Question

I’m having a problem with evenly moving sprites; Currently I’m using a while loop to move them, the problem with this being the faster the computer, the faster the loop goes and the faster the sprites move. I have tried the timer / clock function (wait?) in pygame and it freezes the cursor while it waits, therefore maiking the cursor jumpy.

Is multi-threading the answer?

Here’s a video of my problem;
http://www.youtube.com/watch?v=cFawkUJhf30

Answer 1

You’re dependent of the framerate, faster the framerate is, faster your movement will be.

Usually, we are calculating the time between 2 frames/loop iteration, and we called it the “delta time”. Then we multiply that delta time to the movement vector.

Here is a loop sample:

clock = pygame.time.Clock()
while True:
    # limit the framerate and get the delta time
    dt = clock.tick(60)

    # convert the delta to seconds (for easier calculation)
    speed = 1 / float(dt)

    # do all your stuff, calculate your heroes vector movement
    # if heroes position is "px, py" and movement is "mx, my"
    # then multiply with speed
    px *= mx * speed
    py *= my * speed

Then the movement are following the framerate: if your loop is faster, then the delta is lower, and then the movement are slower per frame => the result will have the same speed whatever the framerate is.

You’re now framerate independent.