Preserving volume in animations that deform meshes

[timetocode]

In a blender armature modifier there is a setting called "Preserve Volume" which basically stops meshes from collapsing on themselves in some bone-related animations. I'm a newbie animator, but I'm aware that there is more to joints+deformations than just checking the preserve volume box and hoping things look good. This is particularly relevant given that some game engines, such as our beloved BabylonJS (also Unity) do not have this feature. So the question here is really what techniques do people recommend for keeping joints rotating/bending and looking nice in Babylon?

An extreme example of volume being preserved versus not preserved occurs when twisting a model comprised of two cubes and two bones. With volume preserved we get what appears to be the twisting of a square column:

Without volume preserved, we get twisting that collapses in the vicinity of the joint, creating something like an hourglass:

If the twisting motion continues the central joint will get all the way squished:

Something similar occurs in other twists such turning a head, in certain shoulder rotations, in internal/external leg rotation at the hip, and probably a bunch of other scenarios. A milder deformation occurs in movements that are mostly single-dimension rotations such as a knee or elbow bend.

 

[Sebavan]

@JCPalmer might have some pretty good feedbacks on this. (Disclaimer: I am totally n00b with creation tools ? )

[JCPalmer]

This is not really a Blender question.  Basically, all a bone is in BJS is a matrix & bone length which is only used as an aid.  I am not sure, but thought about removing some of the weight around each side of a joint (actually programmatically).  Reminds me, @Deltakosh, what happens if the sum of the weights is less than one?

[Sebavan]

If the sum is not normalized, this can lead to some weird behavior in the scene including shadows and so on.