The frame rate or refresh rate is the number of pictures that the program draws per second, and is measured in FPS or frames per second. (On computer monitors, the common name for FPS is hertz. Many monitors have a frame rate of 60 hertz, or 60 frames per second.) A low frame rate in video games can make the game look choppy or jumpy. If the program has too much code to run to draw to the screen frequently enough, then the FPS goes down. But the games in this book are simple enough that this won’t be issue even on old computers.
pygame.time.Clock object can help us make sure our program runs at a certain maximum FPS. This
Clock object will ensure that our game programs don’t run too fast by putting in small pauses on each iteration of the game loop. If we didn’t have these pauses, our game program would run as fast as the computer could run it. This is often too fast for the player, and as computers get faster they would run the game faster too. A call to the
tick() method of a
Clock object in the game loop can make sure the game runs at the same speed no matter how fast of a computer it runs on. The
Clock object is created on line 7 of the
import pygame, sys from pygame.locals import * pygame.init() FPS = 30 # frames per second setting fpsClock = pygame.time.Clock() # set up the window DISPLAYSURF = pygame.display.set_mode((400, 300), 0, 32) pygame.display.set_caption('Animation') WHITE = (255, 255, 255) catImg = pygame.image.load('cat.png') catx = 10 caty = 10 direction = 'right' while True: # the main game loop DISPLAYSURF.fill(WHITE) if direction == 'right': catx += 5 if catx == 280: direction = 'down' elif direction == 'down': caty += 5 if caty == 220: direction = 'left' elif direction == 'left': catx -= 5 if catx == 10: direction = 'up' elif direction == 'up': caty -= 5 if caty == 10: direction = 'right' DISPLAYSURF.blit(catImg, (catx, caty)) for event in pygame.event.get(): if event.type == QUIT: pygame.quit() sys.exit() pygame.display.update() fpsClock.tick(FPS)
tick() method should be called at the very end of the game loop, after the call to
pygame.display.update(). The length of the pause is calculated based on how long it has been since the previous call to
tick(), which would have taken place at the end of the previous iteration of the game loop. (The first time the
tick() method is called, it doesn’t pause at all.) In the animation program, is it run on line 47 as the last instruction in the game loop.
All you need to know is that you should call the
tick() method once per iteration through the game loop at the end of the loop. Usually this is right after the call to
Try modifying the
FPS constant variable to run the same program at different frame rates. Setting it to a lower value would make the program run slower. Setting it to a higher value would make the program run faster.