如果我将整个代码作为 function 放在 pygame 中，为什么某些功能不起作用？

Question

So, i have bean developing this simple game where there is this slingshot and the ball a ball image is hidden right beneath it. and then i have a bird. My games goal is to shot the bird down. everything worked the bird was being shot down my ball was firing. I was in my final stages of this game when i put it all into a function so that after the bird is shot down i can call it all over again and repeat it. so when i put my code in the function and tested it out, the sprites where drawn properly but when i clicked the space bar to fire my ball it did not work. I am using pygame for this project. you can look at my code below:

Thanks in advance

import random
onlystarting = True
def main():
    global onlystarting
    onlystarting = False

    pygame.init()
    screen = pygame.display.set_mode((800, 600))


    postImg = pygame.image.load('post.png')
    postX = 0
    postY = 150

    lineImg = pygame.image.load('line.png')
    lineImg = pygame.transform.scale(lineImg, (610, lineImg.get_height()))

    slingshotImg = pygame.image.load('slingshot.png')
    slingshotX = 340
    slingshotY = 500
    slingshotX_change =  0


    ballImg = pygame.image.load('ball.png')
    ballX = slingshotX
    ballY = 533
    ballYchange = 2
    ballImg = pygame.transform.scale(ballImg, (20, 20))
    ballState = "ready"

    birdImg = pygame.image.load('bird.png')
    birdX = random.randint(300, 600)
    birdY = 240
    birdState = "alive"

    def post(x, y) :
        screen.blit(postImg, (x, y))

    def line(x, y) :
        screen.blit(lineImg, (x, y))

    def slingshot(x, y) :
        screen.blit(slingshotImg, (x, y))

    def fire_ball(x,y):
        global ballState
        ballState = "fire"
        screen.blit(ballImg, (x + 16, y))
    def bird(x,y):
        screen.blit(birdImg, (x, y))

    running = True
    #Game loop
    while running:
        screen.fill((225, 225, 225))
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                running = False
        
            if event.type == pygame.KEYDOWN:
                if event.key == pygame.K_LEFT:
                    slingshotX_change = -0.5

                if event.key == pygame.K_RIGHT:
                    slingshotX_change = 0.5
                
                if event.key == pygame.K_SPACE:
                    if ballState == "ready":
                        ballX = slingshotX
                        fire_ball(ballX, ballY)
            
            if event.type == pygame.KEYUP:
                if event.key == pygame.K_RIGHT or event.key == pygame.K_LEFT:
                    slingshotX_change = 0

            slingshotX += slingshotX_change

        slingshotX += slingshotX_change


        if ballState == "fire":
            fire_ball(ballX, ballY)
            ballY -= ballYchange

        if slingshotX <= 100:
            slingshotX = 100.1

        if slingshotX >= 640:
            slingshotX = 639.9



        distanceX = ballX - birdX
        distanceY = ballY - birdY
        
        if distanceX > -32:
            if distanceX < 32 :
                if distanceY > -32:
                    if distanceY < 32:
                        birdX = 1000
                        birdY = 1000
                        main()


        post(postX, postY)
        post(650, 150)
        line(95, 270)
        line(95, 370)
        slingshot(slingshotX, slingshotY)
        bird(birdX, birdY)
        
        pygame.display.update()
if onlystarting:
    main()```

Answer 1

You have functions in the function using global variables ballState , screen , postImg , lineImg , slingshotImg . ballImg and birdImg . However, these variables are never defined in global scope. These variables are local variables in the main function.

Either use the global statement to make this variables global:

def main():
    global ballState, screen, onlystarting, postImg, lineImg, slingshotImg, ballImg, birdImg
    # [...]

Or pass the variables to the functions:

def draw(screen, surf, x, y) :
    screen.blit(postImg, (x, y))

def fire(screen, surf, x, y):
    global ballState
    ballState = "fire"
    screen.blit(surf, (x + 16, y))

def main():
    global onlystarting, ballState
    # [...]

    for event in pygame.event.get():
            # [...]
        
            if event.type == pygame.KEYDOWN:
                # [...]
           
                if event.key == pygame.K_SPACE:
                    if ballState == "ready":
                        ballX = slingshotX
                        fire(screen, ballImg, ballX, ballY)
            
        # [...]   

        if ballState == "fire":
            fire(screen, ballImg, ballX, ballY)
            ballY -= ballYchange

        # [...]
        
        draw(screen, postImg, postX, postY)
        draw(screen, postImg, 650, 150)
        draw(screen, lineImg, 95, 270)
        draw(screen, lineImg, 95, 370)
        draw(screen, slingshotImg, slingshotX, slingshotY)
        draw(screen, birdImg, birdX, birdY)
        
        pygame.display.update()