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Any good dead reckoning examples?


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#1 BearishSun   Members   -  Reputation: 147

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Posted 20 September 2009 - 11:13 PM

Hi, I'm wondering if there are any good dead reckoning(I hope I'm using the term right) examples? I'm currently working on a MMO, and I have no previous experience with this I'm having problems syncing the data properly. Currently I send 5 updates per second(is this too low?). I run movement on both client and server and try to adjust the client data slightly based on the actual data received from the server although I have problems when character suddenly stops. (I can either have him standing at the wrong position client-side, or I can fix his position which causes him to "glide" to the new position). I'd really like that when he stops he stops pretty much near the actual server position, because I don't notice the gliding in other MMOs(unless under heavy lag). I've tried searching though many books and tutorials but I can't find anything useful, and I plan on spending the next month to have this working perfectly in my game, so it would be helpful to have a working and tested example. Or any advice? Thanks!

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#2 hplus0603   Moderators   -  Reputation: 5165

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Posted 21 September 2009 - 06:08 AM

If you extrapolate, stopping will be a problem no matter what.

An alternative is simply to display every entity based on data that you receive (interpolate between old positions). This will cause some latency in movement to be visible, but that's typically OK when you're doing an RPG.

If you want to do extrapolation, the sample app for the Entity Position Interpolation Code does show what it looks like.


#3 BearishSun   Members   -  Reputation: 147

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Posted 21 September 2009 - 07:18 AM

I do interpolation for the other(non-player) entities(250ms in the past) and that works fairly well.

I implemented and tried your algorithm a while ago although extrapolation just doesn't work too well for me, I guess I just haven't given it a proper try yet since the interpolation works pretty well. (I tried interpolating and switching to extrapolation only when I ran out of updates, which didn't work out too well)

But for the player character I use a different approach since I run the simulation both client and server side. Client sends basically WASD key presses to the server and the server sends a position update every 200ms. If the difference between client and server is too high the client tries to slightly adjust the players movement so that it will be closer to the servers position during the next update. However that doesn't work when stopping...

Problem is with the combat system I'm trying to do(I don't wanna do a WoW-style select&use skill system), but I wanna be able to swing the sword and hit anyone in front of the player. The problem is, when the player goes to attack someone, he stops in front of his enemy although those few ms it takes for the server to update on the server he actually ends up just barely behind his enemy. Therefore when he swings, the server checks if there's anyone in front of him and since there's noone no hit occurs. Although the client clearly sees he's standing in front of his enemy.

I don't know what would be the best way to handle that? Should the target selection happen client-side and then just loosely check if the enemy is range on the server? Although I fear that opens up opportunity for cheating.

Or maybe if the server checked the enemies previous position(when the "sword swing" packet was sent)?

#4 hplus0603   Moderators   -  Reputation: 5165

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Posted 21 September 2009 - 01:34 PM

One way to handle it is to show it "as is" on the client, and then turn the player attacks on the client into commands for the server (and other players) to see.

Another option is to simply delay everything by 250 milliseconds. Then it will all be in sync. The player will learn to compensate, and "brake" 250 milliseconds before he actually wants to stop.

#5 BearishSun   Members   -  Reputation: 147

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Posted 22 September 2009 - 06:03 AM

Thanks for the help, I'll try out a few different ways and see which(if any) work.




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