第五部分5

game_functions.py

@@ -201,3 +201,38 @@ def update_aliens(ai_settings, screen, stats, sb, ship, aliens, bullets):
     # Look for aliens hitting the bottom of the screen.
     check_aliens_bottom(ai_settings, screen, stats, sb, ship, aliens, bullets)
             
+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 get_number_rows(ai_settings, ship_height, alien_height):
+    """Determine the number of rows of aliens that fit on 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 the 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 create_fleet(ai_settings, screen, ship, aliens):
+    """Create a full fleet of aliens."""
+    # Create an alien, and find number of aliens in a row.
+    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 fleet of aliens.
+    for row_number in range(number_rows):
+        for alien_number in range(number_aliens_x):
+            create_alien(ai_settings, screen, aliens, alien_number,
+                row_number)