Repairs crash in RTreeBase::Node::LeastAreaEnlargement

ui/gfx/geometry/r_tree_base.cc

Index: ui/gfx/geometry/r_tree_base.cc
diff --git a/ui/gfx/geometry/r_tree_base.cc b/ui/gfx/geometry/r_tree_base.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e93e1d5b6b1dc7ee1f9fbf85b0be8a5cb2684dfa
--- /dev/null
+++ b/ui/gfx/geometry/r_tree_base.cc
@@ -0,0 +1,658 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/gfx/geometry/r_tree_base.h"
+
+#include <algorithm>
+
+#include "base/logging.h"
+
+
+// Helpers --------------------------------------------------------------------
+
+namespace {
+
+// Returns a Vector2d to allow us to do arithmetic on the result such as
+// computing distances between centers.
+gfx::Vector2d CenterOfRect(const gfx::Rect& rect) {
+  return rect.OffsetFromOrigin() +
+      gfx::Vector2d(rect.width() / 2, rect.height() / 2);
+}
+
+}
+
+namespace gfx {
+
+
+// RTreeBase::NodeBase --------------------------------------------------------
+
+RTreeBase::NodeBase::~NodeBase() {
+}
+
+void RTreeBase::NodeBase::RecomputeBoundsUpToRoot() {
+  RecomputeLocalBounds();
+  if (parent_)
+    parent_->RecomputeBoundsUpToRoot();
+}
+
+RTreeBase::NodeBase::NodeBase(const Rect& rect, NodeBase* parent)
+    : rect_(rect),
+      parent_(parent) {
+}
+
+void RTreeBase::NodeBase::RecomputeLocalBounds() {
+}
+
+// RTreeBase::RecordBase ------------------------------------------------------
+
+RTreeBase::RecordBase::RecordBase(const Rect& rect) : NodeBase(rect, NULL) {
+}
+
+RTreeBase::RecordBase::~RecordBase() {
+}
+
+void RTreeBase::RecordBase::AppendIntersectingRecords(
+    const Rect& query_rect, Records* matches_out) const {
+  if (rect().Intersects(query_rect))
+    matches_out->push_back(this);
+}
+
+void RTreeBase::RecordBase::AppendAllRecords(Records* matches_out) const {
+  matches_out->push_back(this);
+}
+
+scoped_ptr<RTreeBase::NodeBase>
+RTreeBase::RecordBase::RemoveAndReturnLastChild() {
+  return scoped_ptr<NodeBase>();
+}
+
+int RTreeBase::RecordBase::Level() const {
+  return -1;
+}
+
+
+// RTreeBase::Node ------------------------------------------------------------
+
+RTreeBase::Node::Node() : NodeBase(Rect(), NULL), level_(0) {
+}
+
+RTreeBase::Node::~Node() {
+}
+
+scoped_ptr<RTreeBase::Node> RTreeBase::Node::ConstructParent() {
+  DCHECK(!parent());
+  scoped_ptr<Node> new_parent(new Node(level_ + 1));
+  new_parent->AddChild(scoped_ptr<NodeBase>(this));
+  return new_parent.Pass();
+}
+
+void RTreeBase::Node::AppendIntersectingRecords(
+    const Rect& query_rect, Records* matches_out) const {
+  // Check own bounding box for intersection, can cull all children if no
+  // intersection.
+  if (!rect().Intersects(query_rect))
+    return;
+
+  // Conversely if we are completely contained within the query rect we can
+  // confidently skip all bounds checks for ourselves and all our children.
+  if (query_rect.Contains(rect())) {
+    AppendAllRecords(matches_out);
+    return;
+  }
+
+  // We intersect the query rect but we are not are not contained within it.
+  // We must query each of our children in turn.
+  for (Nodes::const_iterator i = children_.begin(); i != children_.end(); ++i)
+    (*i)->AppendIntersectingRecords(query_rect, matches_out);
+}
+
+void RTreeBase::Node::AppendAllRecords(Records* matches_out) const {
+  for (Nodes::const_iterator i = children_.begin(); i != children_.end(); ++i)
+    (*i)->AppendAllRecords(matches_out);
+}
+
+void RTreeBase::Node::RemoveNodesForReinsert(size_t number_to_remove,
+                                             Nodes* nodes) {
+  DCHECK_LE(number_to_remove, children_.size());
+
+  std::partial_sort(children_.begin(),
+                    children_.begin() + number_to_remove,
+                    children_.end(),
+                    &RTreeBase::Node::CompareCenterDistanceFromParent);
+
+  // Move the lowest-distance nodes to the returned vector.
