simpleFluidEmitter.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 <simpleFluidEmitter.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>

#include <maya/MDagPath.h>
#include <maya/MMatrix.h>
#include <maya/MTransformationMatrix.h>
#include <maya/MFnDynSweptGeometryData.h>
#include <maya/MDynSweptTriangle.h>


MTypeId simpleFluidEmitter::id( 0x81020 );

simpleFluidEmitter::simpleFluidEmitter()
{
}


simpleFluidEmitter::~simpleFluidEmitter()
{
}


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


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


MStatus simpleFluidEmitter::compute(const MPlug& plug, MDataBlock& block)
//
//      Description:
//
//              Fluid emitters do not perform emission in their compute() method.
//              Instead, each fluid to which the emitter is connected will call the
//              fluidEmitter() method once per frame, to allow the emitter to emit
//              directly into the fluid.
//
//              It is ESSENTIAL that the compute routine return MS::kUnknownParameter
//              when the "emissionFunction" attribute is being evaluated.  Doing so
//              will trigger the base class default compute() method, which will
//              register this node's "fluidEmitter" function with the fluid.  The
//              mechanisms for doing this are not exposed through the API, so it is
//              important to let the default code handle this case.
//
//              For all other attributes, users can override the compute() method.
//
{
        if( plug.attribute() == mEmissionFunction )
        {
                //      ESSENTIAL!  Let the base class default compute method handle this
                //
                return MS::kUnknownParameter;
        }
        else
        {
                //      can add custom handling for other attributes here
                //
                return MS::kUnknownParameter;
        }
}


MStatus 
simpleFluidEmitter::fluidEmitter( 
        const MObject& fluidObject, 
        const MMatrix& worldMatrix, 
        int plugIndex 
)
//==============================================================================
//
//      Description:
//
//              Callback function that gets called once per frame by each fluid
//              into which this emitter is emitting.  Emits values directly into
//              the fluid object.  The MFnFluid object passed to this routine is
//              not pointing to a DAG object, it is pointing to an internal fluid
//              data structure that the fluid node is constructing, eventually to
//              be set into the fluid's output attribute.
//
//      Parameters:
//
//              fluid:                  fluid into which we are emitting
//              worldMatrix:    object->world matrix for the fluid
//              plugIndex:              identifies which fluid connected to the emitter
//                                              we are emitting into
//
//      Returns:
//
//              MS::kSuccess                    if the method wishes to override the default
//                                                              emitter behaviour
//              MS::kUnknownParameter   if the method wishes to have the default
//                                                              emitter behaviour execute after this routine
//                                                              exits.
//
//      Notes:
//
//              The method first does some work common to all emitter types, then
//              calls one of 4 different methods to actually do the emission.
//              The methods are:
//
//                      omniEmitter:    omni-directional emitter from a point,
//                                                      or from the vertices of an owner object.
//
//                      volumeEmitter:  emits from the surface of an exact cube, sphere,
//                                                      cone, cylinder, or torus.
//
//                      surfaceEmitter: emits from the surface of an owner object.
//
//==============================================================================
{
        //      make sure the fluid is valid.  If it isn't, return MS::kSuccess, indicating
        //      that no work needs to be done.  If we return a failure code, then the default
        //      fluid emitter code will try to run, which is pointless if the fluid is not
        //      valid.
        //
        MFnFluid fluid( fluidObject );
        if( fluid.object() != MObject::kNullObj )
        {
                return MS::kSuccess;
        }

        //      get a data block for the emitter, so we can get attribute values
        //
        MDataBlock block = forceCache();

        //      figure out the time interval for emission for the given fluid
        //
        double dTime = getDeltaTime( plugIndex, block ).as(MTime::kSeconds);
        if( dTime == 0.0 )
        {
                // shouldn't happen, but if the time interval is 0, then no fluid should
                // be emitted
                return MS::kSuccess;
        }

        //      if currentTime <= startTime, return. The startTime is connected to 
        //      the target fluid object.
        //
        MTime cTime = getCurrentTime( block );
        MTime sTime = getStartTime( plugIndex, block );

