I'm trying really hard to come up with a way to take a bone chain, for example of 5 bones, and use a Spline IK to match this bone chain to a curve WHILE controlling the exact position of both the starting and ending bone.
And I want to do this WITHOUT the scaling option that makes the bone stretch to the end of the curve.
What happens currently in the Spline IK is that the root of the IK chain is firmly tied to the beginning of the curve, but then throughout the chain, the chain simply "points" toward the end of the curve, like a damped track. But what I would like is for the chain to actually 100% end with the bone at the same position of the last point of the curve.
I am completely aware that without stretching of any kind, this is not physically possible without restrictions to the length of the curve relative to the bone chain. But assuming that the bone is within the allowed distance, I want it to behave in a way where I can definitively move the end bone along with the end point of the curve, as if the bone was a child of that curve endpoint. And all of this inside a Spline IK for the whole bone chain.
I realize I might be asking for a unicorn, but I've been privately trying to figure this out forever, so I figured I may as well see what other people think.
The application is that I want to create a "Human-Spine Controller" where I can position both the head and the pelvis as endpoints of the bezier, with the bezier deciding the curve of the spine but not affecting the location or rotation of the head and pelvis.