[Opensim-dev] Redesigning the Physics-Interface

[Melanie]

Hi,

I was planning to do that. The idea is to create / delete / modify 
physical composition from creation, linking, and deletion only.
E.g. CreatePhysicsActor(IEntity), RemovePhysicsActor(IEntity), where 
IEntity is a root entity (e.g. not a child of anything).
Link would delete the old physics actor and then create a new one 
from scratch after linking.

Melanie


Gerhard Dünnebeil wrote:
> Stefan,
> 
> sure, you are completely right.
> 
> But you should understand the ideas of the ODE. ODE knows about bodies 
> and geometries.
> 
> A body is something that has a mass and can move over time.
> A geometry describes the collision behaviour of a body but is a distinct 
> concept and the coupling is loose (means you can have bodies without a 
> geometry and geometries without a body).
> 
> An object without a geometry won't collide. If this is something 
> meaningful is another discussion.
> 
> A geometry without an object won't move on a collision. This is a static 
> object in SL speak.
> 
> It is possible to add more than one(!) geometry to one body thus 
> composing an object with a complex geometry but behaving as one rigid 
> entity.
> 
> Currently we create one geometry and one body for each prim. That is -- 
> as far as I understand things -- part of the instability problems. 
> Trying to fix that lead me into a situation where I have to reconstruct 
> the parent/child relationship from a lot of calls to the API. This leads 
> to situations where a child prim is created first -- with a geometry and 
> a body -- then linked to a parent so the body is destroyed again, ......
> 
> This is not only inefficient but very complex and error prone.
> 
> Things would be much easier if linked objects would be given to the 
> physics API as such. After all we want them to behave as exactly that: 
> one object.
> 
> Look at the new approach, you'll find an Orwell situation "each thing is 
> entity but some are more entity than others" as the current approach 
> also knows a hierachical relation ship.
> I just propose, this hierarchy is given to the phys engine in a 
> convenient way as well.
> 
> So "Or, would IEntity have a 'composite mesh' that is a combination of 
> all child meshes?" Not exactly but in a more lenient way of looking at 
> it, you are correct.
>  
> 
> Best regards
> Gerhard
> 
> 
> 
> Stefan Andersson wrote:
>> Errr... actually, aren't we going the exact opposite direction, with 
>> the 'everything is IEntity' approach?
>>
>> Or, would IEntity have a 'composite mesh' that is a combination of all 
>> child meshes?
>>  
>> I guess, to be able to collide with a child, you would still have to 
>> retain it as a separate mesh entity?
>>
>> Best regards,
>> Stefan Andersson
>> Tribal Media AB
>>  
>> Join the 3d web revolution : http://tribalnet.se/
>>  
>>
>>
>>
>>
>>
>> ------------------------------------------------------------------------
>>
>> Date: Sat, 22 Nov 2008 06:44:44 -0600
>> From: james.stallings at gmail.com
>> To: opensim-dev at lists.berlios.de
>> Subject: Re: [Opensim-dev] Redesigning the Physics-Interface
>>
>> Hello Gerhard :D
>>
>> Unless I am sadly mistaken, something of the sort is currently in 
>> progress.
>>
>> Cheers,
>> James
>>
>>
>> On Sat, Nov 22, 2008 at 6:37 AM, Gerhard Dünnebeil 
>> <Gerhard.Duennebeil at chello.at <mailto:Gerhard.Duennebeil at chello.at>> 
>> wrote:
>>
>>     Hi
>>
>>     this is the start of a discussion about the interface to the physics
>>     plugins.
>>
>>     After having tried working on the ODE plugin, specially focussed on
>>     linked objects I think the current interface has a severe short
>>     coming.
>>
>>     The problem I see is, that it is prim orientated while an object
>>     orientation would better suit the needs.
>>
>>     Why is it so?
>>
>>     Currently it seems to me, the information is given to the phys engine
>>     prim by prim. Any object information is only given in fragments.
>>     This leads to the situation that the object relations must be
>>     reconstructed by the phys engine and it often leads to the situation
>>     that individual prims get constructed and shortly after get destructed
>>     again as it turns out that the respective prim is part of a larger
>>     link set.
>>
>>     For that reason I ask your thoughts about a redesign of that
>>     interface.
>>
>>     Best regards
>>     Gerhard
>>
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>>
>>
>>
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