Note
As of OpenSubdiv 3.0, all Hbr dependencies have been removed from the
core APIs (Sdc, Vtr, Far, Osd). The legacy source code of
Hbr is provided purely for regression and legacy purposes. If your code
is currently depending on Hbr functionality, we recommend migrating to the
newer APIs as we cannot guarantee that this code will be maintained in
future releases.
For more information see the 3.0 release notes
Vertex Template API
The Hbr API abstracts the vertex class through templating. Client-code is
expected to provide a vertex class that implements the requisite interpolation
functionality.
Here is an example of a simple vertex class that accounts for 3D position, but
does not support arbitrary variables or varying interpolation.
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 58)
Cannot analyze code. Pygments package not found.
.. code:: c++
struct Vertex {
Vertex() { }
Vertex( int /*i*/ ) { }
Vertex( const Vertex & src ) { _pos[0]=src._pos[0]; _pos[1]=src._pos[1]; _pos[2]=src._pos[2]; }
~Vertex( ) { }
void AddWithWeight(const Vertex& src, float weight, void * =0 ) {
_pos[0]+=weight*src._pos[0];
_pos[1]+=weight*src._pos[1];
_pos[2]+=weight*src._pos[2];
}
void AddVaryingWithWeight(const Vertex& , float, void * =0 ) { }
void Clear( void * =0 ) { _pos[0]=_pos[1]=_pos[2]=0.0f; }
void SetPosition(float x, float y, float z) { _pos[0]=x; _pos[1]=y; _pos[2]=z; }
void ApplyVertexEdit(const OpenSubdiv::HbrVertexEdit<Vertex> & edit) {
const float *src = edit.GetEdit();
switch(edit.GetOperation()) {
case OpenSubdiv::HbrHierarchicalEdit<Vertex>::Set:
_pos[0] = src[0];
_pos[1] = src[1];
_pos[2] = src[2];
break;
case OpenSubdiv::HbrHierarchicalEdit<Vertex>::Add:
_pos[0] += src[0];
_pos[1] += src[1];
_pos[2] += src[2];
break;
case OpenSubdiv::HbrHierarchicalEdit<Vertex>::Subtract:
_pos[0] -= src[0];
_pos[1] -= src[1];
_pos[2] -= src[2];
break;
}
}
void ApplyMovingVertexEdit(const OpenSubdiv::HbrMovingVertexEdit<Vertex> &) { }
// custom functions & data not required by Hbr -------------------------
Vertex( float x, float y, float z ) { _pos[0]=x; _pos[1]=y; _pos[2]=z; }
const float * GetPos() const { return _pos; }
float _pos[3];
};
In some cases, if only topological analysis is required, the class can be left un-implemented.
Far and Osd for instance store vertex data in serialized interleaved vectors. Here
is the Osd::Vertex class for reference:
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 118)
Cannot analyze code. Pygments package not found.
.. code:: c++
class Vertex {
public:
Vertex() {}
Vertex(int /* index */) {}
Vertex(Vertex const & /* src */) {}
void AddWithWeight(Vertex const & /* i */, float /* weight */, void * = 0) {}
void AddVaryingWithWeight(const Vertex & /* i */, float /* weight */, void * = 0) {}
void Clear(void * = 0) {}
void ApplyVertexEdit(FarVertexEdit const &) { }
};
Creating a Mesh
The following tutorial walks through the steps of instantiating a simple Hbr
mesh.
The code found in regression/common/shape_utils.h can also be used as an example.
While this implementation covers many of Hbr's features, it does not provide
coverage for the complete Renderman specification though.
Instantiating an HbrMesh
First we need to instantiate a mesh object.
- Hbr supports 3 subdivision schemes:
- Catmull-Clark (catmark)
- Loop
- Bilinear
The scheme is selected by passing an specialized instance of HbrSubdivision<T>,
HbrCatmarkSubdivision<T> in this case. The scheme can be shared across multiple
mesh objects, so we only need a single instance.
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 165)
Cannot analyze code. Pygments package not found.