        //      if we are at or before the start time, reset the random number
        //      state to the appropriate seed value for the given fluid
        //
        if( cTime < sTime )
        {
                resetRandomState( plugIndex, block );
                return MS::kSuccess;
        }

        //      check to see if we need to emit anything into the target fluid.
        //      if the emission rate is 0, or if the fluid doesn't have a grid
        //      for one of the quantities, then we needn't do any emission
        //
        
        //      emission rates
        double density = fluidDensityEmission( block ); 
        double heat = fluidHeatEmission( block );       
        double fuel = fluidFuelEmission( block );       
        bool doColor = fluidEmitColor( block ); 

        //      fluid grid settings
        MFnFluid::FluidMethod densityMode, tempMode, fuelMode;
        MFnFluid::ColorMethod colorMode;
        MFnFluid::FluidGradient grad;
        MFnFluid::FalloffMethod falloffMode;
        fluid.getDensityMode( densityMode, grad );
        fluid.getTemperatureMode( tempMode, grad );
        fluid.getFuelMode( fuelMode, grad );
        fluid.getColorMode( colorMode );
        fluid.getFalloffMode( falloffMode );

        //      see if we need to emit density, heat, fuel, or color
        bool densityToEmit = (density != 0.0) && ((densityMode == MFnFluid::kDynamicGrid)||(densityMode == MFnFluid::kStaticGrid));
        bool heatToEmit = (heat != 0.0) && ((tempMode == MFnFluid::kDynamicGrid)||(tempMode == MFnFluid::kStaticGrid));
        bool fuelToEmit = (fuel != 0.0) && ((fuelMode == MFnFluid::kDynamicGrid)||(fuelMode == MFnFluid::kStaticGrid));
        bool colorToEmit = doColor && ((colorMode == MFnFluid::kDynamicColorGrid)||(colorMode == MFnFluid::kStaticColorGrid));
        bool falloffEmit = (falloffMode == MFnFluid::kStaticFalloffGrid);
        

        //      nothing to emit, do nothing
        //
        if( !densityToEmit && !heatToEmit && !fuelToEmit && !colorToEmit && !falloffEmit )
        {
                return MS::kSuccess;
        }

        //      get the dropoff rate for the fluid 
        //      
        double dropoff = fluidDropoff( block );

        //      modify the dropoff rate to account for fluids that have
        //      been scaled in worldspace - larger scales mean slower
        //      falloffs and vice versa
        //
        MTransformationMatrix xform( worldMatrix );
        double xformScale[3];
        xform.getScale( xformScale, MSpace::kWorld );
        double dropoffScale = sqrt( xformScale[0]*xformScale[0] + 
                                                                xformScale[1]*xformScale[1] + 
                                                                xformScale[2]*xformScale[2] );
        if( dropoffScale > 0.1 )
        {
                dropoff /= dropoffScale;
        }
        
        //      retrieve the current random state from the "randState" attribute, and
        //      store it in the member variable "randState".  We will use this member 
        //      value numerous times via the randgen() method.  Once we are done emitting,
        //      we will set the random state back into the attribute via setRandomState().
        //
        getRandomState( plugIndex, block );

        //      conversion value used to map user input emission rates into internal
        //      values.
        //
        double conversion = 0.01;

        MEmitterType emitterType = getEmitterType( block );
        switch( emitterType )
        {
                case kOmni:
                        omniFluidEmitter( fluid, worldMatrix, plugIndex, block, dTime,
                                                          conversion, dropoff );
                        break;

                case kVolume:
                        volumeFluidEmitter( fluid, worldMatrix, plugIndex, block, dTime,
                                                            conversion, dropoff );
                        break;
                        
                case kSurface:
                        surfaceFluidEmitter( fluid, worldMatrix, plugIndex, block, dTime,
                                                             conversion, dropoff );
                        break;

                default:
                        break;
        }

        //      store the random state back into the datablock
        //      
        setRandomState( plugIndex, block );
        return MS::kSuccess;
}

