CODEWITHSUNDEEP
c++cgal
Tom Mettam
Tom Mettam

Reputation: 2963

CGAL: Get face data from surface mesh

I'm trying to fill my own struct with data retrieved from a CGAL::Surface_mesh.

You can add a face to a surface mesh via..

CGAL::SM_Face_index face = SM_Surface_Mesh.add_face(SM_Vertex_Index, SM_Vertex_Index, SM_Vertex_Index);

.. but how does one retrieve that face given the SM_Face_Index? I've tried sifting through the documentation but to no avail.

InteropMesh * outputMesh = new InteropMesh();
uint32_t num = mesh1.number_of_vertices();

outputMesh->vertexCount = num;

outputMesh->vertices = new InteropVector3[num];

for (Mesh::Vertex_index vd : mesh1.vertices()) 
{
    uint32_t index = vd; //via size_t

    Point data = mesh1.point(vd);
    outputMesh->vertices[index].x = (float)data.x();
    outputMesh->vertices[index].y = (float)data.y();
    outputMesh->vertices[index].z = (float)data.z();
}

outputMesh->indices = new uint32_t[mesh1.number_of_faces() * 3];

for (CGAL::SM_Face_index fd : mesh1.faces())
{
    //? How do I get the three vertex indices?
}

Upvotes: 3

Views: 3314

Answers (2)

Tipam
Tipam

Reputation: 51

A simple way of getting vertex and face indices can be done like this;

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Surface_mesh<K::Point_3> Mesh;

Mesh sm;

// sm created here or as a result of some CGAL function

std::vector<float> verts;
std::vector<uint32_t> indices;

//Get vertices ...
for (Mesh::Vertex_index vi : sm.vertices()) {
    K::Point_3 pt = sm.point(vi);
    verts.push_back((float)pt.x());
    verts.push_back((float)pt.y());
    verts.push_back((float)pt.z());
}

//Get face indices ...
for (Mesh::Face_index face_index : sm.faces()) {
    CGAL::Vertex_around_face_circulator<Mesh> vcirc(sm.halfedge(face_index), sm), done(vcirc);
    do indices.push_back(*vcirc++); while (vcirc != done);
}

This example assumes triangle output (i.e. every 3 indices describes a triangle) although faces could have more indices as Andry points out.

Another function should be added to check the face index count and split faces into triangles if there are more than 3 indices.

Upvotes: 5

sloriot
sloriot

Reputation: 6253

The Surface_mesh data structure can represent more than only triangle meshes. Meaning that you might have more than 3 vertices per face. Once you get a face, you can navigate on its boundary edges and get the source and target vertices.

For example you can do:

Surface_mesh::Halfedge_index hf = sm.halfedge(fi);
for(Surface_mesh::Halfedge_index hi : halfedges_around_face(hf, sm))
{
  Surface_mesh::Vertex_index vi = target(hi, sm);
}

You can also do it by hand:

Surface_mesh::Halfedge_index hstart = sm.halfedge(fi), hi=hstart;
do{
  Surface_mesh::Vertex_index vi = target(hi, sm);
  hi=sm.next(hi);
}
while(hi!=hstart)

Upvotes: 4

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