Revert 276827 "readability review for luken"

ui/gfx/geometry/r_tree.h

Index: ui/gfx/geometry/r_tree.h
===================================================================
--- ui/gfx/geometry/r_tree.h	(revision 277444)
+++ ui/gfx/geometry/r_tree.h	(working copy)
@@ -2,7 +2,22 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Defines a hierarchical bounding rectangle data structure for Rect objects,
+#ifndef UI_GFX_GEOMETRY_R_TREE_H_
+#define UI_GFX_GEOMETRY_R_TREE_H_
+
+#include <vector>
+
+#include "base/containers/hash_tables.h"
+#include "base/gtest_prod_util.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/gfx_export.h"
+
+namespace gfx {
+
+// Defines a heirarchical bounding rectangle data structure for Rect objects,
 // associated with a generic unique key K for efficient spatial queries. The
 // R*-tree algorithm is used to build the trees. Based on the papers:
 //
@@ -12,169 +27,270 @@
 // N Beckmann, H-P Kriegel, R Schneider, B Seeger 'The R*-tree: an efficient and
 // robust access method for points and rectangles', Proc ACM SIGMOD Int Conf on
 // Management of Data, 322-331, 1990
-
-#ifndef UI_GFX_GEOMETRY_R_TREE_H_
-#define UI_GFX_GEOMETRY_R_TREE_H_
-
-#include "r_tree_base.h"
-
-namespace gfx {
-
-template <typename Key>
-class RTree : public RTreeBase {
+class GFX_EXPORT RTree {
  public:
-  typedef base::hash_set<Key> Matches;
-
-  // RTrees organize pairs of keys and rectangles in a hierarchical bounding
-  // box structure. This allows for queries of the tree within logarithmic time.
-  // |min_children| and |max_children| allows for adjustment of the average size
-  // of the nodes within RTree, which adjusts the base of the logarithm in the
-  // algorithm runtime. Some parts of insertion and deletion are polynomial
-  // in the size of the individual node, so the trade-off with larger nodes is
-  // potentially faster queries but slower insertions and deletions. Generally
-  // it is worth considering how much overlap between rectangles of different
-  // keys will occur in the tree, and trying to set |max_children| as a
-  // reasonable upper bound to the number of overlapping rectangles expected.
-  // Then |min_children| can bet set to a quantity slightly less than half of
-  // that.
   RTree(size_t min_children, size_t max_children);
   ~RTree();
 
   // Insert a new rect into the tree, associated with provided key. Note that if
-  // |rect| is empty, the |key| will not actually be inserted. Duplicate keys
+  // rect is empty, this rect will not actually be inserted. Duplicate keys
   // overwrite old entries.
-  void Insert(const Rect& rect, Key key);
+  void Insert(const Rect& rect, intptr_t key);
 
-  // If present, remove the supplied |key| from the tree.
-  void Remove(Key key);
+  // If present, remove the supplied key from the tree.
+  void Remove(intptr_t key);
 
-  // Fills |matches_out| with all keys having bounding rects intersecting
-  // |query_rect|.
-  void AppendIntersectingRecords(const Rect& query_rect,
-                                 Matches* matches_out) const;
+  // Fills a supplied list matches_out with all keys having bounding rects
+  // intersecting query_rect.
+  void Query(const Rect& query_rect,
+             base::hash_set<intptr_t>* matches_out) const;
 
+  // Removes all objects from the tree.
   void Clear();
 
  private:
-  friend class RTreeTest;
-  friend class RTreeNodeTest;
-
-  class Record : public RecordBase {
+  // Private data structure class for storing internal nodes or leaves with keys
+  // of R-Trees. Note that "leaf" nodes can still have children, the children
+  // will all be Nodes with non-NULL record pointers.
+  class GFX_EXPORT Node {
    public:
-    Record(const Rect& rect, const Key& key);
-    virtual ~Record();
-    const Key& key() const { return key_; }
+    // Level counts from -1 for "record" Nodes, that is Nodes that wrap key
+    // values, to 0 for leaf Nodes, that is Nodes that only have record
+    // children, up to the root Node, which has level equal to the height of the
+    // tree.
+    explicit Node(int level);
 
