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      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  */
     26 class SkTileGrid : public SkBBoxHierarchy {
     27 public:
     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 
     77 private:
     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  */
    105 template <typename T>
    106 void* 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