What's the constraint between skeletal particles and bones? And can I disable it?

[kodra]

When the "Skeleton Sampling" is enabling when generating particles from the softbody blueprint editor, the generated particles since to move along with the bones. My questions are:

1. What's the constraint taking place here? Distance? Pin? Shape matching?

2. Can I disable it? In other words, I'd like the particles to be generated at the positions of the bones, but I'd like them to work just like volume particles and surface particles: bound to other particles by shape matching constraints, but not bound to the bone.

[josemendez]

When the "Skeleton Sampling" is enabling when generating particles from the softbody blueprint editor, the generated particles since to move along with the bones. My questions are:

1. What's the constraint taking place here? Distance? Pin? Shape matching?

No constraints are used, since there’s no physics involved. Bone particles are simply fixed (their inverse mass set to zero) and then their position is updated every frame to match the corresponding bone. Kinda like what static attachments do, but without the hassle of setting up the attachments yourself.

Other particles around them follow the bone particles because they’re linked via shape matching constraints.

2. Can I disable it? In other words, I'd like the particles to be generated at the positions of the bones, but I'd like them to work just like volume particles and surface particles: bound to other particles by shape matching constraints, but not bound to the bone.

There’s no way to disable this, but there’s no technical limitation that prevents it either. It’s just that sampling the bone hierarchy with particles and then have the particles ignore the bones didn’t seem to have any use that would justify a “disable” option: you just don’t provide a skeleton when creating the blueprint.

Could you describe your use case for this?

[kodra]

No constraints are used, since there’s no physics involved. Bone particles are simply fixed (their inverse mass set to zero) and then their position is updated every frame to match the corresponding bone. Kinda like what static attachments do, but without the hassle of setting up the attachments yourself.

Other particles around them follow the bone particles because they’re linked via shape matching constraints.


There’s no way to disable this, but there’s no technical limitation that prevents it either. It’s just that sampling the bone hierarchy with particles and then have the particles ignore the bones didn’t seem to have any use that would justify a “disable” option: you just don’t provide a skeleton when creating the blueprint.

Could you describe your use case for this?

Well, my use case is that the mesh is a curvy tube, like a tentacle. When I sample volume particles from it, it's quite hard to get an result where the particles are distributed nicely and evenly without a very high resolution. The bones already exist in the center of the tentacle, so sampling the bones get better result (I think) than sampling the volume. But I want them to act like normal particles, not fixed by the bone hierarchy.

[josemendez]

Well, my use case is that the mesh is a curvy tube, like a tentacle. When I sample volume particles from it, it's quite hard to get an result where the particles are distributed nicely and evenly without a very high resolution. The bones already exist in the center of the tentacle, so sampling the bones get better result (I think) than sampling the volume. But I want them to act like normal particles, not fixed by the bone hierarchy.

ObiBone is designed specifically for this, and it will give you a great deal more control: you can specify bending /stretching resistance for each axis separately (not with softbodies, as they're isotropic), you can use surface collisions for better spatial sampling with less particles, you can control how much animation/simulation you blend on a per-particle basis by using skin constraints, etc.

kind regards,