Chapter 12: A Ship that Fires Bullets

新建一个alien_invasion文件夹

Installing Pygame

$ python -m pip install --user pygame

• 在mac上如果报错去掉—user

• 如果装了多个python版本，python改为python3

  主文件和settings

  把和设置相关的都放在settings.py里作为module引入

  class Settings:
    """A class to store all settings for Alien Invasion."""
    def __init__(self):
        """Initialize the game's settings."""
        # Screen settings
        self.screen_width = 1200
        self.screen_height = 800
        self.bg_color = (230, 230, 230)

  ```python import sys import pygame

from settings import Settings

class AlienInvasion: “””Overall class to manage game assets and behavior.”””

def __init__(self):
    """Initialize the game, and create game resources."""
    pygame.init()
    self.settings = Settings()
    self.screen = pygame.display.set_mode(
        (self.settings.screen_width, self.settings.screen_height))
    pygame.display.set_caption("Alien Invasion")
def run_game(self):
    """Start the main loop for the game."""
    while True:
        # Watch for keyboard and mouse events.
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                sys.exit()
        # Redraw the screen during each pass through the loop.
        self.screen.fill(self.settings.bg_color)
        # Make the most recently drawn screen visible.
        pygame.display.flip()

if name == ‘main‘:

# Make a game instance, and run the game.
ai = AlienInvasion()
ai.run_game()

<a name="WmSY5"></a>
### 画飞船
pygame默认支持.bmp格式的图片<br />把图片放在images文件夹<br />图片素材网站：[https://pixabay.com/](https://pixabay.com/)<br />创建ship.py
```python
import pygame
class Ship:
    """A class to manage the ship."""
    def __init__(self, ai_game):
        """Initialize the ship and set its starting position."""
        self.screen = ai_game.screen
        self.screen_rect = ai_game.screen.get_rect()
        # Load the ship image and get its rect.
        self.image = pygame.image.load('images/ship.bmp')
        self.rect = self.image.get_rect()
        # Start each new ship at the bottom center of the screen.
        self.rect.midbottom = self.screen_rect.midbottom
    def blitme(self):
        """Draw the ship at its current location."""
        self.screen.blit(self.image, self.rect)

get_rect()可以获取尺寸
pygame把每个物体都看成是长方形
画出飞船

--snip--
from settings import Settings
from ship import Ship
class AlienInvasion:
    """Overall class to manage game assets and behavior."""
    def __init__(self):
    --snip--
    pygame.display.set_caption("Alien Invasion")
    self.ship = Ship(self)
    def run_game(self):
    --snip--
    # Redraw the screen during each pass through the loop.
    self.screen.fill(self.settings.bg_color)
    self.ship.blitme()
    # Make the most recently drawn screen visible.
    pygame.display.flip()
    --snip--

重构Refactoring: The _check_events() and _update_screen()

Methods 在Python, 单下划线开头的代表helper method
将check events 和update screen声明为独立的method, 在class内用self.调用自己的method

--snip--
class AlienInvasion:
    """Overall class to manage game assets and behavior."""
    --snip--
    def run_game(self):
        """Start the main loop for the game."""
        while True:
            self._check_events()
            self._update_screen()
    def _check_events(self):
        """Respond to kekypresses and mouse events."""
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                sys.exit()
    def _update_screen(self):
        """Update images on the screen, and flip to the new screen."""
        self.screen.fill(self.settings.bg_color)
        self.ship.blitme()
        pygame.display.flip()
--snip--