RE: [Algorithms] Game loop timings

[Jon W. <hp...@mi...>]

> there. It shows differences in path that are due to just framerate
> differences, and those that happen when you add truncatenation. Looks like
> step time doesn't make much difference. I believe that he was not using a
> simple Euler integrator there, though. I guess it was implicit Euler, but
> didn't bother to check thoroughly yet.

With non-fixed frame rates, you also have problems with penalty methods,
because object won't come to "rest" as easily. Consider a box lying on
the ground, not yet disabled. Each frame, gravity pulls it down into the
ground, and a penalty force based on penetration depth is added to the
box. With a longer time step, a greater force will be added. If the time
step jitters, then variable forces will be added to the box, leading to
a jittery box. With a fixed time step, the system will work like a
dampened spring, and come to stability.

Other positives of fixed step size include networking consistency, and
recording/replay, as well as consistent reproducibility of bugs.

I really can't think of any really good reason for variable frame time
except that it's sometimes the simplest to implement up-front.

Cheers,

			/ h+