VDB R&D

VDB Data value visualize: 结论从houdini得知.

API常用文字:

interior:内部

Narrow-band:窄带

background:窄带外

SDF: XY plane Data visualize:

{

　　(1)用法:vdb sdf levelset球，采样其体素值到对应的点位置的颜色观察。houdini节点vdb from polygons(参数上Exterior band voxels:3,Interior band voxels:3)没有开启Fill interior

　　则形成体素值：

　　　　interior是-0.3 (这个值是由Interior band voxels:3 得到)

　　　　Narrow-band: 从interior到narrow-band方向:-0.3 到 0

　   　　background:从narrow-band到background方向:0.3 (Exterior band voxels:3)

　　(2)用法:

　　假如要让interior成为一个梯度值，而不是恒定值，houdini做了一个牛逼的按钮，Fill interior.

　　interior里的体素值立马成为梯度的，大概是从-3.73过渡到narrow-band

}

FOG Volume: XY plane Data visualize:

{

　　(1) 普通不勾选fill interior:

　　interior是1

　　Narrow-band: 从interior到narrow-band方向:1 到 0

　   background:从narrow-band到background方向:0

　　(2) 勾选fill interior:

　　interior到narrow-band方向从1->0.3有个过渡

　　Narrow-band: 从interior到narrow-band方向:0.3 到 0

　   background:从narrow-band到background方向:0

}

==================================================================START======================================================

<1> ,make vdb sphere,and convert to volume

#include <openvdb/openvdb.h>
#include <openvdb/tools/LevelSetSphere.h>
using namespace std;

// Populate the given grid with a narrow-band level set representation of a sphere.
// The width of the narrow band is determined by the grid's background value.
// (Example code only; use tools::createSphereSDF() in production.)
template<class GridType>
void
static makeSphere(GridType& grid, float radius, const openvdb::Vec3f& c)
{
    typedef typename GridType::ValueType ValueT;
    // Distance value for the constant region exterior to the narrow band
    const ValueT outside = grid.background();
    // Distance value for the constant region interior to the narrow band
    // (by convention, the signed distance is negative in the interior of
    // a level set)
    const ValueT inside = -outside;
    // Use the background value as the width in voxels of the narrow band.
    // (The narrow band is centered on the surface of the sphere, which
    // has distance 0.)
    int padding = int(openvdb::math::RoundUp(openvdb::math::Abs(outside)));
    // The bounding box of the narrow band is 2*dim voxels on a side.
    int dim = int(radius + padding);
    // Get a voxel accessor.
    typename GridType::Accessor accessor = grid.getAccessor();
    // Compute the signed distance from the surface of the sphere of each
    // voxel within the bounding box and insert the value into the grid
    // if it is smaller in magnitude than the background value.
    openvdb::Coord ijk;
    int &i = ijk[];
    int &j = ijk[];
    int &k = ijk[];
    for (i = c[] - dim; i < c[] + dim; ++i) {
        const float x2 = openvdb::math::Pow2(i - c[]);
        for (j = c[] - dim; j < c[] + dim; ++j) {
            const float x2y2 = openvdb::math::Pow2(j - c[]) + x2;
            for (k = c[] - dim; k < c[] + dim; ++k) {
                // The distance from the sphere surface in voxels
                const float dist = openvdb::math::Sqrt(x2y2
                                                       + openvdb::math::Pow2(k - c[])) - radius;
                // Convert the floating-point distance to the grid's value type.
                ValueT val = ValueT(dist);
                // Only insert distances that are smaller in magnitude than
                // the background value.
                if (val < inside || outside < val) continue;
                // Set the distance for voxel (i,j,k).
                accessor.setValue(ijk, val);
            }
        }
    }
    // Propagate the outside/inside sign information from the narrow band
    // throughout the grid.
    openvdb::tools::signedFloodFill(grid.tree());

