python - Pygame の描画が正しく機能しない

Question

画面に単純な四角形を描くのに問題があります。描画に失敗する理由がわかりません。背景面に描画する、関数呼び出しの順序を変更するなど、いくつかのことを試しましたが、何も描画されないようです。ご覧のとおり、enemy() メソッドは赤い四角形を描画するはずですが、代わりに何も描画しません。それ以外の場合、ゲームは正常に実行されます。私は見落としていた単純なものだと確信しています..イライラします！

import pygame
from pygame.locals import *
from pygame.time import *
from pygame.font import *
from pygame.draw import *
import sys
pygame.font.init()
pygame.init()


screen = pygame.display.set_mode((700,300))
pygame.display.set_caption('something')

#--------------------------------------------------------------------

velX = 0
velY = 0
playerx = 20
player_filename = 'player.png'
player = pygame.image.load(player_filename)
playery = 150
clock = pygame.time.Clock()

#--------------------------------------------------------------------

def draw():         
    global velX
    global velY
    global playerx
    global playery

    red = pygame.Color(255,0,0)
    black = pygame.Color(0,0,0)

    level = "1"
    background = pygame.Surface(screen.get_size())
    background = background.convert()
    background.fill((255,255,255))
    screen.blit(background, (0,0))

    playerx = playerx + velX
    playery = playery + velY
    screen.blit(player, (playerx,playery))
    font = pygame.font.Font(None, 36)
    text = font.render(level, 1, black)
    screen.blit(text, (670,10))
    pygame.display.flip()

#--------------------------------------------------------------------

def enemySquares():
    enemySurf = pygame.Surface(screen.get_size())
    red = pygame.Color(255,0,0)
    enemy = pygame.Rect(200,50,20,20)
    pygame.draw.rect(enemySurf, red, enemy, 0)

#--------------------------------------------------------------------

def collisionWithBorder():
    if playerx > 680 or playerx < 0:
        pygame.quit()
        sys.exit()
    if playery > 280 or playery < 0:
        pygame.quit()
        sys.exit()

#--------------------------------------------------------------------

def playerFunc():
    keys_down = pygame.key.get_pressed()    
    pygame.key.set_repeat(1,50)
    time = 50/1000
    global velX
    global velY
    direction = -1

    if keys_down[K_d]:
        direction = 0
    if keys_down[K_a]:
        direction = 3
    if keys_down[K_w]:
        direction = 1
    if keys_down[K_s]:
        direction = 2

    if direction == 0:
        velX = 50*time
        velY = 0
    if direction == 1:
        velY = -50*time
        velX = 0
    if direction == 2:
        velY = 50*time
        velX = 0
    if direction == 3:
        velX = -50*time
        velY = 0

#--------------------------------------------------------------------

def main(): 
    while True:

        for event in pygame.event.get():   
            if event.type == QUIT:
                pygame.quit()
                sys.exit()

        clock.tick(50)        
        collisionWithBorder()
        draw()
        playerFunc()
        enemySquares()

#--------------------------------------------------------------------

if __name__ == '__main__':
    main()