LC #42 Pipers Alley

View Full Version : Xpresso to link rotation of a shape to a spline point's bezier handles?

05-16-2012, 05:20 PM
Right, so I have to make a quick little animation that demonstrates the function of bezier handles. I figure it will be easy enough to make the shape with a cylinder and a couple of spheres, and I could always just keyframe out the animation of the shape, then follow with a PLA for the handles, but I would like a more elegant solution so that any requested changes are easier to implement.

This seems like a perfect task for XPresso, but sadly beyond simple set driven keys, and PBlurp stuff, I am largely at a loss with the sheer volume of options XPresso presents.

So, my question essentially is twofold: Am I correct in thinking that XPresso can do this? And, if so, could I get a little help in figuring out the way to do it?

Thanks as always,

05-16-2012, 05:44 PM
Hi GruvDOne,

the following expressions could be of interest for you.

tangent-count.xma (
tangent.xma (

Those Expressions are written in Python and read out the number of tangents and the tangents themselves from a Spline. They can be easily modified to set instead of read tangents.


05-16-2012, 06:31 PM
It's no big deal, to transfer the tangents orientation, to the rotation parameters of a cylinder. But I can't give any advice, how to transfer the tangents length. Sorry for that.


05-16-2012, 09:04 PM
You could possibly use spline-ik with your rig for this, since you can specifically set the tangent lengths (through the tag ) of each driven point that's linked to a null controller. This way you could rig up geo under the nulls, then pass the tangent length info to your primitive geo depicting the tangents. ( scaled justified geo, scaled centered geo with pos offset, or range mapped a few ideas for the tangent geo ).

05-16-2012, 09:25 PM
Guess I was thinking something like this, can animate the little circle control along the axis of the points controller. But yea, is going to be a little limited in that you can't control the directional length in either direction for each point, or break tangents, etc...
Although you could use multiple segment rigs to achieve the effects you need possibly.

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