From 2d2507b3644ee9b232cfb4c3a931bb951d01ffdf Mon Sep 17 00:00:00 2001
From: Giles Bathgate <giles.bathgate@gmail.com>
Date: Mon, 3 Jan 2022 16:01:29 +0000
Subject: [PATCH] Implement append operation in Nef_polyhedron_3

---
 Nef_3/include/CGAL/Nef_3/Append_volumes.h | 42 +++++++++++++++++++++++
 Nef_3/include/CGAL/Nef_polyhedron_3.h     | 11 ++++++
 2 files changed, 53 insertions(+)
 create mode 100644 Nef_3/include/CGAL/Nef_3/Append_volumes.h

diff --git a/Nef_3/include/CGAL/Nef_3/Append_volumes.h b/Nef_3/include/CGAL/Nef_3/Append_volumes.h
new file mode 100644
index 00000000000..69a292fa7c2
--- /dev/null
+++ b/Nef_3/include/CGAL/Nef_3/Append_volumes.h
@@ -0,0 +1,42 @@
+// Copyright (c) 2022  Max-Planck-Institute Saarbruecken (Germany).
+// All rights reserved.
+//
+// This file is part of CGAL (www.cgal.org).
+//
+// $URL$
+// $Id$
+// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
+//
+//
+
+#ifndef CGAL_NEF3_APPEND_VOLUMES_H
+#define CGAL_NEF3_APPEND_VOLUMES_H
+
+#include <CGAL/license/Nef_3.h>
+
+
+#include <CGAL/Nef_polyhedron_3.h>
+#include <CGAL/Nef_3/shell_to_nef_3.h>
+
+namespace CGAL {
+
+template<typename Nef_3>
+class Append_volumes : public Modifier_base<typename Nef_3::SNC_structure>
+{
+  typedef typename Nef_3::SNC_structure SNC_structure;
+  typedef typename Nef_3::Shell_entry_const_iterator Shell_entry_const_iterator;
+public:
+   Append_volumes (const Nef_3& n) : nef(n) {}
+
+   void operator()(SNC_structure& snc)
+   {
+     Shell_entry_const_iterator si;
+     CGAL_forall_shells_of(si,nef.volumes_begin())
+       CGAL::shell_to_nef_3(nef,si,snc);
+   }
+private:
+  const Nef_3& nef;
+};
+
+} //namespace CGAL
+#endif // CGAL_NEF3_APPEND_VOLUMES_H
diff --git a/Nef_3/include/CGAL/Nef_polyhedron_3.h b/Nef_3/include/CGAL/Nef_polyhedron_3.h
index 74bb56ba885..48c23dcc085 100644
--- a/Nef_3/include/CGAL/Nef_polyhedron_3.h
+++ b/Nef_3/include/CGAL/Nef_polyhedron_3.h
@@ -43,6 +43,7 @@
 #include <CGAL/Nef_polyhedron_S2.h>
 #include <CGAL/Modifier_base.h>
 #include <CGAL/Nef_3/Mark_bounded_volumes.h>
+#include <CGAL/Nef_3/Append_volumes.h>
 
 #include <CGAL/IO/Verbose_ostream.h>
 #include <CGAL/Nef_3/polygon_mesh_to_nef_3.h>
@@ -1441,6 +1442,16 @@ protected:
     return res;
   }
 
+  Nef_polyhedron_3<Kernel,Items, Mark>
+  append(const Nef_polyhedron_3<Kernel,Items, Mark>& N1)
+  /*{\Mop returns |\Mvar| with N1 appended }*/ {
+    CGAL_NEF_TRACEN(" append between nef3 "<<&*this<<" and "<<&N1);
+    Append_volumes<Nef_polyhedron_3> appender(N1);
+    delegate(appender,true,false);
+    mark_bounded_volumes();
+    return *this;
+  }
+
   Nef_polyhedron_3<Kernel,Items, Mark>
   difference(const Nef_polyhedron_3<Kernel,Items, Mark>& N1) const
   /*{\Mop returns |\Mvar| $-$ |N1|. }*/ {