Shifter: leg_3jnt_01 joint flipping problem

[miquelcampos]

From @Lohult on August 5, 2018 12:42

Hi Miquel,

I have discovered a bit of a flipping problem with the leg_3jnt_01 component.

The leg component has joints ranging from leg_L0_0_jnt through to leg_L0_9_jnt followed by leg_L0_end_jnt.

The flipping occurs when rotating leg_L0_ik_ctl in positive X. 91.068 is the exact number where the flip occurs (the guide is kept in default arrangement for the test).

At 91.068 rotation X on the IK control leg_L0_9_jnt and leg_L0_end_jnt flips from zero to -180. When skinning to these joints it becomes quite obvious when the flipping occurs.

My use case is a cat leg and the IK controller get rotated to curl the paw while walking for example.

Copied from original issue: mgear-dev/mgear_legacy#236

[miquelcampos]

From @Lohult on August 8, 2018 5:29

This problem can perhaps be fixed if the way the foot connects to the leg is setup in a way that it has a control that when rotated only affects the foot but when translated affects both ik effector and foot.

[miquelcampos]

Hi @Lohult I will check this since I also have another bug in this component:
#4

Thanks for the feedback :)

[miquelcampos]

I moving this to the other repository https://github.com/mgear-dev/shifter_classic_components/issues/

[miquelcampos]

Review the component with the feedback from the forum

http://forum.mgear-framework.com/t/hind-legs-for-quadraped-dont-align-with-guides-created/1698/4

Aerys code

import pymel.core as pm
from mgear.core.transform import getChainTransform2

# Pick joint chains
jnts = [pm.PyNode("jnt" + str(i)) for i in range(4)]
helperJnts = [pm.PyNode("helperJnt" + str(i)) for i in range(3)]

# Read world space xforms and positions
jnt_xform = [j.getMatrix(ws=1) for j in jnts]
Jn = [j.translate for j in jnt_xform]
L = sum([(Jn[i + 1] - Jn[i]).length() for i in range(3)])

# Compute ja and Jfull
ja = (Jn[1] - Jn[0])
ja.normalize()
Jfull = Jn[3] - Jn[0]

# Main formula
A = (Jfull * Jfull - L * L) / (2 * (ja * Jfull - L))

# Construct helper joint chain
hj1_pos = [Jn[0], Jn[0] + ja * A, Jn[3]]
hj1_norm = pm.dt.cross(Jn[1] - Jn[0], Jn[2] - Jn[1])
hj_xform = getChainTransform2(hj1_pos, hj1_norm)

helperJnts[0].setMatrix(hj_xform[0], ws=1)
helperJnts[1].setMatrix(hj_xform[1], ws=1)
helperJnts[2].setMatrix(hj_xform[2], ws=1)