#define MIN(x,y) ((x)<(y)?(x):(y))
#define MAX(x,y) ((x)>(y)?(x):(y))

void 
simpleFluidEmitter::omniFluidEmitter(
        MFnFluid&               fluid,
        const MMatrix&  fluidWorldMatrix,
        int                     plugIndex,
        MDataBlock&     block,
        double                  dt,
        double                  conversion,
        double                  dropoff
)
//==============================================================================
//
//      Method: 
//
//              simpleFluidEmitter::omniFluidEmitter
//
//      Description:
//
//              Emits fluid from a point, or from a set of object control points.
//
//      Parameters:
//
//              fluid:                          fluid into which we are emitting
//              fluidWorldMatrix:       object->world matrix for the fluid
//              plugIndex:                      identifies which fluid connected to the emitter
//                                                      we are emitting into
//              block:                          datablock for the emitter, to retrieve attribute
//                                                      values
//              dt:                                     time delta for this frame
//              conversion:                     mapping from UI emission rates to internal units
//              dropoff:                        specifies how much emission rate drops off as
//                                                      we move away from each emission point.
//
//      Notes:
//
//              If no owner object is present for the emitter, we simply emit from
//              the emitter position.  If an owner object is present, then we emit
//              from each control point of that object in an identical fashion.
//              
//              To associate an owner object with an emitter, use the
//              addDynamic MEL command, e.g. "addDynamic simpleFluidEmitter1 pPlane1".
//
//==============================================================================
{
        //      find the positions that we need to emit from
        //
        MVectorArray emitterPositions;
        
        //      first, try to get them from an owner object, which will have its
        //      "ownerPositionData" attribute feeding into the emitter.  These
        //      values are in worldspace
        //
        bool gotOwnerPositions = false;
        MObject ownerShape = getOwnerShape();
        if( ownerShape != MObject::kNullObj )
        {
                MStatus status;
                MDataHandle hOwnerPos = block.inputValue( mOwnerPosData, &status );
                if( status == MS::kSuccess )
                {
                        MObject dOwnerPos = hOwnerPos.data();
                        MFnVectorArrayData fnOwnerPos( dOwnerPos );
                        MVectorArray posArray = fnOwnerPos.array( &status );
                        if( status == MS::kSuccess )
                        {
                                // assign vectors from block to ownerPosArray.
                                //
                                for( unsigned int i = 0; i < posArray.length(); i ++ )
                                {
                                        emitterPositions.append( posArray[i] );
                                }
                                
                                gotOwnerPositions = true;
                        }
                }
        }
        
        //      there was no owner object, so we just use the emitter position for
        //      emission.
        //
        if( !gotOwnerPositions )
        {
                MPoint emitterPos = getWorldPosition();
                emitterPositions.append( emitterPos );
        }

        //      get emission rates for density, fuel, heat, and emission color
        //      
        double densityEmit = fluidDensityEmission( block );
        double fuelEmit = fluidFuelEmission( block );
        double heatEmit = fluidHeatEmission( block );
        bool doEmitColor = fluidEmitColor( block );
        MColor emitColor = fluidColor( block );

        //      rate modulation based on frame time, user value conversion factor, and
        //      standard emitter "rate" value (not actually exposed in most fluid
        //      emitters, but there anyway).
        //
        double theRate = getRate(block) * dt * conversion;

        //      get voxel dimensions and sizes (object space)
        //
        double size[3];
        unsigned int res[3];
        fluid.getDimensions( size[0], size[1], size[2] );
        fluid.getResolution( res[0], res[1], res[2] );
        
        //      voxel sizes
        double dx = size[0] / res[0];
        double dy = size[1] / res[1];
        double dz = size[2] / res[2];
        
        //      voxel centers
        double Ox = -size[0]/2;
        double Oy = -size[1]/2;
        double Oz = -size[2]/2; 

        //      emission will only happen for voxels whose centers lie within
        //      "minDist" and "maxDist" of an emitter position
        //
        double minDist = getMinDistance( block );
        double maxDist = getMaxDistance( block );

        //      bump up the min/max distance values so that they
        //      are both > 0, and there is at least about a half
        //      voxel between the min and max values, to prevent aliasing
        //      artifacts caused by emitters missing most voxel centers
        //
        MTransformationMatrix fluidXform( fluidWorldMatrix );
        double fluidScale[3];
        fluidXform.getScale( fluidScale, MSpace::kWorld );
        
