayer = pygame.image.load("shipcolor.png")
        self.image = pygame.transform.rotate(new_image, self.angle_delta)
        self.colorlayer = pygame.transform.rotate(new_colorlayer, self.angle_delta)
        self.rect = self.image.get_rect()
        self.rect.center = old_image_center
        surface.blit(self.colorlayer,(self.x, self.y))
        surface.blit(self.image,(self.x, self.y))


    def rotate(self):
        if event.type == pygame.KEYDOWN:
            if event.key== pygame.K_RIGHT:
                self.angle_delta += 45
            if event.key== pygame.K_LEFT:
                self.angle_delta -=45

When the image rotates, it's dimensions, and therefore it's centre changes. You need to remember the current position, rotate the image, then reset the position based on the centre. — Kingsley, Feb 27 '19 at 23:44

score 0 · Answer 1 · answered Feb 28 '19 at 00:13

When an image rotates, its size, and therefore centre-point changes.

One way to rotate about a centre-point is to remember the centre-point before the rotation, then re-apply it after the rotation.

class SomeSprite( pygame.sprite.Sprite ):
    def __init__( self, x, y ):
        self.original_image = pygame.image.load("some_filename.png").convert_alpha()
        self.image          = self.original_image
        self.rect           = self.image.get_rect()
        self.rect.center    = ( x, y )

    def rotateTo( self, angle ):
        # rotate and zoom the sprite, starting with an original image
        # this prevents image degradation
        self.image = pygame.transform.rotozoom( self.original_image, angle, 1 )
        # reset it back to original centre
        self.rect  = self.image.get_rect( center=self.rect.center )

Obviously, if the image subject is not centred within the surrounding bitmap, it will definitely rotate about its centre, but still look like that's not the case.

Rotating an image while preserving the center in pygame

1 Answers1