CGAL Lib extrude polygon

Question

I am currently working on a tree generation application with CGAL which is my first time.

Which would be the easiest and/or best way to do a face extrusion? The calculation for the new points is done already.

CGAL is a huge lib, so there are probably better and more robust ways.

Please have a look at the current code (consider the comments):

void TreeGenerator::extrude(Face_handle face, float value)
{
    CGAL_precondition( m_mesh.is_valid());

    //calculate face normal vector direction
    Halfedge_handle halfEdge1 = face->halfedge();
    Halfedge_handle halfEdge2 = halfEdge1->next();
    Halfedge_handle halfEdge3 = halfEdge2->next();
    Halfedge_handle halfEdge4 = halfEdge3->next();

    //vectors from v1 to v2 and from v2 to v3 -> vectors lying on the face
    Vector3 v1(halfEdge1->vertex()->point(), halfEdge2->vertex()->point());
    Vector3 v2(halfEdge2->vertex()->point(), halfEdge3->vertex()->point());

    Vector3 normal_vector = cross_product(v1, v2);

    //HINT: This can be cpu time consuming -> can we remove the sqrt() ?
    normal_vector = (normal_vector / sqrt(normal_vector.squared_length())) * value;

    std::cout << "Normal Vector: " << normal_vector << std::endl;

    Point point1 = halfEdge1->vertex()->point() + normal_vector;
    Point point2 = halfEdge2->vertex()->point() + normal_vector;
    Point point3 = halfEdge3->vertex()->point() + normal_vector;
    Point point4 = halfEdge4->vertex()->point() + normal_vector;

    std::cout << "Point1: " << point1 << std::endl;
    std::cout << "Point2: " << point2 << std::endl;
    std::cout << "Point3: " << point3 << std::endl;
    std::cout << "Point4: " << point4 << std::endl;

    //test space -> try to use a Polyhedron_incremnt_builder_3
    //http://doc.cgal.org/latest/Polyhedron/classCGAL_1_1Polyhedron__incremental__builder__3.html

    //I want to do the extrude code here but what would be the best way?

    CGAL_postcondition( m_mesh.is_valid());
}

It would be awesome if somebody can point me to the correct method or give me a idea.

Thx and bye Darian

DarianAnjuhal DarianAnjuhal · Accepted Answer · 2016-03-17T14:31:52

I almost forgot to answer my question.

I solved this issue by generating a new cube. Move the vertices to the correct position and join the new cube to the current mesh with the cgal method join_loop().

Code:

Face_handle TreeGenerator::extrude(Face_handle face, float value) 
{

CGAL_precondition( m_mesh.is_valid());

//calculate face normal vector direction
Halfedge_handle halfEdge1 = face->halfedge();
Halfedge_handle halfEdge2 = halfEdge1->next();
Halfedge_handle halfEdge3 = halfEdge2->next();
Halfedge_handle halfEdge4 = halfEdge3->next();

Vector3 normal_vector = getNormalVector(face, value);

std::cout << "Normal Vector: " << normal_vector << std::endl;

Point point1 = halfEdge1->vertex()->point() + normal_vector;
Point point2 = halfEdge2->vertex()->point() + normal_vector;
Point point3 = halfEdge3->vertex()->point() + normal_vector;
Point point4 = halfEdge4->vertex()->point() + normal_vector;

Face_handle newCubeFace = make_cube_3(m_mesh, 1.0f);
Face_handle newOppositeFace = newCubeFace->halfedge()->opposite()->next()->next()->opposite()->face();

//edges to the top points
Halfedge_handle newHalfEdge1 = newCubeFace->halfedge();
Halfedge_handle newHalfEdge2 = newHalfEdge1->next();
Halfedge_handle newHalfEdge3 = newHalfEdge2->next();
Halfedge_handle newHalfEdge4 = newHalfEdge3->next();

//edges to the bottom points
Halfedge_handle newHalfEdgeBottom1 = newHalfEdge2->opposite()->next();
Halfedge_handle newHalfEdgeBottom2 = newHalfEdge3->opposite()->next();
Halfedge_handle newHalfEdgeBottom3 = newHalfEdge4->opposite()->next();
Halfedge_handle newHalfEdgeBottom4 = newHalfEdge1->opposite()->next();

//set new positions
newHalfEdge1->vertex()->point() = point1;
newHalfEdge2->vertex()->point() = point2;
newHalfEdge3->vertex()->point() = point3;
newHalfEdge4->vertex()->point() = point4;

newHalfEdgeBottom1->vertex()->point() = halfEdge1->vertex()->point();
newHalfEdgeBottom2->vertex()->point() = halfEdge2->vertex()->point();
newHalfEdgeBottom3->vertex()->point() = halfEdge3->vertex()->point();
newHalfEdgeBottom4->vertex()->point() = halfEdge4->vertex()->point();

m_mesh.join_loop(halfEdge1, newOppositeFace->halfedge());

CGAL_postcondition( m_mesh.is_valid());

return newCubeFace;
}

Maybe it helps somebody.

Thx and bye Darian

CGAL Lib extrude polygon

1 Answers