Time step

[blackbird_dream]

Hi.
I'd like to perform physik at 1000 Hz (constant time step).
Then display the scene with 2 options
1) when it can. at the risk of non smooth motions
2) slow motion (every 10 timesteps)

what are the best settings for that ?
Sorry if it's evergreen content.
I've read posts about the topic but it's not crystal clear in my mind.

Many thks

[Julio Jerez]

you can call the function to set the number of sub steps.
the time step you pass to the engine will be divided by that number.
when running async, the update does not interfere with graphics

[blackbird_dream]

ok thks

[Julio Jerez]

a 1000 fps is probably an over kill, but you can try any combination, I find that for most accurate simulation some from 250 to 300 has always gives expected result using newton for most people who has contacted my. Newton integrators are are RK4 internally so you get an implicit subdivision but a factor of four of the time step, in fact an RK4 step is much, much better than 4 eulers sub steps.
what you have to take int account is that the constraint dynamics there are make highly non linear forces and torque. for example newton is probably one the only physics solver that correctly model gyroscopy toques so that alone make the integration hard and we pay a price in performance for that.
but you can experiment with different time steps.

the function is this
NewtonSetNumberOfSubsteps (m_world, m_solverSubSteps);

you set that before you enter the loop and the you can newton update with the the time step. for example is the then step is 0.016 (that 60 fps) and you want to run the physics at 0.002 ms per step

them you do this
n = 0.016 / 0.002 = 8

then you call

Code: Select all

NewtonSetNumberOfSubsteps (m_world, 8);

and the update loop is

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      while (!exit)
      {
         NewtonUpdateAsync(m_world, 0.016);
      }


or

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      while (!exit)
      {
         NewtonUpdate(m_world, 0.016);
      }


the NewtonUpdateAsync return immidialtlly, so the physics run concurrent with your app.