alien.py

# -*- coding: utf-8 -*-
"""
Created on Thu Sep 27 15:56:24 2018

@author: cz
"""

import pygame
from pygame.sprite import Sprite

class Alien(Sprite):
    def __init__(self,ai_settings,screen):
        super(Alien,self).__init__()
        self.screen = screen
        self.ai_settings = ai_settings
        
        #加载外星人图像，并设置其rect属性
        self.image = pygame.image.load('images/alien.bmp')
        self.rect = self.image.get_rect()
        
        #每个外星人最初都在屏幕左上角
        self.rect.x = self.rect.width - 10
        self.rect.y = self.rect.height
        
        #存储外星人的准确位置
        self.x = float(self.rect.x)
        
    def blitme(self):
        '''在指定位置绘制外星人'''
        self.screen.blit(self.image,self.rect)
        
    def update(self):
        '''向右移动外星人'''
        self.x += (self.ai_settings.alien_speed_factor * self.ai_settings.fleet_direction)
        self.rect.x = self.x
        
    def check_edges(self):
        '''如果外星人位于屏幕边缘就返回True'''
        screen_rect = self.screen.get_rect()
        if self.rect.right >= screen_rect.right:
            return True
        elif self.rect.left <=0:
            return True