[ODE] ODE behavior depends on frame rate. How to avoid this?

[David McClurg]

How long is a tick in your simulation?  I was thinking 0.01s with a collide every 0.03s.

-----Original Message-----
From: Shaul Kedem [mailto:shaul_kedem@yahoo.com]
Sent: Monday, 3 February 2003 6:20 PM
To: David McClurg; Sergey; ode@q12.org
Subject: RE: [ODE] ODE behavior depends on frame rate. How to avoid
this?


Hi,
 I tried your method: in my testing environment (
similar to test_boxstack) I added a tik which every 3
calls to dWorldStep() runs dSpaceCollide() once.
I observed two things:
1. The object were jittering much more. the whole
system looked less stable (although no exploding
occurred)
2. Boxes in the stack penetrated each other, and the
collision/physics library couldn't untangle it later.

Shaul

--- David McClurg <dmcclurg@pandemicstudios.com.au>
wrote:
> I just realized that you don't have to run your
> collisions (dSpaceCollide()) at the same rate as
> your movement (dWorldStep()).  You could run
> collisions every other or every third tick since
> they are so expensive but still run your movement
> every tick for visual smoothness.
> 
> that's a good thing imo for a simple game running in
> a single thread and needing some determinism for
> network play.
> 
> -----Original Message-----
> From: David McClurg 
> Sent: Monday, 3 February 2003 10:36 AM
> To: Sergey; ode@q12.org
> Subject: RE: [ODE] ODE behavior depends on frame
> rate. How to avoid
> this?
> 
> what about replacing
> 
>  dWorldStep (worldID, fTimeBetweenFrames);
> 
> with...
> 
>  while (simTime < curTime)
>  {
>    dWorldStep (worldID, simTick);
>    simTime += simTick;
>  }
> 
> where curTime is the current time, simTime is the
> accumulated simulation time, and simTick is a small
> constant increment.
> 
> sometimes with this approach you'll need to monitor
> the number of sim ticks per frame and if they
> oscillate back and forth like 1,2,1,2,1,2 you need
> to ideally make your sim tick smaller (1/120.f) or
> (1/180.f) or add some smoothing so it goes
> 1,1,1,2,2,2,1,1,1,2,2,2
> 
> -----Original Message-----
> From: Sergey [mailto:sergey_eu@cea.ru]
> Sent: Sunday, 2 February 2003 5:33 AM
> To: ode@q12.org
> Subject: [ODE] ODE behavior depends on frame rate.
> How to avoid this?
> 
> 
> Hello,
> 
> I am creating simple arcade racing game and recently
> have faced the
> following problem: ODE behavior depends on frame
> rate because I use
> dWorldStep (worldID, fTimeBetweenFrames)
> 
> I've read suggestion to divide physics and render
> cycles: use thread
> for physics step and use main game cycle for
> rendering, but this won't
> work in my case because I use modified Windows
> messaging cycle
> (PeekMessage () instead of GetMessage ()) and
> unfortunately threads
> does not work with PeekMessage () :( 
> 
> 
> How can I avoid dependency on frame rate? Any
> suggestions are welcome.
> 
> Sergei.
>