Adds an RTree data structure to gfx/geometry

ui/gfx/geometry/r_tree.h

Index: ui/gfx/geometry/r_tree.h
diff --git a/ui/gfx/geometry/r_tree.h b/ui/gfx/geometry/r_tree.h
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+// Copyright (c) 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.
+
+#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:
+//
+// A Guttman 'R-trees:  a dynamic index structure for spatial searching', Proc
+// ACM SIGMOD Int Conf on Management of Data, 47-57, 1984
+//
+// 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
+class GFX_EXPORT RTree {
+ public:
+  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, this rect will not actually be inserted. Duplicate keys
+  // overwrite old entries.
+  void Insert(const Rect& rect, intptr_t key);
+
+  // If present, remove the supplied key from the tree.
+  void Remove(intptr_t key);
+
+  // 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:
+  // 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:
+    // 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:
+    // Returns all records stored in this node and its children.
+    void GetAllValues(base::hash_set<intptr_t>* matches_out) const;
+
+    // Used for sorting Nodes along vertical and horizontal axes
+    static bool CompareVertical(Node* a, Node* b);
+
+    static bool CompareHorizontal(Node* a, Node* b);
+
+    static bool CompareCenterDistanceFromParent(Node* a, Node* b);
+
+    // 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);
+
+    // Bounds recomputation without calling parents to do the same.
+    void RecomputeBoundsNoParents();
+
+    // 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);
+
+    // 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);
+
+    // 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);
+
+    // 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);
+
+    // 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);
+
+    // 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);
+
+    // 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);
+
+    // This Node's bounding rectangle.
+    Rect rect_;
+
+    // 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_;
+
+    // Pointers to all of our children Nodes.
+    ScopedVector<Node> children_;
+
+    // A weak pointer to our parent Node in the RTree. The root node will have a
+    // NULL value for |parent_|.
+    Node* parent_;
+
+    // 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);
+
+    DISALLOW_COPY_AND_ASSIGN(Node);
+  };
+
+  // Supports re-insertion of Nodes based on the strategies outlined in
+  // Beckmann et al.
+  void InsertNode(Node* node, int* highset_reinsert_level);
+
+  // 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_