+  nodes->insert(
+      nodes->end(), children_.begin(), children_.begin() + number_to_remove);
+  children_.weak_erase(children_.begin(), children_.begin() + number_to_remove);
+}
+
+scoped_ptr<RTreeBase::NodeBase> RTreeBase::Node::RemoveChild(
+    NodeBase* child_node, Nodes* orphans) {
+  DCHECK_EQ(this, child_node->parent());
+
+  scoped_ptr<NodeBase> orphan(child_node->RemoveAndReturnLastChild());
+  while (orphan) {
+    orphans->push_back(orphan.release());
+    orphan = child_node->RemoveAndReturnLastChild();
+  }
+
+  Nodes::iterator i = std::find(children_.begin(), children_.end(), child_node);
+  DCHECK(i != children_.end());
+  children_.weak_erase(i);
+
+  return scoped_ptr<NodeBase>(child_node);
+}
+
+scoped_ptr<RTreeBase::NodeBase> RTreeBase::Node::RemoveAndReturnLastChild() {
+  if (children_.empty())
+    return scoped_ptr<NodeBase>();
+
+  scoped_ptr<NodeBase> last_child(children_.back());
+  children_.weak_erase(children_.end() - 1);
+  last_child->set_parent(NULL);
+  return last_child.Pass();
+}
+
+RTreeBase::Node* RTreeBase::Node::ChooseSubtree(NodeBase* node) {
+  DCHECK(node);
+  // Should never be called on a node at equal or lower level in the tree than
+  // the node to insert.
+  DCHECK_GT(level_, node->Level());
+
+  // If we are a parent of nodes on the provided node level, we are done.
+  if (level_ == node->Level() + 1)
+    return this;
+
+  // Precompute a vector of expanded rects, used by both LeastOverlapIncrease
+  // and LeastAreaEnlargement.
+  Rects expanded_rects;
+  expanded_rects.reserve(children_.size());
+  for (Nodes::iterator i = children_.begin(); i != children_.end(); ++i)
+    expanded_rects.push_back(UnionRects(node->rect(), (*i)->rect()));
+
+  Node* best_candidate = NULL;
+  // For parents of leaf nodes, we pick the node that will cause the least
+  // increase in overlap by the addition of this new node. This may detect a
+  // tie, in which case it will return NULL.
+  if (level_ == 1)
+    best_candidate = LeastOverlapIncrease(node->rect(), expanded_rects);
+
+  // For non-parents of leaf nodes, or for parents of leaf nodes with ties in
+  // overlap increase, we choose the subtree with least area enlargement caused
+  // by the addition of the new node.
+  if (!best_candidate)
+    best_candidate = LeastAreaEnlargement(node->rect(), expanded_rects);
+
+  DCHECK(best_candidate);
+  return best_candidate->ChooseSubtree(node);
+}
+
+size_t RTreeBase::Node::AddChild(scoped_ptr<NodeBase> node) {
+  DCHECK(node);
+  // Sanity-check that the level of the child being added is one less than ours.
+  DCHECK_EQ(level_ - 1, node->Level());
+  node->set_parent(this);
+  set_rect(UnionRects(rect(), node->rect()));
+  children_.push_back(node.release());
+  return children_.size();
+}
+
+scoped_ptr<RTreeBase::NodeBase> RTreeBase::Node::Split(size_t min_children,
+                                                       size_t max_children) {
+  // We should have too many children to begin with.
+  DCHECK_EQ(max_children + 1, children_.size());
+
+  // Determine if we should split along the horizontal or vertical axis.
+  std::vector<NodeBase*> vertical_sort(children_.get());
+  std::vector<NodeBase*> horizontal_sort(children_.get());
+  std::sort(vertical_sort.begin(),
+            vertical_sort.end(),
+            &RTreeBase::Node::CompareVertical);
+  std::sort(horizontal_sort.begin(),
+            horizontal_sort.end(),
+            &RTreeBase::Node::CompareHorizontal);
+
+  Rects low_vertical_bounds;
+  Rects low_horizontal_bounds;
+  BuildLowBounds(vertical_sort,
+                 horizontal_sort,
+                 &low_vertical_bounds,
+                 &low_horizontal_bounds);
+
+  Rects high_vertical_bounds;
+  Rects high_horizontal_bounds;
+  BuildHighBounds(vertical_sort,
+                  horizontal_sort,
+                  &high_vertical_bounds,
+                  &high_horizontal_bounds);
+
+  // Choose |end_index| such that both Nodes after the split will have
+  // min_children <= children_.size() <= max_children.
