Getting nice curvature on a spline back

Moderator: BenChang

Getting nice curvature on a spline back

Postby BenChang » Tue Apr 10, 2012 3:55 am

I'll come back and fill this in with a proper tutorial later, but here's a real quick note about getting nice back curves with IK spline back.

If you followed the previous tutorial, you probably noticed that it can be difficult to achieve good arcs with that back setup. The auto-stretch does a pretty decent job, but the curvature tends to be minimized. Back arch is one of the most useful elements in many poses, so it would be nice to be able to get more dramatic curves.

(You'll also notice that twist isn't implemented yet. I meant to add a post about the Advanced Twist Control option, which is very powerful once you understand its use of coordinate systems. )

Anyway, very briefly, here's the trick. Or rather, two tricks:

1. Moving the pivot point of something away from its center will create rotation on a larger arc
2. Parenting control curve handles in a hierarchy creates hierarchical rotation abilities

In the back rig from the previous tutorial, you have two free-floating joints controlling the splineIK curve through smooth skinning, and a handle curve object controlling the two joints through simple parenting.

You can get a more dramatic curve on the bottom handle by simply moving its pivot up and snapping it to the next joint up the chain.

To add additional curvature control in the middle of the back, create another nurbs curve to use as a handle, position it at the middle of the back, and name it backMidCtrl. Now parent backTopCtrl to it.

Rotating backMidCtrl will bend the back around that middle point, and backTopCtrl can now be used for additional curve tweaking at the top relative to the middle control.
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