}

template <class T>
static void convertToVolume(T &grid)
{

    // Convert the level set sphere to a narrow-band fog volume, in which
// interior voxels have value 1, exterior voxels have value 0, and
// narrow-band voxels have values varying linearly from 0 to 1.
    const float outside = grid->background();
    const float width = 2.0 * outside;
// Visit and update all of the grid's active values, which correspond to
// voxels on the narrow band.
    for (openvdb::FloatGrid::ValueOnIter iter = grid->beginValueOn(); iter; ++iter) {
        float dist = iter.getValue();
        iter.setValue((outside - dist) / width);
    }
// Visit all of the grid's inactive tile and voxel values and update the values
// that correspond to the interior region.
    for (openvdb::FloatGrid::ValueOffIter iter = grid->beginValueOff(); iter; ++iter) {
        if (iter.getValue() < 0.0) {
            iter.setValue(1.0);
            iter.setValueOff();
        } else{
            iter.setValue();
            iter.setValueOff();
        }
    }

}

int main()
{

    openvdb::initialize();
    // Create a shared pointer to a newly-allocated grid of a built-in type:
    // in this case, a FloatGrid, which stores one single-precision floating point
    // value per voxel.  Other built-in grid types include BoolGrid, DoubleGrid,
    // Int32Grid and Vec3SGrid (see openvdb.h for the complete list).
    // The grid comprises a sparse tree representation of voxel data,
    // user-supplied metadata and a voxel space to world space transform,
    // which defaults to the identity transform.
    openvdb::FloatGrid::Ptr grid =
            openvdb::FloatGrid::create(/*background value=*/2.0);
    // Populate the grid with a sparse, narrow-band level set representation
    // of a sphere with radius 50 voxels, located at (1.5, 2, 3) in index space.
    makeSphere(*grid, /*radius=*/50.0, /*center=*/openvdb::Vec3f(1.5, , ));
    // Associate some metadata with the grid.
    grid->insertMeta("radius", openvdb::FloatMetadata(50.0));
    // Associate a scaling transform with the grid that sets the voxel size
    // to 0.5 units in world space.
    grid->setTransform(
            openvdb::math::Transform::createLinearTransform(/*voxel size=*/0.5));
    // Identify the grid as a level set.
    grid->setGridClass(openvdb::GRID_LEVEL_SET);
    //grid->setGridClass(openvdb::GRID_FOG_VOLUME);
    // Name the grid "LevelSetSphere".
    grid->setName("LevelSetSphere");
    // Create a VDB file object.
    openvdb::io::File file("mygrids.vdb");
    // Add the grid pointer to a container.
    openvdb::GridPtrVec grids;

    // Write out the contents of the container.

    grids.push_back(grid);
    file.write(grids);
    file.close();

// ============================================================= convert level set sphere to a fog volume sphere =====================================================
    std::cout << "read a new sdf volume and change it to fog\n";
    openvdb::io::File readFile("mygrids.vdb");
    readFile.open();
    openvdb::GridBase::Ptr readGrid;
    for(openvdb::io::File::NameIterator nameIter = readFile.beginName();nameIter!=readFile.endName();++nameIter)
    {
        if(nameIter.gridName() == "LevelSetSphere")
        {
            readGrid = readFile.readGrid(nameIter.gridName());
        } else
        {
            std::cout << "skip other grid modifile " << nameIter.gridName() <<std::endl;
        }
    }
    openvdb::FloatGrid::Ptr cast_grid = openvdb::gridPtrCast<openvdb::FloatGrid>(readGrid);
    cast_grid->setGridClass(openvdb::GRID_FOG_VOLUME);
    readFile.close();
    convertToVolume(cast_grid);
    openvdb::GridPtrVec WM_grids;
    WM_grids.push_back(cast_grid);
    openvdb::io::File WM_file("mygrids_convertToVolume.vdb");
    WM_file.write(WM_grids);
    WM_file.close();

    return ;
}

<2> vdb from particles

主要观察粒子的density,velocity

#include <openvdb/openvdb.h>

#include <openvdb/tools/ParticlesToLevelSet.h>

#include <iostream>
#include <vector>

struct MyParticle
{
    openvdb::Vec3R p, v;
    openvdb::Real  r;
};

class MyParticleList
{

    // change protected to the public,direct find the mRadiusScale,mVelocityScale
public:

    openvdb::Real           mRadiusScale;
    openvdb::Real           mVelocityScale;
    std::vector<MyParticle> mParticleList;

public:
    std::vector<MyParticle> &get_mPartcileList()
    {
        return mParticleList;
    }

public:

    typedef openvdb::Vec3R  PosType;

