convert Polygon_with_holes_2 To Surface_mesh

[BeginCGAL]

convert Polygon_with_holes_2 To Surface_mesh

[pentacular]

Use CGAL::Polygon_triangulation_decomposition_2 to produce triangles, use Plane_3 to_3d to produce faces, and add_face on the Surface_mesh.

[pentacular]

Ah, but it might be faster to just write a function to print a Polygon_with_holes_2 in obj format, as that is very simple.

[BeginCGAL]

I am a beginner,could you please write a demo (i could't find the demo about Polygon_triangulation_decomposition_2 )? thank you

[pentacular]

Perhaps something like this:

bool PolygonsWithHolesToSurfaceMesh(const Plane& plane,
                                    std::vector<Polygon_with_holes_2>& polygons,
                                    Surface_mesh& result,
                                    Vertex_map& vertex_map, bool flip = false) {
  CGAL::Polygon_triangulation_decomposition_2<Kernel> triangulator;
  for (const Polygon_with_holes_2& polygon : polygons) {
    std::vector<Polygon_2> facets;
    triangulator(polygon, std::back_inserter(facets));
    for (auto& facet : facets) {
      if (facet.orientation() != CGAL::Sign::POSITIVE) {
        facet.reverse_orientation();
      }
      std::vector<Vertex_index> vertices;
      for (const auto& point : facet) {
        vertices.push_back(
            ensureVertex(result, vertex_map, plane.to_3d(point)));
      }
      if (flip) {
        std::reverse(vertices.begin(), vertices.end());
      }
      if (result.add_face(vertices) == Surface_mesh::null_face()) {
        return false;
      }
    }   
  }     
  return true;
} 

But I think you're still going about this the wrong way.

Generating an OBJ file from a Polygon_with_holes_2 should be simpler. :)

[BeginCGAL]

thank you, by the way could you tell me the simpler way Generating an OBJ file from a Polygon_with_holes_2?

[pentacular]

v  0  0  0
v  1  0  0
v  1  1  0
v  0  1  0
v  0.5  0.5  1.6

f  5  2  3
f  4  5  3
f  6  3  2
f  5  6  2
f  4  6  5
f  6  4  3

Just write out the vertices (v) and the faces (f).

You'll still need to do the triangular decomposition since obj doesn't handle holes, but it's very simple.

[BeginCGAL]

i know .obj file format, and i know how to get all vertices . But i don't konw how to get the vertexIndex of every face such as "f 5 2 3", and how to get the "vn" value such as "vn -0.116639 0.196368 -0.973568".

[pentacular]

Just go through all of the vertices and write them out.
The first vertex you write out has index 1, the second has index 2, and so on.

Next go through all of the triangles, mapping each vertex to its index.

Now you're done.

You don't need to add vertex normals, but vn 0 0 1 should be correct since this is a 2d polygon.

[BeginCGAL]

thank you , i have achieved the aim