Did you see the VRC update that dropped? I don't speak unity but they did things with constraints and stuff that my more fluent friends seem excited over
It's very exciting! I haven't gotten to play with it yet but it's gonna be super beneficial for all sorts of avatars. Especially open up a whole new world for Quest avatars.
If you don't know how constraints work the TL;DR is that they copy the position/rotation/scaling of whatever they're "parented" to. This is useful for a lot of things, some examples being:
Making props be able to be used in either hand, so for example on my Cult of The Lamb avatar I have a sword you can swap between the left and right hand, this is done with constraints by changing their parenting between the two hands.
Multiple arms/limbs. It's useful for copying the rotation of another limb such as the arms or legs. I've used it to create quadruped avatars.
Accurate digitigrade legs, it makes it easier to create accurate bends by basically creating a "fake" leg for the real leg to copy off of. There's a guide on FA on how it's done. I do this for my Harold and Naren avatars.
World props, you can create an avatar thats able to place a prop in a certain space of the world and walk away, it'll stay where it is. You can't make pickups with this but you can do a bunch of fun gimmicks. I've seen someone use this to create a working motorcycle for their character in an RP.
Multiple eyes! I use constraints for the newest versions of the Heart model, the top eyes are controlled by the bottom eyes and rotate with them.
LOTS LOTS LOTS MORE. There's an ungodly amount of things you can do with constraints, lots of fun gimmicks. And they're now even more optimized on desktop and now available on Quest/Android! It's hype.
