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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