图像在pygame wind中无法正常移动

Question

我正在做一个项目，我从youtube上的一个教程开始，重新制作一些类似于太空入侵者游戏的东西。我让游戏正常工作，但我想实现一个重启选项，一旦用户游戏结束。我试着把我所有的代码放在一个main（）函数中，这样一旦游戏结束，我就可以给用户一个重新玩的选项，如果他们选择再次玩，我就可以调用main（）函数来重新启动代码。在将代码放入main（）函数后，除了发射子弹之外，其他所有操作都完全相同。它的工作原理应该是，每当用户按下空格键时，一颗子弹就会发射到屏幕的整个高度，然后重置回飞船，或者一旦击中外星飞船就重置。我遇到的问题是，当我按下空格键时，子弹不会离开飞船，它只是在屏幕上的起始位置短暂出现，然后就不动了。下面的所有代码都在我的main函数中，main函数被调用并正常工作。唯一的问题是子弹没有按它应该的那样移动

pygame.init()

backgroundImg = pygame.image.load("Spacepic.jpg")

windowScreen = pygame.display.set_mode((800, 600))

pygame.display.set_caption("Space Invaders Remake")

topIcon = pygame.image.load("space-ship (2).png")

pygame.display.set_icon(topIcon)

score_num = 0
font = pygame.font.Font("freesansbold.ttf", 32)

textX = 10
textY = 10

playerImg = pygame.image.load("space-invaders.png")
playerX = 370
playerY = 480
playerX_change = 0

# Enemy
enemyImg = []
enemyX = []
enemyY = []
enemyX_change = []
enemyY_change = []
num_of_enemies = 30
initial_num_of_enemies = 6

# Bullet
bulletImg = pygame.image.load("bullet.png")
bulletX = 0
bulletY = 480
bulletY_change = 20
bullet_state = "ready"

lives = 3
end_lives = 0

for i in range(num_of_enemies):
    enemyImg.append(pygame.image.load("ufo.png"))
    enemyX.append(random.randint(0, 736))
    enemyY.append(random.randint(0, 0))
    enemyX_change.append(12)
    enemyY_change.append(40)
    num_of_enemies = initial_num_of_enemies

# Collision between bullet and spaceship
def isCollision():
    distance = math.sqrt((math.pow(enemyX[i] - bulletX, 2)) + (math.pow(enemyY[i] - bulletY, 2)))
    if distance < 25:
        return True
    else:
        return False

# Fire bullet function
def bullet(x, y):
    global bullet_state
    bullet_state = "fire"
    windowScreen.blit(bulletImg, (x + 15, y))

def show_score():
    score = font.render("Score: " + str(score_num), True, (255, 255, 255))
    windowScreen.blit(score, (textX, textY))

def show_score_to_win():
    win_score = font.render("Score to win: 100", True, (255, 255, 255))
    windowScreen.blit(win_score, (520, 10))

def you_win_msg():
    win_text = font.render("You win, CONGRATULATIONS!", True, (255, 255, 255))
    windowScreen.blit(win_text, (200, 250))

def game_over():
    lose_text = font.render("You lose, GAME OVER!", True, (255, 255, 255))
    windowScreen.blit(lose_text, (225, 250))

def player():
    windowScreen.blit(playerImg, (playerX, playerY))

def enemy(x, y, i):
    windowScreen.blit(enemyImg[i], (x, y))

def show_lives():
    lives_display = font.render("Lives: " + str(lives), True, (255, 255, 255))
    windowScreen.blit(lives_display, (10, 100))

rungame = True
while rungame:

    windowScreen.fill((0, 0, 0))
    windowScreen.blit(backgroundImg, (0, 0))
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            rungame = False

        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                playerX_change = -5
            if event.key == pygame.K_RIGHT:
                playerX_change = 5

            # If bullet isn't already visible fire once spacebar pressed
            if event.key == pygame.K_SPACE:
                if bullet_state is "ready":
                    bulletX = playerX
                    bullet(bulletX, bulletY)

    if event.type == pygame.KEYUP:
        if event.key == pygame.K_LEFT or event.key == pygame.K_RIGHT:
            playerX_change = 0

    playerX += playerX_change

    if playerX <= 0:
        playerX = 0
    elif playerX >= 736:
        playerX = 736

    for i in range(num_of_enemies):
        enemy(enemyX[i], enemyY[i], i)
        enemyX[i] += enemyX_change[i]
        if 0 <= score_num < 20:
            if enemyX[i] <= 0:
                enemyX_change[i] = 5
                enemyY[i] += enemyY_change[i]
            elif enemyX[i] >= 736:
                enemyX_change[i] = -5
                enemyY[i] += enemyY_change[i]
        elif 20 <= score_num < 40:
            if enemyX[i] <= 0:
                enemyX_change[i] = 6
                enemyY[i] += enemyY_change[i]
            elif enemyX[i] >= 736:
                enemyX_change[i] = -6
                enemyY[i] += enemyY_change[i]
        elif 40 <= score_num < 60:
            if enemyX[i] <= 0:
                enemyX_change[i] = 7
                enemyY[i] += enemyY_change[i]
            elif enemyX[i] >= 736:
                enemyX_change[i] = -7
                enemyY[i] += enemyY_change[i]
        elif 60 <= score_num < 100:
            if enemyX[i] <= 0:
                enemyX_change[i] = 8.5
                enemyY[i] += enemyY_change[i]
            elif enemyX[i] >= 736:
                enemyX_change[i] = -8.5
                enemyY[i] += enemyY_change[i]

        # If collision occurs bullet resets to starting position
        collision = isCollision()
        if collision:
            bulletY = 480
            bullet_state = "ready"
            score_num += 1
            enemyX[i] = random.randint(0, 736)
            enemyY[i] = random.randint(0, 0)

        if 20 <= score_num < 40:
            num_of_enemies = 10
        elif 40 <= score_num < 60:
            num_of_enemies = 15
        elif 60 <= score_num < 100:
            num_of_enemies = 20
        elif score_num == 100:
            for j in range(num_of_enemies):
                enemyY[j] = 1000
            you_win_msg()
            break
        if lives >= end_lives:
            if 435 < enemyY[i] < 900:
                enemyY[i] = 1000
                lives -= 1
                if score_num > 0:
                    score_num -= 1
        if lives == end_lives:
            for j in range(num_of_enemies):
                enemyY[j] = 1000
            game_over()

    # Bullet movement
    if bulletY <= 0:
        bulletY = 480
        bullet_state = "ready"

    if bullet_state is "fire":
        bullet(bulletX, bulletY)
        bulletY -= 100

    player()
    show_score()
    show_score_to_win()
    show_lives()
    pygame.display.update()