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# simpleEmitter.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 <maya/MIOStream.h>
    #include <math.h>
    #include <stdlib.h>

    #include <simpleEmitter.h>

    #include <maya/MVectorArray.h>
    #include <maya/MDoubleArray.h>
    #include <maya/MIntArray.h>
    #include <maya/MMatrix.h>

    #include <maya/MFnDependencyNode.h>
    #include <maya/MFnNumericAttribute.h>
    #include <maya/MFnUnitAttribute.h>
    #include <maya/MFnVectorArrayData.h>
    #include <maya/MFnDoubleArrayData.h>
    #include <maya/MFnArrayAttrsData.h>
    #include <maya/MFnMatrixData.h>

    MTypeId simpleEmitter::id( 0x80014 );

    simpleEmitter::simpleEmitter()
    :   lastWorldPoint(0, 0, 0, 1)
    {
    }

    simpleEmitter::~simpleEmitter()
    {
    }

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

    MStatus simpleEmitter::initialize()
    //
    //  Descriptions:
    //      Initialize the node, create user defined attributes.
    //
    {
        return( MS::kSuccess );
    }

    MStatus simpleEmitter::compute(const MPlug& plug, MDataBlock& block)
    //
    //  Descriptions:
    //      Call emit emit method to generate new particles.
    //
    {
        MStatus status;

        // Determine if we are requesting the output plug for this emitter node.
        //
        if( !(plug == mOutput) )
            return( MS::kUnknownParameter );

        // Get the logical index of the element this plug refers to,
        // because the node can be emitting particles into more
        // than one particle shape.
        //
        int multiIndex = plug.logicalIndex( &status );
        McheckErr(status, "ERROR in plug.logicalIndex.\n");

        // Get output data arrays (position, velocity, or parentId)
        // that the particle shape is holding from the previous frame.
        //
        MArrayDataHandle hOutArray = block.outputArrayValue( mOutput, &status);
        McheckErr(status, "ERROR in hOutArray = block.outputArrayValue.\n");

        // Create a builder to aid in the array construction efficiently.
        //
        MArrayDataBuilder bOutArray = hOutArray.builder( &status );
        McheckErr(status, "ERROR in bOutArray = hOutArray.builder.\n");

        // Get the appropriate data array that is being currently evaluated.
        //
        MDataHandle hOut = bOutArray.addElement(multiIndex, &status);
        McheckErr(status, "ERROR in hOut = bOutArray.addElement.\n");

        // Create the data and apply the function set,
        // particle array initialized to length zero,
        // fnOutput.clear()
        //
        MFnArrayAttrsData fnOutput;
        MObject dOutput = fnOutput.create ( &status );
        McheckErr(status, "ERROR in fnOutput.create.\n");

        // Check if the particle object has reached it's maximum,
        // hence is full. If it is full then just return with zero particles.
        //
        bool beenFull = isFullValue( multiIndex, block );
        if( beenFull )
        {
            return( MS::kSuccess );
        }

        // Get input position and velocity arrays where new particles are from,
        // also known as the owner. An owner is determined if connections exist
        // to the emitter node from a shape such as nurbs, polymesh, curve,
        // or a lattice shape.
        //

        // Get a single position from world transform
        //
        MVectorArray inPosAry;
        inPosAry.clear();

        MPoint worldPos(0.0, 0.0, 0.0);
        status = getWorldPosition( worldPos );
        MVector worldV;
        worldV[0] = worldPos[0];
        worldV[1] = worldPos[1];
        worldV[2] = worldPos[2];
        inPosAry.append( worldV );

        // Create a single velocity
        MVectorArray inVelAry;
        inVelAry.clear();
        MVector velocity(0,0,0);
        inVelAry.append( velocity );

        // Get deltaTime, currentTime and startTime.
        // If deltaTime <= 0.0, or currentTime <= startTime,
        // do not emit new pariticles and return.
        //
        MTime cT = currentTimeValue( block );
        MTime sT = startTimeValue( multiIndex, block );
        MTime dT = deltaTimeValue( multiIndex, block );
        if( (cT <= sT) || (dT <= 0.0) )
        {
            // We do not emit particles before the start time,
            // and do not emit particles when moving backwards in time.
            //

            // This code is necessary primarily the first time to
            // establish the new data arrays allocated, and since we have
            // already set the data array to length zero it does
            // not generate any new particles.
            //
            hOut.set( dOutput );
            block.setClean( plug );

            return( MS::kSuccess );
        }

        // Compute and store an emission rate
        //
        MIntArray emitCountPP;
        emitCountPP.clear();

        int plugIndex = plug.logicalIndex( &status );

