Raycast.inl

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Copyright (c) 2005-2009 David Williams

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namespace PolyVox
{
    // 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<typename VolumeType, typename Callback>
    RaycastResult raycastWithEndpoints(VolumeType* volData, const Vector3DFloat& v3dStart, const Vector3DFloat& v3dEnd, Callback& callback)
    {
        typename VolumeType::Sampler sampler(volData);

        //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 here to adjust for this.
        float x1 = v3dStart.getX() + 0.5f;
        float y1 = v3dStart.getY() + 0.5f;
        float z1 = v3dStart.getZ() + 0.5f;
        float x2 = v3dEnd.getX() + 0.5f;
        float y2 = v3dEnd.getY() + 0.5f;
        float z2 = v3dEnd.getZ() + 0.5f;
        
        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 deltatx = 1.0f / std::abs(x2 - x1);
        float deltaty = 1.0f / std::abs(y2 - y1);
        float deltatz = 1.0f / std::abs(z2 - z1);

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

        sampler.setPosition(i,j,k);

        for(;;)
        {
            if(!callback(sampler))
            {
                return RaycastResults::Interupted;
            }

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

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

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

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

        return RaycastResults::Completed;
    }

    template<typename VolumeType, typename Callback>
    RaycastResult raycastWithDirection(VolumeType* volData, const Vector3DFloat& v3dStart, const Vector3DFloat& v3dDirectionAndLength, Callback& callback)
    {
        Vector3DFloat v3dEnd = v3dStart + v3dDirectionAndLength;
        return raycastWithEndpoints<VolumeType, Callback>(volData, v3dStart, v3dEnd, callback);
    }
}