Refactor to avoid computing uneeded aabb tree.

Former-commit-id: 668efe7d062425d60d9f7d288d0bb5c2e179ae73

include/igl/copyleft/cgal/extract_cells.cpp

@@ -154,12 +154,6 @@ IGL_INLINE size_t igl::copyleft::cgal::extract_cells(
   std::vector< std::vector<Kernel::Triangle_3 > > 
     triangle_lists(num_components);
   std::vector<std::vector<bool> > in_Is(num_components);
-  for (size_t i=0; i<num_components; i++)
-  {
-    Is[i].resize(components[i].size());
-    std::copy(components[i].begin(), components[i].end(),Is[i].data());
-    submesh_aabb_tree(V,F,Is[i],trees[i],triangle_lists[i],in_Is[i]);
-  }
 
   // Find outer facets, their orientations and cells for each component
   Eigen::VectorXi outer_facets(num_components);
@@ -167,6 +161,8 @@ IGL_INLINE size_t igl::copyleft::cgal::extract_cells(
   Eigen::VectorXi outer_cells(num_components);
   for (size_t i=0; i<num_components; i++)
   {
+    Is[i].resize(components[i].size());
+    std::copy(components[i].begin(), components[i].end(),Is[i].data());
     bool flipped;
     igl::copyleft::cgal::outer_facet(V, F, Is[i], outer_facets[i], flipped);
     outer_facet_orientation[i] = flipped?1:0;
@@ -194,9 +190,9 @@ IGL_INLINE size_t igl::copyleft::cgal::extract_cells(
     // construct bounding boxes for each component
     DerivedV bbox_min(num_components, 3);
     DerivedV bbox_max(num_components, 3);
-    // Why not just initialize to numeric_limits::min, numeric_limits::max?
-    bbox_min.rowwise() = V.colwise().maxCoeff().eval();
-    bbox_max.rowwise() = V.colwise().minCoeff().eval();
+    // Assuming our mesh (in exact numbers) fits in the range of double.
+    bbox_min.setConstant(std::numeric_limits<double>::max());
+    bbox_max.setConstant(std::numeric_limits<double>::min());
     // Loop over faces
     for (size_t i=0; i<num_faces; i++)
     {
@@ -240,6 +236,9 @@ IGL_INLINE size_t igl::copyleft::cgal::extract_cells(
       const size_t num_candidate_comps = candidate_comps.size();
       if (num_candidate_comps == 0) continue;
 
+      // Build aabb tree for this component.
+      submesh_aabb_tree(V,F,Is[i],trees[i],triangle_lists[i],in_Is[i]);
+
       // Get query points on each candidate component: barycenter of
       // outer-facet 
       DerivedV queries(num_candidate_comps, 3);