+    // Builds a new record Node.
+    Node(const Rect& rect, intptr_t key);
+
+    virtual ~Node();
+
+    // Deletes all children and any attached record.
+    void Clear();
+
+    // Recursive call to build a list of rects that intersect the query_rect.
+    void Query(const Rect& query_rect,
+               base::hash_set<intptr_t>* matches_out) const;
+
+    // Recompute our bounds by taking the union of all children rects. Will then
+    // call RecomputeBounds() on our parent for recursive bounds recalculation
+    // up to the root.
+    void RecomputeBounds();
+
+    // Removes number_to_remove nodes from this Node, and appends them to the
+    // supplied list. Does not repair bounds upon completion.
+    void RemoveNodesForReinsert(size_t number_to_remove,
+                                ScopedVector<Node>* nodes);
+
+    // Given a pointer to a child node within this Node, remove it from our
+    // list. If that child had any children, append them to the supplied orphan
+    // list. Returns the new count of this node after removal. Does not
+    // recompute bounds, as this node itself may be removed if it now has too
+    // few children.
+    size_t RemoveChild(Node* child_node, ScopedVector<Node>* orphans);
+
+    // Does what it says on the tin. Returns NULL if no children. Does not
+    // recompute bounds.
+    scoped_ptr<Node> RemoveAndReturnLastChild();
+
+    // Given a node, returns the best fit node for insertion of that node at
+    // the nodes level().
+    Node* ChooseSubtree(Node* node);
+
+    // Adds the provided node to this Node. Returns the new count of records
+    // stored in the Node. Will recompute the bounds of this node after
+    // addition.
+    size_t AddChild(Node* node);
+
+    // Returns a sibling to this Node with at least min_children and no greater
+    // than max_children of this Node's children assigned to it, and having the
+    // same parent. Bounds will be valid on both Nodes after this call.
+    Node* Split(size_t min_children, size_t max_children);
+
+    // For record nodes only, to support re-insert, allows setting the rect.
+    void SetRect(const Rect& rect);
+
+    // Returns a pointer to the parent of this Node, or NULL if no parent.
+    Node* parent() const { return parent_; }
+
+    // 0 level() would mean that this Node is a leaf. 1 would mean that this
+    // Node has children that are leaves. Calling level() on root_ returns the
+    // height of the tree - 1. A level of -1 means that this is a Record node.
+    int level() const { return level_; }
+
+    const Rect& rect() const { return rect_; }
+
+    size_t count() const { return children_.size(); }
+
+    intptr_t key() const { return key_; }
+
    private:
-    Key key_;
+    // Returns all records stored in this node and its children.
+    void GetAllValues(base::hash_set<intptr_t>* matches_out) const;
 
-    DISALLOW_COPY_AND_ASSIGN(Record);
-  };
+    // Used for sorting Nodes along vertical and horizontal axes
+    static bool CompareVertical(Node* a, Node* b);
 
-  // A map of supplied keys to their Node representation within the RTree, for
-  // efficient retrieval of keys without requiring a bounding rect.
-  typedef base::hash_map<Key, Record*> RecordMap;
-  RecordMap record_map_;
+    static bool CompareHorizontal(Node* a, Node* b);
 
-  DISALLOW_COPY_AND_ASSIGN(RTree);
-};
+    static bool CompareCenterDistanceFromParent(Node* a, Node* b);
 
-template <typename Key>
-RTree<Key>::RTree(size_t min_children, size_t max_children)
-    : RTreeBase(min_children, max_children) {
-}
+    // Returns the increase in overlap value, as defined in Beckmann et al as
+    // the sum of the areas of the intersection of each |children_| rectangle
+    // (excepting the candidate child) with the argument rectangle. The
+    // expanded_rect argument is computed as the union of the candidate child
+    // rect and the argument rect, and is included here to avoid recomputation.
+    // Here the candidate child is indicated by index in |children_|, and
+    // expanded_rect is the alread-computed union of candidate's rect and
+    // rect.
+    int OverlapIncreaseToAdd(const Rect& rect,
+                             size_t candidate,
+                             const Rect& expanded_rect);
 
-template <typename Key>
-RTree<Key>::~RTree() {
-}
+    // Bounds recomputation without calling parents to do the same.
+    void RecomputeBoundsNoParents();
 
