# bfr_tutorial_3_2.cpp

https://github.com/PixarAnimationStudios/OpenSubdiv/blob/release/tutorials/bfr/tutorial_3_2/bfr_tutorial_3_2.cpp

    //------------------------------------------------------------------------------
    //  Tutorial description:
    //
    //      This tutorial is a variation of tutorials showing simple uniform
    //      tessellation. Rather than constructing and evaluating a Surface at
    //      a time, this tutorial shows how Surfaces can be created and saved
    //      for repeated use.
    //
    //      A simple SurfaceCache class is created that creates and stores the
    //      Surface for each face, along with the patch points associated with
    //      it. The main tessellation function remains essentially the same,
    //      but here it access the Surfaces from the SurfaceCache rather than
    //      computing them locally.
    //
    //      Note that while this example illustrated the retention of all
    //      Surfaces for a mesh, this behavior is not recommended. It does not
    //      scale well for large meshes and undermines the memory savings that
    //      transient use of Surfaces is designed to achieve. Rather than
    //      storing Surfaces for all faces, maintaining a priority queue for a
    //      fixed number may be a reasonable compromise.
    //

    #include <opensubdiv/far/topologyRefiner.h>
    #include <opensubdiv/bfr/refinerSurfaceFactory.h>
    #include <opensubdiv/bfr/surface.h>
    #include <opensubdiv/bfr/tessellation.h>

    #include <vector>
    #include <memory>
    #include <string>
    #include <cstring>
    #include <cstdio>

    //  Local headers with support for this tutorial in "namespace tutorial"
    #include "./meshLoader.h"
    #include "./objWriter.h"

    using namespace OpenSubdiv;

    //
    //  Simple command line arguments to provide input and run-time options:
    //
    class Args {
    public:
        std::string     inputObjFile;
        std::string     outputObjFile;
        Sdc::SchemeType schemeType;
        int             tessUniformRate;
        bool            tessQuadsFlag;

    public:
        Args(int argc, char * argv[]) :
            inputObjFile(),
            outputObjFile(),
            schemeType(Sdc::SCHEME_CATMARK),
            tessUniformRate(5),
            tessQuadsFlag(false) {

            for (int i = 1; i < argc; ++i) {
                if (strstr(argv[i], ".obj")) {
                    if (inputObjFile.empty()) {
                        inputObjFile = std::string(argv[i]);
                    } else {
                        fprintf(stderr,
                            "Warning: Extra Obj file '%s' ignored\n", argv[i]);
                    }
                } else if (!strcmp(argv[i], "-o")) {
                    if (++i < argc) outputObjFile = std::string(argv[i]);
                } else if (!strcmp(argv[i], "-bilinear")) {
                    schemeType = Sdc::SCHEME_BILINEAR;
                } else if (!strcmp(argv[i], "-catmark")) {
                    schemeType = Sdc::SCHEME_CATMARK;
                } else if (!strcmp(argv[i], "-loop")) {
                    schemeType = Sdc::SCHEME_LOOP;
                } else if (!strcmp(argv[i], "-res")) {
                    if (++i < argc) tessUniformRate = atoi(argv[i]);
                } else if (!strcmp(argv[i], "-quads")) {
                    tessQuadsFlag = true;
                } else {
                    fprintf(stderr,
                        "Warning: Unrecognized argument '%s' ignored\n", argv[i]);
                }
            }
        }

    private:
        Args() { }
    };

    //
    //  This simple class creates and dispenses Surfaces for all faces of
    //  a mesh. It consists primarily of an array of simple structs (entries)
    //  for each face and a single array of patch points for all Surfaces
    //  created.
    //
    //  There are many ways to create such a cache depending on requirements.
    //  This is a simple example, but the interface presents some options that
    //  are worth considering. A SurfaceCache is constructed here given the
    //  following:
    //
    //      - a reference to the SurfaceFactory:
    //          - the cache could just as easily take a reference to the mesh
    //            and construct the SurfaceFactory internally
    //
    //      - the position data for the mesh:
    //          - this is needed to compute patch points for the Surfaces
    //          - if caching UVs or any other primvar, other data needs to be
    //            provided -- along with the interpolation type for that data
    //            (vertex, face-varying, etc.)
    //
    //      - option to "cache patch points":
    //          - the cache could store the Surfaces only or also include
    //            their patch points
    //          - storing patch points takes more memory but will eliminate
    //            any preparation time for evaluation of the Surface
    //
    //      - option to "cache all surfaces":
    //          - the benefits to caching simple linear or regular surfaces
    //            are minimal -- and may even be detrimental
    //          - so only caching non-linear irregular surfaces is an option
    //            worth considering
    //
    //  The SurfaceCache implementation here provides the options noted above.
    //  But for simplicity, the actual usage of the SurfaceCache does not deal
    //  with the permutations of additional work that is necessary when the
    //  Surfaces or their patch points are not cached.
    //
    class SurfaceCache {
    public:
        typedef Bfr::Surface<float>          Surface;
        typedef Bfr::RefinerSurfaceFactory<> SurfaceFactory;

