Here's a convoluted solution that seems to work:
1. Create your curve.
2. Animate -> Create -> Skeleton -> Create Control Splines. Keep only
the PointType. Set the two other controls to None.
3. Create a tunnel-like lattice with sufficient subdivisions in x.
4. Create a simple geometry (implicits and nulls won't do) small enough
to fit inside the lattice, make it invisible, and place it at the
"entrance" of the lattice tunnel.
5. Deform this geometry by the lattice.
6. Deform the lattice by the curve, X axis. Translate it along the curve
with the PPG slider until it fits OK.
7. Create a null, constrain it to the curve (Param).
8. lock this constraint PPG open, select the geometry created in 4), hit
ctrl-K. Drag'n'drop the geometry's X position green divot from the Local
Transform PPG to the U location green divot on the null's CurveCns PPG.
Apply the expression.
9. Now if you move the green diamonds, you shape your curve, and
everything follows, and if you translate your geometry along local x, it
moves inside the lattice, which has the same shape as the curve. The
null follows along the curve. Use the null as deformer for an envelope.
10. Repeat 4), 5), 7) and 8) with different positions for the geometries
re. the lattice. You can refine the expressions created in 8, such as
(sphere.kine.local.posx / 3).
Bye,
Christian Rittener
> -----Original Message-----
> From: owner-xsi(at)Softimage.COM
> [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Frank Lenhard
> Sent: October 24, 2007 07:02
> To: XSI(at)Softimage.COM
> Subject: face rig, curves, cycles :)
>
>
> Hello,
>
> i am wondering about how to setup a face rig technically.
> wha tiknow is that i want to use curves with contrained nulls
> (L(0,100)) to get some nice deformations and skin sliding.
> my problem is the control structure which the animator will touch.
>
> i attached a crude sketch to show the problem.
> imagine the green boxes are the controls that can be pulled
> up/dow/left/right. these boxes will deform the curves,
> therefore the nulls and the skin will be enveloped to the
> nulls. so far so good.
>
> what i want is the controls to FOLLOW the curves as well, so
> when i push the green control box to the right(X axis), it
> wont go straight, it will follow the red curve, so the
> animator stays within the models shape. when the animator
> pulls on z it will go out of the head, when he pulls on y it
> will follow the purple curve.
>
> this leads to a cycle obviously, because the control stays on
> a curve that gets deformed BY the controls action. i got that
> far that i can create path constrain of the control to the
> curve, then use a linked with connection to move the control
> from 0-100% of the path realative to x positions. i get a
> cycle warning but it works more or less. this falls apart
> when i bring the second curve (purple) in as i can only
> constrain to one curve 100 percent.
>
> i feel that i didnt get a grip on the whole thing yet and
> that it can be solved in a different manner.
>
> i saw a rig in 3dmax working this way. the rigger used a flaw
> in the max system (at least it looks to me like that) to make it work.
>
> any ideas?
>
> ciao
> franky
>
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