+  size_t end_index = std::min(max_children, children_.size() - min_children);
+  bool is_vertical_split =
+      SmallestMarginSum(min_children,
+                        end_index,
+                        low_horizontal_bounds,
+                        high_horizontal_bounds) <
+      SmallestMarginSum(min_children,
+                        end_index,
+                        low_vertical_bounds,
+                        high_vertical_bounds);
+
+  // Choose split index along chosen axis and perform the split.
+  const Rects& low_bounds(
+      is_vertical_split ? low_vertical_bounds : low_horizontal_bounds);
+  const Rects& high_bounds(
+      is_vertical_split ? high_vertical_bounds : high_horizontal_bounds);
+  size_t split_index =
+      ChooseSplitIndex(min_children, end_index, low_bounds, high_bounds);
+
+  const std::vector<NodeBase*>& sort(
+      is_vertical_split ? vertical_sort : horizontal_sort);
+  return DivideChildren(low_bounds, high_bounds, sort, split_index);
+}
+
+int RTreeBase::Node::Level() const {
+  return level_;
+}
+
+RTreeBase::Node::Node(int level) : NodeBase(Rect(), NULL), level_(level) {
+}
+
+// static
+bool RTreeBase::Node::CompareVertical(const NodeBase* a, const NodeBase* b) {
+  const Rect& a_rect = a->rect();
+  const Rect& b_rect = b->rect();
+  return (a_rect.y() < b_rect.y()) ||
+         ((a_rect.y() == b_rect.y()) && (a_rect.height() < b_rect.height()));
+}
+
+// static
+bool RTreeBase::Node::CompareHorizontal(const NodeBase* a, const NodeBase* b) {
+  const Rect& a_rect = a->rect();
+  const Rect& b_rect = b->rect();
+  return (a_rect.x() < b_rect.x()) ||
+         ((a_rect.x() == b_rect.x()) && (a_rect.width() < b_rect.width()));
+}
+
+// static
+bool RTreeBase::Node::CompareCenterDistanceFromParent(const NodeBase* a,
+                                                      const NodeBase* b) {
+  const NodeBase* p = a->parent();
+
+  DCHECK(p);
+  DCHECK_EQ(p, b->parent());
+
+  Vector2d p_center = CenterOfRect(p->rect());
+  Vector2d a_center = CenterOfRect(a->rect());
+  Vector2d b_center = CenterOfRect(b->rect());
+
+  // We don't bother with square roots because we are only comparing the two
+  // values for sorting purposes.
+  return (a_center - p_center).LengthSquared() <
+         (b_center - p_center).LengthSquared();
+}
+
+// static
+void RTreeBase::Node::BuildLowBounds(
+    const std::vector<NodeBase*>& vertical_sort,
+    const std::vector<NodeBase*>& horizontal_sort,
+    Rects* vertical_bounds,
+    Rects* horizontal_bounds) {
+  Rect vertical_bounds_rect;
+  vertical_bounds->reserve(vertical_sort.size());
+  for (std::vector<NodeBase*>::const_iterator i = vertical_sort.begin();
+       i != vertical_sort.end();
+       ++i) {
+    vertical_bounds_rect.Union((*i)->rect());
+    vertical_bounds->push_back(vertical_bounds_rect);
+  }
+
+  Rect horizontal_bounds_rect;
+  horizontal_bounds->reserve(horizontal_sort.size());
+  for (std::vector<NodeBase*>::const_iterator i = horizontal_sort.begin();
+       i != horizontal_sort.end();
+       ++i) {
+    horizontal_bounds_rect.Union((*i)->rect());
+    horizontal_bounds->push_back(horizontal_bounds_rect);
+  }
+}
+
+// static
+void RTreeBase::Node::BuildHighBounds(
+    const std::vector<NodeBase*>& vertical_sort,
+    const std::vector<NodeBase*>& horizontal_sort,
+    Rects* vertical_bounds,
+    Rects* horizontal_bounds) {
+  Rect vertical_bounds_rect;
+  vertical_bounds->reserve(vertical_sort.size());
+  for (std::vector<NodeBase*>::const_reverse_iterator i =
+           vertical_sort.rbegin();
+       i != vertical_sort.rend();
+       ++i) {
+    vertical_bounds_rect.Union((*i)->rect());
+    vertical_bounds->push_back(vertical_bounds_rect);
+  }
+  std::reverse(vertical_bounds->begin(), vertical_bounds->end());
+
+  Rect horizontal_bounds_rect;
+  horizontal_bounds->reserve(horizontal_sort.size());
+  for (std::vector<NodeBase*>::const_reverse_iterator i =
+           horizontal_sort.rbegin();
+       i != horizontal_sort.rend();
+       ++i) {
+    horizontal_bounds_rect.Union((*i)->rect());
+    horizontal_bounds->push_back(horizontal_bounds_rect);
+  }
+  std::reverse(horizontal_bounds->begin(), horizontal_bounds->end());
+}
+
