This examples shows:
- How to extend the behaviour of entities using traits.
In the previous tutorial we used attributes and changed the type of the data types Point
, Normal
, TexCoord
, and Color
. But we can do even more with traits. We can change the behaviour of the mesh entities Vertex
, Face
, Edge
, and Halfedge
.
One goal in the design was a highly customizable data structure. Using the traits technique makes it possible. We pick up the smoother again and show an alternative way to implement it. Now we place the necessary data and the functions in the vertex itself
{
{
private:
Point cog_;
public:
VertexT() : cog_( Point(0.0f, 0.0f, 0.0f ) ) { }
const Point& cog() const { return cog_; }
void set_cog(const Point& _p) { cog_ = _p; }
};
Note the definition of the vertex entity. We use the supplied define VertexTraits
(which resolves in a rather inconvenient template definition). Similary we can use the defines FaceTraits
, EdgeTraits
, and HalfedgeTraits
to extend these entities. Now we enhanced the vertex, with the additional member variable cog_
, and the get/set-method pair to access the new member.
As before we compute in a first loop the barycenters for all vertices and store the information at the vertices
mesh.data(*v_it).set_cog(cog / valence);
In the second pass we set the new position of each vertex
mesh.set_point( *v_it, mesh.data(*v_it).cog());
It looks neat, but on the other hand we can't remove the data anymore as we could do with properties! By using traits one creates a 'static' configuration, which can't be changed during runtime.
The complete source looks like this:
#include <iostream>
#include <vector>
#include <OpenMesh/Core/IO/MeshIO.hh>
#include <OpenMesh/Core/Mesh/TriMesh_ArrayKernelT.hh>
{
{
private:
Point cog_;
public:
VertexT() : cog_( Point(0.0f, 0.0f, 0.0f ) ) { }
const Point& cog() const { return cog_; }
void set_cog(const Point& _p) { cog_ = _p; }
};
};
#define SIZEOF( entity,b ) \
std::cout << _prefix << "size of " << #entity << ": " \
<< sizeof( entity ) << std::endl; \
b += sizeof( entity )
template <typename Mesh>
void print_size(const std::string& _prefix = "")
{
size_t total=0;
SIZEOF(typename Mesh::Vertex, total);
std::cout << _prefix << "total: " << total << std::endl;
}
#undef SIZEOF
int main(int argc, char **argv)
{
MyMesh mesh;
if (argc < 4 || argc > 5)
{
std::cerr << "Usage: " << argv[0] << " [-s] #iterations infile outfile\n";
exit(1);
}
int idx=2;
if (argc == 5)
{
if (std::string("-s")==argv[idx-1])
{
std::cout << "Enhanced mesh size statistics\n";
print_size<MyMesh>(" ");
std::cout << "Default mesh size statistics\n";
print_size<MyMesh2>(" ");
}
++idx;
}
std::cout<< " Input mesh: " << argv[idx] << std::endl;
{
std::cerr << "Error: Cannot read mesh from " << argv[idx] << std::endl;
return 0;
}
MyMesh::VertexIter v_it, v_end(mesh.vertices_end());
unsigned int i, N(atoi(argv[idx-1]));
std::cout<< "Smooth mesh " << N << " times\n";
for (i=0; i < N; ++i)
{
for (v_it=mesh.vertices_begin(); v_it!=v_end; ++v_it)
{
cog[0] = cog[1] = cog[2] = valence = 0.0;
for (vv_it=mesh.vv_iter(*v_it); vv_it.is_valid(); ++vv_it)
{
cog += mesh.point( *vv_it );
++valence;
}
mesh.data(*v_it).set_cog(cog / valence);
}
for (v_it=mesh.vertices_begin(); v_it!=v_end; ++v_it)
if (!mesh.is_boundary(*v_it))
mesh.set_point( *v_it, mesh.data(*v_it).cog());
}
std::cout<< "Output mesh: " << argv[idx+1] << std::endl;
{
std::cerr << "Error: cannot write mesh to " << argv[idx+1] << std::endl;
return 0;
}
return 1;
}