Rename SkCodec_libpng to SkPngCodec

src/codec/SkCodec_libpng.cpp

Index: src/codec/SkCodec_libpng.cpp
diff --git a/src/codec/SkCodec_libpng.cpp b/src/codec/SkCodec_libpng.cpp
deleted file mode 100644
index b75fb3a84efadf89d7f7f6eae6b649334fbe6b5b..0000000000000000000000000000000000000000
--- a/src/codec/SkCodec_libpng.cpp
+++ /dev/null
@@ -1,787 +0,0 @@
-/*
- * 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_libpng.h"
-#include "SkCodecPriv.h"
-#include "SkColorPriv.h"
-#include "SkColorTable.h"
-#include "SkBitmap.h"
-#include "SkMath.h"
-#include "SkSize.h"
-#include "SkStream.h"
-#include "SkSwizzler.h"
-#include "SkTemplates.h"
-
-///////////////////////////////////////////////////////////////////////////////
-// Helper macros
-///////////////////////////////////////////////////////////////////////////////
-
-#ifndef png_jmpbuf
-#  define png_jmpbuf(png_ptr) ((png_ptr)->jmpbuf)
-#endif
-
-/* These were dropped in libpng >= 1.4 */
-#ifndef png_infopp_NULL
-    #define png_infopp_NULL nullptr
-#endif
-
-#ifndef png_bytepp_NULL
-    #define png_bytepp_NULL nullptr
-#endif
-
-#ifndef int_p_NULL
-    #define int_p_NULL nullptr
-#endif
-
-#ifndef png_flush_ptr_NULL
-    #define png_flush_ptr_NULL nullptr
-#endif
-
-///////////////////////////////////////////////////////////////////////////////
-// Callback functions
-///////////////////////////////////////////////////////////////////////////////
-
-static void sk_error_fn(png_structp png_ptr, png_const_charp msg) {
-    SkCodecPrintf("------ png error %s\n", msg);
-    longjmp(png_jmpbuf(png_ptr), 1);
-}
-
-void sk_warning_fn(png_structp, png_const_charp msg) {
-    SkCodecPrintf("----- png warning %s\n", msg);
-}
-
-static void sk_read_fn(png_structp png_ptr, png_bytep data,
-                       png_size_t length) {
-    SkStream* stream = static_cast<SkStream*>(png_get_io_ptr(png_ptr));
-    const size_t bytes = stream->read(data, length);
-    if (bytes != length) {
-        // FIXME: We want to report the fact that the stream was truncated.
-        // One way to do that might be to pass a enum to longjmp so setjmp can
-        // specify the failure.
-        png_error(png_ptr, "Read Error!");
-    }
-}
-
-#ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
-static int sk_read_user_chunk(png_structp png_ptr, png_unknown_chunkp chunk) {
-    SkPngChunkReader* chunkReader = (SkPngChunkReader*)png_get_user_chunk_ptr(png_ptr);
-    // readChunk() returning true means continue decoding
-    return chunkReader->readChunk((const char*)chunk->name, chunk->data, chunk->size) ? 1 : -1;
-}
-#endif
-
-///////////////////////////////////////////////////////////////////////////////
-// Helpers
-///////////////////////////////////////////////////////////////////////////////
-
-class AutoCleanPng : public SkNoncopyable {
-public:
-    AutoCleanPng(png_structp png_ptr)
-        : fPng_ptr(png_ptr)
-        , fInfo_ptr(nullptr) {}
-
-    ~AutoCleanPng() {
-        // fInfo_ptr will never be non-nullptr unless fPng_ptr is.
-        if (fPng_ptr) {
-            png_infopp info_pp = fInfo_ptr ? &fInfo_ptr : nullptr;
-            png_destroy_read_struct(&fPng_ptr, info_pp, png_infopp_NULL);
-        }
-    }
-
-    void setInfoPtr(png_infop info_ptr) {
-        SkASSERT(nullptr == fInfo_ptr);
-        fInfo_ptr = info_ptr;
-    }
-
-    void detach() {
-        fPng_ptr = nullptr;
-        fInfo_ptr = nullptr;
-    }
-
-private:
-    png_structp     fPng_ptr;
-    png_infop       fInfo_ptr;
-};
-#define AutoCleanPng(...) SK_REQUIRE_LOCAL_VAR(AutoCleanPng)
-
-//checks if there is transparency info in the tRNS chunk
-//image types which could have data in the tRNS chunk include: Index8, Gray8, RGB
-static bool has_transparency_in_tRNS(png_structp png_ptr,
-                                        png_infop info_ptr) {
-    if (!png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) {
-        return false;
-    }
-
-    png_bytep trans;
-    int num_trans;
-    png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans, nullptr);
-    return num_trans > 0;
-}
-
-// Method for coverting to either an SkPMColor or a similarly packed
-// unpremultiplied color.
