[Opensim-dev] scene import/export to another app: oar? dotscene? collada?

[Toni Alatalo]

Paul Fishwick kirjoitti:
> Could OAR be generalized to include scene graphs with meshes? That would
> be really nice as it would create two things not currently supported: 
> hierarchical scene graphs and triangular mesh. If an importer is written to opensim,
>   

It is possible. A simple hack would putting a reference to a mesh asset 
to the place where <shape> entry with the geom data is used for prims. 
As OAR is a serialization of the internal SOG/SOP data structure, and 
ModRex extends those to have the mesh references in the scene, it in a 
way already does that. Like Mikko Pallari commented to this discussion 
on rex-dev yesterday, we could easily add another serializer in ModRex 
that would do that: save OARs where 'prims' are not prims but scene 
nodes with mesh references, and have ogre mesh assets in the assets dir 
of the oar.

That would already be useful for what OARs are for: saving scenes from 
OpenSim and loading them back, in that case just with also the Rex 
(Ogre) data. But it might not be helpful at all for exchanging scenes 
between Opensim and other applications, which is what I'm looking into now.

> then it is a matter of coaxing the viewer to render these.. In your list of 
> options, you might also consider the indexedfaceset of X3D for the mesh (X3D also supports 
> a true scene graph).
>   

Yes, it is a possible format also.

I've now been leaning against writing OAR support elsewhere exactly 
'cause it is the internal structure and perhaps awkward for what need 
now. For example there is no single file with the scene as positions of 
all objects, but a separate file for every object which has both the 
scene pos and in case of prims the shape. And if SOG/SOP refactoring 
happens within OpenSim, it easily changes the OAR 'format' as well, and 
would break reading archives written using some custom thing that would 
write the files as they are now .. right?

DotScene is somewhat attractive 'cause it's simple and there are working 
exporters for Blender, Max, Maya and for some editors written using Ogre 
itself. There's a C# loader we've used in our company before when using 
MOgre, http://www.ogre3d.org/wiki/index.php/MOGRE_dotSceneLoader . 
Downsides of DotScene are that it's Ogre specific, and contains *only* 
the scene, leaving textures and meshes etc. out .. which may be ok 
though, 'cause textures are just images and there is separate code for 
mesh export so getting those over too is just a matter of packaging 
files for transport (perhaps in a .oar like container).

Collada and X3D would be engine independent standards that would 
probably easily cover all I need now, so probably must give them another 
look before starting to port that encouraginly simple dotSceneLoader (a 
single simple 600 lines c# file) to OpenSim.. so will be googling for 
.net libs for Collada and X3D next I guess (there's exports to both from 
Blender, am not sure if the X3D one does scenes though .. and am a bit 
afraid of how complex and big collada stuff may be, but hopefully that 
fear is in vain).

Thanks for input!

> -p
>   

~Toni

> Toni Alatalo wrote:
>   
>> Hi,
>>
>> I started looking into implementing scene exchange between Opensim and 
>> Blender yesterday, and am planning to continue later today. Was reading 
>> OARs and the code in OpenSim.Region.Framework.Scenes.Serialization .. 
>> where SceneObjectPart #region XML Schema seems to be the fields that are 
>> autoserialized by some .net writer, right?
>>
>> It seems well possible to read and write OAR elsewhere, but I'm not sure 
>> if it makes sense, or whether it's more the internal representation in 
>> Opensim. Are there any alternatives? With Ogre we've sometimes used the 
>> simple DotScene (.scene) made for it, and basically that would cover the 
>> info I'm interested in now (positions of meshes in a scene, not prim 
>> geom 'cause am not having prims in Blender at least right now anyway). 
>> There is an existing DotScene exporter for Blender, would it make sense 
>> to write an importer to OpenSim? Or a Collada scene importer perhaps? I 
>> haven't looked (yet) what the scene format there looks like. For the 
>> Ogre format there is a 15 line complete scene example at 
>> http://www.ogre3d.org/wiki/index.php/DotScene
>>
>> In one way the question is: does OAR loading work with 'partial' data, 
>> or would I have to make the exporter write all the fields? Am now 
>> looking into exchanging this data first:
>> <GroupPosition><X>123</X><Y>129.55</Y><Z>29.340004</Z></GroupPosition>
>> <OffsetPosition><X>0</X><Y>0</Y><Z>0</Z></OffsetPosition>
>> <RotationOffset><X>0</X><Y>0</Y><Z>0</Z><W>1</W></RotationOffset>
>> <Scale><X>17.7774</X><Y>22.8028</Y><Z>69.2987</Z></Scale>
>>
>> and things like velocity would not apply .. also, are valid region 
>> handles, creator-id etc. required, and should I generate GUIDs at export?
>>
>> I'll experiment what happens at loads of partial data etc., and of 
>> course can just make the exporter write all those fields, but hints are 
>> welcome so would not be banging my head against the most irrelevant walls.
>>
>> ~Toni
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>>   
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