# far_tutorial_5_3.cpp

https://github.com/PixarAnimationStudios/OpenSubdiv/blob/release/tutorials/far/tutorial_5_3/far_tutorial_5_3.cpp

    //------------------------------------------------------------------------------
    //  Tutorial description:
    //
    //      This tutorial shows how to use a Far::LimitStenciTable to repeatedly
    //      and efficiently evaluate a set of points (and optionally derivatives)
    //      on the limit surface.
    //
    //      A LimitStencilTable derives from StencilTable but is specialized to
    //      factor the evaluation of limit positions and derivatives into stencils.
    //      This allows a set of limit properties to be efficiently recomputed in
    //      response to changes to the vertices of the base mesh.  Constructing
    //      the different kinds of StencilTables can have a high cost, so whether
    //      that cost is worth it will depend on your usage (e.g. if points are
    //      only computed once, using stencil tables is typically not worth the
    //      added cost).
    //
    //      Any points on the limit surface can be identified for evaluation. In
    //      this example we create a crude tessellation similar to tutorial_5_2.
    //      The midpoint of each face and points near the corners of the face are
    //      evaluated and a triangle fan connects them.
    //

    #include "../../../regression/common/arg_utils.h"
    #include "../../../regression/common/far_utils.h"

    #include <opensubdiv/far/topologyDescriptor.h>
    #include <opensubdiv/far/patchTableFactory.h>
    #include <opensubdiv/far/stencilTableFactory.h>
    #include <opensubdiv/far/ptexIndices.h>

    #include <cassert>
    #include <cstdio>
    #include <cstring>
    #include <fstream>
    #include <sstream>

    using namespace OpenSubdiv;

    using Far::Index;

    //
    //  Global utilities in this namespace are not relevant to the tutorial.
    //  They simply serve to construct some default geometry to be processed
    //  in the form of a TopologyRefiner and vector of vertex positions.
    //
    namespace {
        //
        //  Simple structs for (x,y,z) position and a 3-tuple for the set
        //  of vertices of a triangle:
        //
        struct Pos {
            Pos() { }
            Pos(float x, float y, float z) { p[0] = x, p[1] = y, p[2] = z; }

            Pos operator+(Pos const & op) const {
                return Pos(p[0] + op.p[0], p[1] + op.p[1], p[2] + op.p[2]);
            }

            //  Clear() and AddWithWeight() required for interpolation:
            void Clear( void * =0 ) { p[0] = p[1] = p[2] = 0.0f; }

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

            float p[3];
        };
        typedef std::vector<Pos> PosVector;

        struct Tri {
            Tri() { }
            Tri(int a, int b, int c) { v[0] = a, v[1] = b, v[2] = c; }

            int v[3];
        };
        typedef std::vector<Tri> TriVector;

        //
        //  Functions to populate the topology and geometry arrays a simple
        //  shape whose positions may be transformed:
        //
        void
        createCube(std::vector<int> &   vertsPerFace,
                   std::vector<Index> & faceVertsPerFace,
                   std::vector<Pos> &   positionsPerVert) {

            //  Local topology and position of a cube centered at origin:
            static float const cubePositions[8][3] = { { -0.5f, -0.5f, -0.5f },
                                                       { -0.5f,  0.5f, -0.5f },
                                                       { -0.5f,  0.5f,  0.5f },
                                                       { -0.5f, -0.5f,  0.5f },
                                                       {  0.5f, -0.5f, -0.5f },
                                                       {  0.5f,  0.5f, -0.5f },
                                                       {  0.5f,  0.5f,  0.5f },
                                                       {  0.5f, -0.5f,  0.5f } };

            static int const cubeFaceVerts[6][4] = { { 0, 3, 2, 1 },
                                                     { 4, 5, 6, 7 },
                                                     { 0, 4, 7, 3 },
                                                     { 1, 2, 6, 5 },
                                                     { 0, 1, 5, 4 },
                                                     { 3, 7, 6, 2 } };

