hbr_tutorial_1.cpp

https://github.com/PixarAnimationStudios/OpenSubdiv/blob/master/tutorials/hbr/tutorial_1/hbr_tutorial_1.cpp

```//------------------------------------------------------------------------------
// Tutorial description:
//
// This tutorial shows how to safely create Hbr meshes from arbitrary topology.
// Because Hbr is a half-edge data structure, it cannot represent non-manifold
// topology. Ensuring that the geometry used is manifold is a requirement to use
// Hbr safely. This tutorial presents some simple tests to detect inappropriate
// topology.
//

#include <opensubdiv/hbr/mesh.h>
#include <opensubdiv/hbr/catmark.h>

#include <cstdio>

//------------------------------------------------------------------------------
struct Vertex {

// Hbr minimal required interface ----------------------
Vertex() { }

Vertex(int /*i*/) { }

Vertex(Vertex const & src) {
_position[0] = src._position[0];
_position[1] = src._position[1];
_position[2] = src._position[2];
}

void Clear( void * =0 ) { }

void AddWithWeight(Vertex const &, float ) { }

void AddVaryingWithWeight(Vertex const &, float) { }

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

const float * GetPosition() const {
return _position;
}

private:
float _position[3];
};

typedef OpenSubdiv::HbrMesh<Vertex>      Hmesh;
typedef OpenSubdiv::HbrFace<Vertex>      Hface;
typedef OpenSubdiv::HbrVertex<Vertex>    Hvertex;
typedef OpenSubdiv::HbrHalfedge<Vertex>  Hhalfedge;

//------------------------------------------------------------------------------
// Non-manifold geometry from catmark_fan.h
//
//                     o
//                    /|
//                   / |
//                  /  |
//                 /   |
//                o    |
//                | f2 |
//                |    |
//       o--------+----o------------o
//      /         |   /            /
//     /          |  /            /
//    /    f0     | /     f1     /
//   /            |/            /
//  o------------ o------------o
//
// The shared edge of a fan is adjacent to 3 faces, and therefore non-manifold.
//
static float verts[8][3] = {{-1.0,  0.0, -1.0},
{-1.0,  0.0,  0.0},
{ 0.0,  0.0,  0.0},
{ 0.0,  0.0, -1.0},
{ 1.0,  0.0,  0.0},
{ 1.0,  0.0, -1.0},
{ 0.0,  1.0,  0.0},
{ 0.0,  1.0, -1.0}};

static int nverts = 8,
nfaces = 3;

static int facenverts[3] = { 4, 4, 4 };

static int faceverts[12] = { 0, 1, 2, 3,
3, 2, 4, 5,
3, 2, 6, 7 };

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

OpenSubdiv::HbrCatmarkSubdivision<Vertex> * catmark =
new OpenSubdiv::HbrCatmarkSubdivision<Vertex>();

Hmesh * hmesh = new Hmesh(catmark);

Vertex v;
for (int i=0; i<nverts; ++i) {
v.SetPosition(verts[i][0], verts[i][1], verts[i][2]);
hmesh->NewVertex(i, v);
}

// Create the topology
int * fv = faceverts;
for (int i=0; i<nfaces; ++i) {

int nv = facenverts[i];

bool valid = true;

for(int j=0;j<nv;j++) {

Hvertex const * origin      = hmesh->GetVertex(fv[j]),
* destination = hmesh->GetVertex(fv[(j+1)%nv]);
Hhalfedge const * opposite = destination->GetEdge(origin);

// Make sure that the vertices exist in the mesh
if (origin==NULL || destination==NULL) {
printf(" An edge was specified that connected a nonexistent vertex\n");
valid=false;
break;
}

// Check for a degenerate edge
if (origin == destination) {
printf(" An edge was specified that connected a vertex to itself\n");
valid=false;
break;
}

// Check that no more than 2 faces are adjacent to the edge
if (opposite && opposite->GetOpposite() ) {
printf(" A non-manifold edge incident to more than 2 faces was found\n");
valid=false;
break;
}

// Check that the edge is unique and oriented properly
if (origin->GetEdge(destination)) {
printf(" An edge connecting two vertices was specified more than once."
" It's likely that an incident face was flipped\n");
valid=false;
break;
}
}

if (valid) {
hmesh->NewFace(nv, fv, 0);
} else {
printf(" Skipped face %d\n", i);
}

fv+=nv;
}

hmesh->SetInterpolateBoundaryMethod(Hmesh::k_InterpolateBoundaryEdgeOnly);

hmesh->Finish();

printf("Created a fan with %d faces and %d vertices.\n",
hmesh->GetNumFaces(), hmesh->GetNumVertices());

delete hmesh;
delete catmark;
}

//------------------------------------------------------------------------------
```