# far_tutorial_1_2.cpp

https://github.com/PixarAnimationStudios/OpenSubdiv/blob/release/tutorials/far/tutorial_1_2/far_tutorial_1_2.cpp

    //------------------------------------------------------------------------------
    // Tutorial description:
    //
    // This tutorial illustrates two different styles of defining classes for
    // interpolating primvar data with the template methods in Far.  The most
    // common usage involves data of a fixed size, so the focus here is on an
    // alternative supporting variable length data.
    //

    #include <opensubdiv/far/topologyDescriptor.h>
    #include <opensubdiv/far/primvarRefiner.h>

    #include <cstdio>

    using namespace OpenSubdiv;

    //
    //  Vertex data containers for interpolation:
    //      - Coord3 is fixed to support 3 floats
    //      - Coord2 is fixed to support 2 floats
    //      - CoordBuffer can support a specified number of floats
    //
    struct Coord3 {
        Coord3() { }
        Coord3(float x, float y, float z) { _xyz[0] = x, _xyz[1] = y, _xyz[2] = z; }

        void Clear() { _xyz[0] = _xyz[1] = _xyz[2] = 0.0f; }

        void AddWithWeight(Coord3 const & src, float weight) {
            _xyz[0] += weight * src._xyz[0];
            _xyz[1] += weight * src._xyz[1];
            _xyz[2] += weight * src._xyz[2];
        }

        float const * Coords() const { return &_xyz[0]; }

    private:
        float _xyz[3];
    };

    struct Coord2 {
        Coord2() { }
        Coord2(float u, float v) { _uv[0] = u, _uv[1] = v; }

        void Clear() { _uv[0] = _uv[1] = 0.0f; }

        void AddWithWeight(Coord2 const & src, float weight) {
            _uv[0] += weight * src._uv[0];
            _uv[1] += weight * src._uv[1];
        }

        float const * Coords() const { return &_uv[0]; }

    private:
        float _uv[2];
    };

    struct CoordBuffer {
        //
        //  The head of an external buffer and stride is specified on construction:
        //
        CoordBuffer(float * data, int size) : _data(data), _size(size) { }
        CoordBuffer() : _data(0), _size(0) { }

        void Clear() {
            for (int i = 0; i < _size; ++i) {
                _data[i] = 0.0f;
            }
        }

        void AddWithWeight(CoordBuffer const & src, float weight) {
            assert(src._size == _size);
            for (int i = 0; i < _size; ++i) {
                _data[i] += weight * src._data[i];
            }
        }

        float const * Coords() const { return _data; }

        //
        //  Defining [] to return a location elsewhere in the buffer is the key
        //  requirement to supporting interpolatible data of varying size
        //
        CoordBuffer operator[](int index) const {
            return CoordBuffer(_data + index * _size, _size);
        }

    private:
        float * _data;
        int     _size;
    };

    //
    //  Global cube geometry from catmark_cube.h
    //
    //  Topology:
    static int g_nverts = 8;
    static int g_nfaces = 6;

    static int g_vertsperface[6] = { 4, 4, 4, 4, 4, 4 };

    static int g_vertIndices[24] = { 0, 1, 3, 2,
                                     2, 3, 5, 4,
                                     4, 5, 7, 6,
                                     6, 7, 1, 0,
                                     1, 7, 5, 3,
                                     6, 0, 2, 4  };
    //  Primvar data:
    static float g_verts[8][3] = {{  0.0f,  0.0f,  1.0f },
                                  {  1.0f,  0.0f,  1.0f },
                                  {  0.0f,  1.0f,  1.0f },
                                  {  1.0f,  1.0f,  1.0f },
                                  {  0.0f,  1.0f,  0.0f },
                                  {  1.0f,  1.0f,  0.0f },
                                  {  0.0f,  0.0f,  0.0f },
                                  {  1.0f,  0.0f,  0.0f }};

    //
    //  Creates Far::TopologyRefiner from raw geometry above (see tutorial_1_1 for
    //  more details)
    //
    static Far::TopologyRefiner *
    createFarTopologyRefiner() {

        typedef Far::TopologyDescriptor Descriptor;

        Sdc::SchemeType type = OpenSubdiv::Sdc::SCHEME_CATMARK;

        Sdc::Options options;
        options.SetVtxBoundaryInterpolation(Sdc::Options::VTX_BOUNDARY_EDGE_ONLY);

        Descriptor desc;
        desc.numVertices  = g_nverts;
        desc.numFaces     = g_nfaces;
        desc.numVertsPerFace = g_vertsperface;
        desc.vertIndicesPerFace  = g_vertIndices;

