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# simpleSpring.h

    //-
    // ==========================================================================
    // 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.
    // ==========================================================================
    //+

    #include <maya/MIOStream.h>
    #include <maya/MTime.h>
    #include <maya/MVector.h>
    #include <maya/MObject.h>
    #include <maya/MPlug.h>
    #include <maya/MDataBlock.h>
    #include <maya/MFnPlugin.h>
    #include <maya/MPxSpringNode.h>

    class MIntArray;
    class MVectorArray;

    #define McheckErr(stat, msg)        \
        if ( MS::kSuccess != stat )     \
        {                               \
            cerr << msg;                \
            return MS::kFailure;        \
        }

    class simpleSpring: public MPxSpringNode
    {
    public:
        simpleSpring();
        virtual ~simpleSpring();

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

        // will be used to get user defined attributes
        //
        virtual MStatus compute( const MPlug& plug, MDataBlock& block );

        // Override applySpringLaw.
        //
        virtual MStatus applySpringLaw( double stiffness,
                            double damping, double restLength,
                            double endMass1, double endMass2,
                            const MVector &endP1, const MVector &endP2,
                            const MVector &endV1, const MVector &endV2,
                            MVector &forceV1, MVector &forceV2 );

        //=================================================================
        // If you need new attributes, add them here. Below is an example.
        //=================================================================

        // Your numeric attribute
        //
        static MObject  aSpringFactor;

        // Other data members
        //
        static MTypeId  id;

        // INLINEs to get attribute value.
        //
        double  end1WeightValue( MDataBlock& block );
        double  end2WeightValue( MDataBlock& block );

    private:

        // methods to get attribute value.
        //
        double  springFactor( MDataBlock& block );

        // A parameter for this simple spring node.
        //
        double  factor;
    };

    // inlines
    //
    inline double simpleSpring::springFactor( MDataBlock& block )
    {
        MStatus status;

        MDataHandle hValue = block.inputValue( aSpringFactor, &status );

        double value = 0.0;
        if( status == MS::kSuccess )
            value = hValue.asDouble();

        return( value );
    }

    // INLINE
    //
    inline double simpleSpring::end1WeightValue( MDataBlock& block )
    {
        MStatus status;
        MDataHandle hValue = block.inputValue( mEnd1Weight, &status );

        double value = 0.0;
        if( status == MS::kSuccess )
            value = hValue.asDouble();

        return( value );
    }

    inline double simpleSpring::end2WeightValue( MDataBlock& block )
    {
        MStatus status;
        MDataHandle hValue = block.inputValue( mEnd2Weight, &status );

        double value = 0.0;
        if( status == MS::kSuccess )
            value = hValue.asDouble();

        return( value );
    }