As a Roblox developer, it is currently impossible to use inverse kinematics on custom rigs.
I’ve noticed that while animating, all the IK editor does is enforce constraints (you can try it too, for instance, create a HingeConstraint between both Wrist attachments on an arm; you’ll note the editor doesn’t let you twist the wrist) Why this is gated behind only native R15 rigs is perplexing, to say the least. I can see the constraint configuration being ambiguous; but there is no way to manually set up constraints and then have the animation editor enforce those, akin to Inverse Kinematics.
As such, I would like the Inverse Kinematics button to be relabeled “Constraints Mode” and cause a popup asking whether or not you’d like to impose IK constraints on the rig (for R15-compatible rigs) or not. This would greatly increase the versatility of the existing animation editor and enable patient developers to manually define their own Inverse Kinematics using constraints.
Limb IK doesn’t even need to be done - full-body IK suffices (pin all parts with 1 connection automatically) and then the user can pin any parts their weird rig desires.
My personal example is that I want to make a flight-capable humanoid character with articulatable ‘wings’, but it is particularly irritating that I cannot use Inverse Kinematics, despite the fact that the rig is designed such that said constraints apply. If this were added, I could apply the IK constraints (despite it being a custom rig) and then add on my own and use the IK editor in the new Constraints mode to animate the same way as everyone that uses stock rigs.
This would significantly improve my development efficiency and quality because of the increased ease this would lend to making more natural animations. I would prefer to use IK and then tweak the key frames with the normal editor, but given the fact I use custom rigs, this is sadly infeasible at the moment.
Thank you for reading.