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      1 /*
      2  * Copyright 2013 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 SkDecodingImageGenerator_DEFINED
      9 #define SkDecodingImageGenerator_DEFINED
     10 
     11 #include "SkBitmap.h"
     12 #include "SkImageGenerator.h"
     13 
     14 class SkData;
     15 class SkStreamRewindable;
     16 
     17 /**
     18  *  An implementation of SkImageGenerator that calls into
     19  *  SkImageDecoder.
     20  */
     21 namespace SkDecodingImageGenerator {
     22     /**
     23      *  These options will be passed on to the image decoder.  The
     24      *  defaults are sensible.
     25      *
     26      *  @param fSampleSize If set to > 1, tells the decoder to return a
     27      *         smaller than original bitmap, sampling 1 pixel for
     28      *         every size pixels. e.g. if sample size is set to 3,
     29      *         then the returned bitmap will be 1/3 as wide and high,
     30      *         and will contain 1/9 as many pixels as the original.
     31      *         Note: this is a hint, and the codec may choose to
     32      *         ignore this, or only approximate the sample size.
     33      *
     34      *  @param fDitherImage Set to true if the the decoder should try to
     35      *         dither the resulting image when decoding to a smaller
     36      *         color-space.  The default is true.
     37      *
     38      *  @param fRequestedColorType If not given, then use whichever
     39      *         config the decoder wants.  Else try to use this color
     40      *         type.  If the decoder won't support this color type,
     41      *         SkDecodingImageGenerator::Create will return
     42      *         NULL. kIndex_8_SkColorType is not supported.
     43      *
     44      *  @param fRequireUnpremul If true, the decoder will attempt to
     45      *         decode without premultiplying the alpha. If it cannot,
     46      *         the pixels will be set to NULL.
     47      */
     48     struct Options {
     49         Options()
     50             : fSampleSize(1)
     51             , fDitherImage(true)
     52             , fUseRequestedColorType(false)
     53             , fRequestedColorType()
     54             , fRequireUnpremul(false) { }
     55         Options(int sampleSize, bool dither)
     56             : fSampleSize(sampleSize)
     57             , fDitherImage(dither)
     58             , fUseRequestedColorType(false)
     59             , fRequestedColorType()
     60             , fRequireUnpremul(false) { }
     61         Options(int sampleSize, bool dither, SkColorType colorType)
     62             : fSampleSize(sampleSize)
     63             , fDitherImage(dither)
     64             , fUseRequestedColorType(true)
     65             , fRequestedColorType(colorType)
     66             , fRequireUnpremul(false) { }
     67          Options(int sampleSize, bool dither, SkColorType colorType,
     68                  bool requireUnpremul)
     69             : fSampleSize(sampleSize)
     70             , fDitherImage(dither)
     71             , fUseRequestedColorType(true)
     72             , fRequestedColorType(colorType)
     73             , fRequireUnpremul(requireUnpremul) { }
     74         const int         fSampleSize;
     75         const bool        fDitherImage;
     76         const bool        fUseRequestedColorType;
     77         const SkColorType fRequestedColorType;
     78         const bool        fRequireUnpremul;
     79     };
     80 
     81     /**
     82      *  These two functions return a SkImageGenerator that calls into
     83      *  SkImageDecoder.  They return NULL on failure.
     84      *
     85      *  The SkData version of this function is preferred.  If the stream
     86      *  has an underlying SkData (such as a SkMemoryStream) pass that in.
     87      *
     88      *  This object will unref the stream when done or on failure.  Since
     89      *  streams have internal state (position), the caller should not pass
     90      *  a shared stream in.  Pass either a new duplicated stream in or
     91      *  transfer ownership of the stream.  This factory asserts
     92      *  stream->unique().
     93      *
     94      *  For example:
     95      *    SkStreamRewindable* stream;
     96      *    ...
     97      *    SkImageGenerator* gen
     98      *        = SkDecodingImageGenerator::Create(
     99      *            stream->duplicate(), SkDecodingImageGenerator::Options());
    100      *    ...
    101      *    SkDELETE(gen);
    102      *
    103      *  @param Options (see above)
    104      *
    105      *  @return NULL on failure, a new SkImageGenerator on success.
    106      */
    107     SkImageGenerator* Create(SkStreamRewindable* stream,
    108                              const Options& opt);
    109 
    110     /**
    111      *  @param data Contains the encoded image data that will be used by
    112      *         the SkDecodingImageGenerator.  Will be ref()ed by the
    113      *         SkImageGenerator constructor and and unref()ed on deletion.
    114      */
    115     SkImageGenerator* Create(SkData* data, const Options& opt);
    116 };
    117 
    118 //  // Example of most basic use case:
    119 //
    120 //  bool install_data(SkData* data, SkBitmap* dst) {
    121 //     return SkInstallDiscardablePixelRef(
    122 //         SkDecodingImageGenerator::Create(
    123 //             data, SkDecodingImageGenerator::Options()), dst, NULL);
    124 //  }
    125 //  bool install_stream(SkStreamRewindable* stream, SkBitmap* dst) {
    126 //     return SkInstallDiscardablePixelRef(
    127 //         SkDecodingImageGenerator::Create(
    128 //             stream, SkDecodingImageGenerator::Options()), dst, NULL);
    129 //  }
    130 
    131 #endif  // SkDecodingImageGenerator_DEFINED
    132