    MyParticleList(openvdb::Real rScale=, openvdb::Real vScale=)
            : mRadiusScale(rScale), mVelocityScale(vScale) {}
    void add(const openvdb::Vec3R &p, const openvdb::Real &r,
             const openvdb::Vec3R &v=openvdb::Vec3R(,,))
    {
        MyParticle pa;
        pa.p = p;
        pa.r = r;
        pa.v = v;
        mParticleList.push_back(pa);
    }
    /// @return coordinate bbox in the space of the specified transfrom
    openvdb::CoordBBox getBBox(const openvdb::GridBase& grid) {
        openvdb::CoordBBox bbox;
        openvdb::Coord &min= bbox.min(), &max = bbox.max();
        openvdb::Vec3R pos;
        openvdb::Real rad, invDx = /grid.voxelSize()[];
        for (size_t n=, e=this->size(); n<e; ++n) {
            this->getPosRad(n, pos, rad);
            const openvdb::Vec3d xyz = grid.worldToIndex(pos);
            const openvdb::Real   r  = rad * invDx;
            for (int i=; i<; ++i) {
                min[i] = openvdb::math::Min(min[i], openvdb::math::Floor(xyz[i] - r));
                max[i] = openvdb::math::Max(max[i], openvdb::math::Ceil( xyz[i] + r));
            }
        }
        return bbox;
    }
    //typedef int AttributeType;
    // The methods below are only required for the unit-tests
    openvdb::Vec3R pos(int n)   const {return mParticleList[n].p;}
    openvdb::Vec3R vel(int n)   const {return mVelocityScale*mParticleList[n].v;}
    openvdb::Real radius(int n) const {return mRadiusScale*mParticleList[n].r;}

    //////////////////////////////////////////////////////////////////////////////
    /// The methods below are the only ones required by tools::ParticleToLevelSet
    /// @note We return by value since the radius and velocities are modified
    /// by the scaling factors! Also these methods are all assumed to
    /// be thread-safe.

    /// Return the total number of particles in list.
    ///  Always required!
    size_t size() const { return mParticleList.size(); }

    /// Get the world space position of n'th particle.
    /// Required by ParticledToLevelSet::rasterizeSphere(*this,radius).
    void getPos(size_t n,  openvdb::Vec3R&pos) const { pos = mParticleList[n].p; }

    void getPosRad(size_t n,  openvdb::Vec3R& pos, openvdb::Real& rad) const {
        pos = mParticleList[n].p;
        rad = mRadiusScale*mParticleList[n].r;
    }
    void getPosRadVel(size_t n,  openvdb::Vec3R& pos, openvdb::Real& rad, openvdb::Vec3R& vel) const {
        pos = mParticleList[n].p;
        rad = mRadiusScale*mParticleList[n].r;
        vel = mVelocityScale*mParticleList[n].v;
    }
    // The method below is only required for attribute transfer
    void getAtt(size_t n, openvdb::Index32& att) const { att = openvdb::Index32(n); }
};

Particles IO

Buiding the density,and write it out.

int main()
{

    const float voxelSize = 0.2f, halfWidth = 2.0f;
    openvdb::FloatGrid::Ptr density_grid = openvdb::createLevelSet<openvdb::FloatGrid>(voxelSize, halfWidth);

    MyParticleList pa(,); // this multiply is radius scale , velocity scale

    // This particle radius = 1 < 1.5 i.e. it's below the Nyquist frequency and hence ignored
    pa.add(openvdb::Vec3R( ,  ,  ), , openvdb::Vec3R( , , ));
    pa.add(openvdb::Vec3R( ,  ,  ), , openvdb::Vec3R( , , ));
    pa.add(openvdb::Vec3R( , ,  ), , openvdb::Vec3R( , , ));
    pa.add(openvdb::Vec3R( , ,  ), , openvdb::Vec3R( , , ));
    pa.add(openvdb::Vec3R( , ,  ), , openvdb::Vec3R( , , ));

    openvdb::tools::ParticlesToLevelSet<openvdb::FloatGrid> raster(*density_grid);
    raster.rasterizeTrails(pa, 0.75);//scale offset between two instances