    public:
        SurfaceCache(SurfaceFactory     const & surfaceFactory,
                     std::vector<float> const & meshPoints,
                     bool                       cachePatchPoints = true,
                     bool                       cacheAllSurfaces = true);
        SurfaceCache() = delete;
        ~SurfaceCache() = default;

        //
        //  Public methods to retrieved cached Surfaces and their pre-computed
        //  patch points:
        //
        bool FaceHasLimitSurface(int face) { return _entries[face].hasLimit; }

        Surface const * GetSurface(int face) { return _entries[face].surface.get();}

        float const * GetPatchPoints(int face) { return getPatchPoints(face); }

    private:
        //  Simple struct to keep track of Surface and more for each face:
        struct FaceEntry {
            FaceEntry() : surface(), hasLimit(false), pointOffset(-1) { }

            std::unique_ptr<Surface const> surface;
            bool hasLimit;
            int  pointOffset;
        };

        //  Non-const version to be used internally to aide assignment:
        float * getPatchPoints(int face) {
            return (_entries[face].surface && !_points.empty()) ?
                   (_points.data() + _entries[face].pointOffset * 3) : 0;
        }

    private:
        std::vector<FaceEntry> _entries;
        std::vector<float>     _points;
    };

    SurfaceCache::SurfaceCache(SurfaceFactory     const & surfaceFactory,
                               std::vector<float> const & meshPoints,
                               bool                       cachePatchPoints,
                               bool                       cacheAllSurfaces) {

        int numFaces = surfaceFactory.GetNumFaces();

        _entries.resize(numFaces);

        int numPointsInCache = 0;
        for (int face = 0; face < numFaces; ++face) {
            Surface * s = surfaceFactory.CreateVertexSurface<float>(face);
            if (s) {
                FaceEntry & entry = _entries[face];
                entry.hasLimit = true;

                if (cacheAllSurfaces || (!s->IsRegular() && !s->IsLinear())) {
                    entry.surface.reset(s);
                    entry.pointOffset = numPointsInCache;

                    numPointsInCache += s->GetNumPatchPoints();
                } else {
                    delete s;
                }
            }
        }

        if (cachePatchPoints) {
            _points.resize(numPointsInCache * 3);
            for (int face = 0; face < numFaces; ++face) {
                float * patchPoints = getPatchPoints(face);
                if (patchPoints) {
                    GetSurface(face)->PreparePatchPoints(meshPoints.data(), 3,
                                                         patchPoints, 3);
                }
            }
        }
    }

    //
    //  The main tessellation function:  given a mesh and vertex positions,
    //  tessellate each face -- writing results in Obj format.
    //
    void
    tessellateToObj(Far::TopologyRefiner const & meshTopology,
                    std::vector<float>   const & meshVertexPositions,
                    Args                 const & options) {

        //
        //  Use simpler local type names for the Surface and its factory:
        //
        typedef Bfr::RefinerSurfaceFactory<> SurfaceFactory;
        typedef Bfr::Surface<float>          Surface;

        //
        //  Initialize the SurfaceFactory for the given base mesh (very low
        //  cost in terms of both time and space) and tessellate each face
        //  independently (i.e. no shared vertices):
        //
        //  Note that the SurfaceFactory is not thread-safe by default due to
        //  use of an internal cache.  Creating a separate instance of the
        //  SurfaceFactory for each thread is one way to safely parallelize
        //  this loop.  Another (preferred) is to assign a thread-safe cache
        //  to the single instance.
        //
        //  First declare any evaluation options when initializing (though
        //  none are used in this simple case):
        //
        SurfaceFactory::Options surfaceOptions;

        SurfaceFactory meshSurfaceFactory(meshTopology, surfaceOptions);

