Re: [GD-General] Sports Game Replay

[Stephen C. <sc...@in...>]

For the football game I worked on we actually kept game state for each frame
instead of recreating it from stored inputs.  The downside, as you might
expect, was memory cost.  The advantage was that we could easily allow the
player to jog the replay forward or backward a any speed instead of just
presenting a canned replay shot.  Interpolating between frames gave a pretty
good smooth slow-motion effect, too.  Since it was a football game with
discrete downs we only needed to keep a single play's worth of data making
this approach viable.  It all depends on your requirements.

Stephen

----- Original Message ----- 
From: "Kent Quirk" <ken...@co...>
To: <gam...@li...>
Sent: Tuesday, January 25, 2005 5:17 AM
Subject: Re: [GD-General] Sports Game Replay


> It's not naive, but it's not trivial to get right.
>
> You have to make sure you record and play back ALL forms of input -- which
> is basically anything that can affect your performance. This includes
exact
> timing and random number generation. One way of doing it is to feed all
> your input through a queue and include timing information in the input
> stream. It might be easier to think of the timing information as delay
> messages on the input stream, rather than tagging each event with a time.
> (Makes it easier to stretch timing or pause by increasing the delay
> messages without affecting the relationship between other objects.)
>
> One of the difficulties we ran into when we tried this was repeatability
of
> the detailed collision data. We ended up forcing the position of all
> movable objects in the world to something like 4 or 5 digits of precision
> every frame. It kept minor changes in floating point bits from blowing up
> and affecting future actions ("the butterfly effect"). Depending on the
> size of your world, this may be harder.
>
> You also have to have fixed-framerate physics. Don't expect to adjust your
> physics time tick size from frame to frame. If you decide to do
slow-motion
> and want it to look smooth, don't try to run your physics at a higher
frame
> rate in the world -- run the physics at the same rate but interpolate
> between frames.
>
>          Kent
>
>
>
> At 08:35 PM 1/24/2005, you wrote:
> >Hiya,
> >I think this is as good place as any to post this...
> >
> >We're just starting a new sports game project, and we have been asked to
> >provide replays of the action.  We have done many sports games before,
but
> >oddly none had a replay feature (was never requested before by
publisher).
> >Anyways, can anybody provide any tips or insights into things we need to
> >watch out for or methods to support this feature?
> >
> >The game needs to run on the PS2 so memory and IO is limited.  Our
> >characters use virtual controllers for all the movement so is it naive to
> >just compress and store controller inputs for everything and then rerun
the
> >simulation with that?
> >
> >Cheers,
> >-bb
> >
> >
> >
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> ----
> Kent Quirk
> CTO, CogniToy
>
>
>
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