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# particlePathsCmd.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.
    // ==========================================================================
    //+

    /*

        file : particlePathsCmd.cpp
        class: particlePathsCmd
        ----------------------
        Demonstrates how particle ID's can be used to construct curves from
        particle paths.  All particles in the given particle system are followed
        from the start time to the finish time, and their paths are traced out
        using the MNurbsCurve class.  The particle ID is used to identify particles
        at different times.

        The command "particlePaths" supports the following options:

            -s/-start double : Indicates the starting time (in seconds) for
                tracing curves.

            -f/-finish double : Indicates the finish time (in seconds) for
                tracing curves.

            -i/-increment double : Indicates the amount of time (in seconds)
                between sampling the particle system.

        In addition, a particleShape object must be specified either through the
        active selection or by passing the node name to the command.

        Example:
            particlePaths -s 0.0 -f 3.0 -i 0.5 particleShape1

    */

    #include <maya/MGlobal.h>
    #include <maya/MString.h>
    #include <maya/MPointArray.h>
    #include <maya/MVectorArray.h>
    #include <maya/MDoubleArray.h>
    #include <maya/MIntArray.h>
    #include <maya/MArgList.h>
    #include <maya/MFnDependencyNode.h>
    #include <maya/MSelectionList.h>
    #include <maya/MPxCommand.h>
    #include <maya/MFnParticleSystem.h>
    #include <maya/MFnPlugin.h>
    #include <maya/MFnNurbsCurve.h>
    #include <maya/MSyntax.h>
    #include <maya/MArgDatabase.h>
    #include <maya/MTime.h>
    #include <maya/MAnimControl.h>

    #include "particleIdHash.h"

    // Syntax string definitions
    static const char *startFlag = "-s";
    static const char *startLongFlag = "-start";
    static const char *finishFlag = "-f";
    static const char *finishLongFlag = "-finish";
    static const char *incrementFlag = "-i";
    static const char *incrementLongFlag = "-increment";

    static const double TOLERANCE = 1e-10;

    //
    // particlePaths command class
    //

    class particlePathsCmd : public MPxCommand
    {
    public:
                     particlePathsCmd();
        virtual     ~particlePathsCmd();

        virtual MStatus doIt ( const MArgList& args );

        static void* creator();
        static MSyntax newSyntax();

    private:
        MStatus parseArgs ( const MArgList& args );

    private:
        MObject particleNode;
        double start,finish,increment;
    };

    particlePathsCmd::particlePathsCmd() : start(0.0),finish(0.0),increment(0.0)
    {
    }

    particlePathsCmd::~particlePathsCmd()
    {
    }

    MSyntax particlePathsCmd::newSyntax() {
        MSyntax syntax;
        syntax.addFlag( startFlag, startLongFlag, MSyntax::kDouble );
        syntax.addFlag( finishFlag, finishLongFlag, MSyntax::kDouble );
        syntax.addFlag( incrementFlag, incrementLongFlag, MSyntax::kDouble );
        syntax.setObjectType(MSyntax::kSelectionList,1,1);
        syntax.useSelectionAsDefault();
        return syntax;
    }

    MStatus particlePathsCmd::parseArgs( const MArgList& args )
    {
        MArgDatabase argData(syntax(), args);

        //
        // Parse the time flags
        //

        if (argData.isFlagSet(startFlag))
        {
            argData.getFlagArgument(startFlag, 0, start);
        }

        if (argData.isFlagSet(finishFlag))
        {
            argData.getFlagArgument(finishFlag, 0, finish);
        }

        if (argData.isFlagSet(incrementFlag))
        {
            argData.getFlagArgument(incrementFlag, 0, increment);
        }

        if (finish <= start || increment <= 0.0)
        {
            MGlobal::displayError( "Invalid time arguments." );
            return MS::kFailure;
        }

        //
        // Get the particle system object
        //

        MSelectionList selectList;
        argData.getObjects(selectList);

        if( selectList.length() < 1 )
        {
            MGlobal::displayError( "Missing particle node name argument." );
            return MS::kFailure;
        }
        else if( selectList.length() > 1 )
        {
            MGlobal::displayError( "Too many particle nodes given." );
            return MS::kFailure;
        }

        selectList.getDependNode(0,particleNode);

        if (particleNode.isNull() || !particleNode.hasFn(MFn::kParticle))
        {
            MGlobal::displayError( "Invalid node argument." );
            return MS::kFailure;
        }

        return MS::kSuccess;
    }

    //
    // This routine creates the curves for the given particle system
    //

    MStatus particlePathsCmd::doIt( const MArgList& args )
    {
        MStatus stat = parseArgs( args );
        if( stat != MS::kSuccess )
        {
            return stat;
        }

