<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:arial,helvetica,sans-serif;font-size:12pt"><div>Well, also consider, Gerhard that ODE has the notions of "spaces", which are collections of geom's and somewhat analagous to a linked set in OpenSim. We are already using the spaceCollide functions to collide spaces, i.e., collections of prims/geoms.<br><br>Charles<br></div><div style="font-family: arial,helvetica,sans-serif; font-size: 12pt;"><br><div style="font-family: arial,helvetica,sans-serif; font-size: 13px;"><font size="2" face="Tahoma"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> Gerhard Dünnebeil <Gerhard.Duennebeil@chello.at><br><b><span style="font-weight: bold;">To:</span></b> opensim-dev@lists.berlios.de<br><b><span style="font-weight: bold;">Sent:</span></b> Saturday, November 22, 2008 7:28:39 AM<br><b><span style="font-weight: bold;">Subject:</span></b> Re:
[Opensim-dev] Redesigning the Physics-Interface<br></font><br>
Stefan,<br><br>sure, you are completely right.<br><br>But you should understand the ideas of the ODE. ODE knows about bodies <br>and geometries.<br><br>A body is something that has a mass and can move over time.<br>A geometry describes the collision behaviour of a body but is a distinct <br>concept and the coupling is loose (means you can have bodies without a <br>geometry and geometries without a body).<br><br>An object without a geometry won't collide. If this is something <br>meaningful is another discussion.<br><br>A geometry without an object won't move on a collision. This is a static <br>object in SL speak.<br><br>It is possible to add more than one(!) geometry to one body thus <br>composing an object with a complex geometry but behaving as one rigid <br>entity.<br><br>Currently we create one geometry and one body for each prim. That is -- <br>as far as I understand things -- part of the instability problems. <br>Trying to fix that lead me into a
situation where I have to reconstruct <br>the parent/child relationship from a lot of calls to the API. This leads <br>to situations where a child prim is created first -- with a geometry and <br>a body -- then linked to a parent so the body is destroyed again, ......<br><br>This is not only inefficient but very complex and error prone.<br><br>Things would be much easier if linked objects would be given to the <br>physics API as such. After all we want them to behave as exactly that: <br>one object.<br><br>Look at the new approach, you'll find an Orwell situation "each thing is <br>entity but some are more entity than others" as the current approach <br>also knows a hierachical relation ship.<br>I just propose, this hierarchy is given to the phys engine in a <br>convenient way as well.<br><br>So "Or, would IEntity have a 'composite mesh' that is a combination of <br>all child meshes?" Not exactly but in a more lenient way of looking at <br>it, you are
correct.<br> <br><br>Best regards<br>Gerhard<br><br><br><br>Stefan Andersson wrote:<br>> Errr... actually, aren't we going the exact opposite direction, with <br>> the 'everything is IEntity' approach?<br>><br>> Or, would IEntity have a 'composite mesh' that is a combination of all <br>> child meshes?<br>> <br>> I guess, to be able to collide with a child, you would still have to <br>> retain it as a separate mesh entity?<br>><br>> Best regards,<br>> Stefan Andersson<br>> Tribal Media AB<br>> <br>> Join the 3d web revolution : <a href="http://tribalnet.se/" target="_blank">http://tribalnet.se/</a><br>> <br>><br>><br>><br>><br>><br>> ------------------------------------------------------------------------<br>><br>> Date: Sat, 22 Nov 2008 06:44:44 -0600<br>> From: <a ymailto="mailto:james.stallings@gmail.com"
href="mailto:james.stallings@gmail.com">james.stallings@gmail.com</a><br>> To: <a ymailto="mailto:opensim-dev@lists.berlios.de" href="mailto:opensim-dev@lists.berlios.de">opensim-dev@lists.berlios.de</a><br>> Subject: Re: [Opensim-dev] Redesigning the Physics-Interface<br>><br>> Hello Gerhard :D<br>><br>> Unless I am sadly mistaken, something of the sort is currently in <br>> progress.<br>><br>> Cheers,<br>> James<br>><br>><br>> On Sat, Nov 22, 2008 at 6:37 AM, Gerhard Dünnebeil <br>> <<a ymailto="mailto:Gerhard.Duennebeil@chello.at" href="mailto:Gerhard.Duennebeil@chello.at">Gerhard.Duennebeil@chello.at</a> <mailto:<a ymailto="mailto:Gerhard.Duennebeil@chello.at" href="mailto:Gerhard.Duennebeil@chello.at">Gerhard.Duennebeil@chello.at</a>>> <br>> wrote:<br>><br>> Hi<br>><br>> this is the start of a discussion about the interface to the physics<br>>
plugins.<br>><br>> After having tried working on the ODE plugin, specially focussed on<br>> linked objects I think the current interface has a severe short<br>> coming.<br>><br>> The problem I see is, that it is prim orientated while an object<br>> orientation would better suit the needs.<br>><br>> Why is it so?<br>><br>> Currently it seems to me, the information is given to the phys engine<br>> prim by prim. Any object information is only given in fragments.<br>> This leads to the situation that the object relations must be<br>> reconstructed by the phys engine and it often leads to the situation<br>> that individual prims get constructed and shortly after get destructed<br>> again as it turns out that the respective prim is part of
a larger<br>> link set.<br>><br>> For that reason I ask your thoughts about a redesign of that<br>> interface.<br>><br>> Best regards<br>> Gerhard<br>><br>> _______________________________________________<br>> Opensim-dev mailing list<br>> <a ymailto="mailto:Opensim-dev@lists.berlios.de" href="mailto:Opensim-dev@lists.berlios.de">Opensim-dev@lists.berlios.de</a> <mailto:<a ymailto="mailto:Opensim-dev@lists.berlios.de" href="mailto:Opensim-dev@lists.berlios.de">Opensim-dev@lists.berlios.de</a>><br>> <a href="https://lists.berlios.de/mailman/listinfo/opensim-dev" target="_blank">https://lists.berlios.de/mailman/listinfo/opensim-dev</a><br>><br>><br>><br>><br>> -- <br>> ===================================<br>> The wind<br>> scours the earth for prayers<br>> The
night obscures them<br>><br>> <a href="http://osgrid.org" target="_blank">http://osgrid.org</a> <<a href="http://osgrid.org/" target="_blank">http://osgrid.org/</a>><br>> <a href="http://del.icio.us/SPQR" target="_blank">http://del.icio.us/SPQR</a><br>> <a href="http://twitter.com/jstallings2" target="_blank">http://twitter.com/jstallings2</a><br>> <a href="http://www.linkedin.com/pub/5/770/a49" target="_blank">http://www.linkedin.com/pub/5/770/a49</a><br>> ------------------------------------------------------------------------<br>><br>> _______________________________________________<br>> Opensim-dev mailing list<br>> <a ymailto="mailto:Opensim-dev@lists.berlios.de" href="mailto:Opensim-dev@lists.berlios.de">Opensim-dev@lists.berlios.de</a><br>> <a href="https://lists.berlios.de/mailman/listinfo/opensim-dev" target="_blank">https://lists.berlios.de/mailman/listinfo/opensim-dev</a><br>>
<br><br>_______________________________________________<br>Opensim-dev mailing list<br><a ymailto="mailto:Opensim-dev@lists.berlios.de" href="mailto:Opensim-dev@lists.berlios.de">Opensim-dev@lists.berlios.de</a><br><a href="https://lists.berlios.de/mailman/listinfo/opensim-dev" target="_blank">https://lists.berlios.de/mailman/listinfo/opensim-dev</a><br></div></div></div></body></html>