为什么pygame不能渲染我所有的精灵？

Question

我正试图按照本教程学习pygame。我正试图繁殖敌人的物体，但我认为我犯了一个错误，因为没有显示任何东西。

class Player(pygame.sprite.Sprite):
        def __init__(self):
            super(Player, self).__init__()
            self.surf = pygame.Surface((75,25))
            self.surf.fill((0, 0,0))
            self.rect = self.surf.get_rect()

           #Moves sprite based on keypresses(removed for clarity)
class Enemy(pygame.sprite.Sprite):
    def __init__(self):
        super(Enemy, self).__init__()
        self.surf = pygame.Surface((20,10))
        self.surf.fill((0,0,0))
        self.rect = self.surf.get_rect(
            center = (
            random.randint(SCREEN_WIDTH + 20, SCREEN_WIDTH + 100),
            random.randint(0, SCREEN_HEIGHT),
            )
        )
        self.speed = random.randint(5, 20)
        # moves sprite based on speed, remove when passes left edge
        def update(self):
            self.rect.move_ip(-self.speed, 0)
            if self.rect.right < 0:
                self.kill()
                #How sad for them


pygame.init()
#create screen
screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))

#custom events for adding a new Enemy
ADDENEMY = pygame.USEREVENT + 1
pygame.time.set_timer(ADDENEMY, 250)
# Instantiate player
player = Player()
enemies = pygame.sprite.Group()
all_sprites = pygame.sprite.Group()
all_sprites.add(player)
#keep the game running!
running = True


#loop time!
while running:
    #look at all the events
    for event in pygame.event.get():
        #did the user hit a key?
        if event.type == KEYDOWN:
            #Was it escape?  uh oh we gotta stop
            if event.key == K_ESCAPE:
                running = False

        elif event.type ==QUIT:
            running = False

        elif event.type == ADDENEMY:
            #Create the new enemy
            new_enemy = Enemy()
            enemies.add(new_enemy)
            all_sprites.add(new_enemy)
    #gets the keys that were just pressed
    pressed_keys = pygame.key.get_pressed()
    #updates location based on keys
    player.update(pressed_keys)
    #updates enemy position
    enemies.update()
    #fill screen with white
    screen.fill((255, 255, 255))
    #Draw the sprites
    for entity in all_sprites:
        screen.blit(entity.surf, entity.rect)
    # Create a surface and pass in a tuple containing legth and width
    surf = pygame.Surface((50, 50))

    
    pygame.display.flip()

据我所知，我必须创建一个敌人类，然后添加一个事件来添加敌人（ADDENEMY）。当该事件被调用时（由于计时器的作用，每250毫秒一次），它应该会显示一个向左移动的敌人，直到它到达显示的末尾。
我有一组敌人精灵和一组所有精灵，我使用screen.blit和for循环将所有精灵中的每个实体渲染到屏幕上。我错过了什么？当我运行这个（以及我编辑掉的部分）时，我看到玩家精灵很好，它移动了，但我没有看到任何敌人。

Answer 1

您的精灵不在窗口中。由于未正确指定范围，所有精灵都在窗口之外：

random.randint（SCREEN_WIDTH20，SCREEN_WIDTH100）

random.randint(20, SCREEN_WIDTH + 100),

此外，缩进还有一个问题。方法更新需要是类Enemy的作用域：

class Enemy(pygame.sprite.Sprite):
    def __init__(self):
        # [...]

    # INDENTATION

    #<--|
    def update(self):
        # [...]

此外，请参见pygame.sprite.Group.draw（）：

将包含的精灵绘制到Surface参数。这使用了源表面的Sprite.image属性和Sprite.rect。[...]

通过image重命名属性surf，并调用所有精灵。绘制（屏幕）：

class Player(pygame.sprite.Sprite):
        def __init__(self):
            super(Player, self).__init__()
            self.image = pygame.Surface((75,25))
            self.image.fill((0, 0,0))
            self.rect = self.image.get_rect()

class Enemy(pygame.sprite.Sprite):
    def __init__(self):
        super(Enemy, self).__init__()
        self.image = pygame.Surface((20,10))
        self.image.fill((0,0,0))
        self.rect = self.image.get_rect(
            center = (
            random.randint(20, SCREEN_WIDTH + 100),
            random.randint(0, SCREEN_HEIGHT),
            )
        )
        self.speed = random.randint(5, 20) 

while running:
    # [...]

    #for entity in all_sprites:
    #    screen.blit(entity.surf, entity.rect) <---- DELETE


    all_sprites.draw(screen)                   <---- ADD