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 "SkBBoxHierarchy.h"
13#include "SkPictureStateTree.h"
14#include "SkTileGridPicture.h" // for TileGridInfo
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 SkTileGridPicture::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 void rewindInserts() SK_OVERRIDE;
67
68    // Used by search() and in SkTileGridHelper implementations
69    enum {
70        kTileFinished = -1,
71    };
72private:
73    SkTDArray<void*>& tile(int x, int y);
74
75    int fXTileCount, fYTileCount, fTileCount;
76    SkTileGridPicture::TileGridInfo fInfo;
77    SkTDArray<void*>* fTileData;
78    int fInsertionCount;
79    SkIRect fGridBounds;
80    SkTileGridNextDatumFunctionPtr fNextDatumFunction;
81
82    friend class TileGridTest;
83    typedef SkBBoxHierarchy INHERITED;
84};
85
86/**
87 * Generic implementation for SkTileGridNextDatumFunctionPtr. user code may instantiate
88 * this template to get a valid SkTileGridNextDatumFunction implementation
89 *
90 * Returns the next element of tileData[i][tileIndices[i]] for all i and advances
91 * tileIndices[] past them. The order in which data are returned by successive
92 * calls to this method must reflect the order in which the were originally
93 * recorded into the tile grid.
94 *
95 * \param tileData array of pointers to arrays of tile data
96 * \param tileIndices per-tile data indices, indices are incremented for tiles that contain
97 *     the next datum.
98 * \tparam T a type to which it is safe to cast a datum and that has an operator <
99 *     such that 'a < b' is true if 'a' was inserted into the tile grid before 'b'.
100 */
101template <typename T>
102void* SkTileGridNextDatum(SkTDArray<void*>** tileData, SkAutoSTArray<SkTileGrid::kStackAllocationTileCount, int>& tileIndices) {
103    T* minVal = NULL;
104    int tileCount = tileIndices.count();
105    int minIndex = tileCount;
106    int maxIndex = 0;
107    // Find the next Datum; track where it's found so we reduce the size of the second loop.
108    for (int tile = 0; tile < tileCount; ++tile) {
109        int pos = tileIndices[tile];
110        if (pos != SkTileGrid::kTileFinished) {
111            T* candidate = (T*)(*tileData[tile])[pos];
112            if (NULL == minVal || (*candidate) < (*minVal)) {
113                minVal = candidate;
114                minIndex = tile;
115                maxIndex = tile;
116            } else if (!((*minVal) < (*candidate))) {
117                // We don't require operator==; if !(candidate<minVal) && !(minVal<candidate),
118                // candidate==minVal and we have to add this tile to the range searched.
119                maxIndex = tile;
120            }
121        }
122    }
123    // Increment indices past the next datum
124    if (minVal != NULL) {
125        for (int tile = minIndex; tile <= maxIndex; ++tile) {
126            int pos = tileIndices[tile];
127            if (pos != SkTileGrid::kTileFinished && (*tileData[tile])[pos] == minVal) {
128                if (++(tileIndices[tile]) >= tileData[tile]->count()) {
129                    tileIndices[tile] = SkTileGrid::kTileFinished;
130                }
131            }
132        }
133        return minVal;
134    }
135    return NULL;
136}
137
138#endif
139