+size_t RTreeBase::Node::ChooseSplitIndex(size_t start_index,
+                                         size_t end_index,
+                                         const Rects& low_bounds,
+                                         const Rects& high_bounds) {
+  DCHECK_EQ(low_bounds.size(), high_bounds.size());
+
+  int smallest_overlap_area = UnionRects(
+      low_bounds[start_index], high_bounds[start_index]).size().GetArea();
+  int smallest_combined_area = low_bounds[start_index].size().GetArea() +
+      high_bounds[start_index].size().GetArea();
+  size_t optimal_split_index = start_index;
+  for (size_t p = start_index + 1; p < end_index; ++p) {
+    const int overlap_area =
+        UnionRects(low_bounds[p], high_bounds[p]).size().GetArea();
+    const int combined_area =
+        low_bounds[p].size().GetArea() + high_bounds[p].size().GetArea();
+    if ((overlap_area < smallest_overlap_area) ||
+        ((overlap_area == smallest_overlap_area) &&
+         (combined_area < smallest_combined_area))) {
+      smallest_overlap_area = overlap_area;
+      smallest_combined_area = combined_area;
+      optimal_split_index = p;
+    }
+  }
+
+  // optimal_split_index currently points at the last element in the first set,
+  // so advance it by 1 to point at the first element in the second set.
+  return optimal_split_index + 1;
+}
+
+// static
+int RTreeBase::Node::SmallestMarginSum(size_t start_index,
+                                       size_t end_index,
+                                       const Rects& low_bounds,
+                                       const Rects& high_bounds) {
+  DCHECK_EQ(low_bounds.size(), high_bounds.size());
+  DCHECK_LT(start_index, low_bounds.size());
+  DCHECK_LE(start_index, end_index);
+  DCHECK_LE(end_index, low_bounds.size());
+  Rects::const_iterator i(low_bounds.begin() + start_index);
+  Rects::const_iterator j(high_bounds.begin() + start_index);
+  int smallest_sum = i->width() + i->height() + j->width() + j->height();
+  for (; i != (low_bounds.begin() + end_index); ++i, ++j) {
+    smallest_sum = std::min(
+        smallest_sum, i->width() + i->height() + j->width() + j->height());
+  }
+
+  return smallest_sum;
+}
+
+void RTreeBase::Node::RecomputeLocalBounds() {
+  Rect bounds;
+  for (size_t i = 0; i < children_.size(); ++i)
+    bounds.Union(children_[i]->rect());
+
+  set_rect(bounds);
+}
+
+int RTreeBase::Node::OverlapIncreaseToAdd(const Rect& rect,
+                                          const NodeBase* candidate_node,
+                                          const Rect& expanded_rect) const {
+  DCHECK(candidate_node);
+
+  // Early-out when |rect| is contained completely within |candidate|.
+  if (candidate_node->rect().Contains(rect))
+    return 0;
+
+  int total_original_overlap = 0;
+  int total_expanded_overlap = 0;
+
+  // Now calculate overlap with all other rects in this node.
+  for (Nodes::const_iterator it = children_.begin();
+       it != children_.end(); ++it) {
+    // Skip calculating overlap with the candidate rect.
+    if ((*it) == candidate_node)
+      continue;
+    NodeBase* overlap_node = (*it);
+    total_original_overlap += IntersectRects(
+        candidate_node->rect(), overlap_node->rect()).size().GetArea();
+    Rect expanded_overlap_rect = expanded_rect;
+    expanded_overlap_rect.Intersect(overlap_node->rect());
+    total_expanded_overlap += expanded_overlap_rect.size().GetArea();
+  }
+
+  return total_expanded_overlap - total_original_overlap;
+}
+
+scoped_ptr<RTreeBase::NodeBase> RTreeBase::Node::DivideChildren(
+    const Rects& low_bounds,
+    const Rects& high_bounds,
+    const std::vector<NodeBase*>& sorted_children,
+    size_t split_index) {
+  DCHECK_EQ(low_bounds.size(), high_bounds.size());
+  DCHECK_EQ(low_bounds.size(), sorted_children.size());
+  DCHECK_LT(split_index, low_bounds.size());
+  DCHECK_GT(split_index, 0U);
+
+  scoped_ptr<Node> sibling(new Node(level_));
+  sibling->set_parent(parent());
+  set_rect(low_bounds[split_index - 1]);
+  sibling->set_rect(high_bounds[split_index]);
+
+  // Our own children_ vector is unsorted, so we wipe it out and divide the
+  // sorted bounds rects between ourselves and our sibling.
