用pygame动态控制精灵blit顺序

Question

I'm currently writing a Tower Defence game. Everything works fine but there's a visual issue that's bugging me.

Basically, a sprite that has a lower rect.y and should be higher on the map to pass behind a slower mob with a higher rect.y , can be blitted after (and therefore in front of) the foreground sprite.

I could fix it, but not while keeping the random spread-out spawn points that I like.

Could anybody suggest anything to help? I omitted irrelevant code, so there's not much to sift through.

class Pokemon(pygame.sprite.Sprite):
    def __init__(self, name, health, speed, attack, typeOf, typeOf2, level, order):
        pygame.sprite.Sprite.__init__(self)
        self.order = order
        self.image = pygame.image.load('C:/Users/#/#/#/pygames/tower_defense/Distributable/images/POKEMON/%sright.png'%(name))

        self.rect = self.image.get_rect()
        # X/Y axis locations
        self.rect.centerx = 0-self.rect.width - self.order*100
        self.rect.centery = random.randint(500, 540)

Then the creation block -

for e in range(numberOfEnemies):
    poke = random.randint(1, 2)
    if poke == 1:
        level = random.randint(2, 5)
        Pidgey = Pokemon('Pidgey', 15, 2, 5, 'Normal', 'Flying', level, e)
        enemies.append(Pidgey)
        enemy_sprites.add(Pidgey)
    else:
        level = random.randint(2, 4)
        Rattata = Pokemon('Rattata', 13, 3, 5, 'Normal', None, level, e)
        enemies.append(Rattata)
        enemy_sprites.add(Rattata)
    enemyNumber += 1

Answer 1

If you need to control the layers of the sprites, you can use a LayeredUpdates sprite group. The sprites need a self._layer attribute or you can pass the layer when you add the sprite to the group, eg:

layered_group.add(sprite, layer=desired_layer)

When a sprite is moved, you can call the change_layer method of the sprite group:

layered_group.change_layer(sprite, sprite.rect.bottom)

However, if you have to update the layers of all sprites each frame, it would be more efficient to sort the sprites by their rect.bottom position, iterate over the list and blit them:

blit = screen.blit  # Local variable to improve the performance.
for sprite in sorted(all_sprites, key=lambda spr: spr.rect.bottom):
    blit(sprite.image, sprite.rect)