        // Get rate and delta time.
        //
        double rate = rateValue( block );
        MTime dtRate = deltaTimeValue( plugIndex, block );
        double dblCount = rate * dtRate.as( MTime::kSeconds );
        int intCount = (int)dblCount;
        emitCountPP.append( intCount );

        // Get speed, direction vector, and inheritFactor attributes.
        //
        double speed = speedValue( block );
        MVector dirV = directionVector( block );
        double inheritFactor = inheritFactorValue( multiIndex, block );

        // Get the position, velocity, and normalized time arrays to append new particle data.
        //
        MVectorArray fnOutPos = fnOutput.vectorArray("position", &status);
        MVectorArray fnOutVel = fnOutput.vectorArray("velocity", &status);
        MDoubleArray fnOutTime = fnOutput.doubleArray("timeInStep", &status);

        // Convert deltaTime into seconds.
        //
        double dt = dT.as( MTime::kSeconds );

        // Rotate the direction attribute by world transform
        MVector rotatedV = useRotation ( dirV );

        // Start emitting particles.
        //
        emit( inPosAry, inVelAry, emitCountPP,
                dt, speed, inheritFactor, rotatedV, fnOutPos, fnOutVel, fnOutTime );

        // Update the data block with new dOutput and set plug clean.
        //
        hOut.set( dOutput );
        block.setClean( plug );

        return( MS::kSuccess );
    }

    void simpleEmitter::emit
        (
            const MVectorArray &inPosAry,   // points where new particles from
            const MVectorArray &inVelAry,   // initial velocity of new particles
            const MIntArray &emitCountPP,   // # of new particles per point
            double dt,                      // elapsed time
            double speed,                   // speed factor
            double inheritFactor,           // for inherit velocity
            MVector dirV,                   // emit direction
            MVectorArray &outPosAry,        // holding new particles position
            MVectorArray &outVelAry,        // holding new particles velocity
            MDoubleArray &outTimeAry        // holding new particles emitted time
        )
    //
    //  Descriptions:
    //
    {
        // check the length of input arrays.
        //
        int posLength = inPosAry.length();
        int velLength = inVelAry.length();
        int countLength = emitCountPP.length();
        if( (posLength != velLength) || (posLength != countLength) )
            return;

        // Compute total emit count.
        //
        int index;
        int totalCount = 0;
        for( index = 0; index < countLength; index ++ )
            totalCount += emitCountPP[index];

        if( totalCount <= 0 )
            return;

        // Map direction vector into world space and normalize it.
        //
        dirV.normalize();

        // Start emission.
        //
        int emitCount;
        MVector newPos, newVel;
        MVector prePos, sPos, sVel;
        for( index = 0; index < posLength; index++ )
        {
            emitCount = emitCountPP[index];
            if( emitCount <= 0 )
                continue;

            sPos = inPosAry[index];
            sVel = inVelAry[index];
            prePos = sPos - sVel * dt;

            for( int i = 0; i < emitCount; i++ )
            {
                double alpha = ( (double)i + drand48() ) / (double)emitCount;
                newPos = (1 - alpha) * prePos + alpha * sPos;
                newVel = dirV * speed;

                newPos += newVel * ( dt * (1 - alpha) );
                newVel += sVel * inheritFactor;

                // Add new data into output arrays.
                //
                outPosAry.append( newPos );
                outVelAry.append( newVel );
                outTimeAry.append( alpha );
            }
        }
    }

    MStatus simpleEmitter::getWorldPosition( MPoint &point )
    //
    //  Descriptions:
    //      get the emitter position in the world space.
    //      The position value is from inherited attribute, aWorldMatrix.
    //
    {
        MStatus status;

        MObject thisNode = thisMObject();
        MFnDependencyNode fnThisNode( thisNode );

        // get worldMatrix attribute.
        //
        MObject worldMatrixAttr = fnThisNode.attribute( "worldMatrix" );

        // build worldMatrix plug, and specify which element the plug refers to.
        // We use the first element(the first dagPath of this emitter).
        //
        MPlug matrixPlug( thisNode, worldMatrixAttr );
        matrixPlug = matrixPlug.elementByLogicalIndex( 0 );

        // Get the value of the 'worldMatrix' attribute
        //
        MObject matrixObject;
        status = matrixPlug.getValue( matrixObject );
        if( !status )
        {
            status.perror("simpleEmitter::getWorldPosition: get matrixObject");
            return( status );
        }

