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Network Interpolation

Posted on 1998-12-21
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How can I achieve a good network interpolation for realtime games. I want to write code that does the same that is done in Quake. If you have packet loss or if packets arrive in a wrong order the game should still behave approximately as it usually behaves (as in Quake). Please help.
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Question by:MarcoHelmers
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13 Comments
 
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Expert Comment

by:nil_dib
ID: 1326504
Why dont you use stream sockets?
Are you sure that games like quake works with datagram sockets?
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LVL 86

Expert Comment

by:jkr
ID: 1326505
My usual answer to this kind of problem is taking a look at RPC, which makes life easier concerning all the different network transports (TCP, IPX, NetBios etc.)... You might want to take a look at the 'Hello' sample that comes with VC++ ('\DEVSTUDIO\VC\SAMPLES\SDK\RPC\HELLO') before we continue...
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Expert Comment

by:jkr
ID: 1326506
nil_dib - sockets are usually OK, but what to do if there's no TCP/IP installed...?
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Expert Comment

by:nil_dib
ID: 1326507
mhh but in MFC I have socket support for DECNet, TCP/IP, IPX/SPX, NetBui ...
I think its also a problem to decide on which layer to put on ..4,5,6 ...
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Author Comment

by:MarcoHelmers
ID: 1326508
I think you did not understand my problem. I have no problem sending packets or so (I use DirectPlay) ... I only want to know how to interpolate movement in a realtime (3D) game like Quake when you have situations where packets arrive very late (e.g. internet) ! In Quake the server in some way interpolates the movement of the clients so that the game seems to run smooth (even if no packets arrive for a while !!). Can you tell me a good way how to do it ?
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Expert Comment

by:jkr
ID: 1326509
I'd recommend keeping track of the recent packets and 'extrapolate' the movement sequence from the behaviour in the near past (liear or nonlinear, depends on what applies better...)
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Author Comment

by:MarcoHelmers
ID: 1326510
Does that really help ? What if a person ran directly towards a wall and shortly before he can turn around no packets arrive any longer ? Shall he run against the wall for a few seconds ?
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LVL 86

Expert Comment

by:jkr
ID: 1326511
Nope ;-)
But the player has to remain there, as you hardly can make an assumption on what could be done...
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Author Comment

by:MarcoHelmers
ID: 1326512
Ok ... perhaps I did not completely understand you proposal ... could you explain it more precisely or perhaps even give some pseudo-coude to illustrate it ?
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LVL 86

Expert Comment

by:jkr
ID: 1326513
OK ;-)
Think of the following:
- you maintain a list of the last (let's say 2 for explanation purposes...) movement notifications

if there's a packet, all's well, add it to the list & remove the last

if there's no packet, calculate the (vectorial) difference of the last 2 moves and add the difference to the last move to create a new one and use it as if it was the arrived packet (this e.g. helps to maintain a circular movement - ok, it _could_ turn out to give a rediculus result)

if you decide to use more moving states, it might come in handy to treat them as a vectorial signal and use signal processing algorithms to extrapolate it (you see, i usually don't write games, but have done quite a lot signal processing... ;-)
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LVL 86

Expert Comment

by:jkr
ID: 1326514
Hmm, what's gonna happen with this Q? ;-)
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Author Comment

by:MarcoHelmers
ID: 1326515
Ok ... it would have been great if there would have been other ideas and suggestions but as this is not the case:
jkr: Please lock the question so that I can give you the points.
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LVL 86

Accepted Solution

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jkr earned 300 total points
ID: 1326516
Thanx ;-)

BTW/PS: 'MarcoHelmers' sounds quite 'german', so: 'Gruß aus Schwaben' ;-)
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