-typedef uint32_t (*PackColorProc)(U8CPU a, U8CPU r, U8CPU g, U8CPU b);
-
-// Note: SkColorTable claims to store SkPMColors, which is not necessarily
-// the case here.
-bool SkPngCodec::decodePalette(bool premultiply, int* ctableCount) {
-    int numPalette;
-    png_colorp palette;
-    png_bytep trans;
-
-    if (!png_get_PLTE(fPng_ptr, fInfo_ptr, &palette, &numPalette)) {
-        return false;
-    }
-
-    // Note: These are not necessarily SkPMColors
-    SkPMColor colorStorage[256];    // worst-case storage
-    SkPMColor* colorPtr = colorStorage;
-
-    int numTrans;
-    if (png_get_valid(fPng_ptr, fInfo_ptr, PNG_INFO_tRNS)) {
-        png_get_tRNS(fPng_ptr, fInfo_ptr, &trans, &numTrans, nullptr);
-    } else {
-        numTrans = 0;
-    }
-
-    // check for bad images that might make us crash
-    if (numTrans > numPalette) {
-        numTrans = numPalette;
-    }
-
-    int index = 0;
-
-    // Choose which function to use to create the color table. If the final destination's
-    // colortype is unpremultiplied, the color table will store unpremultiplied colors.
-    PackColorProc proc;
-    if (premultiply) {
-        proc = &SkPreMultiplyARGB;
-    } else {
-        proc = &SkPackARGB32NoCheck;
-    }
-    for (; index < numTrans; index++) {
-        *colorPtr++ = proc(*trans++, palette->red, palette->green, palette->blue);
-        palette++;
-    }
-
-    for (; index < numPalette; index++) {
-        *colorPtr++ = SkPackARGB32(0xFF, palette->red, palette->green, palette->blue);
-        palette++;
-    }
-
-    /*  BUGGY IMAGE WORKAROUND
-        Invalid images could contain pixel values that are greater than the number of palette
-        entries. Since we use pixel values as indices into the palette this could result in reading
-        beyond the end of the palette which could leak the contents of uninitialized memory. To
-        ensure this doesn't happen, we grow the colortable to the maximum size that can be
-        addressed by the bitdepth of the image and fill it with the last palette color or black if
-        the palette is empty (really broken image).
-    */
-    int colorCount = SkTMax(numPalette, 1 << SkTMin(fBitDepth, 8));
-    SkPMColor lastColor = index > 0 ? colorPtr[-1] : SkPackARGB32(0xFF, 0, 0, 0);
-    for (; index < colorCount; index++) {
-        *colorPtr++ = lastColor;
-    }
-
-    // Set the new color count
-    if (ctableCount != nullptr) {
-        *ctableCount = colorCount;
-    }
-
-    fColorTable.reset(new SkColorTable(colorStorage, colorCount));
-    return true;
-}
-
-///////////////////////////////////////////////////////////////////////////////
-// Creation
-///////////////////////////////////////////////////////////////////////////////
-
-bool SkPngCodec::IsPng(const char* buf, size_t bytesRead) {
-    return !png_sig_cmp((png_bytep) buf, (png_size_t)0, bytesRead);
-}
-
-// Reads the header and initializes the output fields, if not NULL.
-//
-// @param stream Input data. Will be read to get enough information to properly
-//      setup the codec.
-// @param chunkReader SkPngChunkReader, for reading unknown chunks. May be NULL.
-//      If not NULL, png_ptr will hold an *unowned* pointer to it. The caller is
-//      expected to continue to own it for the lifetime of the png_ptr.
-// @param png_ptrp Optional output variable. If non-NULL, will be set to a new
-//      png_structp on success.
-// @param info_ptrp Optional output variable. If non-NULL, will be set to a new
-//      png_infop on success;
-// @param imageInfo Optional output variable. If non-NULL, will be set to
-//      reflect the properties of the encoded image on success.
-// @param bitDepthPtr Optional output variable. If non-NULL, will be set to the
-//      bit depth of the encoded image on success.
-// @param numberPassesPtr Optional output variable. If non-NULL, will be set to
-//      the number_passes of the encoded image on success.
