1
2/*
3 * Copyright 2012 Google Inc.
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8
9#ifndef SkTileGrid_DEFINED
10#define SkTileGrid_DEFINED
11
12#include "SkBBHFactory.h"
13#include "SkBBoxHierarchy.h"
14#include "SkPictureStateTree.h"
15
16/**
17 * Subclass of SkBBoxHierarchy that stores elements in buckets that correspond
18 * to tile regions, disposed in a regular grid.  This is useful when the tile
19 * structure that will be use in search() calls is known prior to insertion.
20 * Calls to search will return in constant time.
21 *
22 * Note: Current implementation of search() only supports looking-up regions
23 * that are an exact match to a single tile.  Implementation could be augmented
24 * to support arbitrary rectangles, but performance would be sub-optimal.
25 */
26class SkTileGrid : public SkBBoxHierarchy {
27public:
28    enum {
29        // Number of tiles for which data is allocated on the stack in
30        // SkTileGrid::search. If malloc becomes a bottleneck, we may consider
31        // increasing this number. Typical large web page, say 2k x 16k, would
32        // require 512 tiles of size 256 x 256 pixels.
33        kStackAllocationTileCount = 1024
34    };
35
36    typedef void* (*SkTileGridNextDatumFunctionPtr)(SkTDArray<void*>** tileData, SkAutoSTArray<kStackAllocationTileCount, int>& tileIndices);
37
38    SkTileGrid(int xTileCount, int yTileCount, const SkTileGridFactory::TileGridInfo& info,
39        SkTileGridNextDatumFunctionPtr nextDatumFunction);
40
41    virtual ~SkTileGrid();
42
43    /**
44     * Insert a data pointer and corresponding bounding box
45     * @param data The data pointer, may be NULL
46     * @param bounds The bounding box, should not be empty
47     * @param defer Ignored, TileArray does not defer insertions
48     */
49    virtual void insert(void* data, const SkIRect& bounds, bool) SK_OVERRIDE;
50
51    virtual void flushDeferredInserts() SK_OVERRIDE {};
52
53    /**
54     * Populate 'results' with data pointers corresponding to bounding boxes that intersect 'query'
55     * The query argument is expected to be an exact match to a tile of the grid
56     */
57    virtual void search(const SkIRect& query, SkTDArray<void*>* results) SK_OVERRIDE;
58
59    virtual void clear() SK_OVERRIDE;
60
61    /**
62     * Gets the number of insertions
63     */
64    virtual int getCount() const SK_OVERRIDE;
65
66    virtual int getDepth() const SK_OVERRIDE { return -1; }
67
68    virtual void rewindInserts() SK_OVERRIDE;
69
70    // Used by search() and in SkTileGridHelper implementations
71    enum {
72        kTileFinished = -1,
73    };
74
75    int tileCount(int x, int y);  // For testing only.
76
77private:
78    SkTDArray<void*>& tile(int x, int y);
79
80    int fXTileCount, fYTileCount, fTileCount;
81    SkTileGridFactory::TileGridInfo fInfo;
82    SkTDArray<void*>* fTileData;
83    int fInsertionCount;
84    SkIRect fGridBounds;
85    SkTileGridNextDatumFunctionPtr fNextDatumFunction;
86
87    typedef SkBBoxHierarchy INHERITED;
88};
89
90/**
91 * Generic implementation for SkTileGridNextDatumFunctionPtr. user code may instantiate
92 * this template to get a valid SkTileGridNextDatumFunction implementation
93 *
94 * Returns the next element of tileData[i][tileIndices[i]] for all i and advances
95 * tileIndices[] past them. The order in which data are returned by successive
96 * calls to this method must reflect the order in which the were originally
97 * recorded into the tile grid.
98 *
99 * \param tileData array of pointers to arrays of tile data
100 * \param tileIndices per-tile data indices, indices are incremented for tiles that contain
101 *     the next datum.
102 * \tparam T a type to which it is safe to cast a datum and that has an operator <
103 *     such that 'a < b' is true if 'a' was inserted into the tile grid before 'b'.
104 */
105template <typename T>
106void* SkTileGridNextDatum(SkTDArray<void*>** tileData, SkAutoSTArray<SkTileGrid::kStackAllocationTileCount, int>& tileIndices) {
107    T* minVal = NULL;
108    int tileCount = tileIndices.count();
109    int minIndex = tileCount;
110    int maxIndex = 0;
111    // Find the next Datum; track where it's found so we reduce the size of the second loop.
112    for (int tile = 0; tile < tileCount; ++tile) {
113        int pos = tileIndices[tile];
114        if (pos != SkTileGrid::kTileFinished) {
115            T* candidate = (T*)(*tileData[tile])[pos];
116            if (NULL == minVal || (*candidate) < (*minVal)) {
117                minVal = candidate;
118                minIndex = tile;
119                maxIndex = tile;
120            } else if (!((*minVal) < (*candidate))) {
121                // We don't require operator==; if !(candidate<minVal) && !(minVal<candidate),
122                // candidate==minVal and we have to add this tile to the range searched.
123                maxIndex = tile;
124            }
125        }
126    }
127    // Increment indices past the next datum
128    if (minVal != NULL) {
129        for (int tile = minIndex; tile <= maxIndex; ++tile) {
130            int pos = tileIndices[tile];
131            if (pos != SkTileGrid::kTileFinished && (*tileData[tile])[pos] == minVal) {
132                if (++(tileIndices[tile]) >= tileData[tile]->count()) {
133                    tileIndices[tile] = SkTileGrid::kTileFinished;
134                }
135            }
136        }
137        return minVal;
138    }
139    return NULL;
140}
141
142#endif
143