From b67b389d63f686ba2932a7abdcd8eb8a3d0cf34b Mon Sep 17 00:00:00 2001
From: Daniel Funke <daniel.funke@kit.edu>
Date: Mon, 16 Oct 2023 10:40:00 +0200
Subject: [PATCH] move to kNNG

---
 .../demo/CGAL_ipelets/lua/libCGAL_nng.lua     |  4 ++--
 CGAL_ipelets/demo/CGAL_ipelets/nng.cpp        | 23 +++++++++++++++----
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/CGAL_ipelets/demo/CGAL_ipelets/lua/libCGAL_nng.lua b/CGAL_ipelets/demo/CGAL_ipelets/lua/libCGAL_nng.lua
index fc1f4679178..f9207b9b562 100644
--- a/CGAL_ipelets/demo/CGAL_ipelets/lua/libCGAL_nng.lua
+++ b/CGAL_ipelets/demo/CGAL_ipelets/lua/libCGAL_nng.lua
@@ -2,7 +2,7 @@
 -- CGAL NNG ipelet description
 ----------------------------------------------------------------------
 
-label = "Nearest-neighbor graph"
+label = "k-nearest-neighbor graph"
 
 about = [[
 This ipelet is part of the CGAL_ipelet package. See www.cgal.org.
@@ -17,7 +17,7 @@ function run(model, num)
 end
 
 methods = {
-  { label="NNG" },
+  { label="kNNG" },
   { label="Help" },
 }
 
diff --git a/CGAL_ipelets/demo/CGAL_ipelets/nng.cpp b/CGAL_ipelets/demo/CGAL_ipelets/nng.cpp
index be43dc45fd7..896d74f138a 100644
--- a/CGAL_ipelets/demo/CGAL_ipelets/nng.cpp
+++ b/CGAL_ipelets/demo/CGAL_ipelets/nng.cpp
@@ -11,17 +11,19 @@
 #include <CGAL/nearest_neighbor_delaunay_2.h>
 #include <CGAL/CGAL_Ipelet_base.h>
 
+#include <boost/format.hpp>
+
 namespace CGAL_nng {
 
 typedef CGAL::Exact_predicates_inexact_constructions_kernel Kernel;
 typedef CGAL::Delaunay_triangulation_2<Kernel>              Triangulation;
 
 const std::string Slab[] = {
-  "NNG", "Help"
+  "kNNG", "Help"
 };
 
 const std::string Hmsg[] = {
-  "Draw the nearest-neighbor graph of a set of points"
+  "Draw the k-nearest-neighbor graph of a set of points"
 };
 
 struct nngIpelet
@@ -45,15 +47,28 @@ void nngIpelet::protected_run(int /*fn*/)
     return;
   }
 
+  int ret_val;
+  int kNeighbors=1;
+
+  boost::tie(ret_val,kNeighbors)=request_value_from_user<int>((boost::format("Number of nearest neighbors (default : k=%1%)") % kNeighbors).str() );
+  if (ret_val == -1) return;
+  if (ret_val == 0) kNeighbors=1;
+
   Triangulation t(pt_list.begin(), pt_list.end());
 
   for(auto v = t.finite_vertices_begin();
        v != t.finite_vertices_end();
        ++v){
 
-    auto nn = CGAL::nearest_neighbor(t, v);
-    draw_in_ipe(Kernel::Segment_2(v->point(), nn->point()));
+    std::vector<Triangulation::Vertex_handle> kNN;
+    CGAL::nearest_neighbors(t, v, kNeighbors+1, std::back_inserter(kNN)); // +1 as v itself counts as its nearest neigbhor for CGAL::nearest_neighbors
+
+    for(const auto & nn : kNN) {
+      draw_in_ipe(Kernel::Segment_2(v->point(), nn->point()));
+    }
   }
+
+  group_selected_objects_();
 }
 }