        MFnParticleSystem cloud( particleNode );

        if( ! cloud.isValid() )
        {
            MGlobal::displayError( "The function set is invalid!" );
            return MS::kFailure;
        }

        //
        // Create curves from the particle system in two stages.  First, sample
        // all particle positions from the start time to the end time.  Then,
        // use the data that was collected to create curves.
        //

        // Create the particle hash table at a fixed size.  This should work fine
        // for small particle systems, but may become inefficient for larger ones.
        // If the plugin is running very slow, increase the size.  The value should
        // be roughly the number of particles that are expected to be emitted
        // within the time period.
        //
        ParticleIdHash hash(1024);
        MIntArray idList;

        //
        // Stage 1
        //

        MVectorArray positions;
        MIntArray ids;
        int i = 0;
        for (double time = start; time <= finish + TOLERANCE; time += increment)
        {
            MTime timeSeconds(time,MTime::kSeconds);

            // It is necessary to query the worldPosition attribute to force the
            // particle positions to update.
            //
            cloud.evaluateDynamics(timeSeconds,false);
    //      MGlobal::executeCommand(MString("getAttr ") + cloud.name() +
    //          MString(".worldPosition"));

            if (!cloud.isValid())
            {
                MGlobal::displayError( "Particle system has become invalid." );
                return MS::kFailure;
            }

            MGlobal::displayInfo( MString("Received ") + (int)(cloud.count()) +
                " particles, at time " + time);

            // Request position and ID data for particles
            //
            cloud.position( positions );
            cloud.particleIds( ids );

            if (ids.length() != cloud.count() || positions.length() != cloud.count())
            {
                MGlobal::displayError( "Invalid array sizes." );
                return MS::kFailure;
            }

            for (int j = 0; j < (int)cloud.count(); j++)
            {
                // Uncomment to show particle positions as the plugin accumulates
                // samples.
                /*
                MGlobal::displayInfo(MString("(") + (positions[j])[0] + MString(",") +
                    (positions[j])[1] + MString(",") + (positions[j])[2] + MString(")"));
                */

                MPoint pt(positions[j]);
                if (hash.getPoints(ids[j]).length() == 0)
                {
                    idList.append(ids[j]);
                }
                hash.insert(ids[j],pt);
            }

            i++;
        }

        //
        // Stage 2
        //

        for (i = 0; i < (int)(idList.length()); i++)
        {
            MPointArray points = hash.getPoints(idList[i]);

            // Don't bother with single samples
            if (points.length() <= 1)
            {
                continue;
            }

            // Add two additional points, so that the curve covers all sampled
            // values.
            //
            MPoint p1 = points[0]*2 - points[1];
            MPoint p2 = points[points.length()-1]*2 - points[points.length()-2];
            points.insert(p1,0);
            points.append(p2);

            // Uncomment to show information about the generated curves
            /*
            MGlobal::displayInfo( MString("ID ") + (int)(idList[i]) + " has " + (int)(points.length()) + " curve points.");
            for (int j = 0; j < (int)(points.length()); j++)
            {
                MGlobal::displayInfo(MString("(") + points[j][0] + MString(",") + points[j][1] + MString(",") + points[j][2] + MString(")"));
            }
            */

            MDoubleArray knots;
            knots.insert(0.0,0);
            for (int j = 0; j < (int)(points.length()); j++)
            {
                knots.append((double)j);
            }
            knots.append(points.length()-1);

            MStatus status;
            MObject dummy;
            MFnNurbsCurve curve;
            curve.create(points,knots,3,MFnNurbsCurve::kOpen,false,false,dummy,&status);
            if (!status)
            {
                MGlobal::displayError("Failed to create nurbs curve.");
                return MS::kFailure;
            }
        }

        return MS::kSuccess;
    }

    //
    // Bookkeeping
    //

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

    MStatus initializePlugin( MObject obj )
    {
        MFnPlugin plugin(obj, PLUGIN_COMPANY, "6.0", "Any");

        MStatus status = plugin.registerCommand("particlePaths",
                                                particlePathsCmd::creator,
                                                particlePathsCmd::newSyntax);
        if (!status)
            status.perror("registerCommand");

        return status;
    }

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

        MStatus status = plugin.deregisterCommand("particlePaths");
        if (!status)
            status.perror("deregisterCommand");

        return status;
    }