        //      compute smallest voxel diagonal length
        double wsX =  fabs(fluidScale[0]*dx);
        double wsY = fabs(fluidScale[1]*dy);
        double wsZ = fabs(fluidScale[2]*dz);
        double wsMin = MIN( MIN( wsX, wsY), wsZ );
        double wsMax = MAX( MAX( wsX, wsY), wsZ );
        double wsDiag  = wsMin * sqrt(3.0);

        //      make sure emission range is bigger than 0.5 voxels
        if ( maxDist <= minDist || maxDist <= (wsDiag/2.0) ) {
                if ( minDist < 0 ) minDist = 0;

                maxDist = minDist + wsDiag/2.0;
                dropoff = 0;
        }

        //      Now, it's time to actually emit into the fluid:
        //      
        //      foreach emitter point
        //              foreach voxel
        //                      - select some points in the voxel
        //                      - compute a dropoff function from the emitter point
        //                      - emit an appropriate amount of fluid into the voxel
        //
        //      Since we've already expanded the min/max distances to cover
        //      the smallest voxel dimension, we should only need 1 sample per
        //      voxel, unless the voxels are highly non-square.  We increase the
        //      number of samples in these cases.
        //
        //      If the "jitter" flag is enabled, we jitter each sample position,
        //      using the rangen() function, which keeps track of independent 
        //      random states for each fluid, to make sure that results are
        //      repeatable for multiple simulation runs.
        //      

        // basic sample count
        int numSamples = 1;

        // increase samples if necessary for non-square voxels
        if(wsMin >.00001) 
        {
                numSamples = (int)(wsMax/wsMin + .5);
                if(numSamples > 8) 
                        numSamples = 8;
                if(numSamples < 1)
                        numSamples = 1;
        }
        
        bool jitter =  fluidJitter(block);
        if( !jitter )
        {
                //      I don't have a good uniform sample generator for an 
                //      arbitrary number of samples.  It would be a good idea to use
                //      one here.  For now, just use 1 sample for the non-jittered case.
                //
                numSamples = 1;
        }

        for( unsigned int p = 0; p < emitterPositions.length(); p++ )
        {
                MPoint emitterWorldPos = emitterPositions[p];

                //      loop through all voxels, looking for ones that lie at least
                //      partially within the dropoff field around this emitter point
                //
                for( unsigned int i = 0; i < res[0]; i++ )
                {
                        double x = Ox + i*dx;
                        
                        for( unsigned int j = 0; j < res[1]; j++ )
                        {
                                double y = Oy + j*dy;
                                
                                for( unsigned int k = 0; k < res[2]; k++ )
                                {
                                        double z = Oz + k*dz;
        
                                        int si;
                                        for( si = 0; si < numSamples; si++ )
                                        {
                                                //      compute sample point (fluid object space)
                                                //
                                                double rx, ry, rz;
                                                if( jitter )
                                                {
                                                        rx = x + randgen()*dx;
                                                        ry = y + randgen()*dy;
                                                        rz = z + randgen()*dz;
                                                }
                                                else
                                                {
                                                        rx = x + 0.5*dx;
                                                        ry = y + 0.5*dy;
                                                        rz = z + 0.5*dz;
                                                }

                                                //      compute distance from sample to emitter point
                                                //      
                                                MPoint point( rx, ry, rz );
                                                point *= fluidWorldMatrix;
                                                MVector diff = point - emitterWorldPos;
                                                double distSquared = diff * diff;
                                                double dist = diff.length();
                                        
                                                //      discard if outside min/max range
                                                //
                                                if( (dist < minDist) || (dist > maxDist) )
                                                {
                                                        continue;
                                                }
                                                
                                                //      drop off the emission rate according to the falloff
                                                //      parameter, and divide to accound for multiple samples
                                                //      in the voxel
                                                //
                                                double distDrop = dropoff * distSquared;
                                                double newVal = theRate * exp( -distDrop ) / (double)numSamples;

                                                //      emit density/heat/fuel/color into the current voxel
                                                //
                                                if( newVal != 0 )
                                                {
                                                        fluid.emitIntoArrays( (float) newVal, i, j, k, (float)densityEmit, (float)heatEmit, (float)fuelEmit, doEmitColor, emitColor );
                                                }