-template <typename Key>
-void RTree<Key>::Insert(const Rect& rect, Key key) {
-  scoped_ptr<NodeBase> record;
-  // Check if this key is already present in the tree.
-  typename RecordMap::iterator it(record_map_.find(key));
+    // Split() helper methods.
+    //
+    // Given two vectors of Nodes sorted by vertical or horizontal bounds, this
+    // function populates two vectors of Rectangles in which the ith element is
+    // the Union of all bounding rectangles [0,i] in the associated sorted array
+    // of Nodes.
+    static void BuildLowBounds(const std::vector<Node*>& vertical_sort,
+                               const std::vector<Node*>& horizontal_sort,
+                               std::vector<Rect>* vertical_bounds,
+                               std::vector<Rect>* horizontal_bounds);
 
-  if (it != record_map_.end()) {
-    // We will re-use this node structure, regardless of re-insert or return.
-    Record* existing_record = it->second;
-    // If the new rect and the current rect are identical we can skip the rest
-    // of Insert() as nothing has changed.
-    if (existing_record->rect() == rect)
-      return;
+    // Given two vectors of Nodes sorted by vertical or horizontal bounds, this
+    // function populates two vectors of Rectangles in which the ith element is
+    // the Union of all bounding rectangles [i, count()) in the associated
+    // sorted array of Nodes.
+    static void BuildHighBounds(const std::vector<Node*>& vertical_sort,
+                                const std::vector<Node*>& horizontal_sort,
+                                std::vector<Rect>* vertical_bounds,
+                                std::vector<Rect>* horizontal_bounds);
 
-    // Remove the node from the tree in its current position.
-    record = RemoveNode(existing_record);
+    // Returns true if this is a vertical split, false if a horizontal one.
+    // Based on ChooseSplitAxis algorithm in Beckmann et al. Chooses the axis
+    // with the lowest sum of margin values of bounding boxes.
+    static bool ChooseSplitAxis(const std::vector<Rect>& low_vertical_bounds,
+                                const std::vector<Rect>& high_vertical_bounds,
+                                const std::vector<Rect>& low_horizontal_bounds,
+                                const std::vector<Rect>& high_horizontal_bounds,
+                                size_t min_children,
+                                size_t max_children);
 
-    // If we are replacing this key with an empty rectangle we just remove the
-    // old node from the list and return, thus preventing insertion of empty
-    // rectangles into our spatial database.
-    if (rect.IsEmpty()) {
-      record_map_.erase(it);
-      return;
-    }
+    // Used by SplitNode to calculate optimal index of split, after determining
+    // along which axis to sort and split the children rectangles. Returns the
+    // index to the first element in the split children as sorted by the bounds
+    // vectors.
+    static size_t ChooseSplitIndex(size_t min_children,
+                                   size_t max_children,
+                                   const std::vector<Rect>& low_bounds,
+                                   const std::vector<Rect>& high_bounds);
 
-    // Reset the rectangle to the new value.
-    record->set_rect(rect);
-  } else {
-    if (rect.IsEmpty())
-      return;
+    // Takes our children_ and divides them into a new node, starting at index
+    // split_index in sorted_children.
+    Node* DivideChildren(const std::vector<Rect>& low_bounds,
+                         const std::vector<Rect>& high_bounds,
+                         const std::vector<Node*>& sorted_children,
+                         size_t split_index);
 
-    record.reset(new Record(rect, key));
-    record_map_.insert(std::make_pair(key, static_cast<Record*>(record.get())));
-  }
+    // Returns a pointer to the child node that will result in the least overlap
+    // increase with the addition of node_rect, as defined in the Beckmann et al
+    // paper, or NULL if there's a tie found. Requires a precomputed vector of
+    // expanded rectangles where the ith rectangle in the vector is the union of
+    // |children_|[i] and node_rect.
+    Node* LeastOverlapIncrease(const Rect& node_rect,
+                               const std::vector<Rect>& expanded_rects);
 
-  int highest_reinsert_level = -1;
-  InsertNode(record.Pass(), &highest_reinsert_level);
-}
+    // Returns a pointer to the child node that will result in the least area
+    // enlargement if the argument node rectangle were to be added to that
+    // nodes' bounding box. Requires a precomputed vector of expanded rectangles
+    // where the ith rectangle in the vector is the union of |children_|[i] and
+    // node_rect.
+    Node* LeastAreaEnlargement(const Rect& node_rect,
+                               const std::vector<Rect>& expanded_rects);
 
