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