Find the vertices of each mesh face

Rhino Developer
1

I using the rhinocommand(C++), As the title shows, I want to find a single face of the mesh, such as mesh vertices, vertex normal, face normals, etc.
Now I can get all the vertex coordinates and normal vectors of the mesh.

        ON_3dPoint  dV;
	ON_3fVector  N;
	if (mesh->HasSynchronizedDoubleAndSinglePrecisionVertices())
		dV = mesh->m_dV[i];
	if (mesh->HasVertexNormals())
		N = mesh->m_N[i];

But I don’t know which face the information belongs to, and the mesh of the face is a triangle or quad.

Then, I can also get the normal vector of the face, but this can only be used on the cube…

        ON_3fVector  fN;
        if (mesh->HasFaceNormals())
	fN = mesh->m_FN[i];

If you have any ideas, please give us a lot of advice.
Thank you.

2

Hi @t107408022,

Mesh vertices are stored on the ON_Mesh::m_V array.

Mesh faces, ON_MeshFace, are stored on the ON_Mesh::m_F array.

A mesh face’s vertex indices are stored on the ON_Meshface::vi array.

Thus:

  const ON_Mesh& mesh = ......;

  // Get first mesh face
  const ON_MeshFace& face = mesh.m_F[0];
  if (face.IsTriangle())
  {
    ON_3fPoint vertex0 = mesh.m_V[face.vi[0]];
    ON_3fPoint vertex1 = mesh.m_V[face.vi[1]];
    ON_3fPoint vertex2 = mesh.m_V[face.vi[2]];
    // TODO...
  }
  else
  {
    ON_3fPoint vertex0 = mesh.m_V[face.vi[0]];
    ON_3fPoint vertex1 = mesh.m_V[face.vi[1]];
    ON_3fPoint vertex2 = mesh.m_V[face.vi[2]];
    ON_3fPoint vertex3 = mesh.m_V[face.vi[3]];
    // TODO...
  }

Does this help?

– Dale

3

Hello @dale Thank you very much for your assistance.
Next, I need to get is the normal vector of the mesh face. I have tried ON_Mesh::m_FN , but only the cube is m_FN.Count() = m_F.Count() .
I know that ON_Mesh::m_N can get the normal vector of the vertex. Maybe I want to calculate the face vector from the point vector?

If you don’t bother, I would like to ask the parameters in ON_MeshFace::GetPlaneEquation What is ON_3dPointListRef& vertex_list ?

4

Hi @t107408022,

A mesh’s vertex normals are stored in the ON_Mesh::m_N array. You can calculate vertex normals using ON_Mesh::ComputeVertexNormals.

A mesh’s face normals are stored in the ON_Mesh::m_FN array. You can calculate vertex normals using `ON_Mesh::ComputeFaceNormals’.

A list of mesh face vertices.

– Dale