CGAL users discussion list

[gilles <>]

Amy Tabb a écrit :
> Hello,
>
> I recently started using CGAL (but have been using OpenGL for a while) 
> and here's some functions that I use.  I tried to simplify my 
> functions so that you could use them as a template or incorporate the 
> CGAL-specific information easily into your work.  Good luck.
>
>
> Best, Amy
>
>
> The first function draws the points and edges of the polyhedron, 
> assuming that somewhere you have something resembling these typedefs:
>
> typedef Kernel::Point_3                                      Point;
>
>
> typedef CGAL::Polyhedron_3<Kernel, My_items, 
> CGAL::HalfedgeDS_default>  Polyhedron;
> typedef CGAL::Tag_true Supports_removal;
>
> typedef Polyhedron::Vertex                                   Vertex;
> typedef Polyhedron::Vertex_iterator                          
> Vertex_iterator;
> typedef Polyhedron::Halfedge_iterator                        
> Halfedge_iterator;
> typedef Polyhedron::Halfedge_handle                          
> Halfedge_handle;
> typedef Polyhedron::Edge_iterator                            
> Edge_iterator;
>
> ***************************************
> The function:
>
>
> void drawPolyhedronPointsAndLines(Polyhedron P){
>  
>      Facet_iterator f;
>    Vertex_iterator v;
>    Edge_iterator eit;
>    Halfedge_handle h_handle;
>    double x, y, z;
>
>    // this just walks through all of your vertices .... the 3D space 
> data is in vertex_handle->point().x(), .y(), .z() (if a 3D point 
> versus 2D)
>    glBegin(GL_POINTS);
>    for (v = P.vertices_begin(); v != P.vertices_end(); ++v){
>       cout << "Vertex " << v->point() << endl;
>       x = v->point().x();
>       y = v->point().y();
>       z = v->point().z();
>       glVertex3f(x, y, z);
>    }
>    glEnd();
>
>    Point_3_exact pv;
>
>    // then I walk through the edges (not halfedges, though you could 
> do this too) of the Polyhedron.
>      for (eit = P.edges_begin(); eit != P.edges_end(); ++eit){
>                h_handle = eit;
>                     glColor3f(r, g, b);
>
>                glBegin( GL_LINES);
>                pv = h_handle->opposite()->vertex()->point();
>                glVertex3f(pv.x(), pv.y(), pv.z());
>                pv = h_handle->vertex()->point();
>                glVertex3f(pv.x(), pv.y(), pv.z());
>                glEnd();
>    }
> }
>
>
> **********************************************************************
> Depending on your goal, you may want to walk around the edges of one 
> facet so that you can create the faces of the polyhedron.
> I'll include that here as well.
>
>
> Again, the function below assumes another typedef:
> typedef Polyhedron::Halfedge_around_facet_circulator         
> HF_circulator;
>
>
> void drawPolyhedronFacets(Polyhedron P){
>
>    Facet_iterator f;
>    Vertex_iterator v;
>    HF_circulator j;
>    double x, y, z;
>
>    Point pv
>    Point p1; Point p2;
>  
>
>   // I use the GLUtesselator because some of the faces may be concave 
> or have holes.  The documentation for that is with the OpenGL community.
>   // I didn't include all of the GLU tess functions because this is 
> just an example of how to use CGAL to walk around the faces of a 
> Polyhedron.
>    GLUtesselator *tobj;
>    tobj = gluNewTess();
>    gluTessCallback(tobj, GLU_TESS_VERTEX,
>            (void(*)())glVertex3dv);
>    gluTessCallback(tobj, GLU_TESS_BEGIN,
>            (void(*)())beginCallback);
>    gluTessCallback(tobj, GLU_TESS_END,
>            endCallback);
>    gluTessCallback(tobj, GLU_TESS_ERROR,
>            (void(*)())errorCallback);
>    gluTessCallback(tobj, GLU_TESS_COMBINE,
>            (void(*)())combineCallback);
>    // End GLUtesselator declarations
>
>    list<GLdouble*> coords_list;
>    GLdouble* arr_ptr;
>
>    // prepare to tesselate for facets...
>    for(f = P.facets_begin(); f != P.facets_end(); f++){    // create 
> new center vertices
>           j = f->facet_begin();
>
>       // normal computation - there are many ways to do this -
>       // I store the normal of each facet through the use of
>       // My_items (extended dcel records - see above in the typedef 
> declaration of Polyhedron,
>       // but this is another CGAL issue that if interested you'll have 
> to read up on),
>       // though you could compute it as you walk around the facet.
>        n = f->normal/sqrt(f->normal.squared_length());
>        cout << " n " << n << endl;
>
>        // for GLUtesselation               gluTessBeginPolygon(tobj, 
> NULL);
>        gluTessBeginContour(tobj);
>        // for GLUtesselation end          glNormal3f(n.x(),n.y(),n.z());
>        do {
>            cout << j->vertex()->point() << endl;
>            pv = j->vertex()->point();
>                    x = pv.x();
>            y = pv.y();
>            z = pv.z();
>                     // GLU tess specific actions start
>            arr_ptr = new GLdouble[3];
>            arr_ptr[0] = x;
>            arr_ptr[1] = y;
>            arr_ptr[2] = z;
>            gluTessVertex(tobj, arr_ptr, arr_ptr);
>            coords_list.push_back(arr_ptr);
>            // end GLUtess specific actions
>        } while ( ++j != f->facet_begin());
>     
>        gluTessEndContour(tobj);
>        gluTessEndPolygon(tobj);
>
>    }
>
>
>    // more gluTess specific actions
>    gluDeleteTess(tobj);
>    while (coords_list.size() > 0){
>        arr_ptr = coords_list.front(); coords_list.pop_front();
>        delete arr_ptr;
>    }
>
> }
>
> Laurent Rineau (GeometryFactory) wrote:
> > Le mardi 29 septembre 2009 20:55:05, 
> >
> >  a écrit :
> >  
> > > Hello,
> > >
> > > I'm a (very) beginner and I do need help (to start) !!!
> > >
> > > I'm wondering how can get  I from HDS (it's a Polyhedron) the proper 
> > > vertex
> > >  to use afterwards
> > > for rendering in OpenGL.
> > >
> > > For example, I want to convert HDS into triplet of point (forming a
> > >  triangle)
> > >
> > > -> Can anybody helps ?
> > >
> > > That you so much for this little "coup de pouce"
> > >     
> >
> > You should have a look at the source code of the polyhedron demo, in 
> > demo/Polyhedron/, with CGAL>=3.4.
> >
> > In CGAL-3.5, see the "draw" methods in Scene_polyhedron_item.cpp, and 
> > Scene_nef_polyhedron_item.cpp, which use code from 
> > demo/Polyhedron/include/CGAL/gl_render.h and 
> > demo/Polyhedron/Scene_nef_rendering.cpp.
> >
> > The nef case shows the non-triangular case, which is far more 
> > complicated, as one has to triangulate each face of the polyhedron.
> >
> > I hope that can help.
> >
> >   
Hello Amy,

Thank you very much : Life will be a bit better for me now ;)

Gilles