问如何在构建空间入侵者游戏时在屏幕上创建多行外星人？

EN

game_function.py
import pygame
import sys
from bullet import Bullet
from alien import Alien
def update_screen(ai_settings, screen, ship, aliens, bullets):
    # redraw the screen during each pass through the loop
    screen.fill(ai_settings.bg_color)
    ship.blitme()
    aliens.draw(screen)
    # make the most recently drawn screen visible

    """Update images on the screen and flip to the new screen."""
    # redraw all bullets behind ship and aliens
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    pygame.display.flip()

def get_number_rows(ai_settings, ship_height, alien_height):
    """Determine the number of rows of aliens that fit into the screen"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows


def create_alien(ai_settings, screen, aliens, alien_number, row_number):
    """create an alien and place it in a row"""
    alien = Alien(ai_settings, screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)


def get_number_aliens_x(ai_settings, alien_width):
    """Determine the number of aliens that fit in a row"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_aliens_x = int(available_space_x / (2 * alien_width))
    return number_aliens_x


def create_fleet(ai_settings, screen, ship, aliens):
    """Create a full fleet of aliens"""
    # create an alien and find the number of aliens in a row
    # spacing between each alien is equal to one alien width
    alien = Alien(ai_settings, screen)
    number_aliens_x = get_number_aliens_x(ai_settings, alien.rect.width)
    number_rows = get_number_rows(ai_settings, ship.rect.height,
                                  alien.rect.height)
    # create the first row of aliens
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            # create an alien and place it in a row
            create_alien(ai_settings, screen, aliens, alien_number, row_number)

main.py
import pygame
import sys
from settings import Settings
from ship import Ship
import game_functions as gf
from pygame.sprite import Group
from alien import Alien


def run_game():
    # initialize
    # pygame, settings
    # and screen
    # object

    pygame.init()
    ai_settings = Settings()

    screen = pygame.display.set_mode((ai_settings.screen_width, ai_settings.screen_height))
    pygame.display.set_caption("Alien Invasion")
    # make a ship
    ship = Ship(screen, ai_settings)
    # group to store bullets
    bullets = pygame.sprite.Group()
    # make an alien
    alien = Alien(ai_settings, screen)
    # a group to store aliens
    aliens = pygame.sprite.Group()
    # create a fleet of aliens
    gf.create_fleet(ai_settings, screen, ship, aliens)

    # main loop for the game
    while True:
        # watch
        # for keyboard and mouse events
        gf.check_events(ship, ai_settings, screen, bullets)
        ship.update()
        gf.update_bullets(bullets)

        gf.update_screen(ai_settings, screen, ship, aliens, bullets)


run_game()