[PD] Syncing an event with refresh rate in GEM

Roman Haefeli reduzierer at yahoo.de
Fri Oct 12 02:21:43 CEST 2007

On Fri, 2007-10-12 at 01:49 +0200, Roman Haefeli wrote:
> 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. 

yo, it seems, that [gemhead] uses pd's logical time, which probably
makes a lot of sense for many applications. 

but for many other applications it would be better (read: the result
would look nicer), if [gemhead] would get it's tick from the gpu and not
from pd/audiocard, i think.

is that something that would be possible to do and might be worth a
feature request on gem-dev?


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