我严重不明白我的pygame代码出了什么问题

Question

过去几天，我一直在梳理头发，以使愚蠢的菜单屏幕正常工作。

游戏运行正常，当我第一次尝试调用菜单功能时，我什么都没显示。

import pygame
import time
import random

from pygame.locals import *

pygame.init()
pygame.font.init()
pygame.mixer.init()
screen = pygame.display.set_mode((540,620))
pygame.display.set_caption("Space Invaders")
clock = pygame.time.Clock()
current_screen = 0


White = (255,255,255)
Black = (0,0,0)

Width = 540
Height = 620

def draw_text(surf, text, size, x, y):
    font = pygame.font.Font("CaviarDreams.ttf", size)
    text_surface = font.render(text, True, White)
    text_rect = text_surface.get_rect()
    text_rect.midtop = (x, y)
    surf.blit(text_surface, text_rect)


def game_over():
    keep_going = False
    screen.fill(Black)
    draw_text(screen, ("Game Over!"), 40, Width /2, 280)
    pygame.draw.rect(screen, Black, (30,200,50,30))
    draw_text(screen, ("Play again"), 30, 200, 350)

def paused():
    screen.fill(Black)
    draw_text(screen, ("Paused!"), 40, Width /2, 280)   #Pause
    resume_button = pygame.draw.rect(screen, White, (150,350,100,30))


def menu():
    screen.fill(Black)
    draw_text(screen, ("Space Invaders!"), 50, 270, 180)
    draw_text(screen, ("Press Space to play"), 40, 270, 240)
    for ev in pygame.event.get():
        if ev.type == K_SPACE:
            screen.fill(Black)
            current_screen = 1

class Ship(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.image.load("spaceship.bmp")
        self.rect = self.image.get_rect()
        self.rect.centerx = Width / 2
        self.rect.bottom = Height - 10
        self.speedx = 0


    def update(self):
        self.speedx = 0
        keystate = pygame.key.get_pressed()
        if keystate[pygame.K_LEFT]:
            self.speedx = -5
        if keystate[pygame.K_RIGHT]:
            self.speedx = 5
        self.rect.x += self.speedx
        if self.rect.right > screen.get_width():
            self.rect.right = screen.get_width()
        if self.rect.left < 0:
            self.rect.left = 0

    def shoot(self):
        bullet = Bullet(self.rect.centerx, self.rect.top)
        all_sprites.add(bullet)
        bullets.add(bullet)
        pygame.mixer.Sound.play(pew)

class Bullet(pygame.sprite.Sprite):
    def __init__(self, x, y):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.image.load("laser.bmp")
        self.rect = self.image.get_rect()
        self.rect.bottom = y
        self.rect.centerx = x
        self.speedy = -10

    def update(self):
        self.rect.y += self.speedy
        if self.rect.bottom < 0:
            self.kill()

class Invaders(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.image.load("alien.bmp")
        self.rect = self.image.get_rect()
        self.rect.x = random.randrange(Width - self.rect.width)
        self.rect.y = random.randrange(-100, -40)
        self.speedy = random.randrange(3, 8)
        self.speedx = random.randrange(-3, 3)

    def update(self):
        self.rect.x += self.speedx
        self.rect.y += self.speedy
        if self.rect.top > Height + 10 or self.rect.left < -25 or self.rect.right > Width + 20:
            self.rect.x = random.randrange(Width - self.rect.width)
            self.rect.y = random.randrange(-100, -40)
            self.speedy = random.randrange(1, 8)


pew = pygame.mixer.Sound("Laser.wav")
player_death = pygame.mixer.Sound("Explosion.wav")
hit_sound = pygame.mixer.Sound("Hit.wav")

score = 0
all_sprites = pygame.sprite.Group()
enemies = pygame.sprite.Group()
bullets = pygame.sprite.Group()
player = Ship()
all_sprites.add(player)
enemy = Invaders()

for i in range(5):
    basic_enemy = Invaders()
    all_sprites.add(basic_enemy)
    enemies.add(basic_enemy)


def game_loop():
    current_screen = 0
    score = 0
    keep_going = True
    while keep_going:
        screen.fill(Black)
        clock.tick(60)
        if current_screen 0
        menu()
        if current_screen == 1:
            for ev in pygame.event.get():
                if ev.type == pygame.QUIT:

                    quit()

                elif ev.type == pygame.KEYDOWN:
                    if ev.key == pygame.K_SPACE:
                        player.shoot()

                    elif ev.key == pygame.K_ESCAPE:
                        paused()
                        if ev.key == pygame.K_ESCAPE:
                            keep_going = True

            all_sprites.update()

            hits = pygame.sprite.groupcollide(enemies, bullets, True, True)
            for hit in hits:
                score += 100
                pygame.mixer.Sound.play(hit_sound)
                basic_enemy = Invaders()
                all_sprites.add(basic_enemy)
                enemies.add(basic_enemy)

            hits = pygame.sprite.spritecollide(player, enemies, False)
            if hits:
                pygame.mixer.Sound.play(player_death)
                keep_going = False
                game_over()

            all_sprites.draw(screen)
            draw_text(screen, str(score), 20, 500,600)
            pygame.display.flip()






game_loop()