[PD] Syncing an event with refresh rate in GEM

[cyrille henry]

Roman Haefeli a écrit :
...
>> this jitter make it impossible to compute 1 and only 1 frame for each frame on the screen, even with sync on vblank.
> 
> yo, i trapped my self by measuring with [timer].
> 
> anyway, if you calculate the average of these values, you'll come pretty
> close to 50ms (49.9094 to be accurate, though adding another 52.xx value
> will give you a result slightly above 50). 
yes.
> 
> i cannot see that as a prove for your statement, that this would make it
> impossible to show exactly one frame on each screenrefresh. let's say
> each gem render cycle happens just half in between each screen refresh
> tick, 
how could that be possible without syncronisation? 

>then the jitter could be almost 30ms in both directions without
> showing the same frame twice or leaving out one frame.
> 
> i made a patch, that  scrolls an image, whose pixel grid matches the
> pixel grid of the gemwin, by shifting the image an integer pixel value
> on each gem render cycle and i got an (almost) perfectly smooth and
> glitchfree movement, which is for me the empirical proof, that gem is
> able (or at least comes close) to show exactly one frame on each screen
> refresh tick. since gem and the screen apparently use different clocks,
> as mentioned in previous posts, this probably won't be true in the long
> run. 
i think we agree : "almost perfect" is not "perfect"...


cyrille


> i'd rather to not want to send the patch to list (because of the weight
> of the images), but if you want i could send it to you privately.
> 
> roman
> 
> 
> 
> 
> 
> 
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