From 9fe28f84dfa1c7205fff1698be7466cd9a456b63 Mon Sep 17 00:00:00 2001
From: Jeremy HU <huxingyi@msn.com>
Date: Tue, 1 Nov 2022 08:37:03 +1100
Subject: [PATCH] Implement mesh state combine

---
 dust3d/mesh/mesh_state.cc | 55 +++++++++++++++++++++++++++++++++++++++
 dust3d/mesh/mesh_state.h  |  3 +++
 2 files changed, 58 insertions(+)

diff --git a/dust3d/mesh/mesh_state.cc b/dust3d/mesh/mesh_state.cc
index 24e0ec2b..2e77df1a 100644
--- a/dust3d/mesh/mesh_state.cc
+++ b/dust3d/mesh/mesh_state.cc
@@ -20,6 +20,7 @@
  *  SOFTWARE.
  */
 
+#include <dust3d/mesh/mesh_recombiner.h>
 #include <dust3d/mesh/mesh_state.h>
 
 namespace dust3d {
@@ -30,4 +31,58 @@ void MeshState::fetch(std::vector<Vector3>& vertices, std::vector<std::vector<si
         mesh->fetch(vertices, faces);
 }
 
+std::unique_ptr<MeshState> MeshState::combine(const MeshState& first, const MeshState& second,
+    MeshCombiner::Method method)
+{
+    if (first.mesh->isNull() || second.mesh->isNull())
+        return nullptr;
+    std::vector<std::pair<MeshCombiner::Source, size_t>> combinedVerticesSources;
+    auto newMesh = std::unique_ptr<MeshCombiner::Mesh>(MeshCombiner::combine(*first.mesh,
+        *second.mesh,
+        method,
+        &combinedVerticesSources));
+    if (nullptr == newMesh)
+        return nullptr;
+    if (!newMesh->isNull()) {
+        MeshRecombiner recombiner;
+        std::vector<Vector3> combinedVertices;
+        std::vector<std::vector<size_t>> combinedFaces;
+        newMesh->fetch(combinedVertices, combinedFaces);
+        recombiner.setVertices(&combinedVertices, &combinedVerticesSources);
+        recombiner.setFaces(&combinedFaces);
+        if (recombiner.recombine()) {
+            if (MeshState::isWatertight(recombiner.regeneratedFaces())) {
+                auto reMesh = std::make_unique<MeshCombiner::Mesh>(recombiner.regeneratedVertices(), recombiner.regeneratedFaces());
+                if (!reMesh->isNull()) {
+                    newMesh = std::move(reMesh);
+                }
+            }
+        }
+    }
+    if (newMesh->isNull()) {
+        return nullptr;
+    }
+    auto newMeshState = std::make_unique<MeshState>();
+    newMeshState->mesh = std::move(newMesh);
+    return newMeshState;
+}
+
+bool MeshState::isWatertight(const std::vector<std::vector<size_t>>& faces)
+{
+    std::set<std::pair<size_t, size_t>> halfEdges;
+    for (const auto& face : faces) {
+        for (size_t i = 0; i < face.size(); ++i) {
+            size_t j = (i + 1) % face.size();
+            auto insertResult = halfEdges.insert({ face[i], face[j] });
+            if (!insertResult.second)
+                return false;
+        }
+    }
+    for (const auto& it : halfEdges) {
+        if (halfEdges.find({ it.second, it.first }) == halfEdges.end())
+            return false;
+    }
+    return true;
+}
+
 }
diff --git a/dust3d/mesh/mesh_state.h b/dust3d/mesh/mesh_state.h
index ef232ef9..9a43e6a4 100644
--- a/dust3d/mesh/mesh_state.h
+++ b/dust3d/mesh/mesh_state.h
@@ -35,6 +35,9 @@ public:
     std::vector<std::map<std::array<PositionKey, 3>, std::array<Vector2, 3>>> seamTriangleUvs;
 
     void fetch(std::vector<Vector3>& vertices, std::vector<std::vector<size_t>>& faces) const;
+    static std::unique_ptr<MeshState> combine(const MeshState& first, const MeshState& second,
+        MeshCombiner::Method method);
+    static bool isWatertight(const std::vector<std::vector<size_t>>& faces);
 };
 
 }