CGAL users discussion list

[Stephane Tayeb <>]

Hi Vinicius,


 wrote:
> Hello everybody.
> I'm Vinícius and this is my first post in this list. I'm using CGAL and OpenGL
> to draw terrain as Delaunay Triangulation for my graduation project. Im trying
> to draw all the triangles using the finite_facets_iterator but when the OpenGL
> renders the terrain there are some facets that are going to a point which is
> not in the data input and this point is very far away from the others. This
> event is ocurring independent of the data input because I tested it with some
> different cases. I think that point is the infinite vertex but this is not
> possyble. Can someone give me a hand in this situation? The code is below.
>
> void Terreno::desenharTerreno(){
>
>     Finite_facets_iterator3 facetsIter;
>     Vertex_handle3 v;
>     Cell_handle3 cell;
>     Point3 p;
>     double x , y , z;
>     int i;
>
>     glColor3f(1.0 , 1.0 , 1.0);
>     glPolygonMode(GL_FRONT_AND_BACK , GL_FILL);
>
>     for(facetsIter = tri->T.finite_facets_begin(); facetsIter !=
> tri->T.finite_facets_end(); ++facetsIter){
>         cell = facetsIter->first;
>         i = facetsIter->second;
>
>         glBegin( GL_TRIANGLES );
>             for(int j = i + 1 ; j <= i + 3 ; j++){
>                 v = cell->vertex(j % 3);

I suppose you want to get vertices of the facet. Then

v = cell->vertex(j&3); // or v= cell->vertex(j%4);
(x&3 keeps the two last bits of integer x, if you are not familiar with 
this operator)

would probably be better. Actually there are 4 vertices in a cell, so 
you should take the index modulo 4 and not 3.

>                 p = v->point();
>                 x = p.cartesian(0); y = p.cartesian(1); z = p.cartesian(2);
>                 glVertex3d(x , y , z);
>             }
>         glEnd();
>     }
>
>     glColor3f(0.0 , 0.0 , 0.0);
>     glPolygonMode(GL_FRONT_AND_BACK , GL_LINE);
>
>     for(facetsIter = tri->T.finite_facets_begin(); facetsIter !=
> tri->T.finite_facets_end(); ++facetsIter){
>         cell = facetsIter->first;
>         i = facetsIter->second;
>
>         glBegin( GL_TRIANGLES );
>             for(int j = i + 1 ; j <= i + 3 ; j++){
>                 v = cell->vertex(j % 3);
>                 p = v->point();
>                 x = p.cartesian(0); y = p.cartesian(1); z = p.cartesian(2);
>                 glVertex3d(x , y , z);
>             }
>         glEnd();
>     }
> }
>
>
> Best regards,
> Vinícius da Silva.

Best,

--
Stephane Tayeb
Software engineer - INRIA Sophia Antipolis
Geometrica Project-Team