    // always prune to produce a valid narrow-band level set.
    raster.finalize(true);

    density_grid->setGridClass(openvdb::GRID_LEVEL_SET);
    density_grid->setName("density");
    convertToVolume(density_grid);

    // Create a VDB file object.
    openvdb::io::File file("mygrids.vdb");
    // Add the grid pointer to a container.
    openvdb::GridPtrVec grids;
    grids.push_back(density_grid);

    // Write out the contents of the container.
    file.write(grids);
    file.close();

}

particles to volume

一个更好的方法Buiding the density.and write it out

// Note densityGrid allocation memory in this function and transform same as densityGrid
void buildingDensityGrid(openvdb::FloatGrid::Ptr &densityGrid,
                         openvdb::math::Transform::Ptr &transform,MyParticleList &pa,bool isRasterToSphere = true)
{
    float backGround = 0.1f;
    float voxelSize = 0.1;
    transform = openvdb::math::Transform::createLinearTransform(voxelSize);
    densityGrid = openvdb::FloatGrid::create(backGround);
    std::cout << "set density grid class type\n";
    densityGrid->setGridClass(openvdb::GRID_LEVEL_SET);
    densityGrid->setTransform(transform);
    openvdb::tools::ParticlesToLevelSet<openvdb::FloatGrid> raster(*densityGrid);
    if(isRasterToSphere)
    {
        raster.rasterizeSpheres(pa,pa.mRadiusScale);
    } else{
        raster.rasterizeTrails(pa,0.75);
    }
    raster.finalize(true);
    std::cout << "raster to end\n";
}

int main()
{
    MyParticleList pa(,);
    pa.add(openvdb::Vec3R( ,  ,  ), , openvdb::Vec3R( , , ));
    pa.add(openvdb::Vec3R( ,  ,  ), , openvdb::Vec3R( , , ));
    pa.add(openvdb::Vec3R( , ,  ), , openvdb::Vec3R( , , ));
    pa.add(openvdb::Vec3R( , ,  ), , openvdb::Vec3R( , , ));
    pa.add(openvdb::Vec3R( , ,  ), , openvdb::Vec3R( , , ));

    openvdb::FloatGrid::Ptr densityGrid;
    openvdb::math::Transform::Ptr transform;
    buildingDensityGrid(densityGrid,transform,pa);
    densityGrid->setName("density");
    convertToVolume(densityGrid);

    // Create a VDB file object.
    std::cout << "write vdb \n";
    openvdb::io::File file("mygrids.vdb");
    // Add the grid pointer to a container.
    openvdb::GridPtrVec grids;
    grids.push_back(densityGrid);
    // Write out the contents of the container.
    file.write(grids);
    file.close();

}

接下来VelocityBuilding,直接写了个包裹库，并且在houdini测试了下openvdb::Vec3sGrid的运动模糊。

GLY_OpenVdbWrapper.h

//
// Created by gearslogy on 4/13/17.
//

#ifndef ARNOLDVDBPOINTS_GLY_OPENVDBWAPPER_H
#define ARNOLDVDBPOINTS_GLY_OPENVDBWAPPER_H

#include <memory>
#include <openvdb/openvdb.h>
#include <openvdb/tools/ParticlesToLevelSet.h>
#include <openvdb/tools/LevelSetUtil.h>
#include <openvdb/tools/TopologyToLevelSet.h>

