Strap solver beginnings

This is a little something I've been working on recently.

Long story short, I never actually intended on having my characters stuck in a permanent semi-inflated state. Would some of them prefer to remain at a larger size whenever possible? Sure, why not- I suppose that's just as valid of a lifestyle choice as any. However, I always assumed that most of them would want to return to a normal size on occasion, if only so that they could experience the journey of getting bigger all over again.

Part of my excuse for the way Vanessa looks the way she does is because I've never actually been able to figure out a decent system for rigging up swimsuit straps. This is mostly because the straps need to remain dead straight while bridging the gap between the breasts and shoulders, but also because the straps need to be able to stretch out across their entire length. This means that as the chest expands, the straps need to be able to pickup slack from the fabric running down the back of the spine, which then needs to slip up and over the shoulders so that the fabric tension can equalize itself across the entire length of the strap.

Unsurprisingly, this is a *very* complicated problem. As far as I know, it can't be solved in any deterministic manner based solely on the rotational state of the character joints. I'd previously tried to build a setup around an RBF (radial basis function) to try and implement some sort of pose-space based correction system instead, but this didn't work out since the shear number of data points required to fully configure the RBF quickly became both unwieldy and unmanageable.

Around that point I started messing around with arbitrary curve-to-curve tangent matching again, which is actually what the GIF above is showing. The general idea here is that a set of arbitrary curves can be used to define both the curvature of the breasts and shoulders, from which a common tangent can then be approximated. This data can then be used to generate a set of additional curves that run from the breasts to the shoulders and down the back, which can then be leveraged to align a set of joint chains for the left/right edges of the strapping so that they follow around with the character as the chest expands/contracts and the spine/shoulders contort around.

In the example above, the yellow lines represent the tangent angles of each curve, and the green line is the tangent being drawn between the curves. Even as one curve changes shape considerably, the green line maintains a perfectly straight connection between both curves. So far this system seems exceptionally robust and should be capable of implementing what I need to finally get my characters proper inflatable.

Once that happens, I should be able to take someone from a normal size (read: a realistically proportioned human) all the way up to Vanessa's size and beyond. Likewise, it should be possible to simulate the appearance of the fabric sliding down the front of the chest to reveal more and more cleavage as the breasts get bigger and bigger, serving as some extra visual impact to really highlight the extent of the transformation.

Anyways, yeah. I'm still here and all that stuff. Just busy working on rigging right now, which unfortunately isn't very exciting to see until it's actually done.