mirror of
https://github.com/PixarAnimationStudios/OpenSubdiv
synced 2024-11-29 23:01:05 +00:00
638 lines
18 KiB
ReStructuredText
638 lines
18 KiB
ReStructuredText
..
|
|
Copyright 2013 Pixar
|
|
|
|
Licensed under the Apache License, Version 2.0 (the "Apache License")
|
|
with the following modification; you may not use this file except in
|
|
compliance with the Apache License and the following modification to it:
|
|
Section 6. Trademarks. is deleted and replaced with:
|
|
|
|
6. Trademarks. This License does not grant permission to use the trade
|
|
names, trademarks, service marks, or product names of the Licensor
|
|
and its affiliates, except as required to comply with Section 4(c) of
|
|
the License and to reproduce the content of the NOTICE file.
|
|
|
|
You may obtain a copy of the Apache License at
|
|
|
|
http://www.apache.org/licenses/LICENSE-2.0
|
|
|
|
Unless required by applicable law or agreed to in writing, software
|
|
distributed under the Apache License with the above modification is
|
|
distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
|
|
KIND, either express or implied. See the Apache License for the specific
|
|
language governing permissions and limitations under the Apache License.
|
|
|
|
|
|
Using Hbr
|
|
---------
|
|
|
|
.. contents::
|
|
:local:
|
|
:backlinks: none
|
|
|
|
|
|
----
|
|
|
|
.. container:: notebox
|
|
|
|
**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 <release_notes.html>`_
|
|
|
|
|
|
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.
|
|
|
|
.. 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:
|
|
|
|
.. 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.
|
|
|
|
.. 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:
|
|
|
|
.. 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.
|
|
|
|
.. 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, currently **Hbr** is not able to handle `non-manifold <subdivision_surfaces.html#manifold-geometry>`__
|
|
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.
|
|
|
|
.. 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()*:
|
|
|
|
.. 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:
|
|
|
|
.. 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:
|
|
|
|
.. code:: c++
|
|
|
|
mesh->SetInterpolateBoundaryMethod( OpenSubdiv::HbrMesh<Vertex>::k_InterpolateBoundaryEdgeOnly );
|
|
|
|
*Face-varying* data:
|
|
|
|
.. code:: c++
|
|
|
|
mesh->SetFVarInterpolateBoundaryMethod( OpenSubdiv::HbrMesh<Vertex>::k_InterpolateBoundaryEdgeOnly );
|
|
|
|
|
|
Additional information on boundary interpolation rules can be found
|
|
`here <subdivision_surfaces.html#boundary-interpolation-rules>`__ and
|
|
`here <hbr_overview.html#boundary-interpolation-rules>`__
|
|
|
|
.. container:: impnotip
|
|
|
|
**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.
|
|
|
|
.. 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.
|
|
|
|
.. 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.
|
|
|
|
.. 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 );
|
|
|
|
|
|
|
|
.. container:: note
|
|
|
|
**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 that corresponds
|
|
to `this example <subdivision_surfaces.html#hierarchical-edits-paths>`__.
|
|
|
|
.. 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.
|
|
|
|
.. 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:
|
|
|
|
.. 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:
|
|
|
|
.. 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:
|
|
|
|
.. 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)
|
|
|
|
.. 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:
|
|
|
|
.. 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);
|
|
}
|