            //  Initialize verts-per-face and face-vertices for each face:
            vertsPerFace.resize(6);
            faceVertsPerFace.resize(24);
            for (int i = 0; i < 6; ++i) {
                vertsPerFace[i] = 4;
                for (int j = 0; j < 4; ++j) {
                    faceVertsPerFace[i*4+j] = cubeFaceVerts[i][j];
                }
            }

            //  Initialize vertex positions:
            positionsPerVert.resize(8);
            for (int i = 0; i < 8; ++i) {
                float const * p = cubePositions[i];
                positionsPerVert[i] = Pos(p[0], p[1], p[2]);
            }
        }

        //
        //  Create a TopologyRefiner from default geometry created above:
        //
        Far::TopologyRefiner *
        createTopologyRefinerDefault(PosVector & posVector) {

            std::vector<int>   topVertsPerFace;
            std::vector<Index> topFaceVerts;

            createCube(topVertsPerFace, topFaceVerts, posVector);

            typedef Far::TopologyDescriptor Descriptor;

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

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

            Descriptor desc;
            desc.numVertices = (int) posVector.size();
            desc.numFaces = (int) topVertsPerFace.size();
            desc.numVertsPerFace = &topVertsPerFace[0];
            desc.vertIndicesPerFace = &topFaceVerts[0];

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

        //
        //  Create a TopologyRefiner from a specified Obj file:
        //  geometry created internally:
        //
        Far::TopologyRefiner *
        createTopologyRefinerFromObj(std::string const & objFileName,
                                     Sdc::SchemeType schemeType,
                                     PosVector & posVector) {

            const char *  filename = objFileName.c_str();
            const Shape * shape = 0;

            std::ifstream ifs(filename);
            if (ifs) {
                std::stringstream ss;
                ss << ifs.rdbuf();
                ifs.close();
                std::string shapeString = ss.str();

                shape = Shape::parseObj(shapeString.c_str(),
                    ConvertSdcTypeToShapeScheme(schemeType), false);
                if (shape == 0) {
                    fprintf(stderr,
                        "Error:  Cannot create Shape from .obj file '%s'\n",
                        filename);
                    return 0;
                }
            } else {
                fprintf(stderr, "Error:  Cannot open .obj file '%s'\n", filename);
                return 0;
            }

            Sdc::SchemeType sdcType    = GetSdcType(*shape);
            Sdc::Options    sdcOptions = GetSdcOptions(*shape);

            Far::TopologyRefiner * refiner =
                Far::TopologyRefinerFactory<Shape>::Create(*shape,
                    Far::TopologyRefinerFactory<Shape>::Options(
                        sdcType, sdcOptions));
            if (refiner == 0) {
                fprintf(stderr, "Error:  Unable to construct TopologyRefiner "
                    "from .obj file '%s'\n", filename);
                return 0;
            }

            int numVertices = refiner->GetNumVerticesTotal();
            posVector.resize(numVertices);
            std::memcpy(&posVector[0].p[0], &shape->verts[0],
                        numVertices * 3 * sizeof(float));

            delete shape;
            return refiner;
        }

        //
        //  Simple function to export an Obj file for the limit points -- which
        //  provides a simple tessllation similar to tutorial_5_2.
        //
        int writeToObj(
            Far::TopologyLevel const & baseLevel,
            std::vector<Pos> const & vertexPositions,
            int nextObjVertexIndex) {

            for (size_t i = 0; i < vertexPositions.size(); ++i) {
                float const * p = vertexPositions[i].p;
                printf("v %f %f %f\n", p[0], p[1], p[2]);
            }

            //
            //  Connect the sequences of limit points (center followed by corners)
            //  into triangle fans for each base face:
            //
            for (int i = 0; i < baseLevel.GetNumFaces(); ++i) {
                int faceSize = baseLevel.GetFaceVertices(i).size();

                int vCenter = nextObjVertexIndex + 1;
                int vCorner = vCenter + 1;
                for (int k = 0; k < faceSize; ++k) {
                    printf("f %d %d %d\n",
                        vCenter, vCorner + k, vCorner + ((k + 1) % faceSize));
                }
                nextObjVertexIndex += faceSize + 1;
            }
            return nextObjVertexIndex;
        }
    } // end namespace

