# bfr_tutorial_1_1.cpp

https://github.com/PixarAnimationStudios/OpenSubdiv/blob/release/tutorials/bfr/tutorial_1_1/bfr_tutorial_1_1.cpp

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    .. code:: c++

        //------------------------------------------------------------------------------
        //  Tutorial description:
        //
        //      This tutorial illustrates the use of the SurfaceFactory, Surface
        //      and Parameterization classes for creating and evaluating the limit
        //      surface associated with each base face of a mesh.
        //
        //      Following the creation of a connected mesh for a shape (using a
        //      Far::TopologyRefiner, as illustrated in Far tutorials), an instance
        //      of a SurfaceFactory is declared to process its faces.  Each face of
        //      the mesh is evaluated and tessellated independently (with a simple
        //      triangle fan), with results written out in Obj format for inspection.
        //
        //      These classes make it simple to evaluate and tessellate all faces
        //      (quads, tris or others) while supporting the full set of subdivision
        //      options. While a triangle fan may be a trivial tessellation (and so
        //      not very useful) later examples using the Tessellation class provide
        //      more useful results with the same simplicity.
        //

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

        #include <vector>
        #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;

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

                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 {
                        fprintf(stderr,
                            "Warning: Unrecognized argument '%s' ignored\n", argv[i]);
                    }
                }
            }

        private:
            Args() { }
        };

        //
        //  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);

            //
            //  The Surface to be constructed and evaluated for each face -- as
            //  well as the intermediate and output data associated with it -- 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.
            //
            Surface faceSurface;

            std::vector<float> facePatchPoints;

            std::vector<float> outCoords;
            std::vector<float> outPos, outDu, outDv;
            std::vector<int>   outTriangles;

            //
            //  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) {
                //
                //  Initialize the Surface for this face -- if valid (skipping
                //  holes and boundary faces in some rare cases):
                //
                if (!meshSurfaceFactory.InitVertexSurface(faceIndex, &faceSurface)) {
                    continue;
                }

                //
                //  Get the Parameterization of the Surface and use it to identify
                //  coordinates for evaluation -- in this case, at the vertices
                //  and center of the face to create a fan of triangles:
                //
                Bfr::Parameterization faceParam = faceSurface.GetParameterization();

                int faceSize = faceParam.GetFaceSize();

                int numOutCoords = faceSize + 1;
                outCoords.resize(numOutCoords * 2);

                for (int i = 0; i < faceSize; ++i) {
                    faceParam.GetVertexCoord(i, &outCoords[i*2]);
                }
                faceParam.GetCenterCoord(&outCoords[faceSize*2]);

                //
                //  Prepare the patch points for the Surface, then use them to
                //  evaluate output points for all identified coordinates:
                //
                //  Resize patch point and output arrays:
                int pointSize = 3;

                facePatchPoints.resize(faceSurface.GetNumPatchPoints() * pointSize);

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

                //  Populate patch point and output arrays:
                faceSurface.PreparePatchPoints(meshVertexPositions.data(), pointSize,
                                               facePatchPoints.data(), pointSize);

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

                //
                //  Identify the faces of the tessellation, i.e. the triangle fan
                //  connecting points at the vertices to the center (last) point:
                //
                //  Note the need to offset vertex indices for the output faces --
                //  using the number of vertices generated prior to this face.
                //
                int objVertexIndexOffset = objWriter.GetNumVertices();

                outTriangles.resize(faceSize * 3);

                int * outTriangle = outTriangles.data();
                for (int i = 0; i < faceSize; ++i, outTriangle += 3) {
                    outTriangle[0] = objVertexIndexOffset + i;
                    outTriangle[1] = objVertexIndexOffset + (i + 1) % faceSize;
                    outTriangle[2] = objVertexIndexOffset + faceSize;
                }

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

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

                objWriter.WriteFaces(outTriangles, 3, 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;
        }

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

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