Stretchy spline ik spine

[pen-pen]

hey all,

im trying to create a spline ik spine with a control at either end (easy so far) but when either of the controls are translated, the spine should stretch out and follow the control, kapiche? i.e, im trying to make a spine that can do squash and stretch but is spline ik,

--or--

anyone know of a good proffesional rigging tutorial that deals with this sorta thing . . .

any help would be fantastic +3000

[nonquad]

I can't recommend a tutorial, but I can give you a solution.

Create a curveInfo node ("createNode curveInfo").
Attach your spline curve's worldSpace[0] to the curveInfo's input.

The curveInfo node will provide an output called arcLength, which is the length of the curve. Use a multiplyDivide node to divide this length into the appropriate number of sections, and connect that to the joints' scaleX so that they expand and contract along the curve as it changes length.

Connecting to the translateX of the joints will have nearly the same results, but if you bind to it you'll find that the bound joints won't get scaled, so they'll tend to clump at the joints, if the curve stretches much.

You probably also need to break all the inverse scale connections that are created between the spine joints by default. Been a while since I've done this; can't remember for sure.

If you want to be slick about it, also drive the scaleX andZ of the joints based on the arcLength, so that the bound mesh will thin out as it stretches, maintaining its volume.

[pen-pen]

that worked really well,

if i parent joints to this stretchy heirarchy now though
all the joints below and above the spine in the heirarchy inherit the scale transform, is there a way to, for example; untick the inherit transform button, but only for the scale ?

ive tried point contraining the joints, which works, but for skinning reasons id like to keep it all in the same heirarchy . .

sorry for the myriad of questions Nonquad,
but i really appreciate the help
ill pay you in CAANDDYY

[nonquad]

Heirarchy schmeirarchy! Constrain it!

Seriously. I wouldn't put a stretchy spine in the same heirarchy as the rest of the joints unless some specific reason (like a game exporter limitation) compelled me to.

I'm sure you can do it; you could use multiplyDivide nodes to neutralize the scale at the ends, for example. But ... why waste the effort when you can just constrain it in?

[pen-pen]

yeah, your right, i got the rig working with constraints now so iz all sweeet

thanks mAaN !!!

[nonquad]

glad to help!

Now where's my candy?!

[pen-pen]

on its way, with fed ex