// DEFINE OUR PARTICLES STRUCT
namespace TopVertex
{

    struct MyParticle
    {
        openvdb::Vec3R p, v;
        openvdb::Real  r; // per particle has own radius
    };

    class MyParticleList
    {
        // change protected to the public,direct find the mRadiusScale,mVelocityScale
    public:
        openvdb::Real           mRadiusScale;
        openvdb::Real           mVelocityScale;
        std::vector<MyParticle> mParticleList;
        typedef openvdb::Vec3R  PosType;
        MyParticleList(openvdb::Real rScale=, openvdb::Real vScale=)
                : mRadiusScale(rScale), mVelocityScale(vScale) {}
        void add(const openvdb::Vec3R &p, const openvdb::Real &r,
                 const openvdb::Vec3R &v=openvdb::Vec3R(,,))
        {
            MyParticle pa;
            pa.p = p;
            pa.r = r;
            pa.v = v;
            mParticleList.push_back(pa);
        }
        /// @return coordinate bbox in the space of the specified transfrom
        openvdb::CoordBBox getBBox(const openvdb::GridBase& grid) {
            openvdb::CoordBBox bbox;
            openvdb::Coord &min= bbox.min(), &max = bbox.max();
            openvdb::Vec3R pos;
            openvdb::Real rad, invDx = /grid.voxelSize()[];
            for (size_t n=, e=this->size(); n<e; ++n) {
                this->getPosRad(n, pos, rad);
                const openvdb::Vec3d xyz = grid.worldToIndex(pos);
                const openvdb::Real   r  = rad * invDx;
                for (int i=; i<; ++i) {
                    min[i] = openvdb::math::Min(min[i], openvdb::math::Floor(xyz[i] - r));
                    max[i] = openvdb::math::Max(max[i], openvdb::math::Ceil( xyz[i] + r));
                }
            }
            return bbox;
        }
        //typedef int AttributeType;
        // The methods below are only required for the unit-tests
        openvdb::Vec3R pos(int n)   const {return mParticleList[n].p;}
        openvdb::Vec3R vel(int n)   const {return mVelocityScale*mParticleList[n].v;}
        openvdb::Real radius(int n) const {return mRadiusScale*mParticleList[n].r;}

        //////////////////////////////////////////////////////////////////////////////
        /// The methods below are the only ones required by tools::ParticleToLevelSet
        /// @note We return by value since the radius and velocities are modified
        /// by the scaling factors! Also these methods are all assumed to
        /// be thread-safe.

        /// Return the total number of particles in list.
        ///  Always required!
        size_t size() const { return mParticleList.size(); }

        /// Get the world space position of n'th particle.
        /// Required by ParticledToLevelSet::rasterizeSphere(*this,radius).
        void getPos(size_t n,  openvdb::Vec3R&pos) const { pos = mParticleList[n].p; }

        void getPosRad(size_t n,  openvdb::Vec3R& pos, openvdb::Real& rad) const {
            pos = mParticleList[n].p;
            rad = mRadiusScale*mParticleList[n].r;
        }
        void getPosRadVel(size_t n,  openvdb::Vec3R& pos, openvdb::Real& rad, openvdb::Vec3R& vel) const {
            pos = mParticleList[n].p;
            rad = mRadiusScale*mParticleList[n].r;
            vel = mVelocityScale*mParticleList[n].v;
        }
        // The method below is only required for attribute transfer
        void getAtt(size_t n, openvdb::Index32& att) const { att = openvdb::Index32(n); }
    };

}

//
namespace TopVertex
{
    class GLY_OpenVdbWrapper
    {
    public:
        // Rater point parm
        struct RasterParms
        {
            float backGround;
            float voxelSize;
            float halfWidth;
        };

        // define some variable type
        using Ptr = std::shared_ptr<GLY_OpenVdbWrapper>;
        using RasterT = openvdb::tools::ParticlesToLevelSet<openvdb::FloatGrid, openvdb::Index32>;
        enum POINT_RASTER_TYPE{RS_Sphere=0x0,RS_trailer=0x1};

        // define a static pointer to our class
        static GLY_OpenVdbWrapper* creator();

        //
        GLY_OpenVdbWrapper();
        ~GLY_OpenVdbWrapper();

