# far_tutorial_2_1.cpp

https://github.com/PixarAnimationStudios/OpenSubdiv/blob/release/tutorials/far/tutorial_2_1/far_tutorial_2_1.cpp

```//------------------------------------------------------------------------------
// Tutorial description:
//
// Building on tutorial 0, this example shows how to instantiate a simple mesh,
// refine it uniformly and then interpolate additional sets of primvar data.
//

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

#include <cstdio>

//------------------------------------------------------------------------------
// Vertex container implementation.
//
// We are adding a per-vertex color attribute to our primvar data.  While they
// are separate properties and exist in separate buffers (as when read from an
// Alembic file) they are both of the form float[3] and so we can use the same
// underlying type.
//
// While color and position may be the same, we'll make the color a "varying"
// primvar, e.g. it is constrained to being linearly interpolated between
// vertices, rather than smoothly like position and other vertex data.
//
struct Point3 {

// Minimal required interface ----------------------
Point3() { }

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

void AddWithWeight(Point3 const & src, float weight) {
_point[0]+=weight*src._point[0];
_point[1]+=weight*src._point[1];
_point[2]+=weight*src._point[2];
}

// Public interface ------------------------------------
void SetPoint(float x, float y, float z) {
_point[0]=x;
_point[1]=y;
_point[2]=z;
}

const float * GetPoint() const {
return _point;
}

private:
float _point[3];
};

typedef Point3 VertexPosition;
typedef Point3 VertexColor;

//------------------------------------------------------------------------------
// Cube geometry from catmark_cube.h
static float g_verts[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 }};

// Per-vertex RGB color data
static float g_colors[8][3] = {{ 1.0f, 0.0f, 0.5f },
{ 0.0f, 1.0f, 0.0f },
{ 0.0f, 0.0f, 1.0f },
{ 1.0f, 1.0f, 1.0f },
{ 1.0f, 1.0f, 0.0f },
{ 0.0f, 1.0f, 1.0f },
{ 1.0f, 0.0f, 1.0f },
{ 0.0f, 0.0f, 0.0f }};

static int g_nverts = 8,
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  };

using namespace OpenSubdiv;

static Far::TopologyRefiner * createFarTopologyRefiner();

//------------------------------------------------------------------------------
int main(int, char **) {

int maxlevel = 5;

Far::TopologyRefiner * refiner = createFarTopologyRefiner();

// Uniformly refine the topology up to 'maxlevel'
refiner->RefineUniform(Far::TopologyRefiner::UniformOptions(maxlevel));

// Allocate buffers for vertex primvar data.
//
// We assume we received the coarse data for the mesh in separate buffers
// from some other source, e.g. an Alembic file.  Meanwhile, we want buffers
// for the last/finest subdivision level to persist.  We have no interest
// in the intermediate levels.
//
// Determine the sizes for our needs:
int nCoarseVerts = g_nverts;
int nFineVerts   = refiner->GetLevel(maxlevel).GetNumVertices();
int nTotalVerts  = refiner->GetNumVerticesTotal();
int nTempVerts   = nTotalVerts - nCoarseVerts - nFineVerts;

// Allocate and initialize the primvar data for the original coarse vertices:
std::vector<VertexPosition> coarsePosBuffer(nCoarseVerts);
std::vector<VertexColor>    coarseClrBuffer(nCoarseVerts);

for (int i = 0; i < nCoarseVerts; ++i) {
coarsePosBuffer[i].SetPoint(g_verts[i][0], g_verts[i][1], g_verts[i][2]);
coarseClrBuffer[i].SetPoint(g_colors[i][0], g_colors[i][1], g_colors[i][2]);
}

// Allocate intermediate and final storage to be populated:
std::vector<VertexPosition> tempPosBuffer(nTempVerts);
std::vector<VertexPosition> finePosBuffer(nFineVerts);

std::vector<VertexColor> tempClrBuffer(nTempVerts);
std::vector<VertexColor> fineClrBuffer(nFineVerts);

// Interpolate all primvar data -- separate buffers can be populated on
VertexPosition * srcPos = &coarsePosBuffer[0];
VertexPosition * dstPos = &tempPosBuffer[0];

VertexColor * srcClr = &coarseClrBuffer[0];
VertexColor * dstClr = &tempClrBuffer[0];

Far::PrimvarRefiner primvarRefiner(*refiner);

for (int level = 1; level < maxlevel; ++level) {
primvarRefiner.Interpolate(       level, srcPos, dstPos);
primvarRefiner.InterpolateVarying(level, srcClr, dstClr);

srcPos = dstPos, dstPos += refiner->GetLevel(level).GetNumVertices();
srcClr = dstClr, dstClr += refiner->GetLevel(level).GetNumVertices();
}

// Interpolate the last level into the separate buffers for our final data:
primvarRefiner.Interpolate(       maxlevel, srcPos, finePosBuffer);
primvarRefiner.InterpolateVarying(maxlevel, srcClr, fineClrBuffer);

{ // Visualization with Maya : print a MEL script that generates colored
// particles at the location of the refined vertices (don't forget to
// turn shading on in the viewport to see the colors)

int nverts = nFineVerts;

// Output particle positions
printf("particle ");
for (int vert = 0; vert < nverts; ++vert) {
float const * pos = finePosBuffer[vert].GetPoint();
printf("-p %f %f %f\n", pos[0], pos[1], pos[2]);
}
printf(";\n");

// Set particle point size (20 -- very large)
printf("addAttr -is true -ln \"pointSize\" -at long -dv 20 particleShape1;\n");

// Add per-particle color attribute ('rgbPP')
printf("addAttr -ln \"rgbPP\" -dt vectorArray particleShape1;\n");

// Set per-particle color values from our primvar data
printf("setAttr \"particleShape1.rgbPP\" -type \"vectorArray\" %d ", nverts);
for (int vert = 0; vert < nverts; ++vert) {
float const * color = fineClrBuffer[vert].GetPoint();
printf("%f %f %f\n", color[0], color[1], color[2]);
}
printf(";\n");
}

delete refiner;
return EXIT_SUCCESS;
}

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

// Populate a topology descriptor with our raw data

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;
}
//------------------------------------------------------------------------------
```