        MFnMatrixData worldMatrixData( matrixObject, &status );
        if( !status )
        {
            status.perror("simpleEmitter::getWorldPosition: get worldMatrixData");
            return( status );
        }

        MMatrix worldMatrix = worldMatrixData.matrix( &status );
        if( !status )
        {
            status.perror("simpleEmitter::getWorldPosition: get worldMatrix");
            return( status );
        }

        // assign the translate to the given vector.
        //
        point[0] = worldMatrix( 3, 0 );
        point[1] = worldMatrix( 3, 1 );
        point[2] = worldMatrix( 3, 2 );

        return( status );
    }

    MStatus simpleEmitter::getWorldPosition( MDataBlock& block, MPoint &point )
    //
    //  Descriptions:
    //      Find the emitter position in the world space.
    //
    {
        MStatus status;

        MObject thisNode = thisMObject();
        MFnDependencyNode fnThisNode( thisNode );

        // get worldMatrix attribute.
        //
        MObject worldMatrixAttr = fnThisNode.attribute( "worldMatrix" );

        // build worldMatrix plug, and specify which element the plug refers to.
        // We use the first element(the first dagPath of this emitter).
        //
        MPlug matrixPlug( thisNode, worldMatrixAttr );
        matrixPlug = matrixPlug.elementByLogicalIndex( 0 );
        MDataHandle hWMatrix = block.inputValue( matrixPlug, &status );

        McheckErr(status, "ERROR getting hWMatrix from dataBlock.\n");

        if( status == MS::kSuccess )
        {
            MMatrix wMatrix = hWMatrix.asMatrix();
            point[0] = wMatrix(3, 0);
            point[1] = wMatrix(3, 1);
            point[2] = wMatrix(3, 2);
        }
        return( status );
    }

    MVector simpleEmitter::useRotation ( MVector &direction )
    {
        MStatus status;
        MVector rotatedVector;

        MObject thisNode = thisMObject();
        MFnDependencyNode fnThisNode( thisNode );

        // get worldMatrix attribute.
        //
        MObject worldMatrixAttr = fnThisNode.attribute( "worldMatrix" );

        // build worldMatrix plug, and specify which element the plug refers to.
        // We use the first element(the first dagPath of this emitter).
        //
        MPlug matrixPlug( thisNode, worldMatrixAttr );
        matrixPlug = matrixPlug.elementByLogicalIndex( 0 );

        // Get the value of the 'worldMatrix' attribute
        //
        MObject matrixObject;
        status = matrixPlug.getValue( matrixObject );
        if( !status )
        {
            status.perror("simpleEmitter::getWorldPosition: get matrixObject");
            return ( direction );
        }

        MFnMatrixData worldMatrixData( matrixObject, &status );
        if( !status )
        {
            status.perror("simpleEmitter::getWorldPosition: get worldMatrixData");
            return( direction );
        }

        MMatrix worldMatrix = worldMatrixData.matrix( &status );
        if( !status )
        {
            status.perror("simpleEmitter::getWorldPosition: get worldMatrix");
            return( direction );
        }

        rotatedVector = direction * worldMatrix;

        return( rotatedVector );
    }

    #define TORUS_PI 3.14159265
    #define TORUS_2PI 2*TORUS_PI
    #define EDGES 30
    #define SEGMENTS 20

    //
    //  Descriptions:
    //      Draw a set of rings to symbolie the field. This does not override default icon, you can do that by implementing the iconBitmap() function
    //

    void simpleEmitter::draw( M3dView& view, const MDagPath& path, M3dView::DisplayStyle style, M3dView:: DisplayStatus )
    {
        view.beginGL();
        for (int j = 0; j < SEGMENTS; j++ )
        {
            glPushMatrix();
            glRotatef( GLfloat(360 * j / SEGMENTS), 0.0, 1.0, 0.0 );
            glTranslatef( 1.5, 0.0, 0.0 );

            for (int i = 0; i < EDGES; i++ )
            {
                glBegin(GL_LINE_STRIP);
                float p0 = float( TORUS_2PI * i / EDGES );
                float p1 = float( TORUS_2PI * (i+1) / EDGES );
                glVertex2f( cos(p0), sin(p0) );
                glVertex2f( cos(p1), sin(p1) );
                glEnd();
            }
            glPopMatrix();
        }
        view.endGL ();
    }

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

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

        return status;
    }

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

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

        return status;
    }