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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 "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  */
     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 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     };
     72 private:
     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  */
    101 template <typename T>
    102 void* 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