scripted/simpleSolverNode.py

#-
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#+

#
# Creation Date:   4 October 2006
#
# Example Plugin: simpleSolverNode.py
#
#
# Single-bone, single-plane ik-solver.
#
# This plugin demonstrates how to create and register an ik-solver.
# Due to the complex nature of ik solvers, this plugin only 
# works with 2-joint skeletons (1 bone) in the x-y plane.
#
# To use the solver, create a single bone (joint tool).
# Then type the following in the command window:
#
#   import maya.cmds as cmds
#
#   cmds.createNode("spSimpleSolverNode", name="spSimpleSolverNode1")
#   cmds.ikHandle(sol="spSimpleSolverNode1", sj="joint1", ee="joint2")
#
# This creates a handle that can be dragged around in the x-y
# plane.
#

# imports
import maya.OpenMaya as OpenMaya
import maya.OpenMayaUI as OpenMayaUI
import maya.OpenMayaMPx as OpenMayaMPx
import maya.OpenMayaAnim as OpenMayaAnim
import math, sys

# consts
kSolverNodeName = "spSimpleSolverNode"
kSolverNodeId = OpenMaya.MTypeId(0x8700a)


class simpleSolverNode(OpenMayaMPx.MPxIkSolverNode):
    def __init__(self):
        OpenMayaMPx.MPxIkSolverNode.__init__(self)


    def solverTypeName(self):
        return kSolverNodeName

    
    def doSolve(self):
        self.doSimpleSolver()


    def doSimpleSolver(self):
        """
        Solve single joint in the x-y plane
            - first it calculates the angle between the handle and the end-effector.
            - then it determines which way to rotate the joint.
        """
        handle_group = self.handleGroup()
        handle = handle_group.handle(0)
        handlePath = OpenMaya.MDagPath.getAPathTo(handle)
        fnHandle = OpenMayaAnim.MFnIkHandle(handlePath)

        # Get the position of the end_effector
        end_effector = OpenMaya.MDagPath()
        fnHandle.getEffector(end_effector)
        tran = OpenMaya.MFnTransform(end_effector)
        effector_position = tran.rotatePivot(OpenMaya.MSpace.kWorld)

        # Get the position of the handle
        handle_position = fnHandle.rotatePivot(OpenMaya.MSpace.kWorld)

        # Get the start joint position
        start_joint = OpenMaya.MDagPath()
        fnHandle.getStartJoint(start_joint)
        start_transform = OpenMaya.MFnTransform(start_joint)
        start_position = start_transform.rotatePivot(OpenMaya.MSpace.kWorld)

        # Calculate the rotation angle
        v1 = start_position - effector_position
        v2 = start_position - handle_position
        angle = v1.angle(v2)

        # -------- Figure out which way to rotate --------
        #
        #  define two vectors U and V as follows
        #  U   =   EndEffector(E) - StartJoint(S)
        #  N   =   Normal to U passing through EndEffector
        #
        #  Clip handle_position to half-plane U to determine the region it
        #  lies in. Use the region to determine  the rotation direction.
        #
        #             U
        #             ^              Region      Rotation
        #             |  B           
        #            (E)---N            A          C-C-W
        #         A   |                 B           C-W
        #             |  B
        #             |
        #            (S)
        #

        rot = 0.0   # Rotation about Z-axis

        # U and N define a half-plane to clip the handle against
        U = effector_position - start_position
        U.normalize()

        # Get a normal to U
        zAxis = OpenMaya.MVector(0.0, 0.0, 1.0)
        N = U ^ zAxis # Cross product
        N.normalize()

        # P is the handle position vector
        P = handle_position - effector_position

        # Determine the rotation direction
        PdotN = P[0]*N[0] + P[1]*N[1]
        if PdotN < 0:
            rot = angle # counter-clockwise
        else:
            rot = -1.0 * angle  # clockwise

        # get and set the Joint Angles 
        jointAngles = OpenMaya.MDoubleArray()
        try:
            self._getJointAngles(jointAngles)
        except:
            # getting angles failed, do nothing
            pass
        else:
            jointAngles.set(jointAngles[0] + rot, 0)
            self._setJointAngles(jointAngles)


##############################################################################


def nodeCreator():
    return OpenMayaMPx.asMPxPtr(simpleSolverNode())


def nodeInitializer():
    # nothing to initialize
    pass


# initialize the script plug-in
def initializePlugin(mobject):
    mplugin = OpenMayaMPx.MFnPlugin(mobject, "Autodesk", "1.0", "Any")

    try:
        mplugin.registerNode(kSolverNodeName, kSolverNodeId, nodeCreator, nodeInitializer, OpenMayaMPx.MPxNode.kIkSolverNode)
    except:
        sys.stderr.write("Failed to register node: %s" % kSolverNodeName)
        raise


# uninitialize the script plug-in
def uninitializePlugin(mobject):
    mplugin = OpenMayaMPx.MFnPlugin(mobject)
    try:
        mplugin.deregisterNode(kSolverNodeId)
    except:
        sys.stderr.write("Failed to unregister node: %s" % kSolverNodeName)
        raise