Automated~ (Patreon)

I figured out how to do this- it's one of those cases where I knew what I wanted to do but figuring out how to get it working with bone constraints was... weird. But, basically, the y scale of the hole is driven by a bone who's scaled based on it's position away from the start and end of the PP (which are denoted by two other bones)

So, the closer this bone is to the pp end bone, the more it expands. It's not linear though, as thankfully the graph editor gives you some control over how the value increases via bezier curves.

The formula for the driver that controls this is just the normalization formula, which is just

    x - x min
--------------
x max - x min

Where x is the hole control's position, x min is the PP head position and x max is the PP base position (all in world space). This value is multiplied by 2 since the max scale of this bone is 2, as opposed to 1.

This should help a lot with animating this scene (and future ones as well) though one thing I'd like to add is multiple points of interest where the hole expands/contracts, such as around the ring or, say, if I did a pp with a knot in the future... That is something worth looking into I think!

Using a bit of that knowledge I learned from stats in a "real world" scenario~

-Velocirection, chief sexy officer of Pizzass Games