#!/usr/bin/python
import math,sys,time,pygame
pygame.init()
screen = pygame.display.set_mode((640,480),pygame.FULLSCREEN|pygame.DOUBLEBUF|pygame.HWSURFACE)
c=0
while 1:
	c=((c+1)%2)*255
	for event in pygame.event.get():
		if event.type in [2,5,6,12]:
			sys.exit()
	screen.fill((c,c,c))
	pygame.display.flip()

#pygame.display.flip()
#If your display mode is using the flags pygame.HWSURFACE and pygame.DOUBLEBUF,
#this will wait for a vertical retrace and swap the surfaces. If you are using a
#different type of display mode, it will simply update the entire contents of
#the surface.