Polygon_mesh_processing/triangulate_polyline_example.cpp

#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>

#include <CGAL/Polygon_mesh_processing/triangulate_hole.h>
#include <CGAL/utility.h>

#include <vector>
#include <iterator>
#include <cassert>

typedef CGAL::Exact_predicates_inexact_constructions_kernel Kernel;
typedef Kernel::Point_3                                     Point;

int main()
{
  std::vector<Point> polyline;
  polyline.push_back(Point( 1.,0.,0.));
  polyline.push_back(Point( 0.,1.,0.));
  polyline.push_back(Point(-1.,0.,0.));
  polyline.push_back(Point( 1.,1.,0.));
  // repeating first point (i.e. polyline.push_back(Point(1.,0.,0.)) ) is optional

  // any type, having Type(int, int, int) constructor available, can be used to hold output triangles
  typedef CGAL::Triple<int, int, int> Triangle_int;
  std::vector<Triangle_int> patch;
  patch.reserve(polyline.size() -2); // there will be exactly n-2 triangles in the patch

  CGAL::Polygon_mesh_processing::triangulate_hole_polyline(
          polyline,
          std::back_inserter(patch));

  for(std::size_t i = 0; i < patch.size(); ++i)
  {
    std::cout << "Triangle " << i << ": "
      << patch[i].first << " " << patch[i].second << " " << patch[i].third
      << std::endl;
  }

  // note that no degenerate triangles are generated in the patch
  std::vector<Point> polyline_collinear;
  polyline_collinear.push_back(Point(1.,0.,0.));
  polyline_collinear.push_back(Point(2.,0.,0.));
  polyline_collinear.push_back(Point(3.,0.,0.));
  polyline_collinear.push_back(Point(4.,0.,0.));

  std::vector<Triangle_int> patch_will_be_empty;
  CGAL::Polygon_mesh_processing::triangulate_hole_polyline(polyline_collinear,
                                                           back_inserter(patch_will_be_empty));
  assert(patch_will_be_empty.empty());

  return 0;
}