                                                float *fArray = fluid.falloff();
                                                if( fArray != NULL )
                                                {
                                                        MPoint midPoint( x+0.5*dx, y+0.5*dy, z+0.5*dz );
                                                        midPoint.x *= 0.2;
                                                        midPoint.y *= 0.2;
                                                        midPoint.z *= 0.2;

                                                        float fdist = (float) sqrt( midPoint.x*midPoint.x + midPoint.y*midPoint.y + midPoint.z*midPoint.z );
                                                        fdist /= sqrtf(3.0f);
                                                        fArray[fluid.index(i,j,k)] = 1.0f-fdist;
                                                }
                                        }
                                }
                        }
                }
        }
}

void 
simpleFluidEmitter::volumeFluidEmitter(
        MFnFluid&               fluid,
        const MMatrix&  fluidWorldMatrix,
        int                     plugIndex,
        MDataBlock&     block,
        double                  dt,
        double                  conversion,
        double                  dropoff
)
//==============================================================================
//
//      Method: 
//
//              simpleFluidEmitter::volumeFluidEmitter
//
//      Description:
//
//              Emits fluid from points distributed over the surface of the 
//              emitter's owner object.
//
//      Parameters:
//
//              fluid:                          fluid into which we are emitting
//              fluidWorldMatrix:       object->world matrix for the fluid
//              plugIndex:                      identifies which fluid connected to the emitter
//                                                      we are emitting into
//              block:                          datablock for the emitter, to retrieve attribute
//                                                      values
//              dt:                                     time delta for this frame
//              conversion:                     mapping from UI emission rates to internal units
//              dropoff:                        specifies how much emission rate drops off as
//                                                      we move away from the local y-axis of the 
//                                                      volume emitter shape.
//
//==============================================================================
{
        //      get emitter position and relevant matrices 
        //      
        MPoint emitterPos = getWorldPosition();
        MMatrix emitterWorldMatrix = getWorldMatrix();
        MMatrix fluidInverseWorldMatrix = fluidWorldMatrix.inverse();
        
        //      get emission rates for density, fuel, heat, and emission color
        //      
        double densityEmit = fluidDensityEmission( block );
        double fuelEmit = fluidFuelEmission( block );
        double heatEmit = fluidHeatEmission( block );
        bool doEmitColor = fluidEmitColor( block );
        MColor emitColor = fluidColor( block );
        
        //      rate modulation based on frame time, user value conversion factor, and
        //      standard emitter "rate" value (not actually exposed in most fluid
        //      emitters, but there anyway).
        //
        double theRate = getRate(block) * dt * conversion;
        
        //      get voxel dimensions and sizes (object space)
        //
        double size[3];
        unsigned int res[3];
        fluid.getDimensions( size[0], size[1], size[2] );
        fluid.getResolution( res[0], res[1], res[2] );

        //      voxel sizes
        double dx = size[0] / res[0];
        double dy = size[1] / res[1];
        double dz = size[2] / res[2];
        
        //      voxel centers
        double Ox = -size[0]/2;
        double Oy = -size[1]/2;
        double Oz = -size[2]/2; 

        //      find the voxels that intersect the bounding box of the volume
        //      primitive associated with the emitter
        //
        MBoundingBox bbox;
        if( !volumePrimitiveBoundingBox( bbox ) )
        {
                //      shouldn't happen
                //
                return;
        }
        
        //      transform volume primitive into fluid space
        //
        bbox.transformUsing( emitterWorldMatrix );
        bbox.transformUsing( fluidInverseWorldMatrix );
        MPoint lowCorner = bbox.min();
        MPoint highCorner = bbox.max();

        //      get fluid voxel coord range of bounding box
        //
        int3 lowCoords;
        int3 highCoords;
        fluid.toGridIndex( lowCorner, lowCoords );
        fluid.toGridIndex( highCorner, highCoords );
        
        int i;
        for ( i = 0; i < 3; i++ )
        {
                if ( lowCoords[i] < 0 ) {
                        lowCoords[i] = 0;
                } else if ( lowCoords[i] > ((int)res[i])-1 ) {
                        lowCoords[i] = ((int)res[i])-1;
                }

                if ( highCoords[i] < 0 ) {
                        highCoords[i] = 0;
                } else if ( highCoords[i] > ((int)res[i])-1 ) {
                        highCoords[i] = ((int)res[i])-1;
                }
                
