From 363df4c42432ed2a3433a9c1b3d75a4228d84114 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mael=20Rouxel-Labb=C3=A9?=
 <mael.rouxel.labbe@geometryfactory.com>
Date: Wed, 19 Jun 2024 16:00:23 +0200
Subject: [PATCH] Add an operation to add triangle faces from vertex selection

---
 Lab/demo/Lab/Plugins/PMP/Selection_plugin.cpp | 20 ++++++-
 .../Lab/Scene_polyhedron_selection_item.h     | 60 +++++++++++++++++++
 2 files changed, 79 insertions(+), 1 deletion(-)

diff --git a/Lab/demo/Lab/Plugins/PMP/Selection_plugin.cpp b/Lab/demo/Lab/Plugins/PMP/Selection_plugin.cpp
index a3424d44163..eaf633c7cf5 100644
--- a/Lab/demo/Lab/Plugins/PMP/Selection_plugin.cpp
+++ b/Lab/demo/Lab/Plugins/PMP/Selection_plugin.cpp
@@ -236,7 +236,8 @@ public:
       "Select Edges Incident to Selected Facets"        ,
       "Select Vertices Incident to Selected Edges"         ,
       "Select Edges on the Boundary of Regions of Selected Facets",
-      "Select Vertices of Selected Facets"
+      "Select Vertices of Selected Facets",
+      "Add Triangle Face from Selected Vertices"
     };
 
     operations_map[operations_strings[0]] = 0;
@@ -249,6 +250,7 @@ public:
     operations_map[operations_strings[7]] = 7;
     operations_map[operations_strings[8]] = 8;
     operations_map[operations_strings[9]] = 9;
+    operations_map[operations_strings[10]] = 10;
   }
   virtual void closure() override
   {
@@ -904,6 +906,20 @@ public Q_SLOTS:
       selection_item->itemChanged();
       break;
     }
+    //Add Triangle Face to FaceGraph
+    case 10:
+    {
+      Scene_polyhedron_selection_item* selection_item = getSelectedItem<Scene_polyhedron_selection_item>();
+      if(!selection_item) {
+        print_message("Error: there is no selected polyhedron selection item!");
+        return;
+      }
+      if(selection_item->selected_vertices.size() != 3) {
+        print_message("Error: there is not exactly 3 vertices selected!");
+        return;
+      }
+      selection_item->add_facet_from_selected_vertices();
+    }
     default :
       break;
     }
@@ -1173,6 +1189,8 @@ void filter_operations()
   if(has_v)
   {
     ui_widget.operationsBox->addItem(operations_strings[0]);
+    if(selection_item->selected_vertices.size() == 3)
+      ui_widget.operationsBox->addItem(operations_strings[10]);
   }
   if(has_e)
   {
diff --git a/Lab/demo/Lab/Scene_polyhedron_selection_item.h b/Lab/demo/Lab/Scene_polyhedron_selection_item.h
index c74837396e4..7a2cc2f16bd 100644
--- a/Lab/demo/Lab/Scene_polyhedron_selection_item.h
+++ b/Lab/demo/Lab/Scene_polyhedron_selection_item.h
@@ -781,6 +781,66 @@ public:
     return num_vertices(*out) > 0;
   }
 
+  fg_face_descriptor add_facet_from_selected_vertices()
+  {
+    fg_face_descriptor null_face = boost::graph_traits<Face_graph>::null_face();
+
+    if(selected_vertices.size() != 3) // NYI
+      return null_face;
+
+    // since the selected vertices are a set, we lost order in the process,
+    // so find back the correct orientation
+    std::array<fg_vertex_descriptor, 3> vs;
+    for(std::size_t i=0; i<3; ++i)
+      vs[i] = *(std::next(selected_vertices.begin(), i));
+
+    int pos_counter = 0, neg_counter = 0;
+    for(std::size_t i=0; i<3; ++i)
+    {
+      auto res = halfedge(vs[i], vs[(i+1)%3], *polyhedron());
+      if(res.second && !is_border(res.first, *polyhedron()))
+      {
+        // the halfedge 'vs[i] - vs[i+1]' already exists in the graph and is not border,
+        // so vote for orienting the facet the other way
+        ++neg_counter;
+      }
+
+      res = halfedge(vs[(i+1)%3], vs[i], *polyhedron());
+      if(res.second && !is_border(res.first, *polyhedron()))
+      {
+        // the halfedge 'vs[i+1] - vs[i]' already exists in the graph and is not border,
+        // so vote for keeping the current orientationorientation
+        ++pos_counter;
+      }
+    }
+
+    if(pos_counter > 0 && neg_counter > 0)
+    {
+      // disagreement, can't insert the face (@todo duplicate and insert?)
+      std::cerr << "Failed to find a valid orientation (" << pos_counter << " VS " << neg_counter << ")!" << std::endl;
+      return null_face;
+    }
+    else if(neg_counter > 0)
+    {
+      std::swap(vs[0], vs[1]);
+    }
+
+    fg_face_descriptor new_f = CGAL::Euler::add_face(vs, *polyhedron());
+    const bool successful_insertion = (new_f != null_face);
+    if(successful_insertion)
+    {
+      selected_vertices.clear();
+      invalidateOpenGLBuffers();
+      changed_with_poly_item();
+    }
+    else
+    {
+      std::cerr << "Failed to insert face!" << std::endl;
+    }
+
+    return new_f;
+  }
+
   void select_sharp_edges(const double angle)
   {
     CGAL::detect_sharp_edges(polyhedron(), angle);