On Wed, Feb 3, 2010 at 3:30 PM, R. Alan Monroe <amon...@columbus.rr.com>wrote:
> > The nice thing about limiting the framerate versus having calculations be > > done based on time passed is that it is much more consistent. With dt > > calculations you will often get huge jumps on slower computers and extra > > slow movement in cases on fast machines, just do to inaccuracies and > error > > in the calculation. On a slower machine, no matter which timing method > you > > use it will be unpleasant. > > What kind of innacuracies, specifically? > > Any time-step based integration of non-linear functions will have errors and inaccuracies, which are larger the larger the time-step is. ...and pretty much all interesting real world physics are non-linear functions. So gravity for instance - if acceleration = time*gravity and position = time*acceleration, the relationship between position and gravity over time is nonlinear, specifically it changes with the square of time elapsed (position = time*time*gravity). Doing that calculation as the sum of repeated linear calculations, will have error. The magnitude of that error will change with your time-step size. The way that's a problem with a game, is when a level is dsigned so that gap is exactly the right distance to be able to jump across it - but then some slower computer uses a different larger time-step than your level designer - so on that fast computer, you can't make the jump, cause the error on the gravity effect is higher, so it pulls the player down sooner. Some other examples of non-linear places with error are springs, friction, application of the force of explosions that aren't instantaneous, etc. etc. All those things and more will behave differently based on your time-step.
