PERF: TriangleToTetMap now in O(n+m) instead of O(n*m)

Source/GeometryMappers/imstkTriangleToTetMap.cpp

@@ -58,17 +58,14 @@ TriangleToTetMap::computeTriToTetMap(std::unordered_map<int, int>& triToTetMap)
     auto tetMesh  = std::dynamic_pointer_cast<TetrahedralMesh>(getParentGeometry());
     auto surfMesh = std::dynamic_pointer_cast<SurfaceMesh>(getChildGeometry());
 
-    //std::shared_ptr<VecDataArray<double, 3>> tetVerticesPtr = tetMesh->getVertexPositions();
-    //const VecDataArray<double, 3>& tetVertices = *tetVerticesPtr;
     std::shared_ptr<VecDataArray<int, 4>> tetIndicesPtr = tetMesh->getTetrahedraIndices();
     const VecDataArray<int, 4>&           tetIndices    = *tetIndicesPtr;
 
-    //std::shared_ptr<VecDataArray<double, 3>> surfVerticesPtr = surfMesh->getVertexPositions();
-    //const VecDataArray<double, 3>& surfVertices = *surfVerticesPtr;
     std::shared_ptr<VecDataArray<int, 3>> surfIndicesPtr = surfMesh->getTriangleIndices();
     const VecDataArray<int, 3>&           surfIndices    = *surfIndicesPtr;
 
-    // Brute force
+    // Hash all the triangles from the surface
+    std::unordered_map<TriCell, int> triToFaceId;
     for (int i = 0; i < surfIndices.size(); i++)
     {
         const Vec3i& tri = surfIndices[i];
@@ -82,22 +79,30 @@ TriangleToTetMap::computeTriToTetMap(std::unordered_map<int, int>& triToTetMap)
         // Hash the triangle with the tet mesh ids
         TriCell cell_a(id0, id1, id2);
 
-        // Find the corresponding tet
-        for (int j = 0; j < tetIndices.size(); j++)
-        {
-            const Vec4i& tet = tetIndices[j];
+        triToFaceId[cell_a] = i;
+    }
 
-            // For every face of the tet
-            for (int k = 0; k < 4; k++)
+    // Hash all the triangles from the tetrahedron faces. Take note of
+    // collisions
+    // Find the corresponding tet
+    for (int i = 0; i < tetIndices.size(); i++)
+    {
+        const Vec4i& tet = tetIndices[i];
+
+        // For every face of the tet
+        for (int k = 0; k < 4; k++)
+        {
+            TriCell cell_b(
+                tet[facePattern[k][0]],
+                tet[facePattern[k][1]],
+                tet[facePattern[k][2]]);
+
+            // If this tet face exists in the map of hashed triangles
+            auto iter = triToFaceId.find(cell_b);
+            if (iter != triToFaceId.end())
             {
-                TriCell cell_b(
-                    tet[facePattern[k][0]],
-                    tet[facePattern[k][1]],
-                    tet[facePattern[k][2]]);
-                if (cell_a == cell_b)
-                {
-                    triToTetMap[i] = j;
-                }
+                const int triId = iter->second;
+                triToTetMap[triId] = i; // Map tri to tet id
             }
         }
     }