View Full Version : Rigging spine for a game character

12 December 2010, 12:27 PM
To start off with I need to explain my question.
At work we're using Unity game engine and I haven't done a lot of tests yet.
I assume you can use a stretchy spine feature, but would a broken joint hierarchy work?

I'm looking for a way to rig a spine, but I assume a broken joint hierarchy is not an option?
On all the ik spline spines I've seen they make it stretchy and use a broken hierarhchy structure.

When not using the stretchy feature and you'd constrain the arm directly to the spine_end_jnt you will get wobbles as it's conforming to a curve. To get rid of this you constrain the arms and head to the upperbody_ctrl and make the spine stretchy so when the upperbody_ctrl moves the spine stretch to reach, otherwise it will just look broken if you move the upperbody_ctrl. So now you obviously need to constantly check the scale of the spine and offset it if it's getting to short or long. This is the way I'm used to and will give you very good control over the spine.

But, would this work aswell when exporting to a game engine or should I abandon the IKspline an use FK explicitly?

12 December 2010, 02:11 PM
I ran into the same issue with my Rapid Rig Advanced ( , a lot of requests were from people trying to integrate it into a game engine. So what I did was create an option for the user to generate a single hierarchy joint chain on top of the existing one. So all you have to do is rig your character with the spline ik or whatever method you choose, then create another set that matches exactly. Then parent constrain the single hierarchy joints to the broken hierarchy.

You will run into scaling issues potentially, but what I found worked ok (and what a lot of people use for simplicity, although less accurate) to stretch the joint, is to just have the child joint translate, rather than using scale on the parent to adjust the length. This won't be as realistic of a deformation as scaling, but for a game engine, it should suffice. If your joints are oriented so that the x axis is pointing down the chain, you can probably still get away with using a scale constraint for the y and z axis, for volume control.

You probably want to use constraints rather than direct connections, because if you are baking your animation to the joints for export, connections probably won't get baked.

Good luck!

12 December 2010, 04:12 PM
I just saw some inaccuracy in my description.
A normal ik spline shape would of course work, the problem arises first when your scaling the joints based on the curveLength.

Ok, thanks will look into using constraints!
But what about the top hiearchy, like where the arms and neck are parented under. How should I go about parenting in that cause I guess it's necessary, but I think I have some things to go on now and will try out some things before asking again.
Thanks alot!

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12 December 2010, 04:12 PM
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