From 4bd1aa4d9a2d5e40954f5d0b8e3e8a9f19c32add Mon Sep 17 00:00:00 2001
From: root <root>
Date: Sun, 23 May 2021 00:14:20 -0500
Subject: [PATCH] add checking watertight feature

---
 meshing/TriMesh.cpp | 40 ++++++++++++++++++++++++++++++++++++++++
 meshing/TriMesh.h   |  2 ++
 2 files changed, 42 insertions(+)

diff --git a/meshing/TriMesh.cpp b/meshing/TriMesh.cpp
index 3df2f66e..38caa318 100644
--- a/meshing/TriMesh.cpp
+++ b/meshing/TriMesh.cpp
@@ -3,12 +3,14 @@
 #include <locale.h>
 #include <iostream>
 #include <utils/stringutils.h>
+#include <utils/IntPair.h>
 #include <math3d/geometry3d.h>
 #include <math3d/misc.h>
 #include <GLdraw/GL.h>
 #include <GLdraw/drawextra.h>
 #include <fstream>
 #include <algorithm>
+#include <map>
 #include <errors.h>
 namespace Meshing {
 
@@ -98,6 +100,44 @@ bool TriMesh::IsValid() const
   return res;
 }
 
+bool TriMesh::IsWatertight() const
+{
+  size_t numedges = tris.size()*3;
+  std::map<IntPair, int> edgegroup = {};
+  for(size_t i=0;i<tris.size();i++) {
+    for(int j=0;j<3;j++) {
+      int v1, v2;
+      GetEdge(i,j,v1,v2);
+      if(v1>v2) {
+        std::swap(v1,v2);
+      }
+      IntPair edge(v1,v2);
+
+      std::map<IntPair, int>::iterator it;
+      it = edgegroup.find(edge);
+      if(it==edgegroup.end()) {
+        edgegroup.insert(std::make_pair(edge,1));
+      } else {
+        it->second++;
+      }
+    }
+  }
+
+  size_t numsharededges = 0;
+  std::map<IntPair, int>::iterator it;
+  for(it=edgegroup.begin();it!=edgegroup.end();it++) {
+    if(it->second==2) {
+      numsharededges++;
+    }
+  }
+
+  if(numsharededges*2==numedges) {
+    return true;
+  } else {
+    return false;
+  }
+}
+
 void TriMesh::GetAABB(Vector3& bmin, Vector3& bmax) const
 {
   bmin.set(Inf);
diff --git a/meshing/TriMesh.h b/meshing/TriMesh.h
index a1474314..c9b7fd9a 100644
--- a/meshing/TriMesh.h
+++ b/meshing/TriMesh.h
@@ -65,6 +65,8 @@ struct TriMesh
   ///@name Calculations
   //@{
   bool IsValid() const;
+  //returns true if every edge of a triangle is shared by two triangles
+  bool IsWatertight() const;
   void GetAABB(Vector3& bmin, Vector3& bmax) const;
   //returns the closest/collided triangle
   int ClosestPoint(const Vector3& pt,Vector3& cp) const;