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Remember the Subsurfaces from the last step ? And remember that the snake had always the same grinning facial expression ? Now, let's make some animated sprites1) - not pygame sprites, but surfaces that show different images of an animation cycle, like a bird flapping it wings.
Instead of painting all the single pictures of an animation cycle myself i prefer to use ready-made sprite sheets. In the data folder, you will find a spritesheet2) from Ari Feldmann ( http://www.flyingyogi.com ) showing several pictures of an animal. If you use Ari's sprite's, make sure to include his license information into your program.
With the help of pygame's subsurface command, i will show you how to extract single images from the sprite sheet and use them.
# -*- coding: utf-8 -*- """ step008.py animation & spritesheet url: http://thepythongamebook.com/en:part2:pygame:step008 author: email@example.com spritesheet from http://www.flyingyogi.com """ import pygame import random import os pygame.init() screen=pygame.display.set_mode((800,480)) # try out larger values and see what happens ! screenrect = screen.get_rect() background = pygame.Surface((screen.get_size())) backgroundrect = background.get_rect() background.fill((255,255,255)) # fill white background = background.convert() screen.blit(background,(0,0)) # mypicture = pygame.image.load("picturefile.jpg") # simple method if picture in same folder folder = "data" # replace with "." if pictures lay in the same folder as program spritesheet = pygame.image.load(os.path.join(folder, "char9.bmp")).convert() # all in one line lions =  # a list for the lion images # the spritesheet has lions, 128 x 64 pixels for nbr in range(1,5,1): # first line contains 4 picutres of lions lions.append(spritesheet.subsurface((127*(nbr-1),64,127,127))) for nbr in range(5,7,1): # second line contains 2 pictures of lions lions.append(spritesheet.subsurface((127*(nbr-5),262-64,127,127))) print "len:",len(lions) for nbr in range(len(lions)): lions[nbr].set_colorkey((0,0,0)) # black transparent lions[nbr] = lions[nbr].convert_alpha() print "converted nbr", nbr for nbr in range(len(lions)): screen.blit(lions[nbr], (nbr*127, 0)) #blit the ball surface on the screen (on top of background) print "blitted nbr", nbr screen.blit(lions[nbr], (nbr*127, 0)) #blit the ball surface on the screen (on top of background) #screen.blit(lions, (x, clock = pygame.time.Clock() #create pygame clock object mainloop = True FPS = 60 # desired max. framerate in frames per second. playtime = 0 cycletime = 0 newnr = 0 # index of the first lionimage to display oldnr = 0 # needed to compare if image has changed interval = .15 # how long one single images should be displayed in seconds while mainloop: milliseconds = clock.tick(FPS) # milliseconds passed since last frame seconds = milliseconds / 1000.0 # seconds passed since last frame (float) playtime += seconds cycletime += seconds if cycletime > interval: cycletime = 0 newnr += 1 picnr = int(newnr % 5) # the remainder of a division by 5, because 6 pictures are present (0...5) mypicture = lions[picnr] if newnr > oldnr: #print "change to picture nr %i" % picnr # clean dirty rec (a bit larger than original rect): screen.blit(background.subsurface((300,300,128,66)),(300,300)) # blit new lion picture: screen.blit(mypicture, (300,300)) oldnr = newnr # save oldnr for event in pygame.event.get(): if event.type == pygame.QUIT: mainloop = False # pygame window closed by user elif event.type == pygame.KEYDOWN: if event.key == pygame.K_ESCAPE: mainloop = False # user pressed ESC pygame.display.set_caption("[FPS]: %.2f picture: %i" % (clock.get_fps(), picnr)) #this would repaint the whole screen (secure, but slow) #screen.blit(background, (0,0)) #draw background on screen (overwriting all) pygame.display.flip() # flip the screen 30 times a second print "This 'game' was played for %.2f seconds" % playtime