    //
    //  Command line arguments parsed to provide run-time options:
    //
    class Args {
    public:
        std::string     inputObjFile;
        Sdc::SchemeType schemeType;
        int             maxPatchDepth;
        int             numPoses;
        Pos             poseOffset;
        bool            deriv1Flag;
        bool            noPatchesFlag;
        bool            noOutputFlag;

    public:
        Args(int argc, char ** argv) :
            inputObjFile(),
            schemeType(Sdc::SCHEME_CATMARK),
            maxPatchDepth(3),
            numPoses(0),
            poseOffset(1.0f, 0.0f, 0.0f),
            deriv1Flag(false),
            noPatchesFlag(false),
            noOutputFlag(false) {

            //  Parse and assign standard arguments and Obj files:
            ArgOptions args;
            args.Parse(argc, argv);

            maxPatchDepth = args.GetLevel();
            schemeType = ConvertShapeSchemeToSdcType(args.GetDefaultScheme());

            const std::vector<const char *> objFiles = args.GetObjFiles();
            if (!objFiles.empty()) {
                for (size_t i = 1; i < objFiles.size(); ++i) {
                    fprintf(stderr,
                        "Warning: .obj file '%s' ignored\n", objFiles[i]);
                }
                inputObjFile = std::string(objFiles[0]);
            }

            //  Parse remaining arguments specific to this example:
            const std::vector<const char *> &rargs = args.GetRemainingArgs();
            for (size_t i = 0; i < rargs.size(); ++i) {
                if (!strcmp(rargs[i], "-d1")) {
                    deriv1Flag = true;
                } else if (!strcmp(rargs[i], "-nopatches")) {
                    noPatchesFlag = true;
                } else if (!strcmp(rargs[i], "-poses")) {
                    if (++i < rargs.size()) numPoses = atoi(rargs[i]);
                } else if (!strcmp(rargs[i], "-offset")) {
                    if (++i < rargs.size()) poseOffset.p[0] = (float)atof(rargs[i]);
                    if (++i < rargs.size()) poseOffset.p[1] = (float)atof(rargs[i]);
                    if (++i < rargs.size()) poseOffset.p[2] = (float)atof(rargs[i]);
                } else if (!strcmp(rargs[i], "-nooutput")) {
                    noOutputFlag = true;
                } else {
                    fprintf(stderr, "Warning: Argument '%s' ignored\n", rargs[i]);
                }
            }
        }

    private:
        Args() { }
    };

    //
    //  Assemble the set of locations for the limit points.  The resulting
    //  vector of LocationArrays can contain arbitrary locations on the limit
    //  surface -- with multiple locations for the same patch grouped into a
    //  single array.
    //
    //  In this case, for each base face, coordinates for the center and its
    //  corners are specified -- from which we will construct a triangle fan
    //  providing a crude tessellation (similar to tutorial_5_2).
    //
    typedef Far::LimitStencilTableFactory::LocationArray   LocationArray;

    int assembleLimitPointLocations(Far::TopologyRefiner const & refiner,
                                    std::vector<LocationArray> & locations) {
        //
        //  Coordinates for the center of the face and its corners (slightly
        //  inset).  Unlike most of the public interface for patches, the
        //  LocationArray refers to parameteric coordinates as (s,t), so that
        //  convention will be followed here.
        //
        //  Note that the (s,t) coordinates in a LocationArray are referred to
        //  by reference.  The memory holding these (s,t) values must persist
        //  while the LimitStencilTable is constructed -- the arrays here are
        //  declared as static for that purpose.
        //
        static float const quadSCoords[5] = { 0.5f, 0.05f, 0.95f, 0.95f, 0.05f };
        static float const quadTCoords[5] = { 0.5f, 0.05f, 0.05f, 0.95f, 0.95f };

        static float const triSCoords[4] = { 0.33f, 0.05f, 0.95f, 0.05f };
        static float const triTCoords[4] = { 0.33f, 0.05f, 0.00f, 0.95f };

        static float const irregSCoords[2] = { 1.0f, 0.05f };
        static float const irregTCoords[2] = { 1.0f, 0.05f };