+  children_.weak_clear();
+  children_.insert(children_.end(),
+                   sorted_children.begin(),
+                   sorted_children.begin() + split_index);
+  sibling->children_.insert(sibling->children_.end(),
+                            sorted_children.begin() + split_index,
+                            sorted_children.end());
+
+  for (size_t i = 0; i < sibling->children_.size(); ++i)
+    sibling->children_[i]->set_parent(sibling.get());
+
+  return sibling.PassAs<NodeBase>();
+}
+
+RTreeBase::Node* RTreeBase::Node::LeastOverlapIncrease(
+    const Rect& node_rect,
+    const Rects& expanded_rects) {
+  NodeBase* best_node = children_.front();
+  int least_overlap_increase =
+      OverlapIncreaseToAdd(node_rect, children_[0], expanded_rects[0]);
+  for (size_t i = 1; i < children_.size(); ++i) {
+    int overlap_increase =
+        OverlapIncreaseToAdd(node_rect, children_[i], expanded_rects[i]);
+    if (overlap_increase < least_overlap_increase) {
+      least_overlap_increase = overlap_increase;
+      best_node = children_[i];
+    } else if (overlap_increase == least_overlap_increase) {
+      // If we are tied at zero there is no possible better overlap increase,
+      // so we can report a tie early.
+      if (overlap_increase == 0)
+        return NULL;
+
+      best_node = NULL;
+    }
+  }
+
+  // Ensure that our children are always Nodes and not Records.
+  DCHECK_GE(level_, 1);
+  return static_cast<Node*>(best_node);
+}
+
+RTreeBase::Node* RTreeBase::Node::LeastAreaEnlargement(
+    const Rect& node_rect,
+    const Rects& expanded_rects) {
+  DCHECK(!children_.empty());
+  DCHECK_EQ(children_.size(), expanded_rects.size());
+
+  NodeBase* best_node = children_.front();
+  int least_area_enlargement =
+      expanded_rects[0].size().GetArea() - best_node->rect().size().GetArea();
+  for (size_t i = 1; i < children_.size(); ++i) {
+    NodeBase* candidate_node = children_[i];
+    int area_change = expanded_rects[i].size().GetArea() -
+                      candidate_node->rect().size().GetArea();
+    DCHECK_GE(area_change, 0);
+    if (area_change < least_area_enlargement) {
+      best_node = candidate_node;
+      least_area_enlargement = area_change;
+    } else if (area_change == least_area_enlargement &&
+        candidate_node->rect().size().GetArea() <
+            best_node->rect().size().GetArea()) {
+      // Ties are broken by choosing the entry with the least area.
+      best_node = candidate_node;
+    }
+  }
+
+  // Ensure that our children are always Nodes and not Records.
+  DCHECK_GE(level_, 1);
+  return static_cast<Node*>(best_node);
+}
+
+
+// RTreeBase ------------------------------------------------------------------
+
+RTreeBase::RTreeBase(size_t min_children, size_t max_children)
+    : root_(new Node()),
+      min_children_(min_children),
+      max_children_(max_children) {
+  DCHECK_GE(min_children_, 2U);
+  DCHECK_LE(min_children_, max_children_ / 2U);
+}
+
+RTreeBase::~RTreeBase() {
+}
+
+void RTreeBase::InsertNode(
+    scoped_ptr<NodeBase> node, int* highest_reinsert_level) {
+  // Find the most appropriate parent to insert node into.
+  Node* parent = root_->ChooseSubtree(node.get());
+  DCHECK(parent);
+  // Verify ChooseSubtree returned a Node at the correct level.
+  DCHECK_EQ(parent->Level(), node->Level() + 1);
+  Node* insert_parent = static_cast<Node*>(parent);
+  NodeBase* needs_bounds_recomputed = insert_parent->parent();
+  Nodes reinserts;
+  // Attempt to insert the Node, if this overflows the Node we must handle it.
