src/codec/SkCodec_libpng.h

/*
 * Copyright 2015 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "SkCodec.h"
#include "SkColorTable.h"
#include "SkPngChunkReader.h"
#include "SkEncodedFormat.h"
#include "SkImageInfo.h"
#include "SkRefCnt.h"
#include "SkSwizzler.h"

#include "png.h"

class SkStream;

class SkPngCodec : public SkCodec {
public:
    static bool IsPng(SkStream*);

    // Assume IsPng was called and returned true.
    static SkCodec* NewFromStream(SkStream*, SkPngChunkReader* = NULL);

    virtual ~SkPngCodec();

protected:
    Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*, int*)
            override;
    SkEncodedFormat onGetEncodedFormat() const override { return kPNG_SkEncodedFormat; }
    bool onRewind() override;
    uint32_t onGetFillValue(SkColorType colorType, SkAlphaType alphaType) const override;
    bool onReallyHasAlpha() const final;

    // Helper to set up swizzler and color table. Also calls png_read_update_info.
    Result initializeSwizzler(const SkImageInfo& requestedInfo, const Options&,
                              SkPMColor*, int* ctableCount);
    SkSampler* getSampler(bool createIfNecessary) override {
        SkASSERT(fSwizzler);
        return fSwizzler;
    }

    SkPngCodec(const SkImageInfo&, SkStream*, SkPngChunkReader*, png_structp, png_infop, int, int);

    png_structp png_ptr() { return fPng_ptr; }
    SkSwizzler* swizzler() { return fSwizzler; }
    SkSwizzler::SrcConfig srcConfig() const { return fSrcConfig; }
    int numberPasses() const { return fNumberPasses; }

    enum AlphaState {
        // This class has done no decoding, or threw away its knowledge (in
        // scanline decodes).
        kUnknown_AlphaState,
        // This class found the image (possibly partial, in the case of a
        // scanline decode) to be opaque.
        kOpaque_AlphaState,
        // Ths class found the image to have alpha.
        kHasAlpha_AlphaState,
    };

    virtual AlphaState alphaInScanlineDecode() const = 0;

private:
    SkAutoTUnref<SkPngChunkReader>  fPngChunkReader;
    png_structp                     fPng_ptr;
    png_infop                       fInfo_ptr;

    // These are stored here so they can be used both by normal decoding and scanline decoding.
    SkAutoTUnref<SkColorTable>      fColorTable;    // May be unpremul.
    SkAutoTDelete<SkSwizzler>       fSwizzler;

    SkSwizzler::SrcConfig           fSrcConfig;
    const int                       fNumberPasses;
    int                             fBitDepth;
    AlphaState                      fAlphaState;

    bool decodePalette(bool premultiply, int* ctableCount);
    void destroyReadStruct();

    typedef SkCodec INHERITED;
};