import pygame

def start_loop():
	global g_timer, g_elapsed
	g_elapsed = 0
	g_timer = pygame.time.get_ticks()
	
def next_frame():
	global g_timer, g_elapsed
	newticks = pygame.time.get_ticks()
	g_elapsed = newticks - g_timer
	g_timer = newticks
	
def elapsed():
	"""
	get the amount of time passed since the last frame was displayed
	"""
	return g_elapsed