在 Pygame (python) 中翻转图像的问题

Question

I am trying to create a game in which you can move a character with arrow keys. When moving left or right, I want the character (an image) to flip and point left/right accordingly. The original image/character is pointing left. But I cannot get the character to flip, please help me, thanks.

import pygame
pygame.init()#initiate pygame
black = (0,0,0)
white = (255,255,255)
red = (255,0,0)
display_width = 1200
display_height = 800
display = pygame.display.set_mode((display_width,display_height))
characterimg = pygame.image.load(r'/Users/ye57324/Desktop/Make/coding/python/characterimg.png')
def soldier(x,y):
    display.blit(characterimg, (x,y))
x = (display_width * 0.45)
y = (display_height * 0.1)
pygame.display.set_caption('Game')
clock = pygame.time.Clock()#game clock
flip_right = False
x_change = 0
y_change = 0
start = True


while start:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            start = False
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                x_change += -5
                if flip_right == True:
                    pygame.transform.flip(characterimg, True, False)
                    flip_right = False
            elif event.key == pygame.K_RIGHT:
                x_change += 5
                if flip_right == False:
                    pygame.transform.flip(characterimg, True, False)
                    flip_right = True
            elif event.key == pygame.K_UP:
                y_change += -5
            elif event.key == pygame.K_DOWN:
                y_change += 5
        if event.type == pygame.KEYUP:
            if event.key == pygame.K_LEFT:
                x_change += 5
            elif event.key == pygame.K_RIGHT:
                x_change += -5
            elif event.key == pygame.K_UP:
                y_change += 5
            elif event.key == pygame.K_DOWN:
                y_change += -5

    x += x_change
    y += y_change
    display.fill(white)
    soldier(x,y)
    pygame.display.update()
    clock.tick(60)#fps

Answer 1

Pygame's doc-page about pygame.transform.flip states

Flipping a Surface is non-destructive and returns a new Surface with the same dimensions.

This means that the surface you pass to that method remains unaffected. You have to keep the return -value around in order to see any effect.

In practice, this means that you should replace

pygame.transform.flip(characterimg, True, False)

with

characterimg = pygame.transform.flip(characterimg, True, False)

So that characterimg point to the new, flipped version of the image.

Note: Performance wise, this is not a very good method of doing things. Each time you call pygame.transform.flip , pygame has to allocated new memory for the new surface, go over each pixel of the original surface and copy it over to the new surface, transforming its position in the process. You'd better flip the image once at the beginning of your program, so that you have a variable characterimg_left and characterimg_right and then just assign those to your characterimg variable.