# far_tutorial_1_2.cpp

https://github.com/PixarAnimationStudios/OpenSubdiv/blob/master/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");
}
}
```