Only add one vertex per edge

QTProject/subdivision.cpp

@@ -113,6 +113,21 @@ void insert_edge(QMap<Triangle, QVector<Triangle::Edge>> &opposite_edges, const
     opposite_edges.insert(triangle, edges);
 }
 
+struct Edge {
+    unsigned int a;
+    unsigned int b;
+
+    friend bool operator<(const Edge &l, const Edge &r) {
+        if (l.a < r.a) {
+            return true;
+        } else if (l.a > r.a) {
+            return false;
+        } else {
+            return l.b < r.b;
+        }
+    }
+};
+
 /**
  * @brief Subdivision::precomputeTables
  * @param mesh
@@ -147,6 +162,9 @@ Subdivision::Tables Subdivision::precomputeTables(Input input) {
     // First the edge shared with the triangles uv edge, then vw and wu.
     QMap<Triangle, QVector<Triangle::Edge>> opposite_edges;
 
+    // Maps edges to the index of the new vertex added on that edge. The keys are the indices of the two vertices defining the edge and must be in the order uv, vw or uw.
+    QMap<Edge, unsigned int> edge_indices;
+
     unsigned int edge_index = vb.length();//offset in new index buffer for edge vertices
     for (int i = 0; i < triangles.length(); i++){
         //schaue alle dreiecke an
@@ -175,24 +193,55 @@ Subdivision::Tables Subdivision::precomputeTables(Input input) {
         // indices of the three vertices added to the edges of this triangle
         unsigned int uv, vw, wu;
 
-        uv = edge_index++;
-        vw = edge_index++;
-        wu = edge_index++;
+        Edge edge;
 
-        tables.edge_indices.push_back(triangle.u_idx());
-        tables.edge_indices.push_back(triangle.v_idx());
-        tables.edge_indices.push_back(triangle.w_idx());
-        tables.edge_indices.push_back(opposite[0].c);
+        edge = { triangle.u_idx(), triangle.v_idx() };
+        if (edge_indices.contains(edge)) {
+            uv = edge_indices.value(edge);
+        } else {
+            uv = edge_index++;
+            edge_indices.insert(edge, uv);
+
+            edge = { opposite[0].a, opposite[0].b };
+            edge_indices.insert(edge, uv);
 
-        tables.edge_indices.push_back(triangle.v_idx());
-        tables.edge_indices.push_back(triangle.w_idx());
-        tables.edge_indices.push_back(triangle.u_idx());
-        tables.edge_indices.push_back(opposite[1].c);
+            tables.edge_indices.push_back(triangle.u_idx());
+            tables.edge_indices.push_back(triangle.v_idx());
+            tables.edge_indices.push_back(triangle.w_idx());
+            tables.edge_indices.push_back(opposite[0].c);
+        }
 
-        tables.edge_indices.push_back(triangle.w_idx());
-        tables.edge_indices.push_back(triangle.u_idx());
-        tables.edge_indices.push_back(triangle.v_idx());
-        tables.edge_indices.push_back(opposite[2].c);
+        edge = { triangle.v_idx(), triangle.w_idx() };
+        if (edge_indices.contains(edge)) {
+            vw = edge_indices.value(edge);
+        } else {
+            vw = edge_index++;
+            edge_indices.insert(edge, vw);
+
+            edge = { opposite[1].a, opposite[1].b };
+            edge_indices.insert(edge, vw);
+
+            tables.edge_indices.push_back(triangle.v_idx());
+            tables.edge_indices.push_back(triangle.w_idx());
+            tables.edge_indices.push_back(triangle.u_idx());
+            tables.edge_indices.push_back(opposite[1].c);
+        }
+
+        edge = { triangle.w_idx(), triangle.u_idx() };
+        if (edge_indices.contains(edge)) {
+            wu = edge_indices.value(edge);
+        } else {
+            wu = edge_index++;
+            edge_indices.insert(edge, wu);
+
+            edge = { opposite[2].a, opposite[2].b };
+            edge_indices.insert(edge, wu);
+
+            tables.edge_indices.push_back(triangle.w_idx());
+            tables.edge_indices.push_back(triangle.u_idx());
+            tables.edge_indices.push_back(triangle.v_idx());
+            tables.edge_indices.push_back(opposite[2].c);
+        }
 
         //add indices to new index buffer
         tables.index_buffer.push_back(triangle.u_idx());