-// @return true on success, in which case the caller is responsible for calling
-//      png_destroy_read_struct(png_ptrp, info_ptrp).
-//      If it returns false, the passed in fields (except stream) are unchanged.
-static bool read_header(SkStream* stream, SkPngChunkReader* chunkReader,
-                        png_structp* png_ptrp, png_infop* info_ptrp,
-                        SkImageInfo* imageInfo, int* bitDepthPtr, int* numberPassesPtr) {
-    // The image is known to be a PNG. Decode enough to know the SkImageInfo.
-    png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, nullptr,
-                                                 sk_error_fn, sk_warning_fn);
-    if (!png_ptr) {
-        return false;
-    }
-
-    AutoCleanPng autoClean(png_ptr);
-
-    png_infop info_ptr = png_create_info_struct(png_ptr);
-    if (info_ptr == nullptr) {
-        return false;
-    }
-
-    autoClean.setInfoPtr(info_ptr);
-
-    // FIXME: Could we use the return value of setjmp to specify the type of
-    // error?
-    if (setjmp(png_jmpbuf(png_ptr))) {
-        return false;
-    }
-
-    png_set_read_fn(png_ptr, static_cast<void*>(stream), sk_read_fn);
-
-#ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
-    // Hookup our chunkReader so we can see any user-chunks the caller may be interested in.
-    // This needs to be installed before we read the png header.  Android may store ninepatch
-    // chunks in the header.
-    if (chunkReader) {
-        png_set_keep_unknown_chunks(png_ptr, PNG_HANDLE_CHUNK_ALWAYS, (png_byte*)"", 0);
-        png_set_read_user_chunk_fn(png_ptr, (png_voidp) chunkReader, sk_read_user_chunk);
-    }
-#endif
-
-    // The call to png_read_info() gives us all of the information from the
-    // PNG file before the first IDAT (image data chunk).
-    png_read_info(png_ptr, info_ptr);
-    png_uint_32 origWidth, origHeight;
-    int bitDepth, colorType;
-    png_get_IHDR(png_ptr, info_ptr, &origWidth, &origHeight, &bitDepth,
-                 &colorType, int_p_NULL, int_p_NULL, int_p_NULL);
-
-    if (bitDepthPtr) {
-        *bitDepthPtr = bitDepth;
-    }
-
-    // sanity check for size
-    {
-        int64_t size = sk_64_mul(origWidth, origHeight);
-        // now check that if we are 4-bytes per pixel, we also don't overflow
-        if (size < 0 || size > (0x7FFFFFFF >> 2)) {
-            return false;
-        }
-    }
-
-    // Tell libpng to strip 16 bit/color files down to 8 bits/color
-    if (bitDepth == 16) {
-        png_set_strip_16(png_ptr);
-    }
-#ifdef PNG_READ_PACK_SUPPORTED
-    // Extract multiple pixels with bit depths of 1, 2, and 4 from a single
-    // byte into separate bytes (useful for paletted and grayscale images).
-    if (bitDepth < 8) {
-        png_set_packing(png_ptr);
-    }
-#endif
-    // Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel.
-    if (colorType == PNG_COLOR_TYPE_GRAY && bitDepth < 8) {
-        png_set_expand_gray_1_2_4_to_8(png_ptr);
-    }
-
-    // Now determine the default SkColorType and SkAlphaType and set required transforms
-    SkColorType skColorType = kUnknown_SkColorType;
-    SkAlphaType skAlphaType = kUnknown_SkAlphaType;
-    switch (colorType) {
-        case PNG_COLOR_TYPE_PALETTE:
-            skColorType = kIndex_8_SkColorType;
-            skAlphaType = has_transparency_in_tRNS(png_ptr, info_ptr) ?
