/*
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* Copyright 2012 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef SkRTree_DEFINED
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#define SkRTree_DEFINED
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#include "SkBBoxHierarchy.h"
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#include "SkRect.h"
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#include "SkTDArray.h"
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/**
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* An R-Tree implementation. In short, it is a balanced n-ary tree containing a hierarchy of
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* bounding rectangles.
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*
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* It only supports bulk-loading, i.e. creation from a batch of bounding rectangles.
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* This performs a bottom-up bulk load using the STR (sort-tile-recursive) algorithm.
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*
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* TODO: Experiment with other bulk-load algorithms (in particular the Hilbert pack variant,
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* which groups rects by position on the Hilbert curve, is probably worth a look). There also
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* exist top-down bulk load variants (VAMSplit, TopDownGreedy, etc).
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*
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* For more details see:
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*
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* Beckmann, N.; Kriegel, H. P.; Schneider, R.; Seeger, B. (1990). "The R*-tree:
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* an efficient and robust access method for points and rectangles"
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*/
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class SkRTree : public SkBBoxHierarchy {
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public:
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/**
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* If you have some prior information about the distribution of bounds you're expecting, you
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* can provide an optional aspect ratio parameter. This allows the bulk-load algorithm to
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* create better proportioned tiles of rectangles.
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*/
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explicit SkRTree(SkScalar aspectRatio = 1);
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~SkRTree() override {}
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void insert(const SkRect[], int N) override;
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void search(const SkRect& query, SkTDArray<int>* results) const override;
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size_t bytesUsed() const override;
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// Methods and constants below here are only public for tests.
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// Return the depth of the tree structure.
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int getDepth() const { return fCount ? fRoot.fSubtree->fLevel + 1 : 0; }
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// Insertion count (not overall node count, which may be greater).
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int getCount() const { return fCount; }
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// Get the root bound.
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SkRect getRootBound() const override;
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// These values were empirically determined to produce reasonable performance in most cases.
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static const int kMinChildren = 6,
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kMaxChildren = 11;
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private:
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struct Node;
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struct Branch {
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union {
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Node* fSubtree;
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int fOpIndex;
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};
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SkRect fBounds;
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};
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struct Node {
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uint16_t fNumChildren;
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uint16_t fLevel;
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Branch fChildren[kMaxChildren];
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};
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void search(Node* root, const SkRect& query, SkTDArray<int>* results) const;
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// Consumes the input array.
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Branch bulkLoad(SkTDArray<Branch>* branches, int level = 0);
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// How many times will bulkLoad() call allocateNodeAtLevel()?
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static int CountNodes(int branches, SkScalar aspectRatio);
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Node* allocateNodeAtLevel(uint16_t level);
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// This is the count of data elements (rather than total nodes in the tree)
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int fCount;
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SkScalar fAspectRatio;
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Branch fRoot;
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SkTDArray<Node> fNodes;
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typedef SkBBoxHierarchy INHERITED;
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};
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#endif
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