Mesh workflows

[Rage Riptide]

Hi team.

I got into mesh when sculpts arrived. Sculpties are not normal modelling as I am aware and it's difucult to master the texture stretching etc.

Now for real mesh. To import a good model, one must resolve 5 meshes. One for each LOD level and one for the physics shell.

Q. Do all games use this method? Or something similar. Or is this unique to SL, designed for streaming content. None of which is "installed".

I can not rely on the uploader to make the decompositions correctly. So how does one begin? Do you start with the physics shell shape and work up to full detail or would you go all the way first and then remove verts till you get the low lod.

Might you use shape keys for each level so you work on just one model but it has several complexities at key points like morphing.

I don't think any particular workflow would work for everything but people with experience are allowed to drop in here and give a few lines on how they might do a model project. Small details could go a long way to keep some from wasting many hours in pursiut of an easier way. Any help will help.

[DanielRavenNest Noe]

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Rage Riptide wrote:  To import a good model, one must resolve 5 meshes. One for each LOD level and one for the physics shell. Q. Do all games use this method? Or something similar. Or is this unique to SL, designed for streaming content. None of which is "installed".

I can not rely on the uploader to make the decompositions correctly. So how does one begin? Do you start with the physics shell shape and work up to full detail or would you go all the way first and then remove verts till you get the low lod.

Might you use shape keys for each level so you work on just one model but it has several complexities at key points like morphing.

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"Levels of Detail" are used in other graphics engines, both for models and textures.  For example the CryEngine (used for the Crysis series of games) can have up to 6 levels for models, and uses a special type of texture that contains lower detail versions as well as the highest detail one.  Then the engine picks what version of the model and textures to use based on distance and size of the object.  Second Life uses levels of detail for streaming textures.  It only loads a lower detail version if the object is far away/small, then fetches the higher detail one if needed later.

For me it's easier to start with the high detail model, and work down.  In fact, it is quite common in game modeling to start with a higher detail model than you will actually use.  You can bake in shading from the higher details into a texture to use on the lower detail version.  If your 3D program has a function to "decimate" or "optimize" a model (reduce triangle count), you can apply that with the right percentage reduction (which is 75%/LOD for SL), then manually clean up any parts that need it.  Auto-reduction is fast, but it doesn't always know where to keep needed details.  The lowest visible LOD can use planes with a picture of part or all of the object.  That is seen at long distance, so a flat representation (called a "billboard" in the computer graphics field) can substitute for a fully 3 dimensional version.  The physics shape is not seen, and should be as simple as possible and still get the collisions with avatars and other objects to appear correct.

I don't know what shape keys are, but generally I keep all the LODs and physics shape in one 3ds Max file, hiding and unhiding them as needed so I can compare.  When it's time  to export, I save out copies with all but one deleted, and then export the single LOD versions as Collada .dae files.

[Ashasekayi Ra]

No, I wouldn't use shape keys to make LODs. You can just store each LOD and the physics hull on their own layers. Then, you can just select them one by one and export them out as dae. Make sure you have "export selected" checked. (If you are using Blender 2.5x, the dae exporter isn't complete and can't just export a selection; therefore, it is more tedious because you'll have to delete all the objects except the one you want to export.)

As for workflow, I build up from low to high in Blender usually unless I sculpted something in Zbrush first. I make the physics mesh last. I use the low version of the model as a starting point for that one and remove edge loops aggressively.

[Tapple Gao]

If you want to try the export selected feature in blender 2.5, you can apply this patch and compile blender. I had trouble applying it against a revision besides the one spcecified: http://codereview.appspot.com/4530081/

[Rage Riptide]

Cool Daniel, that's the direction I wanted. Good info, thanks for that.

I was assuming,SL would handle mesh very differently than other engines making it more difficult to mesh-out, refering to sculpties and how dificult they are if you don't make rocks.

I had started some models, working up by copying each level but by the time I get to high detail, the topology might change and I may have to go backwards and make good again. I suppose it depends on the model too.

Blender shape keys.
Shape keys store different shapes of a same object (mesh, curve, surface or lattice). In other 3D applications they are called “morph targets”, “blend shapes”, or even “vertex keys” in older versions of Blender. They are the only way to directly animate the shape of your object.

It works well with scupts because their topology doesn't change, I know it won't work with mesh properly, I just threw that in there because it's awesome with sculpties.

I'm gonna say no to you're offer Tapple. I don't want to go near any compiling anymore. I've had enough of that. I'll just wait like the rest, or...

I export the whole scene from 2.5 as collada. Import into 2.49 as collada and export just the object I need, again as collada from 2.49. That really only takes a minute or so. I still get errors which brings up another question.

Using materials in the workflow.

I understand there can be up to eight material slots. So does each material have to be in the same place, in the same topology of each iteration of the mesh?

With the upload errors I get, or silent fail uploads, I assume yes and I haven't done that.

If you finsh with 5 materials should each level have 5?

Enough q's.

[Drongle McMahon]

"I understand there can be up to eight material slots. So does each material have to be in the same place, in the same topology of each iteration of the mesh?"

No. You can move them around however you like. It is useful, for example, to put a material on a hidden triangle in the high LOD so that you can use it for the billboard (or similar) at lowest LOD. Parts of the mesh with a given material do not have to be contiguous. That can be very useful.

"If you finsh with 5 materials should each level have 5?"

Yes. The uploader will refuse to upload if the LOD meshes hve different numbers of materials. Which goes where presently depends only on the order of the triangle/poly lists in the Collada file (at least for Blender). There have been complaints about this, because it doesn't necessarily reflect the intended linkage with other sofware, and it may be ammended to respect the material ID assignments, as you might expect. There are no extra texture slots for each LOD. So you have to have the UV maps correct for using the same set of textures on all of them.