-                    kUnpremul_SkAlphaType : kOpaque_SkAlphaType;
-            break;
-        case PNG_COLOR_TYPE_RGB:
-            if (has_transparency_in_tRNS(png_ptr, info_ptr)) {
-                //convert to RGBA with tranparency information in tRNS chunk if it exists
-                png_set_tRNS_to_alpha(png_ptr);
-                skAlphaType = kUnpremul_SkAlphaType;
-            } else {
-                skAlphaType = kOpaque_SkAlphaType;
-            }
-            skColorType = kN32_SkColorType;
-            break;
-        case PNG_COLOR_TYPE_GRAY:
-            if (has_transparency_in_tRNS(png_ptr, info_ptr)) {
-                //FIXME: support gray with alpha as a color type
-                //convert to RGBA if there is transparentcy info in the tRNS chunk
-                png_set_tRNS_to_alpha(png_ptr);
-                png_set_gray_to_rgb(png_ptr);
-                skColorType = kN32_SkColorType;
-                skAlphaType = kUnpremul_SkAlphaType;
-            } else {
-                skColorType = kGray_8_SkColorType;
-                skAlphaType = kOpaque_SkAlphaType;
-            }
-            break;
-        case PNG_COLOR_TYPE_GRAY_ALPHA:
-            //FIXME: support gray with alpha as a color type 
-            //convert to RGBA 
-            png_set_gray_to_rgb(png_ptr);
-            skColorType = kN32_SkColorType;
-            skAlphaType = kUnpremul_SkAlphaType;
-            break;
-        case PNG_COLOR_TYPE_RGBA:
-            skColorType = kN32_SkColorType;
-            skAlphaType = kUnpremul_SkAlphaType;
-            break;
-        default:
-            //all the color types have been covered above
-            SkASSERT(false);
-    }
-
-    int numberPasses = png_set_interlace_handling(png_ptr);
-    if (numberPassesPtr) {
-        *numberPassesPtr = numberPasses;
-    }
-
-    // FIXME: Also need to check for sRGB ( https://bug.skia.org/3471 ).
-
-    if (imageInfo) {
-        *imageInfo = SkImageInfo::Make(origWidth, origHeight, skColorType, skAlphaType);
-    }
-    autoClean.detach();
-    if (png_ptrp) {
-        *png_ptrp = png_ptr;
-    }
-    if (info_ptrp) {
-        *info_ptrp = info_ptr;
-    }
-
-    return true;
-}
-
-SkPngCodec::SkPngCodec(const SkImageInfo& info, SkStream* stream, SkPngChunkReader* chunkReader,
-                       png_structp png_ptr, png_infop info_ptr, int bitDepth, int numberPasses)
-    : INHERITED(info, stream)
-    , fPngChunkReader(SkSafeRef(chunkReader))
-    , fPng_ptr(png_ptr)
-    , fInfo_ptr(info_ptr)
-    , fSrcConfig(SkSwizzler::kUnknown)
-    , fNumberPasses(numberPasses)
-    , fBitDepth(bitDepth)
-{}
-
-SkPngCodec::~SkPngCodec() {
-    this->destroyReadStruct();
-}
-
-void SkPngCodec::destroyReadStruct() {
-    if (fPng_ptr) {
-        // We will never have a nullptr fInfo_ptr with a non-nullptr fPng_ptr
-        SkASSERT(fInfo_ptr);
-        png_destroy_read_struct(&fPng_ptr, &fInfo_ptr, png_infopp_NULL);
-        fPng_ptr = nullptr;
-        fInfo_ptr = nullptr;
-    }
-}
-
-///////////////////////////////////////////////////////////////////////////////
-// Getting the pixels
-///////////////////////////////////////////////////////////////////////////////
-
-SkCodec::Result SkPngCodec::initializeSwizzler(const SkImageInfo& requestedInfo,
-                                               const Options& options,
-                                               SkPMColor ctable[],
-                                               int* ctableCount) {
-    // FIXME: Could we use the return value of setjmp to specify the type of
-    // error?
-    if (setjmp(png_jmpbuf(fPng_ptr))) {
-        SkCodecPrintf("setjmp long jump!\n");
-        return kInvalidInput;
-    }
-    png_read_update_info(fPng_ptr, fInfo_ptr);  
-
-    //srcColorType was determined in read_header() which determined png color type
-    const SkColorType srcColorType = this->getInfo().colorType();
-
-    switch (srcColorType) {
-        case kIndex_8_SkColorType:
-            //decode palette to Skia format
-            fSrcConfig = SkSwizzler::kIndex;
-            if (!this->decodePalette(kPremul_SkAlphaType == requestedInfo.alphaType(),
-                    ctableCount)) {
-                return kInvalidInput;
-            }
-            break;
-        case kGray_8_SkColorType:
-            fSrcConfig = SkSwizzler::kGray;
-            break; 
-        case kN32_SkColorType:
-            if (this->getInfo().alphaType() == kOpaque_SkAlphaType) {
-                    fSrcConfig = SkSwizzler::kRGB;
-                } else {
-                    fSrcConfig = SkSwizzler::kRGBA;
-            }
-            break;
-        default:
-            //would have exited before now if the colorType was supported by png
-            SkASSERT(false);
-    }  
-
-    // Copy the color table to the client if they request kIndex8 mode
-    copy_color_table(requestedInfo, fColorTable, ctable, ctableCount);
-
-    // Create the swizzler.  SkPngCodec retains ownership of the color table.
