From 9b99d0e754dbe8d8114c8f6e45ef7852ee59b9ad Mon Sep 17 00:00:00 2001
From: Jane Tournois <jane.tournois@geometryfactory.com>
Date: Thu, 19 Jun 2025 12:00:26 +0200
Subject: [PATCH] reorganize example and use non-manifold input

---
 .../ccdt_3_check_preconditions.cpp            | 47 ++++++++++++-------
 1 file changed, 29 insertions(+), 18 deletions(-)

diff --git a/Constrained_triangulation_3/examples/Constrained_triangulation_3/ccdt_3_check_preconditions.cpp b/Constrained_triangulation_3/examples/Constrained_triangulation_3/ccdt_3_check_preconditions.cpp
index d7bf6c54402..ca240232885 100644
--- a/Constrained_triangulation_3/examples/Constrained_triangulation_3/ccdt_3_check_preconditions.cpp
+++ b/Constrained_triangulation_3/examples/Constrained_triangulation_3/ccdt_3_check_preconditions.cpp
@@ -10,6 +10,7 @@
 
 #include <CGAL/draw_constrained_triangulation_3.h>
 #include <CGAL/IO/polygon_mesh_io.h>
+#include <CGAL/IO/polygon_soup_io.h>
 #include <CGAL/IO/write_MEDIT.h>
 
 #include <vector>
@@ -45,38 +46,47 @@ bool verify_preconditions_soup(const PointRange& points, const PolygonRange& pol
 int main(int argc, char* argv[])
 {
   const auto filename = (argc > 1) ? argv[1]
-                       : CGAL::data_file_path("meshes/mpi_and_sphere.off");
+                       : CGAL::data_file_path("meshes/cubes.off");
 
-  CGAL::Surface_mesh<K::Point_3> mesh;
-  if(!CGAL::IO::read_polygon_mesh(filename, mesh))
+  // Read polygon soup
+  using Points = std::vector<Point>;
+  using PLC_face = std::vector<std::size_t>;
+  using PLC_faces = std::vector<PLC_face>;
+  Points points;
+  PLC_faces faces;
+  if(!CGAL::IO::read_polygon_soup(filename, points, faces))
   {
     std::cerr << "Error: cannot read file " << filename << std::endl;
     return EXIT_FAILURE;
   }
 
-  std::cout << "Number of facets in " << filename << ": "
-            << mesh.number_of_faces() << "\n";
+  // When possible, convert polygon soup to polygon mesh
+  CGAL::Surface_mesh<K::Point_3> mesh;
+  if(CGAL::Polygon_mesh_processing::is_polygon_soup_a_polygon_mesh(faces))
+  {
+    CGAL::Polygon_mesh_processing::polygon_soup_to_polygon_mesh(points, faces, mesh);
+    std::cout << "Number of facets in " << filename << ": " << mesh.number_of_faces() << "\n";
+  }
 
   // Verify preconditions for the mesh input
-  if(!verify_preconditions_mesh(mesh))
+  const bool is_polygon_mesh = !mesh.is_empty();
+  if(is_polygon_mesh && !verify_preconditions_mesh(mesh))
   {
-    // If the mesh is not a valid triangle mesh or has self-intersections,
-    // convert it to a polygon soup and verify the preconditions for the soup
-    std::vector<K::Point_3> points;
-    std::vector<std::vector<std::size_t>> polygons;
-    CGAL::Polygon_mesh_processing::polygon_mesh_to_polygon_soup(mesh, points, polygons);
-    if(!verify_preconditions_soup(points, polygons))
-    {
-      std::cerr << "Error: input polygon soup is not a valid input for CCDT_3\n";
-      return EXIT_FAILURE;
-    }
-
     std::cerr << "Error: input mesh is not a valid input for CCDT_3\n";
     return EXIT_FAILURE;
   }
+  else if(!verify_preconditions_soup(points, faces))
+  {
+    std::cerr << "Error: input polygon soup is not a valid input for CCDT_3\n";
+    return EXIT_FAILURE;
+  }
 
-  auto ccdt = CGAL::make_conforming_constrained_Delaunay_triangulation_3(mesh);
+  // Build conforming constrained Delaunay triangulation
+  auto ccdt = is_polygon_mesh
+    ? CGAL::make_conforming_constrained_Delaunay_triangulation_3(mesh)
+    : CGAL::make_conforming_constrained_Delaunay_triangulation_3(points, faces);
 
+  // Print mesh details
   if(ccdt.number_of_constrained_facets() == 0)
   {
     std::cerr << "Error: no constrained facets in the CDT.\n";
@@ -87,6 +97,7 @@ int main(int argc, char* argv[])
   std::cout << "Number of constrained facets in the CDT: "
             << ccdt.number_of_constrained_facets() << '\n';
 
+  // Output
   std::ofstream ofs(argc > 2 ? argv[2] : "out.mesh");
   ofs.precision(17);
   CGAL::IO::write_MEDIT(ofs, ccdt);