.. code:: c++
static OpenSubdiv::HbrCatmarkSubdivision<Vertex> _scheme;
OpenSubdiv::HbrMesh<Vertex> * mesh = new OpenSubdiv::HbrMesh<Vertex>( _scheme );
Creating Vertices
Adding vertices to the mesh is accomplished using the HbrMesh::NewVertex() method.
Because Hbr uses a dedicated vertex allocator to help alleviate the performance
impact of intensive fragmented memory allocations. This optimization results in
the following design pattern:
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 182)
Cannot analyze code. Pygments package not found.
.. code:: c++
Vertex vtx;
for(int i=0;i<numVerts; i++ ) {
Vertex * v = mesh->NewVertex( i, vtx);
// v->SetPosition();
}
We instantiate a single "default" vertex object named 'vtx' on the stack. We then
recover the pointer to the actual vertex created in the mesh from the NewVertex()
method. Once we have recovered that pointer, we can set the data for our vertex
by using any of the custom accessors.
Creating Faces
Once all the vertices have been registered in the mesh, we can start adding the
faces with HbrMesh::NewFace(). Assuming we had an obj style reader, we need
to know the number of vertices in the face and the indices of these vertices.
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 205)
Cannot analyze code. Pygments package not found.
.. code:: c++
for (int f=0; f<numFaces; ++f) {
int nverts = obj->GetNumVertices(f);
const int * faceverts = obj->GetFaceVerts(f);
mesh->NewFace(nv, fv, 0);
}
However, Hbr is not able to handle non-manifold
geometry. In order to avoid tripping asserts or causing memory violations, let's
rewrite the previous loop with some some prototype code to check the validity of
the topology.
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 221)
Cannot analyze code. Pygments package not found.
.. code:: c++
for (int f=0; f<numFaces; ++f) {
int nv = obj->GetNumVertices(f);
const int * fv = obj->GetFaceVerts(f);
// triangles only for Loop subdivision !
if ((scheme==kLoop) and (nv!=3)) {
printf("Trying to create a Loop subd with non-triangle face\n");
continue;
}
// now check the half-edges connectivity
for(int j=0;j<nv;j++) {
OpenSubdiv::HbrVertex<T> * origin = mesh->GetVertex( fv[j] );
OpenSubdiv::HbrVertex<T> * destination = mesh->GetVertex( fv[(j+1)%nv] );
OpenSubdiv::HbrHalfedge<T> * opposite = destination->GetEdge(origin);
if(origin==NULL || destination==NULL) {
printf(" An edge was specified that connected a nonexistent vertex\n");
continue;
}
if(origin == destination) {
printf(" An edge was specified that connected a vertex to itself\n");
continue;
}
if(opposite && opposite->GetOpposite() ) {
printf(" A non-manifold edge incident to more than 2 faces was found\n");
continue;
}
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");
continue;
}
}
mesh->NewFace(nv, fv, 0);
}
Wrapping Things Up
Once we have vertices and faces set in our mesh, we still need to wrap things up
by calling HbrMesh::Finish():
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 274)
Cannot analyze code. Pygments package not found.
.. code:: c++
mesh->Finish()
Finish iterates over the mesh to apply the boundary interpolation rules and
checks for singular vertices. At this point, there is one final topology check
remaining to validate the mesh:
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 282)
Cannot analyze code. Pygments package not found.
.. code:: c++
mesh->Finish()
if (mesh->GetNumDisconnectedVertices()) {
printf("The specified subdivmesh contains disconnected surface components.\n");
// abort or iterate over the mesh to remove the offending vertices
}
Boundary Interpolation Rules
The rule-set can be selected using the following accessors:
Vertex and varying data:
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 303)
Cannot analyze code. Pygments package not found.
.. code:: c++
mesh->SetInterpolateBoundaryMethod( OpenSubdiv::HbrMesh<Vertex>::k_InterpolateBoundaryEdgeOnly );
Face-varying data:
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 309)
Cannot analyze code. Pygments package not found.
.. code:: c++
mesh->SetFVarInterpolateBoundaryMethod( OpenSubdiv::HbrMesh<Vertex>::k_InterpolateBoundaryEdgeOnly );
Additional information on boundary interpolation rules can be found
here
Warning
The boundary interpolation rules must be set before the call to
HbrMesh::Finish(), which sets the sharpness values to boundary edges
and vertices based on these rules.
