[SDL] object's speed control against different framerates

[C.Alvarez]

do you know some documentation that could help me to learn a best way
to implement fixed time step against free framerate?

2007/4/28, Tommy Hinks <tommy.hinks at gmail.com>:
> The thing to watch out for is if you have more complicated equations
> to solve. In your case it seems to be x = v*dt. This equation is not
> extremely sensitive for large timesteps, but other equations are. The
> problem is then that if the framerate drops, the physics of the
> simulation crash. Just something to be aware of. You might even notice
> this effect if you add acceleration to the equations you have now.
>
> One solution to this problem is to simply set a maximum allowed
> timestep, but this means that the application is no longer produces
> the same results for the same amount of frames.
>
> Tommy
>
> On 27/04/07, Jeffrey Grembecki <tophatfox at gmail.com> wrote:
> > On Fri, 27 Apr 2007 16:48:58 +0200
> > C.Alvarez <blubzouf at gmail.com> wrote:
> >
> > > For time based movements, I use a basic pos = pos + speed * lastframetime
> > > When I move an object with constant speed during constant time, one
> > > second for example, I have no problem to end the movement at the same
> > > position in any framerate.
> > >
> > > When I tried to include variable speed movement, this seems to be a
> > > little more complicated to interpolate the speed variation.
> > >
> > > I have made this little code to explain what I mean, it just need to
> > > press space to start the test, runs a desired movement, decreases the
> > > speed, and automatically ends ( with log in stdout.txt ).
> >
> > Without looking at the code it sounds like a lack of precision. I've found the
> > best method for timing is to use a fixed timer on the game loop, say 25 fps
> > and within the render function do interpolation.
> >
> > This method while very good does add a little complication with the addition
> > of prediction of events within the render function.
> >
> > The advantage is your game loop will always result in the same output no
> > matter what frame rate you have and it is also possible to record player
> > input for a replay.
> >
> > There's a good article on the subject at
> > http://dewitters.koonsolo.com/gameloop.html
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