Comments on: Fix Your Timestep!

By: Glenn Fiedler

Glenn Fiedler — Tue, 07 Sep 2010 03:39:02 +0000

There is more to come… an analysis of input latency and multithreaded approaches etc. but these will have to wait for a bit later. I felt the old article was getting a bit stale and I’m a bit happier with it now! cheers

By: Mitchell

Mitchell — Mon, 06 Sep 2010 21:58:41 +0000

Yea, that’s what I meant, thanks a lot for covering it, I understand it better now.

By: Glenn Fiedler

Glenn Fiedler — Mon, 06 Sep 2010 18:50:55 +0000

I’ve published the article update, let me know what you think!

By: Glenn Fiedler

Glenn Fiedler — Mon, 06 Sep 2010 03:18:07 +0000

It’s a lot simpler but it does not step forward with fixed delta time. If you don’t care about completely fixed delta time then it’s a perfectly good technique. I have a reworked version of this article which includes this as one of the options discussed.

By: Mitchell

Mitchell — Sat, 04 Sep 2010 23:56:54 +0000

Wouldn’t it be a lot simpler to just have a max time delta, so a physics step is never bigger than that maximum? Like this, keeping with your pseudocode:

double currentTime = hires_time_in_seconds();
State state;
double maxdt = 1.0 / 60.0;

while ( !quit )
{
double newTime = hires_time_in_seconds();
double dt = newTime – currentTime;
currentTime = newTime;

while (dt > maxdt) {
state.physicsStep(maxdt);
dt -= maxdt;
}
state.physicsStep(dt);

render(state);
}

By: admin

admin — Sun, 01 Aug 2010 09:01:18 +0000

Basically integrate just means to advance the simulation state forward. You can try it with something simpler like euler integration, eg. x += dxdt * dt if you like. cheers

By: admin

admin — Sun, 01 Aug 2010 08:59:25 +0000

This is a suitable implementation if you don’t need a fixed delta time, but for general 100% repeatability and same results each time run, I generally prefer the full fixed dt myself. cheers

By: Gregor

Gregor — Sat, 17 Jul 2010 08:47:52 +0000

siggraph course is brilliant, thank you

By: Glenn Fiedler

Glenn Fiedler — Fri, 16 Jul 2010 16:15:11 +0000

either way is good and it depends on the error you consider most acceptable during a sharp change in velocity – consider a particle moving very quickly and bouncing @ 45 degrees, cheers

By: Glenn Fiedler

Glenn Fiedler — Fri, 16 Jul 2010 16:13:47 +0000

if your game physics is mostly simple linear motion, you’ll probably get no real benefit. if you have more complex physics you’ll benefit from more consistent behavior with fixed timesteps.

so, work out how differently your game sim code behaves depending on framerate and if it’s significant or problematic then fixing the timestep is a good idea. some examples of where this is good, tunneling at low framerates if you don’t raycast, different behavior of springs at different delta time due to integrator errors etc.