CGAL users discussion list

[Olivier Devillers <>]

karine hins-mallet a écrit :
> Hi,
>
> In the Polygon Delaunay Graph demo, there is a Drawing function which 
> draws the Voronoï cells of the diagram. This is the code of the function:
>
> typename T::Finite_edges_iterator eit = sdg.finite_edges_begin();
>
> for (; eit != sdg.finite_edges_end(); ++eit) {
>
> if ( eit->first->vertex( sdg.cw(eit->second) )->info() !=
>
> eit->first->vertex( sdg.ccw(eit->second) )->info() ) {
>
> {sdg.draw_dual_edge(*eit, widget);}
>
> In that code, I understand that a test is performed on all the edges 
> of the Delaunay graph, and that if the test succeeds then the dual 
> Voronoï edge is drawn. But what I don’t understand is what is done (or 
> checked) in the “if” test. Can someone explain it to me?
it looks like

*eit is an edge (that is a pair of a face [triangle] and an index [to 
choose which edge in the triangle is the required edge])

the vertices of the triangulation have an extra information,
you draw only the Voronoi edges which are the dual of a Delaunay edge 
that links two vertices with different extra information.