Geometry Control using Nodes

bm_geoCtrl.py

import maya.cmds as cmds
import maya.mel as mel


def geoCtrl(name="geoCtrl_1", geo=[], child=None):
    """
    :param name: The name for our geometry control.
    :param geo: The list of our face selection. You can just pass it cmds.ls(sl=1)
    :param child: The child that our control will manipulate.
    :return: [ctrl, ctrlShape]
    """

    if len(geo) == 0:
        return
    if not child:
        return

    # get the object's name
    object = geo[0][0:geo[0].index(".")]
    objectShape = cmds.pickWalk(object, d="down")[0]

    cmds.select(cl=1)

    # first duplicate our object
    ctrl = cmds.duplicate(object, name=name)[0]
    ctrlShape = cmds.pickWalk(ctrl, d="down")[0]

    # now create a "transformGeometry" node. This will allow us to get rid of our double transforms
    tGeo = cmds.createNode("transformGeometry", n=name + "_transformGEO_#")

    # connect our objectShape's outMesh to the inputMesh of the transformGeometry node
    cmds.connectAttr(objectShape + ".outMesh", tGeo + ".inputGeometry")

    # connect our control's worldInverseMatrix to the transformGeometry's transform input
    cmds.connectAttr(ctrl + ".worldInverseMatrix[0]", tGeo + ".transform")

    # now connect the transformGeometry's outputGeometry to our ctrlShape's inputGeometry
    cmds.connectAttr(tGeo + ".outputGeometry", ctrlShape + ".inMesh")

    # select the original selection again but this time on our new mesh. Invert the selection and delete it
    cmds.select(cl=1)
    for sel in geo:
        cmds.select(ctrl + sel[sel.index("."):], add=1)

    mel.eval("invertSelection;")
    cmds.delete()
    cmds.select(cl=1)

    # center our control's pivot based on it's new geometry
    cmds.xform(ctrl, cp=1)

    # unlock all of the keyable transform attributes in our new control
    for attr in cmds.listAttr(ctrl, k=1):
        cmds.setAttr(ctrl + ".%s" % attr, l=0)

    # finally parent our control to the child we wanted
    cmds.parentConstraint(ctrl, child, mo=1)

    return [ctrl, ctrlShape]