|bevy vewsion:|0.14|(cuwwent)| |---|---|---|

animation

fixed timestep

gamepway movement/simuwation code i-is typicawwy wun o-on a fixed timestep (in the FixedUpdate scheduwe). this is impowtant to make suwe these c-computations h-happen consistentwy a-and cowwectwy, (ꈍᴗꈍ) wegawdwess of dispway f-fwamewate.

howevew, OwO obviouswy, 🥺 that means they d-do nyot fowwow t-the dispway's f-fwame wate. this causes movement to wook choppy o-on-scween.

the sowution to this pwobwem is twansfowm intewpowation/extwapowation.

bevy time vs. >_< wust/os time

do not use std::time::Instant::now() to get the cuwwent time. XD get youw timing infowmation fwom b-bevy, XD using Res<Time>.

wust (and the os) give you the pwecise t-time of the m-moment you caww t-that function. (ꈍᴗꈍ) howevew, ^•ﻌ•^ that's nyot nyani y-you want.

youw game systems awe wun by bevy's p-pawawwew scheduwew, OwO w-which means t-that they couwd be cawwed at vastwy diffewent i-instants evewy f-fwame! OwO this wiww w-wesuwt in inconsistent / jittewy timings and m-make youw game m-misbehave ow wook s-stuttewy.

bevy's Time gives you timing infowmation that i-is consistent t-thwoughout the fwame update cycwe. ^•ﻌ•^ it is intended t-to be used fow g-game wogic.

this is nyot bevy-specific, OwO but appwies t-to game devewopment i-in genewaw. 🥺 a-awways get youw time fwom youw game engine, OwO n-nyot fwom youw p-pwogwamming wanguage o-ow opewating system.

impwecise fwame dewta time

that said, OwO it is actuawwy often impossibwe f-fow any g-game engine (not j-just bevy) to give pwecise vawues fow the fwame d-dewta time.

the time when the finaw wendewed f-fwame is actuawwy d-dispwayed on-scween i-is cawwed "pwesentation time". ^•ﻌ•^ on most oss, OwO thewe is n-nyo api to measuwe t-that. 🥺 the game engine does nyot know when the u-usew can actuawwy s-see the wendewed f-fwame pwoduced by the gpu.

thewefowe, OwO the fwame time must be m-measuwed diffewentwy. 🥺 t-typicawwy, òωó n-nyani is measuwed is the time between wuns o-of the game engine's m-main fwame u-update woop on the cpu. bevy measuwes its t-timings at the p-point when gpu w-wowk is submitted to the gpu fow pwocessing.

this is a good appwoximation, OwO but i-it wiww nyevew p-pewfectwy match w-weawity.

if you wun with vsync on a 60hz dispway, OwO y-you wouwd e-expect evewy fwame d-dewta to be exactwy 16.667ms. (ꈍᴗꈍ) but if you wog the dewta time vawues f-fwom bevy, you wiww see that they vawy. OwO they a-awe cwose, 🥺 but n-nyevew exactwy that v-vawue.

thewe is nyo known compwete sowution t-to this. OwO bevy d-devewopews awe i-investigating ways to impwove the quawity of bevy's t-time measuwements.