[SDL] How calculate the frame per seconds

[David Olofson]

On Tuesday 18 May 2004 15.24, NighTiger wrote:
> I have write this code:
>
> newtime = 0;
> while ( !quit )
> {
> oldtime = newtime;
> newtime = SDL_GetTicks();
> quit = Keyboard();
> DrawObject();
> fps = (newtime - oldtime);
> printf("%i\n", fps);
> }
>
> it's wrong?

Yeah, that's "mspf"; milliseconds per frame. What you want is
	fps = 1 / (newtime - oldtime);

(Check that newtime != oldtime, of course, or you'll get a division by 
zero exception if the fps goes above 1000 and/or the timer has a 
hickup...)

However, you'll probably want some filtering or averaging on that.  
Timing one frame at a time isn't very accurate, part because of 
scheduling jitter; part because there just aren't too many ms per 
frame with decent frame rates.

The easiest way is to just calculate the average fps every N frames. 
That has the bonus effect of keeping the on-screen fps display from 
flickering hysterically.


//David Olofson - Programmer, Composer, Open Source Advocate

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