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Re: [pygame] Why does pygame get so high CPU usage?

Psymaster wrote:

while 1:
    for event in pygame.event.get(QUIT):
        sys.exit()
    pygame.event.pump()
this is the part of your program that is burning cpu. this will get the same cpu usage as something like

while 1:
a = 5

something like this will use 100% cpu in any programming language on any platform. the program will use every available resource to constantly run what is in the loop. the good news is pygame gives you a few ways to scale back your program and use 0% of the cpu.

the first and easiest is usually used by simple games or test programs. you simply call "pygame.time.wait(1)" somewhere in your mainloop. on all platforms, the wait() function 'releases' the process control back to the os kernel. a wait value of 1 in your loop will drop the cpu down to about 2-5%. if you go all the way up to wait(5) the program will definitely be under 1%. the wait method is simple, but it doesn't get the cpu usage as low as it can go, and it doesn't work well for games where framerate is important.

for programs that have no real animation there is a better way. this is similar to the method used inside all GUI libraries. the trick is that the program doesn't need to do anything until the user does something with it. there is another 'wait' function in the event module. "pygame.event.wait()". this will freeze your program until there is some sort of event from the user or window system. using this method the program really will take 0% of the cpu, unless the user is interacting with the program. note that the MOUSEMOTION event can happen very often when the user is moving the mouse. if you don't care
about the mouse movement you can block those messages and save even more cpu time. your mainloop would look like this using the event.wait,

pygame.event.set_blocked(MOUSEMOTION)
while 1:
event = pygame.event.wait()
if event.type == QUIT:
sys.exit()


the other method involves using the pygame.time.Clock objects to help limit the program framerate. this would be more useful in larger games, but overkill for an image viewer.

hmm, time to start a FAQ.