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# surfaceTwistCmd.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.
    // ==========================================================================
    //+

    #include <math.h>
    #include <maya/MIOStream.h>
    #include <maya/MPxCommand.h>
    #include <maya/MStatus.h>
    #include <maya/MObject.h>
    #include <maya/MFnPlugin.h>
    #include <maya/MString.h>
    #include <maya/MArgList.h>
    #include <maya/MGlobal.h>
    #include <maya/MPoint.h>
    #include <maya/MVector.h>
    #include <maya/MMatrix.h>
    #include <maya/MDagPath.h>

    #include <maya/MSelectionList.h>
    #include <maya/MItSelectionList.h>
    #include <maya/MItSurfaceCV.h>
    #include <maya/MItMeshVertex.h>

    // Class Definition //

    class surfaceTwist : public MPxCommand {
    public:

                        surfaceTwist();
        virtual         ~surfaceTwist();

        virtual MStatus doIt( const MArgList& args );

        static void*    creator();
    };

    // Class Implementation //

    #define NUM_SPANS        30
    #define WIDTH            10.0
    #define VERTICAL_SCALING 4.0

    surfaceTwist::~surfaceTwist() {}

    surfaceTwist::surfaceTwist() {}

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

    static MStatus twistNurbsSurface(MDagPath& objectPath, MObject& component)
    {
        MStatus status;

        MPoint  center;
        MVector toCenter( -center.x, 0.0, -center.y );
        double  rotFactor = 0.5;

        // We have a nurbs surface or component
        //
        MItSurfaceCV cvIter( objectPath, component, true, &status );

        if ( MS::kSuccess == status ) {
            // We successfully created a nurbs surface iterator
            //
            for ( ; !cvIter.isDone(); cvIter.nextRow() ) {
                for ( ; !cvIter.isRowDone(); cvIter.next() ) {
                    // Get the location of the CV
                    //
                    MPoint pnt = cvIter.position( MSpace::kWorld );
                    pnt = pnt + toCenter;
                    // Calculate rotation in radians about the y-axis
                    //
                    double rotation = pnt.y * rotFactor;
                    MMatrix rotMatrix;
                    // Set matrix to a rotation about the y axis
                    //
                    rotMatrix(0,0) = cos( rotation );
                    rotMatrix(0,2) = sin( rotation );
                    rotMatrix(2,0) = -sin( rotation );
                    rotMatrix(2,2) = cos( rotation );
                    pnt = ( pnt * rotMatrix ) - toCenter;

                    status = cvIter.setPosition( pnt, MSpace::kWorld );
                    if ( MS::kSuccess != status )
                        break;
                }
            }
            // Tell maya to redraw the surface with all of our changes
            //
            cvIter.updateSurface();
            return MS::kSuccess;
        } else
            return MS::kFailure;
    }

    static MStatus twistPolygon(MDagPath& objectPath, MObject& component)
    {
        MStatus status;

        MPoint  center;
        MVector toCenter( -center.x, 0.0, -center.y );
        double  rotFactor = 0.5;

        MItMeshVertex vertIter( objectPath, component, &status );

        if ( MS::kSuccess == status ) {
            // We successfully created a polygon vertex iterator
            //

            for ( ; !vertIter.isDone(); vertIter.next() ) {
                // Get the location of the vertex
                //
                MPoint pnt = vertIter.position( MSpace::kWorld );
                pnt = pnt + toCenter;
                // Calculate rotation in radians about the y-axis
                //
                double rotation = pnt.y * rotFactor;
                MMatrix rotMatrix;
                // Set matrix to a rotation about the y axis
                //
                rotMatrix(0,0) = cos( rotation );
                rotMatrix(0,2) = sin( rotation );
                rotMatrix(2,0) = -sin( rotation );
                rotMatrix(2,2) = cos( rotation );
                pnt = ( pnt * rotMatrix ) - toCenter;

                status = vertIter.setPosition( pnt, MSpace::kWorld );
                if ( MS::kSuccess != status )
                    break;
            }
            // Tell maya to redraw the surface with all of our changes
            //
            vertIter.updateSurface();
            return MS::kSuccess;
        } else
            return MS::kFailure;
    }

    MStatus surfaceTwist::doIt( const MArgList& )
    //
    //  Description:
    //      Plugin command to test Selection List Iterator.
    //
    //
    {
        MStatus status;

        // Create an iterator for the active selection list
        //
        MSelectionList slist;
        MGlobal::getActiveSelectionList( slist );
        MItSelectionList iter( slist );

        if (iter.isDone()) {
            cerr << "Nothing selected\n";
            return MS::kFailure;
        }

        MDagPath objectPath;
        MObject component;

        for ( ; !iter.isDone(); iter.next() ) {
            status = iter.getDagPath( objectPath, component );

            if (objectPath.hasFn(MFn::kNurbsSurface))
                status = twistNurbsSurface(objectPath, component);
            else if (objectPath.hasFn(MFn::kMesh))
                status = twistPolygon(objectPath, component);
            else {
                cerr << "Selected object is not a NURBS surface or a polygon\n";
                return MS::kFailure;
            }
        }
        return status;
    }

    // Register command with system //

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

        status = plugin.registerCommand( "surfaceTwist", surfaceTwist::creator );
        if (!status) {
            status.perror("registerCommand");
            return status;
        }

        return status;
    }

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

        status = plugin.deregisterCommand( "surfaceTwist" );
        if (!status) {
            status.perror("deregisterCommand");
            return status;
        }

        return status;
    }