[PD] Syncing an event with refresh rate in GEM

Roman Haefeli reduzierer at yahoo.de
Fri Oct 12 01:49:15 CEST 2007

On Fri, 2007-10-12 at 00:48 +0200, cyrille henry wrote:
> Thomas O Fredericks a écrit :
> > "sync to vblank will sync swapping buffer with the screen frame rate, but
> > that's not the original question.
> > to my knowledge, there is no possibility to sync gem rendering with the
> > screen frame rate.
> > if you fix both at 60Hz, you can have jitter (not a lot, but some)."
> > 
> > You are not technically syncing gem to the screen frame rate.
> yes
> > You are
> > syncing the open gl redraw to the framerate. 
> yes
> >The GPU takes care of that.
> > 
> i don't understand this.
> if you get gem to render a 60FPS, you will have 60fps based on the pd (cpu) clock.

i don't know this by reading the code, but for me it would only make
sense to get the clock from the audio-card, nothing else. this is also
what i experienced, when pd was running on jackd, while jackd was
believing to be running at 44100Hz, while it was actually at 48000Hz.
all [metro]s were too fast and all pitches too high. the only objects,
that seems to work not with the audio-clock, that come to my mind, are
[cputime] and [realtime] (is that true?)

> if you set your screen at 60fps, you will have 60fps based on the gpu.
> there is no way to make the cpu clock to be exactely the same speed as the gpu clock.
> so, sometime (specially with big patch), you can have desincronisation between this 2 clocks, even if they should be at the same speed.
> (there is a also a lot's of jitter in pd clock)

what makes you think that? i 'd claim, that pd's clock is stable, unless
you get audio drop-outs. 


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