+  while (insert_parent &&
+         insert_parent->AddChild(node.Pass()) > max_children_) {
+    // If we have yet to re-insert nodes at this level during this data insert,
+    // and we're not at the root, R*-Tree calls for re-insertion of some of the
+    // nodes, resulting in a better balance on the tree.
+    if (insert_parent->parent() &&
+        insert_parent->Level() > *highest_reinsert_level) {
+      insert_parent->RemoveNodesForReinsert(max_children_ / 3, &reinserts);
+      // Adjust highest_reinsert_level to this level.
+      *highest_reinsert_level = insert_parent->Level();
+      // RemoveNodesForReinsert() does not recompute bounds, so mark it.
+      needs_bounds_recomputed = insert_parent;
+      break;
+    }
+
+    // Split() will create a sibling to insert_parent both of which will have
+    // valid bounds, but this invalidates their parent's bounds.
+    node = insert_parent->Split(min_children_, max_children_);
+    insert_parent = static_cast<Node*>(insert_parent->parent());
+    needs_bounds_recomputed = insert_parent;
+  }
+
+  // If we have a Node to insert, and we hit the root of the current tree,
+  // we create a new root which is the parent of the current root and the
+  // insert_node. Note that we must release() the |root_| since
+  // ConstructParent() will take ownership of it.
+  if (!insert_parent && node) {
+    root_ = root_.release()->ConstructParent();
+    root_->AddChild(node.Pass());
+  }
+
+  // Recompute bounds along insertion path.
+  if (needs_bounds_recomputed)
+    needs_bounds_recomputed->RecomputeBoundsUpToRoot();
+
+  // Complete re-inserts, if any. The algorithm only allows for one invocation
+  // of RemoveNodesForReinsert() per level of the tree in an overall call to
+  // Insert().
+  while (!reinserts.empty()) {
+    Nodes::iterator last_element = reinserts.end() - 1;
+    NodeBase* temp_ptr(*last_element);
+    reinserts.weak_erase(last_element);
+    InsertNode(make_scoped_ptr(temp_ptr), highest_reinsert_level);
+  }
+}
+
+scoped_ptr<RTreeBase::NodeBase> RTreeBase::RemoveNode(NodeBase* node) {
+  // We need to remove this node from its parent.
+  Node* parent = static_cast<Node*>(node->parent());
+  // Record nodes are never allowed as the root, so we should always have a
+  // parent.
+  DCHECK(parent);
+  // Should always be a leaf that had the record.
+  DCHECK_EQ(0, parent->Level());
+
+  Nodes orphans;
+  scoped_ptr<NodeBase> removed_node(parent->RemoveChild(node, &orphans));
+
+  // It's possible that by removing |node| from |parent| we have made |parent|
+  // have less than the minimum number of children, in which case we will need
+  // to remove and delete |parent| while reinserting any other children that it
+  // had. We traverse up the tree doing this until we remove a child from a
+  // parent that still has greater than or equal to the minimum number of Nodes.
+  while (parent->count() < min_children_) {
+    NodeBase* child = parent;
+    parent = static_cast<Node*>(parent->parent());
+
+    // If we've hit the root, stop.
+    if (!parent)
+      break;
+
+    parent->RemoveChild(child, &orphans);
+  }
+
+  // If we stopped deleting nodes up the tree before encountering the root,
+  // we'll need to fix up the bounds from the first parent we didn't delete
+  // up to the root.
+  if (parent)
+    parent->RecomputeBoundsUpToRoot();
+  else
+    root_->RecomputeBoundsUpToRoot();
+
+  while (!orphans.empty()) {
+    Nodes::iterator last_element = orphans.end() - 1;
+    NodeBase* temp_ptr(*last_element);
+    orphans.weak_erase(last_element);
+    int starting_level = -1;
+    InsertNode(make_scoped_ptr(temp_ptr), &starting_level);
+  }
+
+  return removed_node.Pass();
+}
+
+void RTreeBase::PruneRootIfNecessary() {
+  if (root()->count() == 1 && root()->Level() > 0) {
+    // Awkward reset(cast(release)) pattern here because there's no better way
+    // to downcast the scoped_ptr from RemoveAndReturnLastChild() from NodeBase
+    // to Node.
+    root_.reset(
+        static_cast<Node*>(root_->RemoveAndReturnLastChild().release()));
+  }
+}
+
+void RTreeBase::ResetRoot() {
+  root_.reset(new Node());
+}
+
+}  // namespace gfx