        //
        //  Since these are references to patches to be evaluated, we require
        //  use of the Ptex indices to identify the top-most parameterized
        //  patch, which is essential to dealing with non-quad faces (in the
        //  case of Catmark).
        //
        Far::TopologyLevel const & baseLevel = refiner.GetLevel(0);

        Far::PtexIndices basePtexIndices(refiner);

        int regFaceSize = Sdc::SchemeTypeTraits::GetRegularFaceSize(
            refiner.GetSchemeType());

        //
        //  For each base face, simply refer to the (s,t) arrays for regular quad
        //  and triangular patches with a single LocationArray.  Otherwise, for
        //  irregular faces, the corners of the face come from different patches
        //  and so must be referenced in separate LocationArrays.
        //
        locations.clear();

        int numLimitPoints = 0;
        for (int i = 0; i < baseLevel.GetNumFaces(); ++i) {
            int baseFaceSize = baseLevel.GetFaceVertices(i).size();
            int basePtexId   = basePtexIndices.GetFaceId(i);

            bool faceIsRegular = (baseFaceSize == regFaceSize);
            if (faceIsRegular) {
                //  All coordinates are on the same top-level patch:
                LocationArray loc;
                loc.ptexIdx = basePtexId;
                loc.numLocations = baseFaceSize + 1;
                if (baseFaceSize == 4) {
                    loc.s = quadSCoords;
                    loc.t = quadTCoords;
                } else {
                    loc.s = triSCoords;
                    loc.t = triTCoords;
                }
                locations.push_back(loc);
            } else {
                //  Center coordinate is on the first sub-patch while those on
                //  near the corners are on each successive sub-patch:
                LocationArray loc;
                loc.numLocations = 1;
                for (int j = 0; j <= baseFaceSize; ++j) {
                    bool isPerimeter = (j > 0);
                    loc.ptexIdx = basePtexId + (isPerimeter ? (j-1) : 0);
                    loc.s = &irregSCoords[isPerimeter];
                    loc.t = &irregTCoords[isPerimeter];

                    locations.push_back(loc);
                }
            }
            numLimitPoints += baseFaceSize + 1;
        }
        return numLimitPoints;
    }

    //
    //  Load command line arguments and geometry, build the LimitStencilTable
    //  for a set of points on the limit surface and compute those points for
    //  several orientations of the mesh:
    //
    int
    main(int argc, char **argv) {

        Args args(argc, argv);

        //
        //  Create or load the base geometry (command line arguments allow a
        //  .obj file to be specified), providing a TopologyRefiner and a set
        //  of base vertex positions to work with:
        //
        std::vector<Pos> basePositions;

        Far::TopologyRefiner * refinerPtr = args.inputObjFile.empty() ?
                createTopologyRefinerDefault(basePositions) :
                createTopologyRefinerFromObj(args.inputObjFile, args.schemeType,
                                             basePositions);
        assert(refinerPtr);
        Far::TopologyRefiner & refiner = *refinerPtr;

        Far::TopologyLevel const & baseLevel = refiner.GetLevel(0);

        //
        //  Use of LimitStencilTable requires either explicit or implicit use
        //  of a PatchTable.  A PatchTable is not required to construct a
        //  LimitStencilTable -- one will be constructed internally for use
        //  and discarded -- but explicit construction is recommended to control
        //  the many legacy options for PatchTable, rather than relying on
        //  internal defaults.  Adaptive refinement is required in both cases
        //  to indicate the accuracy of the patches.
        //
        //  Note that if a TopologyRefiner and PatchTable are not used for
        //  any other purpose than computing the limit points, that specifying
        //  the subset of faces containing those limit points in the adaptive
        //  refinement and PatchTable construction can avoid unnecessary
        //  overhead.
        //
        Far::PatchTable * patchTablePtr = 0;

