Enemy character is being overdrawn by game's b

问题:

I am working on a game which spawns enemies. Though once these enemies are spawned, they instantly disappear again because the background is drawn on top of them.

Is there a way to have a layer system in Pygame?

Code to recreate the problem:

import pygame
import threading
from random import randint
from time import sleep

pygame.init()
window = pygame.display.set_mode((900, 900))
bg=pygame.image.load("Background.png").convert()

def Gameplay():
    while True:  
        window.blit(bg, [0,0])
        pygame.display.update()

def spawn_enemy():
    enemyW = 50
    enemyH = 50
    enemyX = 420
    enemyY = 850
    pygame.draw.rect(window, (93,124,249),(enemyX,enemyY,enemyW, enemyH))
    print("an enemy has been spawned")
    return True # would be "return enemy" after you create your enemy entity

def EnemySpawn():
    enemy_list = [] # to maintain records of all enemies made
    while True: # make enemies forever
        sleep(randint(1,5))
        enemy_list.append(spawn_enemy()) # call our function we made above which spawns enemies

Gameplay = threading.Thread(target=Gameplay)
Gameplay.start()
EnemySpawn = threading.Thread(target=EnemySpawn)
EnemySpawn.start()

回答1:

I do not understand pygame and it for some reason becomes generally unresponsive when I run this, but it does generate enemies and show how one would implement a class to store their variables (perhaps a pygame expert could edit it to become responsive or comment what my code is doing that makes the window "freeze up"):

import pygame
import threading
from random import randint
from time import sleep
import random

pygame.init()
window = pygame.display.set_mode((900, 900))
bg = pygame.image.load("Background.png").convert()

class Enemy:
    def __init__(self):
        self.W = random.randint(30, 50)
        self.H = random.randint(30, 50)
        self.X = random.randint(0, 900)
        self.Y = random.randint(0, 900)

def Gameplay():
    global enemy_list
    while True:
        window.blit(bg, [0, 0])
        for enemy in enemy_list:
            pygame.draw.rect(window, (93, 124, 249), (enemy.X, enemy.Y, enemy.W, enemy.H))
        pygame.display.update()

def EnemySpawn():
    global enemy_list
    while True: # make enemies forever
        sleep(randint(1, 5))
        print("Spawned an enemy")
        enemy_list.append(Enemy()) # make an instance of our class

enemy_list = [] # to maintain records of all enemies made
game_thread = threading.Thread(target=Gameplay)
game_thread.start()
enemy_spawner_thread = threading.Thread(target=EnemySpawn)
enemy_spawner_thread.start()

The key points to note are the use of enemy_list being in the global space and then calling it into functions with global enemy_list so they are accessing the same list object. The class does essentially the same thing you were doing in your function, but gives the enemies random spawn points. As @Rabbid pointed out, you need to draw the enemies in the same part of your code that draws the background.

P.S. You should not use Gameplay = threading.Thread(target=Gameplay) as this overwrites your function. I've implemented a different variable for the thread in my code