PolyVoxCore/include/PolyVoxCore/Raycast.inl

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Copyright (c) 2005-2009 David Williams

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namespace PolyVox
{
    template< template<typename> class VolumeType, typename VoxelType>
    Raycast<VolumeType, VoxelType>::Raycast(VolumeType<VoxelType>* volData, const Vector3DFloat& v3dStart, const Vector3DFloat& v3dDirection, RaycastResult& result)
        :m_result(result)
        ,m_volData(volData)
        ,m_sampVolume(volData)
        ,m_v3dStart(v3dStart)
        ,m_v3dDirection(v3dDirection)
    {
    }

    template< template<typename> class VolumeType, typename VoxelType>
    void Raycast<VolumeType, VoxelType>::setStart(const Vector3DFloat& v3dStart)
    {
        m_v3dStart = v3dStart;
    }

    template< template<typename> class VolumeType, typename VoxelType>
    void Raycast<VolumeType, VoxelType>::setDirection(const Vector3DFloat& v3dDirection)
    {
        m_v3dDirection = v3dDirection;
    }

    template< template<typename> class VolumeType, typename VoxelType>
    void Raycast<VolumeType, VoxelType>::execute(void)
    {
        //The doRaycast function is assuming that it is iterating over the areas defined between
        //voxels. We actually want to define the areas as being centered on voxels (as this is
        //what the CubicSurfaceExtractor generates). We add (0.5,0.5,0.5) here to adjust for this.
        Vector3DFloat v3dStart = m_v3dStart + Vector3DFloat(0.5f, 0.5f, 0.5f);

        //Compute the end point
        Vector3DFloat v3dEnd = v3dStart + m_v3dDirection;

        //Do the raycast
        doRaycast(v3dStart.getX(), v3dStart.getY(), v3dStart.getZ(), v3dEnd.getX(), v3dEnd.getY(), v3dEnd.getZ());
    }

    // This function is based on Christer Ericson's code and description of the 'Uniform Grid Intersection Test' in
    // 'Real Time Collision Detection'. The following information from the errata on the book website is also relevent:
    //
    //  pages 326-327. In the function VisitCellsOverlapped() the two lines calculating tx and ty are incorrect.
    //  The less-than sign in each line should be a greater-than sign. That is, the two lines should read:
    //
    //  float tx = ((x1 > x2) ? (x1 - minx) : (maxx - x1)) / Abs(x2 - x1);
    //  float ty = ((y1 > y2) ? (y1 - miny) : (maxy - y1)) / Abs(y2 - y1);
    //
    //  Thanks to Jetro Lauha of Fathammer in Helsinki, Finland for reporting this error.
    //
    //  Jetro also points out that the computations of i, j, iend, and jend are incorrectly rounded if the line
    //  coordinates are allowed to go negative. While that was not really the intent of the code — that is, I
    //  assumed grids to be numbered from (0, 0) to (m, n) — I'm at fault for not making my assumption clear.
    //  Where it is important to handle negative line coordinates the computation of these variables should be
    //  changed to something like this:
    //
    //  // Determine start grid cell coordinates (i, j)
    //  int i = (int)floorf(x1 / CELL_SIDE);
    //  int j = (int)floorf(y1 / CELL_SIDE);
    //
    //  // Determine end grid cell coordinates (iend, jend)
    //  int iend = (int)floorf(x2 / CELL_SIDE);
    //  int jend = (int)floorf(y2 / CELL_SIDE);
    //
    //  page 328. The if-statement that reads "if (ty <= tx && ty <= tz)" has a superfluous condition.
    //  It should simply read "if (ty <= tz)".
    //
    //  This error was reported by Joey Hammer (PixelActive). 
    template< template<typename> class VolumeType, typename VoxelType>
    void Raycast<VolumeType, VoxelType>::doRaycast(float x1, float y1, float z1, float x2, float y2, float z2)
    {
        int i = (int)floorf(x1);
        int j = (int)floorf(y1);
        int k = (int)floorf(z1);

        int iend = (int)floorf(x2);
        int jend = (int)floorf(y2);
        int kend = (int)floorf(z2);

        int di = ((x1 < x2) ? 1 : ((x1 > x2) ? -1 : 0));
        int dj = ((y1 < y2) ? 1 : ((y1 > y2) ? -1 : 0));
        int dk = ((z1 < z2) ? 1 : ((z1 > z2) ? -1 : 0));

        float minx = floorf(x1), maxx = minx + 1.0f;
        float tx = ((x1 > x2) ? (x1 - minx) : (maxx - x1)) / abs(x2 - x1);
        float miny = floorf(y1), maxy = miny + 1.0f;
        float ty = ((y1 > y2) ? (y1 - miny) : (maxy - y1)) / abs(y2 - y1);
        float minz = floorf(z1), maxz = minz + 1.0f;
        float tz = ((z1 > z2) ? (z1 - minz) : (maxz - z1)) / abs(z2 - z1);

        float deltatx = 1.0f / abs(x2 - x1);
        float deltaty = 1.0f / abs(y2 - y1);
        float deltatz = 1.0f / abs(z2 - z1);

        m_sampVolume.setPosition(i,j,k);
        m_result.previousVoxel = Vector3DInt32(i,j,k);

        for(;;)
        {
            if(m_sampVolume.getVoxel().getDensity() > VoxelType::getThreshold())
            {
                m_result.foundIntersection = true;
                m_result.intersectionVoxel = Vector3DInt32(i,j,k);
                return;
            }
            m_result.previousVoxel = Vector3DInt32(i,j,k);

            if(tx <= ty && tx <= tz)
            {
                if(i == iend) break;
                tx += deltatx;
                i += di;

                if(di == 1) m_sampVolume.movePositiveX();
                if(di == -1) m_sampVolume.moveNegativeX();
            } else if (ty <= tz)
            {
                if(j == jend) break;
                ty += deltaty;
                j += dj;

                if(dj == 1) m_sampVolume.movePositiveY();
                if(dj == -1) m_sampVolume.moveNegativeY();
            } else 
            {
                if(k == kend) break;
                tz += deltatz;
                k += dk;

                if(dk == 1) m_sampVolume.movePositiveZ();
                if(dk == -1) m_sampVolume.moveNegativeZ();
            }
        }

        //Didn't hit anything
        m_result.foundIntersection = false;
        m_result.intersectionVoxel = Vector3DInt32(0,0,0);
        m_result.previousVoxel = Vector3DInt32(0,0,0);
    }
}