Adding Creases
Hbr supports a sharpness attribute on both edges and vertices.
Sharpness is set using the SetSharpness(float) accessors.
Vertex Creases
Given an index, vertices are very easy to access in the mesh.
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 340)
Cannot analyze code. Pygments package not found.
.. code:: c++
int idx; // vertex index
float sharp; // the edge sharpness
OpenSubdiv::HbrVertex<Vertex> * v = mesh->GetVertex( idx );
if(v) {
v->SetSharpness( std::max(0.0f, sharp) );
} else
printf("cannot find vertex for corner tag (%d)\n", idx );
Edge Creases
Usually, edge creases are described with a vertex indices pair. Here is some
sample code to locate the matching half-edge and set a crease sharpness.
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 360)
Cannot analyze code. Pygments package not found.
.. code:: c++
int v0, v1; // vertex indices
float sharp; // the edge sharpness
OpenSubdiv::HbrVertex<Vertex> * v = mesh->GetVertex( v0 ),
* w = mesh->GetVertex( v1 );
OpenSubdiv::HbrHalfedge<Vertex> * e = 0;
if( v && w ) {
if((e = v->GetEdge(w)) == 0)
e = w->GetEdge(v);
if(e) {
e->SetSharpness( std::max(0.0f, sharp) );
} else
printf("cannot find edge for crease tag (%d,%d)\n", v0, v1 );
}
Holes
Hbr faces support a "hole" tag.
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 389)
Cannot analyze code. Pygments package not found.
.. code:: c++
int idx; // the face index
OpenSubdiv::HbrFace<Vertex> * f = mesh->GetFace( idx );
if(f) {
f->SetHole();
} else
printf("cannot find face for hole tag (%d)\n", idx );
Note
The hole tag is hierarchical : sub-faces can also be marked as holes.
See: Hierarchical Edits
Hierarchical Edits
Hbr supports the following types of hierarchical edits:
Type |
Function |
Corner edits |
Modify vertex sharpness |
Crease edits |
Modify edge sharpness |
FaceEdit |
Modify custom "face data" |
FVarEdit |
Modify face-varying data |
VertexEdit |
Modify vertex and varying data |
HoleEdit |
Set "hole" tag |
Modifications are one of the following 3 operations:
Operation |
Set |
Add |
Subtract |
Here is a simple example that creates a hierarchical vertex edit.
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 446)
Cannot analyze code. Pygments package not found.
.. code:: c++
// path = 655, 2, 3, 0
int faceid = 655,
nsubfaces = 2,
subfaces[2] = { 2, 3 },
vertexid = 0;
int offset = 0, // offset to the vertex or varying data
numElems = 3; // number of elements to apply the modifier to (x,y,z = 3)
bool isP = false; // shortcut to identify modifications to the vertex position "P"
OpenSubdiv::HbrHierarchicalEdit<Vertex>::Operation op =
OpenSubdiv::HbrHierarchicalEdit<T>::Set;
float values[3] = { 1.0f, 0.5f, 0.0f }; // edit values
OpenSubdiv::HbrVertexEdit<T> * edit =
new OpenSubdiv::HbrVertexEdit<T>(faceid,
nsubfaces,
subfaces,
vertexid,
offset,
floatwidth,
isP,
op,
values);
Face-varying Data
Here is a walk-through of how to store face-varying data for a (u,v) pair.
Unlike vertex and varying data which is accessed through the templated vertex
API, face-varying data is directly aggregated as vectors of float data.
Instantiating the HbrMesh
The HbrMesh needs to retain some knowledge about the face-varying data that it
carries in order to refine it correctly.
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 491)
Cannot analyze code. Pygments package not found.
.. code:: c++
int fvarwidth = 2; // total width of the fvar data
static int indices[1] = { 0 }, // 1 offset set to 0
widths[1] = { 2 }; // 2 floats in a (u,v) pair
int const fvarcount = fvarwidth > 0 ? 1 : 0,
* fvarindices = fvarwidth > 0 ? indices : NULL,
* fvarwidths = fvarwidth > 0 ? widths : NULL;
mesh = new OpenSubdiv::HbrMesh<T>( &_scheme,
fvarcount,
fvarindices,
fvarwidths,
fvarwidth );
Setting the Face-Varying Data
After the topology has been created, Hbr is ready to accept face-varying data.
