第五部分3

game_functions.py

@@ -97,3 +97,58 @@ def update_screen(ai_settings, screen, stats, sb, ship, aliens, bullets,
     # Make the most recently drawn screen visible.
     pygame.display.flip()
     
+def update_bullets(ai_settings, screen, stats, sb, ship, aliens, bullets):
+    """Update position of bullets, and get rid of old bullets."""
+    # Update bullet positions.
+    bullets.update()
+
+    # Get rid of bullets that have disappeared.
+    for bullet in bullets.copy():
+        if bullet.rect.bottom <= 0:
+            bullets.remove(bullet)
+            
+    check_bullet_alien_collisions(ai_settings, screen, stats, sb, ship,
+        aliens, bullets)
+        
+def check_high_score(stats, sb):
+    """Check to see if there's a new high score."""
+    if stats.score > stats.high_score:
+        stats.high_score = stats.score
+        sb.prep_high_score()
+            
+def check_bullet_alien_collisions(ai_settings, screen, stats, sb, ship,
+        aliens, bullets):
+    """Respond to bullet-alien collisions."""
+    # Remove any bullets and aliens that have collided.
+    collisions = pygame.sprite.groupcollide(bullets, aliens, True, True)
+    
+    if collisions:
+        for aliens in collisions.values():
+            stats.score += ai_settings.alien_points * len(aliens)
+            sb.prep_score()
+        check_high_score(stats, sb)
+    
+    if len(aliens) == 0:
+        # If the entire fleet is destroyed, start a new level.
+        bullets.empty()
+        ai_settings.increase_speed()
+        
+        # Increase level.
+        stats.level += 1
+        sb.prep_level()
+        
+        create_fleet(ai_settings, screen, ship, aliens)
+    
+def check_fleet_edges(ai_settings, aliens):
+    """Respond appropriately if any aliens have reached an edge."""
+    for alien in aliens.sprites():
+        if alien.check_edges():
+            change_fleet_direction(ai_settings, aliens)
+            break
+        
+def change_fleet_direction(ai_settings, aliens):
+    """Drop the entire fleet, and change the fleet's direction."""
+    for alien in aliens.sprites():
+        alien.rect.y += ai_settings.fleet_drop_speed
+    ai_settings.fleet_direction *= -1
+