        // SAMPLE POINTS API
        void samplePointsSetPoints(const std::vector<openvdb::Vec3R> &posList);
        void samplePointsSetPoints(double *array,int rawSize);
        void samplePointsSetRadius(double *array,int rawSize);
        void samplePointsSetRadius(const std::vector<openvdb::Real> &radiusList);
        void samplePointsSetVelocity(const std::vector<openvdb::Vec3R> &vel);
        void samplePointsSetVelocity(double *array,int rawsize);
        void samplePointsSetRadiusScale(double radius);
        void samplePointsSetVelocityScale(double v);
        void samplePointsAppendPoint(openvdb::Vec3R p,openvdb::Vec3R v,openvdb::Real radius);
        void samplePointsRasterDensityGrid(POINT_RASTER_TYPE type,openvdb::FloatGrid::Ptr &gridPtr,RasterParms &rasterParm);
        void samplePointsRasterVelocityGrid(openvdb::math::Transform::Ptr &density_transform,openvdb::Vec3SGrid::Ptr &velocityGrid);

    private:
        class SamplePoints;
        std::unique_ptr<SamplePoints> mPimplSamplePoints;
    };
}

#endif //ARNOLDVDBPOINTS_GLY_OPENVDBWAPPER_H

GLY_OpenVdbWrapper.cpp

//
// Created by gearslogy on 4/13/17.
//

#include "GLY_OpenVdbWrapper.h"
#include <assert.h>
#include <algorithm>
using namespace TopVertex;

//=======================================SamplePoints details=================================
//
class GLY_OpenVdbWrapper::SamplePoints
{
public:
    SamplePoints():mParticleListPtr(new MyParticleList(,))
    {
    }
    ~SamplePoints()
    {
        std::cout << "Release SamplePoints memory\n";
    }
    void setRadiusScale(double radius)
    {
        mParticleListPtr->mRadiusScale = radius;
    }
    void setVelocityScale(double v)
    {
        mParticleListPtr->mVelocityScale = v;
    }

    void setPoints(const std::vector<openvdb::Vec3R> &posList)
    {
        auto &pa = mParticleListPtr->mParticleList;
        pa.resize(posList.size());
        for(int i=;i<posList.size();i++)
        {
            pa[i].p = posList[i];
        }
    }
    void setPoints(double *array,int rawsize)
    {
        assert(rawsize%==);
        auto &pa = mParticleListPtr->mParticleList;
        pa.resize(rawsize/);
        for(int i=;i<rawsize/;i++)
        {
            double x = array[i];
            double y = array[i+];
            double z = array[i+];
            auto t = openvdb::Vec3R(x,y,z);
            pa[i].p = t;
        }
    }
    void setRadius(const std::vector<openvdb::Real> &radiusList)
    {
        assert(radiusList.size()==mParticleListPtr->mParticleList.size());
        auto &pa = mParticleListPtr->mParticleList;
        for(int i=;i<pa.size();i++)
        {
            pa[i].r = radiusList[i];
        }
    }
    void setRadius(double *array,int pointsNum)
    {
        assert(pointsNum==mParticleListPtr->mParticleList.size());
        auto &pa = mParticleListPtr->mParticleList;
        for(int i=;i<pa.size();i++)
        {
            pa[i].r = array[i];
        }
    }
    void setVelocity(const std::vector<openvdb::Vec3R> &vel)
    {
        assert(vel.size() == mParticleListPtr->mParticleList.size());
        auto &pa = mParticleListPtr->mParticleList;
        for(int i=;i<vel.size();i++)
        {
            pa[i].v = vel[i];
        }
    }
    void setVelocity(double *array,int rawsize)
    {
        assert(rawsize%==);
        auto &pa = mParticleListPtr->mParticleList;
        for(int i=;i<rawsize/;i++)
        {
            double x = array[i];
            double y = array[i+];
            double z = array[i+];
            auto t = openvdb::Vec3R(x,y,z);
            pa[i].v = t;
        }
    }
    void appendPoint(openvdb::Vec3R p,openvdb::Vec3R v,openvdb::Real radius)
    {
        mParticleListPtr->add(p,radius,v);
    }
    void clearPoints(){mParticleListPtr->mParticleList.clear();}
    void rasterDensity(POINT_RASTER_TYPE type,openvdb::FloatGrid::Ptr &gridPtr,RasterParms &rasterParm)
    {

