[sldev] movement within the client

[Lawson English]

John Hurliman wrote:
> Callum Lerwick wrote:
>> On Mon, 2007-12-31 at 15:06 -0600, Argent Stonecutter wrote:
>>  
>>> On 2007-12-31, at 14:06, Callum Lerwick wrote:
>>>    
>>>> (And of course we can and should always ask the question, "How does
>>>> Quake 1/2/3, Doom3, HL 1/2, Unreal etc etc game engines handle this?",
>>>> they've been doing this for years... AFAIK a major difference is they
>>>> all perform collisions/physics simultaneously on the client and  
>>>> server,
>>>> and resolve any de-synchronization by holding the server  
>>>> authoritative.)
>>>>       
>>> Would that require making Havok part of the client code?
>>>     
>>
>> Good question, actually. I'd like to know how Doom3 (Which is apparently
>> "id Tech 4" now) and Source handle this. Do all clients really perform
>> full physics simulation? Is the physics simulation predictable enough to
>> do this on large numbers of colliding objects? The Source engine is
>> Havok based, actually. However John Carmack has to reinvent the wheel as
>> usual.
>>
>> Still, full client prediction of physics is orthogonal to the
>> functionality I/we want. Better client prediction would be nice. The
>> "fall through the ground then suddenly pop backwards" thing that happens
>> in laggy situations, especially when crossing sims, especially in
>> vehicles, is really annoying and I don't even understands why this
>> happens. Is the client simulating gravity? As well as the "walk forever"
>> thing that happens. The client does not seem to have any code in it that
>> does something like "I have not received any updates from the sim in x
>> seconds/milliseconds, I should stop moving the avatar as it is likely
>> not what is intended by the user".
>>   
>
> Second Life clients use http://en.wikipedia.org/wiki/Dead_reckoning 
> based on position, velocity, acceleration, angular acceleration, and 
> an attempt to synchronize time steps between the client and the sim. 
> If you jump in the air and then start falling down or you stop flying 
> and the sim hiccups in sending you position updates, or you are 
> crossing a border at the time and the handover goes less then 
> seamlessly you will probably start falling through the earth. The 
> client *could* do basic collision detection with the avatar and the 
> terrain heightmap to prevent this effect.
>

That might help get rid of the worst of the errors, but it won't give SL 
WOW/EQ fighting capabilties, I think.

In the long run, the clients will have to be modded to allow for this 
functionality on certain grids, even if the "pure" SL grid doesn't do 
it. IN WW Groupies, we've been talking about allowing for P2P 
capabilities in some future version of the client. That way, clients on 
a given sim could pass physics and other data to each other without 
havig to wait for the all-too-slow SL strategy of physics handling. Same 
kind of thing could allow for distributed processing in AI sims, or 
sharing/synchronization of MIDI/audio data in some kind of performance 
sim, etc.

Lawson