        //
        //  Initialize a SurfaceCache to construct Surfaces for all faces.
        //  From this point forward the SurfaceFactory is no longer used to
        //  access Surfaces. Note also that usage below is specific to the
        //  options used to initialize the SurfaceCache:
        //
        bool cachePatchPoints = true;
        bool cacheAllSurfaces = true;
        SurfaceCache surfaceCache(meshSurfaceFactory, meshVertexPositions,
                                  cachePatchPoints, cacheAllSurfaces);

        //
        //  As with previous tutorials, output data associated with the face
        //  can be declared in the scope local to each face. But since dynamic
        //  memory is involved with these variables, it is preferred to declare
        //  them outside that loop to preserve and reuse that dynamic memory.
        //
        std::vector<float> outCoords;
        std::vector<float> outPos, outDu, outDv;
        std::vector<int>   outFacets;

        //
        //  Assign Tessellation Options applied for all faces.  Tessellations
        //  allow the creating of either 3- or 4-sided faces -- both of which
        //  are supported here via a command line option:
        //
        int const tessFacetSize = 3 + options.tessQuadsFlag;

        Bfr::Tessellation::Options tessOptions;
        tessOptions.SetFacetSize(tessFacetSize);
        tessOptions.PreserveQuads(options.tessQuadsFlag);

        //
        //  Process each face, writing the output of each in Obj format:
        //
        tutorial::ObjWriter objWriter(options.outputObjFile);

        int numFaces = meshSurfaceFactory.GetNumFaces();
        for (int faceIndex = 0; faceIndex < numFaces; ++faceIndex) {
            //
            //  Retrieve the Surface for this face when present:
            //
            if (!surfaceCache.FaceHasLimitSurface(faceIndex)) continue;

            Surface const & faceSurface = * surfaceCache.GetSurface(faceIndex);

            //
            //  Declare a simple uniform Tessellation for the Parameterization
            //  of this face and identify coordinates of the points to evaluate:
            //
            Bfr::Tessellation tessPattern(faceSurface.GetParameterization(),
                                          options.tessUniformRate, tessOptions);

            int numOutCoords = tessPattern.GetNumCoords();

            outCoords.resize(numOutCoords * 2);

            tessPattern.GetCoords(outCoords.data());

            //
            //  Retrieve the patch points for the Surface, then use them to
            //  evaluate output points for all identified coordinates:
            //
            float const * facePatchPoints = surfaceCache.GetPatchPoints(faceIndex);

            int pointSize = 3;

            outPos.resize(numOutCoords * pointSize);
            outDu.resize(numOutCoords * pointSize);
            outDv.resize(numOutCoords * pointSize);

            for (int i = 0, j = 0; i < numOutCoords; ++i, j += pointSize) {
                faceSurface.Evaluate(&outCoords[i*2],
                                     facePatchPoints, pointSize,
                                     &outPos[j], &outDu[j], &outDv[j]);
            }

            //
            //  Identify the faces of the Tessellation:
            //
            //  Note the need to offset vertex indices for the output faces --
            //  using the number of vertices generated prior to this face. One
            //  of several Tessellation methods to transform the facet indices
            //  simply translates all indices by the desired offset.
            //
            int objVertexIndexOffset = objWriter.GetNumVertices();

            int numFacets = tessPattern.GetNumFacets();
            outFacets.resize(numFacets * tessFacetSize);
            tessPattern.GetFacets(outFacets.data());

            tessPattern.TransformFacetCoordIndices(outFacets.data(),
                                                   objVertexIndexOffset);

            //
            //  Write the evaluated points and faces connecting them as Obj:
            //
            objWriter.WriteGroupName("baseFace_", faceIndex);

            objWriter.WriteVertexPositions(outPos);
            objWriter.WriteVertexNormals(outDu, outDv);

            objWriter.WriteFaces(outFacets, tessFacetSize, true, false);
        }
    }

    //
    //  Load command line arguments, specified or default geometry and process:
    //
    int
    main(int argc, char * argv[]) {

        Args args(argc, argv);

        Far::TopologyRefiner * meshTopology = 0;
        std::vector<float>     meshVtxPositions;
        std::vector<float>     meshFVarUVs;

        meshTopology = tutorial::createTopologyRefiner(
                args.inputObjFile, args.schemeType, meshVtxPositions, meshFVarUVs);
        if (meshTopology == 0) {
            return EXIT_FAILURE;
        }

        tessellateToObj(*meshTopology, meshVtxPositions, args);

        delete meshTopology;
        return EXIT_SUCCESS;
    }

    //------------------------------------------------------------------------------