Category: Scripting

Node-based matrix twist calculator python snippet

Following on Vasil Shotarov’s awesome tutorial, I’ve scripted a setup to read angles and have been using it a lot lately. Pretty stable and saves me a lot of time!

def quatTwistReader(name, axis='x'):
    # returns grp, reader, quaternionNode
    reader = cmds.group(empty=True, name=name+"_twist_reader")
    reader_grp = cmds.group(reader, name=reader+"_grp")
    mm = cmds.createNode("multMatrix", name=name+"_mm")
    cmds.connectAttr(reader+".worldMatrix[0]", mm+".matrixIn[0]")
    cmds.connectAttr(reader_grp+".worldInverseMatrix[0]", mm+".matrixIn[1]")
    dm = cmds.createNode("decomposeMatrix", name=name+"_dm")
    cmds.connectAttr(mm+".matrixSum", dm+".inputMatrix")
    qte = cmds.createNode("quatToEuler", name=name+"_qte")
    cmds.connectAttr(dm+".outputQuat"+axis.upper(), qte+".inputQuat"+axis.upper())
    cmds.connectAttr(dm+".outputQuatW", qte+".inputQuatW")

    return reader_grp, reader, qte

Usage example of a wrist twist:

STEP 1
Run quatTwistReader(“l_wrist”, “x”). Double-check your rig for the desired axis you want to extract but it’s usually X as in the axis that goes along a chain.

STEP 2
Parent constrain the top “l_wrist_twist_reader_grp” (reader_grp variable) result to your hierarchy so the reader is always in the correct orientation. For the wrist it should constrained to the last bendy joint of the forearm, right before the hand.

STEP 3
Orient constrain the hand joint to command the “l_wrist_twist_reader” (reader variable).

STEP 4
Use the “outputRotateX” of the “l_wrist_qte” (qte variable – quatToEuler node) for your objective, it should be outputting only the twisting in the X axis.

STEP 5
Profit 😎


Tip: if you’re getting flips before 180 and everything is aligned properly, try changing the inputRotateOrder in the quatToEuler node to match your ctrls/jnts

Fixing Maya’s camera focus

Sometimes Maya camera gets corrupted and when you try to focus on objects it just goes really far away and usually this behavior persists on all scenes you open from there on.

A quick way that has worked for me to fix it is to first close all open Maya sessions, then find your userPrefs.mel file and search for this line:

-fv "defaultFitFactor" 0

Just change the value to 1 and it should fix your issue.

If you don’t want to edit the file directly you can run the following MEL command inside Maya:

optionVar -fv "defaultFitFactor" 1;

Or the alternative Python command:

from maya import cmds
cmds.optionVar( fv=('defaultFitFactor', 1) )

When applying any of these fixes make sure there is only the current Maya session running or you might overwrite the fix by closing a Maya session that still has the old value set.