Fix Your Timestep!, Unstable Physics & Smooth Animation Options

[abaraba]

in case you've been using some implementation of simulation stepping function based on, or similar to what is described in this article:
"Fix Your Timestep!"
http://www.gaffer.org/game-physics/fix-your-timestep

..then, you might be interested in 2nd opinion on these matters,
actually, after completing intensive research there was a realization that it turns out almost "everyone" is using some version of this algorithm with interpolation, including popular Physics engines, libraries and commercial console and PC games

..anyway, there is "a paper" on this,
and some 'bonus material' that actually turns this tech. paper into an Allegory Novella and couple of more other things.. how wonderful!


TITLE: Three Bugs With One Stone.. allegory continues
(RealTime Allegory Novel, Technical Paper and Chronological account of an Algorithm discovery)
http://www.geocities.com/ze_aks/myBooK/Thr...thOneStone.html

Chapters:
I) Genesis, anecdote
II) Divina Commedia, abysm spirale
III) Seraphim snd Nephilim, the chronicles
IV) Aspidochelone, physiologus
V) ..alegoria continua

..among other themes,
book most obviously and most practically addresses these issues:

---------------------------------------------------------------------
Common bugs in Havok, PhysX, Bullet, ODE, Ogre, Newton.. SOLVED!

Bug 1.) Few subSteps: "Moon gravity effects"
bUg 2.) A lot of subSteps: "Spiraling to death"
buG 3.) Interpolation VS. Temporal Distribution


Common mistakes and bugs related to fixedTimeStepping - UNCOVERED

a.) Design-Time Planning and Recognition of Hardware Min. Sys. Requirements
b.) "Scaling the World": Gravity, Mass, Size and Hidden Effects of fixedTimeStepping
c.) Jitter, Wobbles, Choppiness and Slowdowns: Unstable Physics & Smooth Animation
---------------------------------------------------------------------
Quick Overview: www.geocities.com/ze_aks/test/sampleTest.html

[Ylisar]

>>"I've spent a few minutes reverse engineering.."

hahaha, what are you talking about, algorithm is 3-5 lines of code

Oh rly?

+++"Half-solution A"
//----------------------------------------------------------------------
//-------------------------- *** 1st algo - scaling the TIME "inside"
static btClock realTime;
double simDT, anmDT, STEP;
double secCnt, deltaTime = 0.0;
int cnt, FPS, SPS, fpsTensor= 60;
int btDiscreteDynamicsWorld::stepSimulation(btScalar timeStep, int maxSubSteps, btScalar fixedTimeStep)
{
deltaTime= double(realTime.getTimeMicroseconds())*0.000001f;
if(deltaTime > 0.75) deltaTime= 0; STEP= fixedTimeStep;
m_localTime+= deltaTime; realTime.reset(); FPS++;
saveKinematicState(fixedTimeStep); applyGravity();
anmDT= deltaTime - simDT; if(cnt > 0) simDT/= cnt; cnt= 0;
while( m_localTime >= fixedTimeStep )
{
cnt++; SPS++; internalSingleStepSimulation(fixedTimeStep);
m_localTime-= (simDT >= STEP)? simDT+(STEP*anmDT*fpsTensor) : STEP;
}
synchronizeMotionStates(); clearForces();
simDT= double(realTime.getTimeMicroseconds())*0.000001f;
return cnt;
}


+++"Full-solution A" (simplistic accumulator)
//----------------------------------------------------------------------
//-------------------------- *** 2nd algo - capping the TIME "outside"
int btDiscreteDynamicsWorld::stepSimulation(
btScalar timeStep,int maxSubSteps, btScalar fixedTimeStep)
{
m_localTime+= (timeStep < fixedTimeStep*2)? timeStep : fixedTimeStep*2;
saveKinematicState(fixedTimeStep); applyGravity(); maxSubSteps= 0;
while( m_localTime >= fixedTimeStep )
{
internalSingleStepSimulation(fixedTimeStep);
m_localTime-= fixedTimeStep; maxSubSteps++;
}
synchronizeMotionStates(); clearForces();
return maxSubSteps;
}
//--------------------------------------------------------------------------------
//================================================================================

Anyway, send me a pm or something if you want some explanations Dunge, I'll probably exit the discussion with the clown.