[ODE] interpolating between physics frames to get the actual positions in the render time

[John DeWeese]

If I understand correctly, you are running a physics simulation on a 
server as well as all clients simultaneously? If so, what exactly is 
being communicated between server and client? Sounds more like a 
peer-to-peer solution... problem is that it is beyond a huge pain in the 
ass to synchronize communication without big overhead. With 
client-server, you usually have an understanding that the states will be 
different, and that's OK as long as it's reasonably close. Thus, 
client-server model plus fancy client extrapolation for remote sessions.

If that's not the case, and when you say you "need deterministic results 
of the physics across different clients" you mean that you just want 
starting conditions to generate the same results on any kind of 
server... In this case you may be better off just implementing a state + 
event recording feature, and playing it back at whatever update rate the 
recording specifies, then you can just do interpolation between recent 
and nearest future state.

If this is a multi-player dealy, your input is going to be arbitrary and 
asynchronous anyway, so you won't care about the predictability of 
locking into one constant update rate for your clients.

juhani honkala wrote:

>thanks for your replies..
>
>I'm using 100 hz physics coz it's used in the multiplayer client/server so I
>need deterministic results of the physics across
>different clients(and in the server as well). This efficiently means that I
>can't lock the physics rate to an integer multiply of
>the screen refresh rate until I force the screen refresh rate(or frame rate)
>being 50 hz flat or some other meaningful value
>the every client can maintain. It's really the thing I don't want to do (not
>100% about that anymore tho;) Without need for
>the exact synchronization between the server and client would I definitely
>adjust the physics step to an integer multiply of
>the actual frame rate.. or even using variable physics timestep but in this
>case it's no-go i think.
>
>the idea of extrapolating instead on interpolating between the frames was
>kinda nice..would keep the lag smaller.
>
>Have to think about it.
>
>
>
>
>juhani
>
>
>
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