text: 
  # date: 2019.04.05
  # https://stackoverflow.com/a/55533542/1832058
  
  import pygame
  
  black = (0,0,0)
  white = (255,255,255)
  gray  = (128,128,128)
  red   = (255,0,0)
  
  pygame.init()
  gameDisplay = pygame.display.set_mode( (800,600))
  clock = pygame.time.Clock()
  
  def button(msg,x,y,w,h,ic,ac,action=None):
      mouse = pygame.mouse.get_pos()
      click = pygame.mouse.get_pressed()
      
      if x+w > mouse[0] > x and y+h > mouse[1] > y:
          pygame.draw.rect(gameDisplay, ac, (x,y,w,h))
          if click[0] == 1 and action != None:
              action()         
      else:
          pygame.draw.rect(gameDisplay, ic, (x,y,w,h))
  
      smallText = pygame.font.SysFont("comicsansms",20)
      textSurf = smallText.render(msg, True, red)
      textRect = textSurf.get_rect()
      textRect.center = ( (x+(w/2)), (y+(h/2)) )
      gameDisplay.blit(textSurf, textRect)
  
  def change_draw_to_intro():
      global draw
      draw = draw_intro
  
  def change_draw_to_other():
      global draw
      draw = draw_other
  
  def change_draw_to_BE01():
      global draw
      draw = draw_BE01
  
  def draw_BE01():
      gameDisplay.fill(white)
      #gameDisplay.blit(BE01Img,(0,0))
      button("BACK",350,450,100,50,black,gray,change_draw_to_intro)
  
  def draw_intro():
      gameDisplay.fill(white)
      #gameDisplay.blit(introImg,(0,0))
      button("START",350,450,100,50,black,gray,change_draw_to_other)
  
  def draw_other():
      gameDisplay.fill(white)
      #gameDisplay.blit(scene01Img,(0,0))
      button("1",200,450,100,50,black,gray,change_draw_to_BE01)
      
  def quitgame():
      pygame.quit()
      quit()   
  
  def game_loop():
      global draw
      
      draw = draw_intro
      
      gameExit = False
  
      while not gameExit:
  
          for event in pygame.event.get():
              if event.type == pygame.QUIT:
                  pygame.quit()
                  quit()
  
          draw()
  
          pygame.display.update()
          clock.tick(60)
  
  game_loop()
  pygame.quit()
  quit()
  