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# simpleSolverNode.cpp

    //-
    // ==========================================================================
    // Copyright 1995,2006,2008 Autodesk, Inc. All rights reserved.
    //
    // Use of this software is subject to the terms of the Autodesk
    // license agreement provided at the time of installation or download,
    // or which otherwise accompanies this software in either electronic
    // or hard copy form.
    // ==========================================================================
    //+

    //
    // 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:
    //
    //   ikHandle -sol simpleSolverNode -sj joint1 -ee joint2
    //
    // This creates a handle that can be dragged around in the x-y
    // plane.
    //

    #include <maya/MIOStream.h>

    #include <maya/MPxIkSolverNode.h>
    #include <maya/MString.h>
    #include <maya/MFnPlugin.h>
    #include <maya/MObject.h>
    #include <maya/MIkHandleGroup.h>
    #include <maya/MFnIkHandle.h>
    #include <maya/MDagPath.h>
    #include <maya/MVector.h>
    #include <maya/MPoint.h>
    #include <maya/MDoubleArray.h>

    #define MAX_ITERATIONS 1
    #define kSolverType "simpleSolverNode"

    //
    // Class declaration
    //
    class simpleSolverNode : public MPxIkSolverNode {

    public:
                        simpleSolverNode();
        virtual         ~simpleSolverNode();

        virtual MStatus doSolve();
        virtual MString solverTypeName() const;

        static  void*   creator();
        static  MStatus         initialize();

        static  MTypeId id;

    private:
        MStatus         doSimpleSolver();

    };

    MTypeId simpleSolverNode::id( 0x80100 );

    //
    // Implementation
    //
    simpleSolverNode::simpleSolverNode()
        : MPxIkSolverNode()
    {
        // setMaxIterations( MAX_ITERATIONS );
    }

    simpleSolverNode::~simpleSolverNode() {}

    void* simpleSolverNode::creator()
    {
        return new simpleSolverNode;
    }

    MStatus simpleSolverNode::initialize()
    {
        return MS::kSuccess;
    }

    MString simpleSolverNode::solverTypeName() const
    //
    // This method returns the type name used to identify this solver.
    //
    {
        return MString( kSolverType );
    }

    MStatus simpleSolverNode::doSolve()
    //
    // This is the core solver.
    //
    {
        doSimpleSolver();
        return MS::kSuccess;
    }

    MStatus simpleSolverNode::doSimpleSolver()
    //
    // 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.
    //
    {
        MStatus stat;

        // Get the handle and create a function set for it
        //
        MIkHandleGroup * handle_group = handleGroup();
        if (NULL == handle_group) {
            return MS::kFailure;
        }
        MObject handle = handle_group->handle( 0 );
        MDagPath handlePath = MDagPath::getAPathTo( handle );
        MFnIkHandle fnHandle(handlePath, &stat);

        // Get the position of the end_effector
        //
        MDagPath end_effector;
        fnHandle.getEffector(end_effector);
        MFnTransform tran( end_effector );
        MPoint effector_position = tran.rotatePivot( MSpace::kWorld );

        // Get the position of the handle
        //
        MPoint handle_position = fnHandle.rotatePivot( MSpace::kWorld );

        // Get the start joint position
        //
        MDagPath start_joint;
        fnHandle.getStartJoint( start_joint );
        MFnTransform start_transform( start_joint );
        MPoint start_position = start_transform.rotatePivot( MSpace::kWorld );

        // Calculate the rotation angle
        //
        MVector v1 = start_position - effector_position;
        MVector v2 = start_position - handle_position;
        double 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)
        //
        #define CW       rot = -1.0 * angle;    // clockwise
        #define CCW      rot = angle;           // counter-clockwise

        double rot = 0.0;   // Rotation about Z-axis

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

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

        // P is the handle position vector
        //
        MVector P = handle_position - effector_position;

        // Determine the rotation direction
        //
        double PdotN = P[0]*N[0] + P[1]*N[1];
        if ( PdotN < 0 ) {
            CCW;
        } else {
            CW;
        }

        // get and set the Joint Angles
        //
        MDoubleArray jointAngles;
        if ( getJointAngles( jointAngles ) ) {
            jointAngles.set( jointAngles[0] + rot, 0 );
            setJointAngles( jointAngles );
        }
        return MS::kSuccess;
    }

    //
    // Register the solver
    //
    MStatus initializePlugin( MObject obj )
    {
        MStatus         status;
        MFnPlugin   plugin( obj, PLUGIN_COMPANY, "3.0", "Any");

        status = plugin.registerNode("simpleSolverNode",
                                     simpleSolverNode::id,
                                     &simpleSolverNode::creator,
                                     &simpleSolverNode::initialize,
                                     MPxNode::kIkSolverNode);
        if (!status) {
            status.perror("registerNode");
            return status;
        }

        return status;
    }

    MStatus uninitializePlugin( MObject obj )
    {
        MStatus         status;
        MFnPlugin   plugin( obj );

        status = plugin.deregisterNode(simpleSolverNode::id);
        if (!status) {
            status.perror("deregisterNode");
            return status;
        }

        return status;
    }