-template <typename Key>
-void RTree<Key>::Clear() {
-  record_map_.clear();
-  ResetRoot();
-}
+    // This Node's bounding rectangle.
+    Rect rect_;
 
-template <typename Key>
-void RTree<Key>::Remove(Key key) {
-  // Search the map for the leaf parent that has the provided record.
-  typename RecordMap::iterator it = record_map_.find(key);
-  if (it == record_map_.end())
-    return;
+    // The height of the node in the tree, counting from -1 at the record node
+    // to 0 at the leaf up to the root node which has level equal to the height
+    // of the tree.
+    int level_;
 
-  Record* record = it->second;
-  record_map_.erase(it);
-  RemoveNode(record);
+    // Pointers to all of our children Nodes.
+    ScopedVector<Node> children_;
 
-  // Lastly check the root. If it has only one non-leaf child, delete it and
-  // replace it with its child.
-  PruneRootIfNecessary();
-}
+    // A weak pointer to our parent Node in the RTree. The root node will have a
+    // NULL value for |parent_|.
+    Node* parent_;
 
-template <typename Key>
-void RTree<Key>::AppendIntersectingRecords(
-      const Rect& query_rect, Matches* matches_out) const {
-  RTreeBase::Records matching_records;
-  root()->AppendIntersectingRecords(query_rect, &matching_records);
-  for (RTreeBase::Records::const_iterator it = matching_records.begin();
-       it != matching_records.end();
-       ++it) {
-    const Record* record = static_cast<const Record*>(*it);
-    matches_out->insert(record->key());
-  }
-}
+    // If this is a record Node, then |key_| will be non-NULL and will contain
+    // the key data. Otherwise, NULL.
+    intptr_t key_;
 
+    friend class RTreeTest;
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeBuildHighBounds);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeBuildLowBounds);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeChooseSplitAxisAndIndex);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeChooseSubtree);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeCompareCenterDistanceFromParent);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeCompareHorizontal);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeCompareVertical);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeDivideChildren);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeLeastAreaEnlargement);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeLeastOverlapIncrease);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeOverlapIncreaseToAdd);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeRemoveAndReturnLastChild);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeRemoveChildNoOrphans);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeRemoveChildOrphans);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeRemoveNodesForReinsert);
+    FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeSplit);
 
-// RTree::Record --------------------------------------------------------------
+    DISALLOW_COPY_AND_ASSIGN(Node);
+  };
 
-template <typename Key>
-RTree<Key>::Record::Record(const Rect& rect, const Key& key)
-    : RecordBase(rect),
-      key_(key) {
-}
+  // Supports re-insertion of Nodes based on the strategies outlined in
+  // Beckmann et al.
+  void InsertNode(Node* node, int* highset_reinsert_level);
 
-template <typename Key>
-RTree<Key>::Record::~Record() {
-}
+  // Supports removal of nodes for tree without deletion.
+  void RemoveNode(Node* node);
 
+  // A pointer to the root node in the RTree.
+  scoped_ptr<Node> root_;
+
+  // The parameters used to define the shape of the RTree.
+  size_t min_children_;
+  size_t max_children_;
+
+  // A map of supplied keys to their Node representation within the RTree, for
+  // efficient retrieval of keys without requiring a bounding rect.
+  base::hash_map<intptr_t, Node*> record_map_;
+
+  friend class RTreeTest;
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeBuildHighBounds);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeBuildLowBounds);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeChooseSplitAxisAndIndex);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeChooseSubtree);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeCompareCenterDistanceFromParent);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeCompareHorizontal);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeCompareVertical);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeDivideChildren);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeLeastAreaEnlargement);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeLeastOverlapIncrease);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeOverlapIncreaseToAdd);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeRemoveAndReturnLastChild);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeRemoveChildNoOrphans);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeRemoveChildOrphans);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeRemoveNodesForReinsert);
+  FRIEND_TEST_ALL_PREFIXES(RTreeTest, NodeSplit);
+
+  DISALLOW_COPY_AND_ASSIGN(RTree);
+};
+
 }  // namespace gfx
 
 #endif  // UI_GFX_GEOMETRY_R_TREE_H_