koobas.hobune.stream
I need a point midway between two bones' rest positions
I can't get matrices to work in my head. There should be a simple multiplication to get this, but my feeble attempts result in seemingly random placement of the 'midpoint'.
I have an animated character (its bones are not in their rest position), and I need to get a point 'along a bone' - specifically, the point is directly on the line between two bone transforms.
Getting that point in the animation space or world space is easy, but I need to get it in the armature's 'rest space', working back from the animation space somehow. SkinnedMeshRenderer.bindposes seems to be related, but I'm at a loss. Any math gurus able to expand on this?
bones : List.<Transform> = new List.<Transform>( smr.bones ); // copy bones into a list for IndexOf
// find point between bone #index and #index2:
var ray : Ray;
ray.origin = bones[index].position;
ray.direction = bones[index2].position-ray.origin;
centerInWorldSpace = ray.origin + ray.direction * desiredLength; // works!
ray.origin = smr.bindposes[index] * bones[index].position; // doesn't land on the bone line
// or is that right, and the complex logic i haven't copied here is getting the wrong index? i don't even know where to look.
centerInAnimationSpace = ray.origin + ray.direction * desiredlength; // would work if the ray was built correctly
Well the bindpose converts the position of the bone relative to the parent (root) of the mesh in local coordinates. So don't you need to do:
ray.origin = (smr.bindposes[index] * (bones[index].position - meshHolder.position))+meshHolder.position;
Sorry - think I'm being thick their - now I think it's actually the parent it's offseting from so it would be:
ray.origin = (smr.bindposes[index] * (bones[index].localPosition))+meshHolder.position;
Got me pointed in the right direction! From your snippet I managed to get the bones to clump together in a reasonable pattern, but it's clear (now, to me) that the bindpose relies on the parent bone and not just the mesh itself.
It seems like I need to reset the bind poses of each bone in order to reconstruct the original bone structure.
So, uh. Can I set a transform's data from the bindpose matrix with a function? I'd hardly trust me to write that, I am horrendous with mathematics.
Resetting localPosition and localRotation of each bone using bindpose somehow should snap the skeleton to its default pose, then I can just store the bone relationships and restore the pose it WAS in.
Argh, it might be better to write a helper component to just store this stuff on Start... it's late, I'll wonder more when I wake up.
I am an utter failure at applied math, so I made a purely logical solution ins$$anonymous$$d :S
Now I've just got a helper component sitting on objects that might want this functionality - it has to be set up in edit mode, but as it turns out, I want to exclude helper bones anyway so it's kind of a good thing.
Answer marked as accepted because someone who knows what mathwords mean can certainly make it work from there.