        // Instantiate a Far::TopologyRefiner from the descriptor
        Far::TopologyRefiner * refiner =
                Far::TopologyRefinerFactory<Descriptor>::Create(desc,
                        Far::TopologyRefinerFactory<Descriptor>::Options(type, options));

        return refiner;
    }

    //
    //  Overview of main():
    //      - create a Far::TopologyRefiner and uniformly refine it
    //      - allocate separate and combined data buffers for vertex positions and UVs
    //      - populate all refined data buffers and compare results
    //      - write the result in Obj format
    //
    //  Disable warnings for exact floating point comparisons:
    #ifdef __INTEL_COMPILER
    #pragma warning disable 1572
    #endif

    int main(int, char **) {

        //  Instantiate a Far::TopologyRefiner from the global geometry:
        Far::TopologyRefiner * refiner = createFarTopologyRefiner();

        //  Uniformly refine the topology up to 'maxlevel'
        int maxlevel = 2;

        refiner->RefineUniform(Far::TopologyRefiner::UniformOptions(maxlevel));

        //  Allocate and populate data buffers for vertex primvar data -- positions and
        //  UVs. We assign UV coordiantes by simply projecting/assigning XY values.
        //  The position and UV buffers use their associated data types, while the
        //  combined buffer uses 5 floats per vertex.
        //
        int numBaseVertices  = g_nverts;
        int numTotalVertices = refiner->GetNumVerticesTotal();

        std::vector<Coord3> posData(numTotalVertices);
        std::vector<Coord2> uvData(numTotalVertices);

        int                 combinedStride = 3 + 2;
        std::vector<float>  combinedData(numTotalVertices * combinedStride);

        for (int i = 0; i < numBaseVertices; ++i) {
            posData[i] = Coord3(g_verts[i][0], g_verts[i][1], g_verts[i][2]);
            uvData[i]  = Coord2(g_verts[i][0], g_verts[i][1]);

            float * coordCombined = &combinedData[i * combinedStride];
            coordCombined[0] = g_verts[i][0];
            coordCombined[1] = g_verts[i][1];
            coordCombined[2] = g_verts[i][2];
            coordCombined[3] = g_verts[i][0];
            coordCombined[4] = g_verts[i][1];
        }

        //  Interpolate vertex primvar data
        Far::PrimvarRefiner primvarRefiner(*refiner);

        Coord3 * posSrc = &posData[0];
        Coord2 * uvSrc  = & uvData[0];

        CoordBuffer combinedSrc(&combinedData[0], combinedStride);

        for (int level = 1; level <= maxlevel; ++level) {
            int numLevelVerts = refiner->GetLevel(level-1).GetNumVertices();

            Coord3 * posDst = posSrc + numLevelVerts;
            Coord2 * uvDst  = uvSrc + numLevelVerts;

            CoordBuffer combinedDst = combinedSrc[numLevelVerts];

            primvarRefiner.Interpolate(level, posSrc, posDst);
            primvarRefiner.Interpolate(level, uvSrc, uvDst);
            primvarRefiner.Interpolate(level, combinedSrc, combinedDst);

            posSrc = posDst;
            uvSrc = uvDst;
            combinedSrc = combinedDst;
        }

        //  Verify that the combined coords match the separate results:
        for (int i = numBaseVertices; i < numTotalVertices; ++i) {
            float const * posCoords = posData[i].Coords();
            float const * uvCoords  = uvData[i].Coords();

            float const * combCoords = &combinedData[combinedStride * i];

            assert(combCoords[0] == posCoords[0]);
            assert(combCoords[1] == posCoords[1]);
            assert(combCoords[2] == posCoords[2]);
            assert(combCoords[3] == uvCoords[0]);
            assert(combCoords[4] == uvCoords[1]);
        }

        //
        //  Output OBJ of the highest level refined:
        //
        Far::TopologyLevel const & refLastLevel = refiner->GetLevel(maxlevel);

        int firstOfLastVerts = numTotalVertices - refLastLevel.GetNumVertices();

        //  Print vertex positions
        printf("#  Vertices:\n");
        for (int vert = firstOfLastVerts; vert < numTotalVertices; ++vert) {
            float const * pos = &combinedData[vert * combinedStride];
            printf("v %f %f %f\n", pos[0], pos[1], pos[2]);
        }

        printf("#  UV coordinates:\n");
        for (int vert = firstOfLastVerts; vert < numTotalVertices; ++vert) {
            float const * uv = &combinedData[vert * combinedStride] + 3;
            printf("vt %f %f\n", uv[0], uv[1]);
        }

        //  Print faces
        int numFaces = refLastLevel.GetNumFaces();

        printf("#  Faces:\n");
        for (int face = 0; face < numFaces; ++face) {
            Far::ConstIndexArray fverts = refLastLevel.GetFaceVertices(face);

            printf("f ");
            for (int fvert = 0; fvert < fverts.size(); ++fvert) {
                int objIndex = 1 + fverts[fvert]; // OBJ uses 1-based arrays...
                printf("%d/%d ", objIndex, objIndex);
            }
            printf("\n");
        }

        delete refiner;
        return EXIT_SUCCESS;
    }