        }

        //      figure out the emitter size relative to the voxel size, and compute
        //      a per-voxel sampling rate that uses 1 sample/voxel for emitters that
        //      are >= 2 voxels big in all dimensions.  For smaller emitters, use up
        //      to 8 samples per voxel.
        //
        double emitterVoxelSize[3];
        emitterVoxelSize[0] = (highCorner[0]-lowCorner[0])/dx;
        emitterVoxelSize[1] = (highCorner[1]-lowCorner[1])/dy;
        emitterVoxelSize[2] = (highCorner[2]-lowCorner[2])/dz;
                
        double minVoxelSize = MIN(emitterVoxelSize[0],MIN(emitterVoxelSize[1],emitterVoxelSize[2]));
        if( minVoxelSize < 1.0 )
        {
                minVoxelSize = 1.0;
        }
        int maxSamples = 8;
        int numSamples = (int)(8.0/(minVoxelSize*minVoxelSize*minVoxelSize) + 0.5);
        if( numSamples < 1 ) numSamples = 1;
        if( numSamples > maxSamples ) numSamples = maxSamples;
        
        //      non-jittered, just use one sample in the voxel center.  Should replace
        //      with uniform sampling pattern.
        //
        bool jitter = fluidJitter(block);
        if( !jitter )
        {
                numSamples = 1;
        }
        
        //      for each voxel that could potentially intersect the volume emitter
        //      primitive, take some samples in the voxel.  For those inside the
        //      volume, compute their dropoff relative to the primitive's local y-axis,
        //      and emit an appropriate amount into the voxel.
        //
        for( i = lowCoords[0]; i <= highCoords[0]; i++ )
        {
                double x = Ox + (i+0.5)*dx;
                        
                for( int j = lowCoords[1]; j < highCoords[1]; j++ )
                {
                        double y = Oy + (j+0.5)*dy;

                        for( int k = lowCoords[2]; k < highCoords[2]; k++ )
                        {
                                double z = Oz + (k+0.5)*dz;
                                
                                for ( int si = 0; si < numSamples; si++) {
                                        
                                        //      compute voxel sample point (object space)
                                        //
                                        double rx, ry, rz;
                                        if(jitter) {
                                                rx = x + dx*(randgen() - 0.5);
                                                ry = y + dy*(randgen() - 0.5);
                                                rz = z + dz*(randgen() - 0.5);
                                        } else {
                                                rx = x;
                                                ry = y;
                                                rz = z;
                                        }
                                        
                                        //      to world space
                                        MPoint pt( rx, ry, rz );
                                        pt *= fluidWorldMatrix;

                                        //      test to see if point is inside volume primitive
                                        //
                                        if( volumePrimitivePointInside( pt, emitterWorldMatrix ) )
                                        {
                                                //      compute dropoff
                                                //
                                                double dist = pt.distanceTo( emitterPos );
                                                double distDrop = dropoff * (dist*dist);
                                                double newVal = (theRate * exp( -distDrop )) / (double)numSamples;
                                                
                                                //      emit into arrays
                                                //
                                                if( newVal != 0.0 )
                                                {
                                                        fluid.emitIntoArrays( (float) newVal, i, j, k, (float)densityEmit, (float)heatEmit, (float)fuelEmit, doEmitColor, emitColor );
                                                }
                                        }
                                }
                        }
                }
        }
}

