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      1 /*
      2  * Copyright 2017 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 #ifndef SkPngEncoder_DEFINED
      9 #define SkPngEncoder_DEFINED
     10 
     11 #include "SkEncoder.h"
     12 #include "SkDataTable.h"
     13 
     14 class SkPngEncoderMgr;
     15 class SkWStream;
     16 
     17 class SK_API SkPngEncoder : public SkEncoder {
     18 public:
     19 
     20     enum class FilterFlag : int {
     21         kZero  = 0x00,
     22         kNone  = 0x08,
     23         kSub   = 0x10,
     24         kUp    = 0x20,
     25         kAvg   = 0x40,
     26         kPaeth = 0x80,
     27         kAll   = kNone | kSub | kUp | kAvg | kPaeth,
     28     };
     29 
     30     struct Options {
     31         /**
     32          *  Selects which filtering strategies to use.
     33          *
     34          *  If a single filter is chosen, libpng will use that filter for every row.
     35          *
     36          *  If multiple filters are chosen, libpng will use a heuristic to guess which filter
     37          *  will encode smallest, then apply that filter.  This happens on a per row basis,
     38          *  different rows can use different filters.
     39          *
     40          *  Using a single filter (or less filters) is typically faster.  Trying all of the
     41          *  filters may help minimize the output file size.
     42          *
     43          *  Our default value matches libpng's default.
     44          */
     45         FilterFlag fFilterFlags = FilterFlag::kAll;
     46 
     47         /**
     48          *  Must be in [0, 9] where 9 corresponds to maximal compression.  This value is passed
     49          *  directly to zlib.  0 is a special case to skip zlib entirely, creating dramatically
     50          *  larger pngs.
     51          *
     52          *  Our default value matches libpng's default.
     53          */
     54         int fZLibLevel = 6;
     55 
     56         /**
     57          *  If the input is premultiplied, this controls the unpremultiplication behavior.
     58          *  The encoder can convert to linear before unpremultiplying or ignore the transfer
     59          *  function and unpremultiply the input as is.
     60          */
     61         SkTransferFunctionBehavior fUnpremulBehavior = SkTransferFunctionBehavior::kRespect;
     62 
     63         /**
     64          *  Represents comments in the tEXt ancillary chunk of the png.
     65          *  The 2i-th entry is the keyword for the i-th comment,
     66          *  and the (2i + 1)-th entry is the text for the i-th comment.
     67          */
     68         sk_sp<SkDataTable> fComments;
     69     };
     70 
     71     /**
     72      *  Encode the |src| pixels to the |dst| stream.
     73      *  |options| may be used to control the encoding behavior.
     74      *
     75      *  Returns true on success.  Returns false on an invalid or unsupported |src|.
     76      */
     77     static bool Encode(SkWStream* dst, const SkPixmap& src, const Options& options);
     78 
     79     /**
     80      *  Create a png encoder that will encode the |src| pixels to the |dst| stream.
     81      *  |options| may be used to control the encoding behavior.
     82      *
     83      *  |dst| is unowned but must remain valid for the lifetime of the object.
     84      *
     85      *  This returns nullptr on an invalid or unsupported |src|.
     86      */
     87     static std::unique_ptr<SkEncoder> Make(SkWStream* dst, const SkPixmap& src,
     88                                            const Options& options);
     89 
     90     ~SkPngEncoder() override;
     91 
     92 protected:
     93     bool onEncodeRows(int numRows) override;
     94 
     95     SkPngEncoder(std::unique_ptr<SkPngEncoderMgr>, const SkPixmap& src);
     96 
     97     std::unique_ptr<SkPngEncoderMgr> fEncoderMgr;
     98     typedef SkEncoder INHERITED;
     99 };
    100 
    101 static inline SkPngEncoder::FilterFlag operator|(SkPngEncoder::FilterFlag x,
    102                                                  SkPngEncoder::FilterFlag y) {
    103     return (SkPngEncoder::FilterFlag)((int)x | (int)y);
    104 }
    105 
    106 #endif
    107