        std::cout << "Start process samplePoints Raster Density\n";
        float backGround = rasterParm.backGround;
        float voxelSize = rasterParm.voxelSize;
        float halfWidth = rasterParm.halfWidth;
        openvdb::math::Transform::Ptr transform = openvdb::math::Transform::createLinearTransform(voxelSize);
        //gridPtr = openvdb::FloatGrid::create(backGround); //this is simple and can work
        gridPtr = openvdb::createLevelSet<openvdb::FloatGrid>(voxelSize, halfWidth);

        gridPtr->setGridClass(openvdb::GRID_LEVEL_SET);
        gridPtr->setTransform(transform);
        openvdb::tools::ParticlesToLevelSet<openvdb::FloatGrid,openvdb::Index> raster(*gridPtr);
        if(type==0x0) // RS_Sphere
        {
            raster.rasterizeSpheres(*mParticleListPtr);
        } else
        {
            raster.rasterizeTrails(*mParticleListPtr,0.75);
        }
        raster.finalize(true);
        openvdb::tools::sdfToFogVolume(*gridPtr);
        gridPtr->setName("density");
        mId=raster.attributeGrid();
    }

    void rasterVelocityGrid(openvdb::math::Transform::Ptr &density_transform,openvdb::Vec3SGrid::Ptr &gridPtr)
    {
        typedef typename openvdb::Int32Grid::TreeType::ValueConverter<openvdb::Vec3s >::Type TreeTypeWarpVec;
        typedef typename openvdb::Grid<TreeTypeWarpVec> GridType;
        typename TreeTypeWarpVec::Ptr tree(
                new TreeTypeWarpVec(mId->tree(), openvdb::Vec3s(,,) , openvdb::TopologyCopy()));
        //typename GridType::Ptr velocity_grid(GridType::create(tree)); //为grid开辟内存*/

        gridPtr = openvdb::Vec3SGrid::create(tree);
        gridPtr->setVectorType(openvdb::VecType());
        // MY Method
        openvdb::Coord ijk;
        openvdb::Vec3SGrid::Accessor vel_accessor = gridPtr->getAccessor();
        for(auto iter = mId->beginValueOn();iter.test();++iter)
        {
            auto d = *iter;
            //std::cout << " D:..." <<d <<std::endl;
            ijk = iter.getCoord();
            openvdb::math::Vec3s vel =  mParticleListPtr->vel(d);
            vel*=;
            vel_accessor.setValue(ijk,vel);

        }
        gridPtr->setName("vel");
        gridPtr->setTransform(density_transform);
    }

private:
    std::unique_ptr<MyParticleList > mParticleListPtr;
    RasterT::AttGridType::Ptr mId; //remeber the id of point in voxel
};

//

//============================================GLY_OpenVdbWrapper==================================================
// GLY_OpenVdbWrapper Details