        if (args.noPatchesFlag) {
            refiner.RefineAdaptive(
                Far::TopologyRefiner::AdaptiveOptions(args.maxPatchDepth));
        } else {
            Far::PatchTableFactory::Options patchOptions(args.maxPatchDepth);
            patchOptions.useInfSharpPatch = true;
            patchOptions.generateLegacySharpCornerPatches = false;
            patchOptions.generateVaryingTables = false;
            patchOptions.generateFVarTables = false;
            patchOptions.endCapType =
                Far::PatchTableFactory::Options::ENDCAP_GREGORY_BASIS;

            refiner.RefineAdaptive(patchOptions.GetRefineAdaptiveOptions());

            patchTablePtr = Far::PatchTableFactory::Create(refiner, patchOptions);
            assert(patchTablePtr);
        }

        //
        //  Assemble the set of locations for the limit points.  For each base
        //  face, coordinates for the center and its corners are specified --
        //  from which we will construct a triangle fan providing a crude
        //  tessellation (similar to tutorial_5_2).
        //
        std::vector<LocationArray> locations;

        int numLimitPoints = assembleLimitPointLocations(refiner, locations);

        //
        //  Construct a LimitStencilTable from the refiner, patch table (optional)
        //  and the collection of limit point locations.  Stencils can optionally
        //  be created for computing dervatives -- the default is to compute 1st
        //  derivative stencils, so be sure to disable that if not necessary:
        //
        Far::LimitStencilTableFactory::Options limitOptions;
        limitOptions.generate1stDerivatives = args.deriv1Flag;

        Far::LimitStencilTable const * limitStencilTablePtr =
            Far::LimitStencilTableFactory::Create(refiner, locations,
                0,             // optional StencilTable for the refined points
                patchTablePtr, // optional PatchTable
                limitOptions);
        assert(limitStencilTablePtr);
        Far::LimitStencilTable const & limitStencilTable = *limitStencilTablePtr;

        //
        //  Apply the constructed LimitStencilTable to compute limit positions
        //  from the base level vertex positions.  This is trivial if computing
        //  all positions in one invokation.  The UpdateValues method (and those
        //  for derivatives) are overloaded to optionally accept a subrange of
        //  indices to distribute the computation:
        //
        std::vector<Pos> limitPositions(numLimitPoints);

        limitStencilTable.UpdateValues(basePositions, limitPositions);

        //  Call with the optional subrange:
        limitStencilTable.UpdateValues(basePositions, limitPositions,
                                       0, numLimitPoints / 2);
        limitStencilTable.UpdateValues(basePositions, limitPositions,
                                       (numLimitPoints / 2) + 1, numLimitPoints);

        // Write vertices and faces in Obj format for the original limit points:
        int objVertCount = 0;

        if (!args.noOutputFlag) {
            printf("g base_mesh\n");
            objVertCount = writeToObj(baseLevel, limitPositions, objVertCount);
        }

        //
        //  Recompute the limit points and output faces for different "poses" of
        //  the original mesh -- in this case simply translated.  Also optionally
        //  compute 1st derivatives (though they are not used here):
        //
        std::vector<Pos> posePositions(basePositions);

        std::vector<Pos> limitDu(args.deriv1Flag ? numLimitPoints : 0);
        std::vector<Pos> limitDv(args.deriv1Flag ? numLimitPoints : 0);

        for (int i = 0; i < args.numPoses; ++i) {
            // Trivially transform the base vertex positions and re-compute:
            for (size_t j = 0; j < basePositions.size(); ++j) {
                posePositions[j] = posePositions[j] + args.poseOffset;
            }

            limitStencilTable.UpdateValues(posePositions, limitPositions);
            if (args.deriv1Flag) {
                limitStencilTable.UpdateDerivs(posePositions, limitDu, limitDv);
            }

            if (!args.noOutputFlag) {
                printf("\ng pose_%d\n", i);
                objVertCount = writeToObj(baseLevel, limitPositions, objVertCount);
            }
        }
        delete refinerPtr;
        delete patchTablePtr;
        delete limitStencilTablePtr;

        return EXIT_SUCCESS;
    }