cairo_move_to(context_resource, _x[0], _y[0]);
for(int n = 0; n < _nb_vertices; n++) {
cairo_line_to(context_resource, _x[n], _y[n]);
cairo_move_to(context_resource, _x[0], _y[0]);
for(int n = 0; n < _nb_vertices; n++) {
cairo_line_to(context_resource, _x[n], _y[n]);