Here is some sample code:
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 514)
Cannot analyze code. Pygments package not found.
.. code:: c++
for (int i=0, idx=0; i<numFaces; ++i ) {
OpenSubdiv::HbrFace<Vertex> * f = mesh->GetFace(i);
int nv = f->GetNumVertices(); // note: this is not the fastest way
OpenSubdiv::HbrHalfedge<Vertex> * e = f->GetFirstEdge();
for (int j=0; j<nv; ++j, e=e->GetNext()) {
OpenSubdiv::HbrFVarData<Vertex> & fvt = e->GetOrgVertex()->GetFVarData(f);
float const * fvdata = GetFaceVaryingData( i, j );
if (not fvt.IsInitialized()) {
// if no fvar daa exists yet on the vertex
fvt.SetAllData(2, fvdata);
} else if (not fvt.CompareAll(2, fvdata)) {
// if there already is fvar data and there is a boundary add the new data
OpenSubdiv::HbrFVarData<T> & nfvt = e->GetOrgVertex()->NewFVarData(f);
nfvt.SetAllData(2, fvdata);
}
}
}
Retrieving the Face-Varying Data
The HbrFVarData structures are expanded during the refinement process, with every
sub-face being assigned a set of interpolated face-varying data. This data can be
accessed in 2 ways :
From a face, passing a vertex index:
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 555)
Cannot analyze code. Pygments package not found.
.. code:: c++
// OpenSubdiv::HbrFace<Vertex> * f
OpenSubdiv::HbrFVarData const &fv = f.GetFVarData(vindex);
const float * data = fv.GetData()
From a vertex, passing a pointer to an incident face:
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 566)
Cannot analyze code. Pygments package not found.
.. code:: c++
// OpenSubdiv::HbrFace<Vertex> * f
OpenSubdiv::HbrFVarData const &fv = myVertex.GetFVarData(f);
const float * data = fv.GetData()
Valence Operators
When manipulating meshes, it is often necessary to iterate over neighboring faces
or vertices. Rather than gather lists of pointers and return them, Hbr exposes
an operator pattern that guarantees consistent mesh traversals.
The following example shows how to use an operator to count the number of neighboring
vertices (use HbrVertex::GetValence() for proper valence counts)
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 587)
Cannot analyze code. Pygments package not found.
.. code:: c++
//OpenSubdiv::HbrVertex<Vertex> * v;
class MyOperator : public OpenSubdiv::HbrVertexOperator<Vertex> {
public:
int count;
MyOperator() : count(0) { }
virtual void operator() (OpenSubdiv::HbrVertex<Vertex> &v) {
++count;
}
};
MyOperator op;
v->ApplyOperatorSurroundingVertices( op );
Managing Singular Vertices
Certain topological configurations would force vertices to share multiple
half-edge cycles. Because Hbr is a half-edge representation, these "singular"
vertices have to be duplicated as part of the HbrMesh::Finish() phase of the
instantiation.
These duplicated vertices can cause problems for client-code that tries to
populate buffers of vertex or varying data. The following sample code shows
how to match the vertex data to singular vertex splits:
System Message: WARNING/2 (/builddir/build/BUILD/OpenSubdiv-3_5_0/documentation/using_osd_hbr.rst, line 621)
Cannot analyze code. Pygments package not found.
.. code:: c++
// Populating an OsdCpuVertexBuffer with vertex data (positions,...)
float const * vtxData = inMeshFn.getRawPoints(&returnStatus);
OpenSubdiv::OsdCpuVertexBuffer *vertexBuffer =
OpenSubdiv::OsdCpuVertexBuffer::Create(numVertexElements, numFarVerts);
vertexBuffer->UpdateData(vtxData, 0, numVertices );
// Duplicate the vertex data into the split singular vertices
std::vector<std::pair<int, int> > const splits = hbrMesh->GetSplitVertices();
for (int i=0; i<(int)splits.size(); ++i) {
vertexBuffer->UpdateData(vtxData+splits[i].second*numVertexElements, splits[i].first, 1);
}