GLY_OpenVdbWrapper::GLY_OpenVdbWrapper():mPimplSamplePoints(new GLY_OpenVdbWrapper::SamplePoints())
{
}
GLY_OpenVdbWrapper::~GLY_OpenVdbWrapper()
{
    std::cout << "Release Wrapper memory\n";
}
void GLY_OpenVdbWrapper::samplePointsSetPoints(const std::vector<openvdb::Vec3R> &posList)
{
    mPimplSamplePoints->setPoints(posList);
}
void GLY_OpenVdbWrapper::samplePointsSetPoints(double *array,int rawSize)
{
    mPimplSamplePoints->setPoints(array,rawSize);
}
void GLY_OpenVdbWrapper::samplePointsSetRadius(double *array, int rawSize) {
    mPimplSamplePoints->setRadius(array,rawSize);
}
void GLY_OpenVdbWrapper::samplePointsSetRadius(const std::vector<openvdb::Real> &radiusList) {
    mPimplSamplePoints->setRadius(radiusList);
}
void GLY_OpenVdbWrapper::samplePointsSetVelocity(const std::vector<openvdb::Vec3R> &vel) {
    mPimplSamplePoints->setVelocity(vel);
}
void GLY_OpenVdbWrapper::samplePointsSetVelocity(double *array, int rawsize) {
    mPimplSamplePoints->setVelocity(array,rawsize);
}
void GLY_OpenVdbWrapper::samplePointsSetRadiusScale(double radius) {
    mPimplSamplePoints->setRadiusScale(radius);
}
void GLY_OpenVdbWrapper::samplePointsSetVelocityScale(double v) {
    mPimplSamplePoints->setVelocityScale(v);
}
void GLY_OpenVdbWrapper::samplePointsAppendPoint(openvdb::Vec3R p, openvdb::Vec3R v, openvdb::Real radius)
{
    mPimplSamplePoints->appendPoint(p,v,radius);
}
GLY_OpenVdbWrapper* GLY_OpenVdbWrapper::creator() {
    return new GLY_OpenVdbWrapper;
}
void GLY_OpenVdbWrapper::samplePointsRasterDensityGrid(POINT_RASTER_TYPE type, openvdb::FloatGrid::Ptr &gridPtr,
                                                       RasterParms &rasterParm) {
    mPimplSamplePoints->rasterDensity(type,gridPtr,rasterParm);
}
void GLY_OpenVdbWrapper::samplePointsRasterVelocityGrid(openvdb::math::Transform::Ptr &density_transform,
                                                        openvdb::Vec3SGrid::Ptr &velocityGrid)
{
    mPimplSamplePoints->rasterVelocityGrid(density_transform,velocityGrid);
}

main.cpp:

//
// Created by gearslogy on 4/14/17.
//

#include "GLY_OpenVdbWrapper.h"
using namespace std;
using namespace TopVertex;
int main()
{
    GLY_OpenVdbWrapper::Ptr wrapper(GLY_OpenVdbWrapper::creator());
    wrapper->samplePointsAppendPoint(openvdb::Vec3R(,  ,  ), openvdb::Vec3R( , , ) ,);
    wrapper->samplePointsAppendPoint(openvdb::Vec3R(,  ,  ), openvdb::Vec3R( , , ) ,1.5);
    wrapper->samplePointsAppendPoint(openvdb::Vec3R(,  ,  ), openvdb::Vec3R( , , ) ,2.0);
    wrapper->samplePointsAppendPoint(openvdb::Vec3R(,  ,  ), openvdb::Vec3R( , , ) ,2.5);
    wrapper->samplePointsAppendPoint(openvdb::Vec3R(,  ,  ), openvdb::Vec3R( , , ) ,3.0);

    // create grid named "density"
    openvdb::FloatGrid::Ptr  densityGrid;
    GLY_OpenVdbWrapper::RasterParms parms;
    parms.backGround = 0.1;
    parms.voxelSize = 0.1;
    parms.halfWidth = 0.5;
    wrapper->samplePointsRasterDensityGrid(GLY_OpenVdbWrapper::RS_Sphere,densityGrid,parms);

    // Create velocity Grid "velocity"
    openvdb::Vec3SGrid::Ptr velocityGrid;
    auto densityTransform = densityGrid->transformPtr();
    wrapper->samplePointsRasterVelocityGrid(densityTransform,velocityGrid);

    // IO Operator
    openvdb::io::File file("mygrids.vdb");
    openvdb::GridPtrVec grids;
    grids.push_back(densityGrid);
    grids.push_back(velocityGrid);
    file.write(grids);
    file.close();

}

Test plugin for katana:

Update katana plugin:

升级了光线求交，直接快的飞起来

Arnold粒子体积渲染(Arnold particles volume rendering):

插件loading模式:AlembicAPI->OpenvdbAPI->ArnoldAPI

然后KatanaAPI再写个插件 读取这个ArnoldAPI写出来的proc,

update volume:

重要的事情不说两遍，static 关键字在一个so上被一个进程，2个instance调用，全局的static object内存地址是他妈一样的,也就是说是共享的地址。会导致你假如创建两个instance,你却希望有两份不一样的全局变量内容，结果，太感人了，确实是错的，是一样的。

如果独立进程，独立instance调用so上的全局变量，ok没问题。

Rendering the cd field: