SLS-2 Working with rigged Mesh I

The Second Life constraints listed above need some more explanations. We will get back to this later in this course. For now all we need to ensure is that our modelling tool does export the Model such that it can be imported to SL.

SL specific pitfall: Rigged Mesh without Rig

There is one specialty with Second Life that is worth to be mentioned: The SL Character’s rig is already fully specified in the SL Viewer. Actually by default the SL Viewer uses the same (locally defined) Rig for all characters. And because of this there is no need at all to import the Rig itself to Second Life over and over again¹. Furthermore the SL Importer by default ignores all Rig information (Bone sizes and bone locations) and it only takes care about the skinning information (the bone weights).

Blender specific details

Early versions of the Blender Collada exporter ( before 2.63 ) omitted the export of the Armature objects and they only exported what the SL Importer really needed. But this implementation created invalid Collada files. Because of that Blender’s Collada exporter has been improved. It now takes care to create valid Collada files depending on what objects are contained in the export selection:

When no Armature is selected:

Then Blender only exports the static part of the mesh, that is the mesh model itself. In this case Blender ignores the Bone weight maps and the exported Collada file now contains a statue instead of an animateable object.

When an Armature is selected together with a mesh:

Then Blender exports all armature data and all mesh data as before. But if the mesh is bound to the Armature, then also the mesh’s bone weight maps are exported (thus the mesh can later be rigged in SL).

However the Export panel has a setting that enforces the export of Armatures even when they where not added to the selection:

When you have enabled the option Include Armatures then Blender detects on its own which armatures it should export along with the selected meshes even if the armatures have not been selected.

Note: You also can use the option Include Children. In that case you can simply select the Skeleton, and all its assigned meshes will be exported along with the selected Armature.

¹  The SL Importer has a mode where it actually does import the rig, that is when you enable the SL Import option With Joint Offsets. We will get back to this when it becomes relevant.

Blender’s native Collada Exporter in action

for Blender users: You just select the three body parts of the mesh (The Head, the Upper Body, and the Lower Body). Then you open the Collada exporter and follow the instructions below.

If you do not use blender, skip the export part and proceed with the chapter about the SL Importer below.

You find the Collada exporter in the Menu

File -> Export -> Collada (Default)

Please ensure that for the Avatar from the Workbench we must use the Default Collada exporter!

Note: If you have Avastar and you try to use the Avastar exporter together with the Avatar from the Workbench, then you will end up in a mess.

Blender’s Collada Export Panel

As soon as you have opened the Exporter, you will see a file selection window. Here you can either select a file to which the data shall be exported, or you can specify a new file.
Hint:  Hover the mouse over the magnifier to see an orientation map:

The Export Properties Panel

The export panel contains many options to allow to configure the exported data as needed. We will have to set the options as follows:

Enable:

• Selection Only (avoids exporting hidden objects)
• Include Armatures (to ensure the rig data is exported)
• Only Active UV Layer (SL only supports one layer)
• Export for OpenSim (very special settings)
• Triangulate (to avoid that the SL Importer does it)
• Sort by Object Name (for multi part objects)

Disable:

• Include shape keys (SL does not support this)
• Use Object Instances (SL Importer does not support this)

We have added 2 Operator presets (see first line in the panel) from where you can recall the SL specific settings with one mouse click:

Presets for Second Life

Note: The operator Preset definitions and the Export for SL/OpenSim Option have been added to Blender’s official distribution. There is no extra Addon involved here. Also note that in Blender 2.73 the label of this option will change to Export to SL/OpenSim.

And… ready to export.

Once you have set the export options, and the name and location of the export file, you can click on the [Export Collada] button (see the orientation map above) to finally generate your export file.

Important: Please ensure that the file appendix of your export file is “.dae”  If for any reason your exported file does use a different file extension, then please repeat the export procedure and take care that you use a correct file name (including the extension .dae ) in the file input box (see image)

Ensure to use the extension .dae

You might see a notice like this when you try to import a Collada file:

If you want to import Mesh of any kind, then you have to do 2 additional steps before the model Importer will work for you:

1. You need to provide payment information to avoid illegal activities (i.e. importing of proprietary mesh work).
2. You have to take a small survey (10 questions) about rights and license policies.

Please step to the related Webpage on the Secondlife website to Find out how to get certified. From there you will be guided further. And once you have fulfilled all requirements (don’t worry, its actually not much that you need to do), then you can proceed with your Mesh Upload.

Meshes can have an arbitrary complexity. the simplest mesh is just a planar triangle, while complex meshes can have many thousands of faces. And the more complex a mesh is, the more resources are needed to get it displayed on a user’s computer screen.

Linden Lab has tried to evaluate the overall delivery costs for meshes. they ended up with a complex calculation that involves the number of objects (Server), their number of vertices, faces, normals, UV Faces, UV Island count (Download), and the complexity of the mesh physics shape (Physics).

The atomic face (1 Tri)

Upper Body (3700 Tris)

Land Impact and Prim Count

Note: When you want to optimize your meshes Land impact, then you will always aim to reduce the highest valued costs component, which in our example is the Physics costs.

The custom settings panels are the most important part of the SL Model Importer. Here i will only give you some brief information that is necessary to get your meshes imported. If you want to gain a deep understanding, then the best approach is most probably to just take the time and experiment with the settings.

The Level of Detail Panel

The Importer is capable to generate the lower LOD levels for you. But in most cases you will get much better results when you create your LOD levels manually in your 3D Editor.However, for worn meshes the LOD’s seem to take effect much later compared to when the same meshes are rezzed in world. So in most cases the generated LOD will be sufficient while you wear your mesh creations. Further down i will show you how you can do a quick optimization for testing your meshes.

The Physics Panel

If you just import a mesh and rezz it in world, then the Second Life server actually has to take care about 2 topics:

• The Object needs to be visualized (rendered at the right place in the environment)
• The object might need to interact in some way with the environment. The easiest type of interaction is when an Avatar runs into an object. Then the character should bump (think of a wall for example), or the object should move away (like a ball for example that is kicked). This is called the object’s physical behavior.

Now you might think that determining when 2 objects bump into each other is just a matter of finding the touch points between the objects. So the idea could be to just use the object’s meshes them self for this and we are done. But unfortunately the calculation of the touch points become very expensive when the mesh shapes of the interacting objects get more and more detailed. So while it is possible to just use the meshes for the physics behavior, very often you can determine the physical behavior by using a dramatically simplified low polygon model of your objects. This is the physics model of your object.

The SL Model Importer always wants to assign a physics mesh to any of the imported Objects. But it gives you some control over the physics shape, which is good. In more detail: you can either select one of your LOD meshes (the medium LOD is chosen by default), or you can put in your very own physics shape (from file) which is in almost all cases the better alternative.

Special case: Rigged Mesh

There is one thing that you must know about worn rigged items. That is, they do not use their physics mesh (even when it is defined!). Worn items get their physics shape from a specific set of Collision Volume Objects.

The Collision Volumes are simple (normally invisible) octahedron objects (see image). The size (actually the scale) of the Collision Volumes is controlled by a specific set of bones, the Collision Volume Bones (not visible in the image). Thus the Collision Volume Bones are a very simplistic representation of the character which is optimized for calculating the physics behavior of the Avatar.

So we can forget about physics for worn meshes (for now). But unfortunately (as mentioned further up) the SL Model Importer insists to assign a physics mesh to each object. However, since our mesh is rigged and it is mainly made to be worn, we can attach any physic mesh that we want. So we also can use very simple meshes for this.

Create your own physic mesh

You have seen above (when we talked about the Land Impact) that our mesh has physics costs of about 21.  This is because the default choice (the medium LOD) for the physics mesh is still a very complex mesh which raises the physics costs unnecessarily.

So we can either select the lowest LOD here or we can provide our own super simplified physics mesh versions (the brown transparent triangles in the image.

Caveat: When you provide your physics mesh for an Object that has been combined from several parts (3 in our case), then you need to provide one physics mesh per part. Actually (since the physic mesh is not used at all) you can just provide 3 triangles, one for the head, one for the upper body, and one for the lower body.

Export order of multi part meshes

For Blender Users: Blender allows to export meshes sorted by Object name (see the Blender export options panel) so we only need to ensure that the objects name are sorted in the same order for the meshes and their physic representations.

Thus when you name a mesh and its physics mesh in the same way, but also add an appendix to each physics mesh, then the sort order will remain the same and the SL Model Importer keeps happy.

Important: You have to create a separate Collada file for your physic meshes. Exporting all meshes in one Collada file does not work!

So, now when you have your Physic mesh Collada file at hand, you can specify it in the SL Model Importer as your physics mesh. Then you can click on the Calculate Weights&fee button again. Now the physics costs have changed dramatically from 21 to less than 1.

But you also see that the Land Impact is now determined by the Download costs (the Mesh complexity). So when you want to reduce the Land Impact further you now have to look at the Mesh and its LOD’s again.

Sidenote: Many creators seem to use the reduced physics mesh also for the lowest LOD (in the Level of Detail panel of the SL Model Importer) . So when you do this, then your Download costs will get reduced significantly as well.

But beware, your character will then collapse into 3 triangles when seen from far away.

You can use the physics model also for the lowest LOD (in the Level of Detail panel)

Mesh with very simple lowest LOD (seen from far far away with zoom in at max)

Same mesh with default camera setting. (The avatar is in the center of the yellow circle)

The Upload Options Panel

This panel can be overlooked easily, especially because its naming implies that it is just for variations of the default settings. But this is a major pitfall (and i can tell you that i stumble into this pitfall more often than you might expect). The SL Model Importer does not automatically import the skin weights for a mesh! Hence you need to check the option…

Include Skin weight

So we are talking about rigged meshes. And rigged meshes always contain weight maps (see lesson 1). And you always want to import these weight maps! Unfortunately you must set the Include Skin weight option on your own. And you have to remember to do this for every new mesh that you want to upload.

In most cases this is actually all that you need to do on this panel, however there are some more options here…

Include joint positions

As long as you make attachments for the default SL Avatar or for human meshes which use the same rig as the default SL Avatar, then you never want to enable this option! Because when you enable this option then the SL Model importer assumes that you have defined your own rig variant (you have edited the bone locations) and thus it imports this rig as a replacement for the default Avatar Rig. And this can become a serious issue, especially if you wear this attachment together with a mesh character that also provides its own rig variant… Too complicated ? yes, i know. For now just remind:

Z-Offset

Did you ever see that your avatar starts hovering above ground as soon as you wear a mesh attachment ? This happens mostly with child avatars. Or your avatar sinks into ground ? this is a disease that infects mostly giant avatars…

well, in the early days of mesh this issue could be corrected by adding a z-offset here. However, Linden Lab was not able to tell how the z-offset needs to be calculated. So setting this value was a lot of try and error. So since a while we have an option added to the in world shape editor. there you can adjust the hover value of your Avatar interactively which is a great improvement over try and error.

So you rarely need to set the z-offset nowadays. Just keep it at 0.000 and adjust the setting later by using the shape editor.

Include Textures

This is yet another annoyance. This option only works when your mesh does not contain weights. We know where the problem is, and it is actually easy to fix in the SL Viewer. Actually it has been fixed twice in the past, but the fix broke again always shortly after it was released.

So in short: You can not import textures together with your rigged mesh.

The workaround is to import the textures separately (with the image importer) and apply the textures later in world.

Scale

I am not sure gor what reason we have this option. I just keep it at 1.0 all the time.