void 
simpleFluidEmitter::surfaceFluidEmitter(
        MFnFluid&               fluid,
        const MMatrix&  fluidWorldMatrix,
        int                     plugIndex,
        MDataBlock&     block,
        double                  dt,
        double                  conversion,
        double                  dropoff
)
//==============================================================================
//
//      Method: 
//
//              simpleFluidEmitter::surfaceFluidEmitter
//
//      Description:
//
//              Emits fluid from one of a predefined set of volumes (cube, sphere,
//              cylinder, cone, torus).
//
//      Parameters:
//
//              fluid:                          fluid into which we are emitting
//              fluidWorldMatrix:       object->world matrix for the fluid
//              plugIndex:                      identifies which fluid connected to the emitter
//                                                      we are emitting into
//              block:                          datablock for the emitter, to retrieve attribute
//                                                      values
//              dt:                                     time delta for this frame
//              conversion:                     mapping from UI emission rates to internal units
//              dropoff:                        specifies how much emission rate drops off as
//                                                      the surface points move away from the centers
//                                                      of the voxels in which they lie.
//
//      Notes:
//              
//              To associate an owner object with an emitter, use the
//              addDynamic MEL command, e.g. "addDynamic simpleFluidEmitter1 pPlane1".
//
//==============================================================================
{
        //      get relevant world matrices
        //
        MMatrix fluidInverseWorldMatrix = fluidWorldMatrix.inverse();
        
        //      get emission rates for density, fuel, heat, and emission color
        //      
        double densityEmit = fluidDensityEmission( block );
        double fuelEmit = fluidFuelEmission( block );
        double heatEmit = fluidHeatEmission( block );
        bool doEmitColor = fluidEmitColor( block );
        MColor emitColor = fluidColor( block );
        
        //      rate modulation based on frame time, user value conversion factor, and
        //      standard emitter "rate" value (not actually exposed in most fluid
        //      emitters, but there anyway).
        //
        double theRate = getRate(block) * dt * conversion;

        //      get voxel dimensions and sizes (object space)
        //
        double size[3];
        unsigned int res[3];
        fluid.getDimensions( size[0], size[1], size[2] );
        fluid.getResolution( res[0], res[1], res[2] );
                
        //      voxel sizes
        double dx = size[0] / res[0];
        double dy = size[1] / res[1];
        double dz = size[2] / res[2];
        
        //      voxel centers
        double Ox = -size[0]/2;
        double Oy = -size[1]/2;
        double Oz = -size[2]/2; 

        //      get the "swept geometry" data for the emitter surface.  This structure
        //      tracks the motion of each emitter triangle over the time interval
        //      for this simulation step.  We just use positions on the emitter
        //      surface at the end of the time step to do the emission.
        //
        MDataHandle sweptHandle = block.inputValue( mSweptGeometry );
        MObject sweptData = sweptHandle.data();
        MFnDynSweptGeometryData fnSweptData( sweptData );

        //      for "non-jittered" sampling, just reset the random state for each 
        //      triangle, which gives us a fixed set of samples all the time.
        //      Sure, they're still jittered, but they're all jittered the same,
        //      which makes them kinda uniform.
        //
        bool jitter = fluidJitter(block);
        if( !jitter )
        {
                resetRandomState( plugIndex, block );
        }

        if( fnSweptData.triangleCount() > 0 )
        {
                //      average voxel face area - use this as the canonical unit that
                //      receives the emission rate specified by the users.  Scale the
                //      rate for other triangles accordingly.
                //
                double vfArea = pow(dx*dy*dz, 2.0/3.0);
                
                //      very rudimentary support for textured emission rate and
                //      textured emission color.  We simply sample each texture once
                //      at the center of each emitter surface triangle.  This will 
                //      cause aliasing artifacts when these triangles are large.
                //
                MFnDependencyNode fnNode( thisMObject() );
                MObject rateTextureAttr = fnNode.attribute( "textureRate" );
                MObject colorTextureAttr = fnNode.attribute( "particleColor" );

                bool texturedRate = hasValidEmission2dTexture( rateTextureAttr );
                bool texturedColor = hasValidEmission2dTexture( colorTextureAttr );
                
                //      construct texture coordinates for each triangle center
                //      
                MDoubleArray uCoords, vCoords;
                if( texturedRate || texturedColor )
                {
                        uCoords.setLength( fnSweptData.triangleCount() );
                        vCoords.setLength( fnSweptData.triangleCount() );
                        
                        int t;
                        for( t = 0; t < fnSweptData.triangleCount(); t++ )
                        {
                                MDynSweptTriangle tri = fnSweptData.sweptTriangle( t );
                                MVector uv0 = tri.uvPoint(0);
                                MVector uv1 = tri.uvPoint(1);
                                MVector uv2 = tri.uvPoint(2);
                                
