Spine
General
Stretchy Ik
-- not particular to spine, but filing under for now.
-node to get curve length is 'arcLengthDimension'
// Measure the arcLength of curve curveShape1 at u = 0.5
curve -d 3 -p -9.3 0 3.2 -p -4.2 0 5.0 -p 6.0 0 8.6 -p 2.1 0 -1.9 -k 0 -k 0 -k 0 -k 1 -k 2 -k 2;
arcLengthDimension curveShape1.u[0.5];
problem with arcLengthDimension, it will make WORLD/global scale difficult if you are piping the va. back into the scale.
OR 'curveInfo' node..
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Hey Guys,
I'm looking into creating a custom Stretchy Spline IK setup that doesn't
pop (over & under extends in extreme situations).
But I seem to be unable to wrap my head around how to calculate
orientations on points on the curve.
Since the points on the curve don't have any orientation (well, they do
have tangents or something like that?) I have no clue on how to actually
start with this.
My main references of tools in Maya would be the Motion Path and the Spline
IK (with Advanced Twist controlled by a start and end object).
If anybody has any starting points for this it would be greatly appreciated!
Thanks in advance.
Regards,
Roy
Hey Roy,
I've done a sort of 'manual' setup like this by writing a 'pointAtArclen' node and then wiring the rest with existing nodes. In my case I used aim constraints for each joint, but you can do something similar within your solver- get the orientation by figuring out where each joint needs to be on the curve and what the vector would be if you were aiming each joint at the next.
-JP
Hey JP,
Actually I know how to get the point on the curve. Aiming at the next joint is also a relatively easy step.
On the other hand knowing/calculating the up vector for the aim is something I'm unaware of how to do it. How did you solve/calculate the up vector for the aim constraint?
I'm especially interested in allowing a twisting motion along the curve.
-Roy
John Patrick
I would think about it like this: for each point/joint along the curve,
you should have some sort of 'up vector'. You could get that a number of
ways - a start/end 'twist' amount, an array of 'up' target objects for each
joint, etc. The end result is that each point along the curve should have
a vector to some other target to help determine the twist.
Next, you'll need to know what your joint's aim-axis is. The built-in
spline ik node assumes an 'x' aim axis (which blows), but you could have an
input attr for the aim axis.
Zero out whichever axis is the aim-axis in your 'up vector', then convert
that vector into an MMatrix. Now you have a matrix you can multiply your
existing aimed-joint-matrix by to twist it.
I think it would be nice to have an array of world matrices for up-objects,
which you would plug the controls for the spline into. You could get the
closest point along the curve for each and treat a particular axis as the
'up vector' for that point along the curve, then interpolate between them.
Hey John,
Thanks for the quick replies. I'm not sure what you mean with the following:
*
*
*Zero out whichever axis is the aim-axis in your 'up vector', then convert
that vector into an MMatrix. Now you have a matrix you can multiply your
existing aimed-joint-matrix by to twist it.*
Why would that be helpful or what would those steps produce? If I zero out
the up vector and convert that into an MMatrix ain't I creating a zero
matrix? (Default matrix)
-Roy
John Patrick
That was a lot of shorthand on my part.
For instance, lets say you're using some sort of 'target' object for the
up-axis. And let's say the aim-axis of the joint is y, and the up-axis is
x. Pretend your joint is at position [0,3,0] and the 'target' object is at
[1,4,1], so the aim vector is [1,1,1]. If your target is perfectly on-plane
with your joint, ie it lies on the x-z plane of your joint, then you don't
need any work; but usually, a target object might be 'offset' from this
plane, as is the case here. You need to remove the 'y' part of this vector
so that you don't wobble the joint - so the aim vector becomes [1,0,1].
aimVec = OM.MVector(1,0,1)
basisVec = OM.MVector(1,0,0) #since the aim-axis is x
quat = basisVec.rotateTo(aimVec)
twistMatrix = quat.asMatrix()
newJointMatrix = aimMatrix * twistMatrix
There are other things you'll need to take into account - rotation orders,
parent matrices, inverse scale compensation, etc, to get the final euler
rotation values of each joint. Hopefully this gets you pointed in the
right direction. Good luck!
Muscle spline rigging tool (Autodesk help)
How to script Ik Handles properly?
around line 211, you mention something about the pole vectors and such flipping out. we actually used to have a module where we would have ik's built on every joint (it was like a super-offset arm), and when the ik's were built between every joint, we actually had to execute that backwards for maya to not freak out. so we would build the end ik's first and work our way up the chain. i don't believe we ever figured out the problem, but we don't really use those modules these days anyway.
Breathing Controls
automatic expression here
Spine Types
(from Character Rigging Best Practices- link dead)
IK/FK Hybrid
Good for: action animations, expressive perfomance, whip driven animations
Pros- "FK flexibility with IK smoothness"
Cons - complicated setup, fk limitations
SplineIK
try smoothCurve with history for smoother spine curve
Good for: performance animation, managing large # of bones, dynamic balance
Pros- smooth sinuous motion
Cons - popping, snapping, odd key scopes
say I make a joint chain
i'd like to make a curve on that joint chain with one cv / each joint
(KingFarrukh)
basically what you could do it get the world position of each joint and put that vector (x,y,z value) into the curve command.
example:
string $jnt[] = {"exampleJntA","exampleJntB","exampleJntC"}; // <-- there are better ways to get the jnt list but this is for the example
// this stores each jnts worldPosition
vector $storePositions[];
int $x = 0;
for ($i in $jnt)
{
$storePositions[$x] = `xform -query -worldSpace -translation $i`;
$x++;
}
//this creates the curve command
int $degree = 1; //<-- incase u want to change the degree type
string $buildCurve = ("curve -d " + $degree);
for ($each in $storePositions)
{
$buildCurve += (" -p " + $each);
}
eval $buildCurve;
(Sean Kealey)
Contraposto
ex. 'Ribbon', 'Awesome', 'Isner'-- separate control of hip and chest areas
Good for: Performance, action animation, movement cycles
Pros- intuitive posing, best weight shifts
Cons- control motion overlaps, no whip action
More Spinse
'Divine Spine' (Erick Miller)
TD Matt's spine
"The Isner Spine for XSI"
http://www.isner.com/isnerspine/spine_introduction.htm
Matt Berglund's "Awesome Spine" (i adapted for my rig..)