And again I've made some progress. Or at least got some type of lookAt
algorithm working.
Still not sure on how to actually use this for calculating the twist around the
curve.
I'm not so sure about the used algorithm (just searched around on the internet
and rewrote it for Maya) since I'm not really understanding how it works, got
to look into Quaternions some more before I understand what's going on here.
Here's the code:
Testing on a scene with object's names ("pCube1", "pCube2", "pSphere1")
########
import maya.cmds as mc
import maya.OpenMaya as om
from math import sqrt
def getDependNodeByName( name ):
selList = om.MSelectionList ()
selList.add (name)
node = om.MObject()
selList.getDependNode (0, node)
return node
def gsOrthonormalize( normal, tangent ):
# Gram-Schmidt Orthonormalization
normal.normalize()
proj = normal * ( tangent * normal ) # normal * dotProduct(tangent,normal)
tangent = tangent - proj
tangent.normalize()
return normal, tangent
def lookAt( lookDirection=om.MVector(0,0,0), upDirection=om.MVector(0,0,0) ):
# Returns a quaternion that aims the Y-axes to lookDirection and Z-axes
(orthogonal to Y) to upDirection
forward = lookDirection
up = upDirection
up, forward = gsOrthonormalize(forward, up)
right = lookDirection ^ upDirection # cross product
right.normalize()
quat = om.MQuaternion()
quat.w = sqrt(1.0 + right.x + up.y + forward.z ) * 0.5
w4_recip = 1.0 / (4.0 * quat.w)
quat.x = (up.z - forward.y) * w4_recip
quat.y = (forward.x - right.z) * w4_recip
quat.z = (right.y - up.x) * w4_recip
return quat
def getTranslationByTransformName( name ):
node = getDependNodeByName( name )
fnTransform = om.MFnTransform( node )
transformMatrix = fnTransform.transformation()
return transformMatrix.getTranslation(om.MSpace.kWorld)
def aimObject( object, aimToObject, aimUpObject ):
srcTranslate = getTranslationByTransformName(object)
targetTranslate = getTranslationByTransformName(aimToObject)
upTranslate = getTranslationByTransformName(aimUpObject)
aimVec = targetTranslate - srcTranslate
upVec = upTranslate - srcTranslate
quat = lookAt( aimVec, upVec )
srcNode = getDependNodeByName(object)
fnTransform = om.MFnTransform(srcNode)
srcTransformMatrix = fnTransform.transformation()
srcTransformMatrix.setRotationQuaternion( quat.x, quat.y, quat.z, quat.w,
om.MSpace().kTransform )
# Set the adjusted matrix
fnTransform.set(srcTransformMatrix)
mc.refresh()
aimObject("pSphere1","pCube1","pCube2")
#########
Looking forward to any tips from you guys on this guy. It's all giving me a
headache.
-Roy
From: roy_niete...@hotmail.com
To: python_inside_maya@googlegroups.com
Subject: RE: [Maya-Python] API: Custom Spline IK (or Motion Path)
Date: Tue, 13 Nov 2012 20:17:41 +0100
So I've been trying hard to understand how to perform the 'lookAt' stuff with
the API, which I think is the basics of what I need to understand to achieve
what I want.
This is what I got so far. Use it in a scene with a sphere and two cubes with
their default names. ;)
###########
import maya.cmds as mc
import maya.OpenMaya as om
def getDependNodeByName( name ):
selList = om.MSelectionList ()
selList.add (name)
node = om.MObject()
selList.getDependNode (0, node)
return node
srcNode = getDependNodeByName("pSphere1")
targetNode = getDependNodeByName("pCube1")
upNode = getDependNodeByName("pCube2")
fnSrc = om.MFnTransform(srcNode)
fnTarget = om.MFnTransform(targetNode)
fnUp = om.MFnTransform(upNode)
srcTransformMatrix = fnSrc.transformation()
srcTranslate = srcTransformMatrix.getTranslation(om.MSpace.kWorld)
srcQuatRotation = srcTransformMatrix.rotation()
targetTransformMatrix = fnTarget.transformation()
targetTranslate = targetTransformMatrix.getTranslation(om.MSpace.kWorld)
upTransformMatrix = fnUp.transformation()
upTranslate = upTransformMatrix.getTranslation(om.MSpace.kWorld)
# Aim Axis (hardcoded to x)
basisAimVec = om.MVector(0,0,0)
basisAimVec.x = 1
basisAimVec = basisAimVec.rotateBy(srcQuatRotation)
aimVec = targetTranslate - srcTranslate
quat = basisAimVec.rotateTo(aimVec)
srcTransformMatrix.addRotationQuaternion( quat.x, quat.y, quat.z, quat.w,
om.MSpace().kTransform )
srcQuatRotation = srcTransformMatrix.rotation()
# Up Axis (hardcoded to y)
"""
basisUpVec = om.MVector(0,0,0)
basisUpVec.y = 1
basisUpVec = basisUpVec.rotateBy(srcQuatRotation)
upVec = upTranslate - srcTranslate
quat = basisUpVec.rotateTo(upVec)
srcTransformMatrix.addRotationQuaternion( quat.x, quat.y, quat.z, quat.w,
om.MSpace().kTransform );
"""
# Set the adjusted matrix
fnSrc.set(srcTransformMatrix)
mc.refresh()
###########
So I haven't been able to implement the up axis in this. Any tips would be
greatly appreciated.
I also had to refresh at the end otherwise Maya ended up not updating the
viewport, anybody knows what that's all about?
Love to get into this more so thanks in advance for any help!
Regards,
Roy
From: jspatr...@gmail.com
Date: Mon, 12 Nov 2012 08:57:06 -0800
Subject: Re: [Maya-Python] API: Custom Spline IK (or Motion Path)
To: python_inside_maya@googlegroups.com
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!
On Mon, Nov 12, 2012 at 7:51 AM, Roy Nieterau <royniete...@gmail.com> wrote:
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
On Monday, November 12, 2012 4:34:14 PM UTC+1, JP wrote:
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.
On Mon, Nov 12, 2012 at 7:13 AM, Roy Nieterau <roy_ni...@hotmail.com> wrote:
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
CC: python_in...@googlegroups.com
From: jspa...@gmail.com
Subject: Re: [Maya-Python] API: Custom Spline IK (or Motion Path)
Date: Mon, 12 Nov 2012 07:08:48 -0800
To: python_in...@googlegroups.com
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
Sent from my iPhone
On Nov 12, 2012, at 2:00 AM, Roy Nieterau <royni...@gmail.com> wrote:
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
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