how much m-bone weighting to use under Fitted Mesh?

[Quarrel Kukulcan]

I found an old article that says you can rig to a blend of normal deform bones and Fitted Mesh bones and still have animations work properly; the only real effect is that shape sliders won't affect your object by their full amount.

My question is: isn't that a huge freaking issue? If your clothes and your body are rigged to different proportions of Fitted vs. non-fitted bones, their shapes won't match each other except near the defaults. Who cares if your animations won't distort under such a scheme?

(I presume I'd want 100% Fitted Mesh use to make clothes for the default avatar. Are there actually mesh bodies out there that use less?)

Edited October 29, 2020 by Quarrel Kukulcan

[KjartanEno]

In SL, you get up to four bone weights for every vertex on a rigged mesh. For arms, legs, hands, and feet, four weights is enough to get smooth transitions and allow for a mix of animation and volume bones. Generally speaking, volume bones would be weighted on areas that you want to increase muscle or fat volume with the appropriate sliders. Joints like knees and elbows should not expand as much, and the topology in the joints would be carefully weighted with mostly animation bone weights. It gets a bit more complicated in the torso. Most people want to be able to adjust the size of the butt, love handles, saddle bags, and breasts/pectorals. And then there are shoulders... All of which is to say that weighting is one of the more challenging jobs in creating a mesh body.

Some body styles lend themselves to a non-fitted mesh approach. I'm almost certain that Piggu bodies have no fitted sliders. They are simply designed to be fat already, so the vertices are all weighted exclusively to animation bones. That is not to say one couldn't do the same with a thin or muscled body, but customers would need to know that what they see is what they get. Clothing made for this kind of body is much more likely to fit well since the designer knows from the start exactly what it will look like on the body.

A fully fitted approach sounds like a good idea for getting smooth weight transitions and giving customers the ability to create more varied shapes. However, it tends to be more difficult for clothing designers. Any time volume-based sliders are taken to extremes, there will be issues involving poke through in places that are hard to predict and deal with using alphas.

The Big Brands for human avatars all use a combination of animation and volume bones. With each body, the designer has a certain look in mind but takes into account the expected range of certain sliders. In the end, it's up to YOU to decide how to weight your mesh. It may also be up to you to create all the clothing for that mesh in the beginning since clothing creators want to see a customer base before investing time and effort into clothing for yet another body.

[Ada Radius]

The volume (fitted) bones are each clamped to an mBone. So any vert weighted to a volume bone will move with its clamped mBone. For the Ruth and Roth mesh bodies, to get around the 4 weights per vertex limitation, and the 110 vertex weights import limitation, I weighted almost entirely to the volume bones whenever possible. The Bento bones are different - those mBones also respond like volume bones in the sliders.

There's a list of how the armature is structured here (the ods spreadsheet):  https://github.com/RuthAndRoth/Reference/tree/master/Ada%20Radius.  You can take a look at how the how the Ruth and Roth mesh bodies are weighted in the other files at that Github repository.