Mesh and OpenSim

Myst-Uru Guild Hall

Mesh is Changing

The Lindens have reasons to change how mesh is handled in Second Life. The changes are format changes to the mesh data set. The reason given is performance and compatibility issues with the existing SL software.

For those of us that are not up on C# or C++ and object oriented data that doesn’t tell us much. Suffice to say mesh is sort of changing from a round peg to a square peg. That means all the holes for mesh have to change too. The place in the asset database where mesh information is stored must change. How the physics engine deals with mesh has to change. The inventory handlers, the build/edit dialog, render pipeline, and other parts of the viewer handling mesh must change.

This week the movers and shakers in OpenSim have been looking at how this change will affect OpenSim. Justincc has a post up on what is known now. His post is probably the most authoritative words on the subject for OpenSim. See: Warning: Don’t rely on meshes uploaded to OpenSim (just yet)

The take-away from the article is the Linden Lab changes will break existing mesh on the SL grid. As viewers adapt to the change that will make mesh on OpenSim grids unusable and probably invisible. What other problems may come from having old style mesh and new style mesh in the system is unknown. We’ll eventually find out.

How Much is Lost

The changes are only in the Viewer, SL and OpenSim simulator software. This means the mesh objects uploaded to either grid will be lost (as in unusable). The actual 3D models in Blender or 3DS are ok. That part does NOT change. The existing exports from Blender will probably still be usable. One will have to upload the mesh’s Collada file using a new viewer changed to use the new mesh format.

So, some work will have to be done over. Upload again and all in-world building, using mesh, will have to be done over.

Are We Sure

Yep. We know for sure things are changing. Tateru, of, has information from Linden Lab saying they will give us new information on mesh and the roll out date by the end of this month. The Mesh Team’s meeting minutes (5/2 & 9) are clear that things will change and break existing uploaded mesh.

Once we have the Linden information and the tech side information then those building the software for OpenSim will know what has to change. At that point we will find out the techie details for openSim.


Collada is an XML data format for exchanging 3D models. See It is an open source project managed by the Khronos Group.

3D modeling programs use Collada as an export format. The format is not fully supported in Blender. (See: Blender Collada Plan) The 2.49b version of Blender is said to have the best implementation of Collada. However, Blender 2.57 is becoming popular and is much easier to learn (if you know 3D modeling). But, it’s Collada export has some problems. I have been able to get it to work, but it gives surprising results now and then. If you import a Blender 2.57 export to a grid and nothing appears, look around. It likely rezzed in some unexpected place. The object center thingy kicks in.

Myst-Uru D'ni Era Guild Hall

Blender View

There are some aspects of Collada for which the Lab is making work-arounds. So, some minor things like Blender object centers and SL pivot points are wacky. How faces will work has me confused. And there are other oddities that have yet to be worked out or explained to those of us playing with mesh models. And there are parts of Collada that SL and OpenSim are not going to support for the foreseeable future.

So, use of mesh in OpenSim is an experiment. Don’t count on it. May be in a month or two things will stabilize.


We know mesh is coming… soon… weeks, provided there are no major glitches. We know mesh is changing and current imports are going to break. We know viewers will have to change to handle the changes. I think Justincc and other OpenSim programmers are hoping the asset and grid servers will need little change, but some change will likely be required.

Many of us are busy modeling things for the grids. As this change propagates through we will be testing the meshes in SL’s ADITI grid with new viewers. For a time we will be able test mesh in OpenSim with the pre-change viewers. At some point that will change over and only post change mesh will be in use on OpenSim.

The OpenSim mesh use will be a bit of a dance as the viewers and simulators are likely to go out of sync for a short time. We’ll have to watch Justincc’s site and announcements in the OpenSim worlds.

We cannot count on mesh objects. They are changing and they could change again. Even after mesh is released to the main SL grid, things could change. Linden Lab is doing their best to make sure they have mesh right before the official release. But, an unforeseen problem may jump up to bite us.

Moving a head on mesh models is reasonable. Importing them and using them for elaborate builds in OpenSim is risky. But. someday soon…

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