求助pygame只运行程序不显示窗体

import pygame
from pygame.locals import *
import sys
SCREENWIDTH = 822
SCREENHEIGHT = 199
FPS = 30
def mainGame():
    score = 0
    over = False
    global SCREEN, FPSCLOCK
    pygame.init()
    FPSCLOCK = pygame.time.Clock()
    SCREEN = pygame.set_mode((SCREENWIDTH, SCREENHEIGHT))
    pygame.display.set_caption('玛丽冒险')
    while True:
        for event in pygame.event.get():
            if event.type == QUIT:
                pygame.quit()
                sys.exit()
        pygame.display.update()
        FPSCLOCK.tick(FPS)
if __name__ == '__main__':
    mainGame