How do you constrain Scale to Position?

madmuffin

I am constantly in need of constraining scale of a bone to position of another bone. I cannot find a way to do this and its endlessly frustrating and maddening that you can't do it stock with just a Transform constraint.

I KNOW it can be done but I'm just too stupid to figure it out, and I can't find any resources on the net. Attached is a gif example that I hand-animated, but I need this to work based on position alone, no keyframes.

ALSO it has to work in BOTH directions, working one way but getting even WIDER in the other direction is completely useless to me.

Attached is the end result I need.

This is the answer.
But what is the sollution that achieve this answer - specifically working in ANY direction, driven by a single target bone??????

Misaki

You can use IK constraints for this purpose. There are two types of IK constraints: one-bone IK and two-bone IK. Each has a bit different options and you can find the guide for them here:
IK constraints - Spine User Guide: Properties
If you use one-bone IK and enable Compress and Stretch, you can stretch the constrained bone according to the position of the IK target bone.

There is a tutorial here for a rig that makes good use of one bone IK, which I think will help you understand how to use one-bone IK:
Blog: Distance limit setup for eyes