                                MVector uvMid = (uv0+uv1+uv2)/3.0;
                                uCoords[t] = uvMid[0];
                                vCoords[t] = uvMid[1];
                        }
                }

                //      evaluate textured rate and color values at the triangle centers
                //
                MDoubleArray texturedRateValues;
                if( texturedRate )
                {
                        texturedRateValues.setLength( uCoords.length() );
                        evalEmission2dTexture( rateTextureAttr, uCoords, vCoords, NULL, &texturedRateValues );
                }
                
                MVectorArray texturedColorValues;
                if( texturedColor )
                {
                        texturedColorValues.setLength( uCoords.length() );
                        evalEmission2dTexture( colorTextureAttr, uCoords, vCoords, &texturedColorValues, NULL );
                }
                
                for( int t = 0; t < fnSweptData.triangleCount(); t++ )
                {
                        //      calculate emission rate and color values for this triangle
                        //
                        double curTexturedRate = texturedRate ? texturedRateValues[t] : 1.0;
                        MColor curTexturedColor;
                        if( texturedColor )
                        {
                                MVector& curVec = texturedColorValues[t];
                                curTexturedColor.r = (float)curVec[0];
                                curTexturedColor.g = (float)curVec[1];
                                curTexturedColor.b = (float)curVec[2];
                                curTexturedColor.a = 1.0;
                        }
                        else
                        {
                                curTexturedColor = emitColor;
                        }

                        MDynSweptTriangle tri = fnSweptData.sweptTriangle( t );
                        MVector v0 = tri.vertex(0);
                        MVector v1 = tri.vertex(1);
                        MVector v2 = tri.vertex(2);

                        //      compute number of samples for this triangle based on area,
                        //      with large triangles receiving approximately 1 sample for 
                        //      each voxel that they intersect
                        //
                        double triArea = tri.area();
                        int numSamples = (int)(triArea / vfArea);
                        if( numSamples < 1 ) numSamples = 1;
                        
                        //      compute emission rate for the points on the triangle.
                        //      Scale the canonical rate by the area ratio of this triangle
                        //      to the average voxel size, then split it amongst all the samples.
                        //
                        double triRate = (theRate*(triArea/vfArea))/numSamples;
                        
                        triRate *= curTexturedRate;
                        
                        for( int j = 0; j < numSamples; j++ )
                        {
                                //      generate a random point on the triangle,
                                //      map it into fluid local space
                                //
                                double r1 = randgen();
                                double r2 = randgen();
                                
                                if( r1 + r2 > 1 )
                                {
                                        r1 = 1-r1;
                                        r2 = 1-r2;
                                }
                                double r3 = 1 - (r1+r2);
                                MPoint randPoint = r1*v0 + r2*v1 + r3*v2;
                                randPoint *= fluidInverseWorldMatrix;
                                
                                //      figure out where the current point lies
                                //
                                int3 coord;
                                fluid.toGridIndex( randPoint, coord );
                                
                                if( (coord[0]<0) || (coord[1]<0) || (coord[2]<0) ||
                                        (coord[0]>=(int)res[0]) || (coord[1]>=(int)res[1]) || (coord[2]>=(int)res[2]) )
                                {
                                        continue;
                                }
                                
                                //      do some falloff based on how far from the voxel center 
                                //      the current point lies
                                //
                                MPoint gridPoint;
                                gridPoint.x = Ox + (coord[0]+0.5)*dx;
                                gridPoint.y = Oy + (coord[1]+0.5)*dy;
                                gridPoint.z = Oz + (coord[2]+0.5)*dz;
                                
                                MVector diff = gridPoint - randPoint;
                                double distSquared = diff * diff;
                                double distDrop = dropoff * distSquared;
                                
                                double newVal = triRate * exp( -distDrop );
                
                                //      emit into the voxel
                                //
                                if( newVal != 0 )
                                {
                                        fluid.emitIntoArrays( (float) newVal, coord[0], coord[1], coord[2], (float)densityEmit, (float)heatEmit, (float)fuelEmit, doEmitColor, curTexturedColor );              
                                }
                        }
                }
        }
}

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

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

        return status;
}

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

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

        return status;
}