-    const SkPMColor* colors = get_color_ptr(fColorTable.get());
-    fSwizzler.reset(SkSwizzler::CreateSwizzler(fSrcConfig, colors, requestedInfo, options));
-    if (!fSwizzler) {
-        // FIXME: CreateSwizzler could fail for another reason.
-        return kUnimplemented;
-    }
-    return kSuccess;
-}
-
-
-bool SkPngCodec::onRewind() {
-    // This sets fPng_ptr and fInfo_ptr to nullptr. If read_header
-    // succeeds, they will be repopulated, and if it fails, they will
-    // remain nullptr. Any future accesses to fPng_ptr and fInfo_ptr will
-    // come through this function which will rewind and again attempt
-    // to reinitialize them.
-    this->destroyReadStruct();
-
-    png_structp png_ptr;
-    png_infop info_ptr;
-    if (!read_header(this->stream(), fPngChunkReader.get(), &png_ptr, &info_ptr,
-                     nullptr, nullptr, nullptr)) {
-        return false;
-    }
-
-    fPng_ptr = png_ptr;
-    fInfo_ptr = info_ptr;
-    return true;
-}
-
-SkCodec::Result SkPngCodec::onGetPixels(const SkImageInfo& requestedInfo, void* dst,
-                                        size_t dstRowBytes, const Options& options,
-                                        SkPMColor ctable[], int* ctableCount,
-                                        int* rowsDecoded) {
-    if (!conversion_possible(requestedInfo, this->getInfo())) {
-        return kInvalidConversion;
-    }
-    if (options.fSubset) {
-        // Subsets are not supported.
-        return kUnimplemented;
-    }
-
-    // Note that ctable and ctableCount may be modified if there is a color table
-    const Result result = this->initializeSwizzler(requestedInfo, options, ctable, ctableCount);
-    if (result != kSuccess) {
-        return result;
-    }
-    // FIXME: Could we use the return value of setjmp to specify the type of
-    // error?
-    int row = 0;
-    // This must be declared above the call to setjmp to avoid memory leaks on incomplete images.
-    SkAutoTMalloc<uint8_t> storage;
-    if (setjmp(png_jmpbuf(fPng_ptr))) {
-        // Assume that any error that occurs while reading rows is caused by an incomplete input.
-        if (fNumberPasses > 1) {
-            // FIXME (msarett): Handle incomplete interlaced pngs.
-            return kInvalidInput;
-        }
-        // FIXME: We do a poor job on incomplete pngs compared to other decoders (ex: Chromium,
-        // Ubuntu Image Viewer).  This is because we use the default buffer size in libpng (8192
-        // bytes), and if we can't fill the buffer, we immediately fail.
-        // For example, if we try to read 8192 bytes, and the image (incorrectly) only contains
-        // half that, which may have been enough to contain a non-zero number of lines, we fail
-        // when we could have decoded a few more lines and then failed.
-        // The read function that we provide for libpng has no way of indicating that we have
-        // made a partial read.
-        // Making our buffer size smaller improves our incomplete decodes, but what impact does
-        // it have on regular decode performance?  Should we investigate using a different API
-        // instead of png_read_row(s)?  Chromium uses png_process_data.
-        *rowsDecoded = row;
-        return kIncompleteInput;
-    }
-
-    // FIXME: We could split these out based on subclass.
-    void* dstRow = dst;
-    if (fNumberPasses > 1) {
-        const int width = requestedInfo.width();
-        const int height = requestedInfo.height();
-        const int bpp = SkSwizzler::BytesPerPixel(fSrcConfig);
-        const size_t srcRowBytes = width * bpp;
-
-        storage.reset(width * height * bpp);
-        uint8_t* const base = storage.get();
-
-        for (int i = 0; i < fNumberPasses; i++) {
-            uint8_t* srcRow = base;
-            for (int y = 0; y < height; y++) {
-                uint8_t* bmRow = srcRow;
-                png_read_rows(fPng_ptr, &bmRow, png_bytepp_NULL, 1);
-                srcRow += srcRowBytes;
-            }
-        }
-
-        // Now swizzle it.
-        uint8_t* srcRow = base;
-        for (int y = 0; y < height; y++) {
-            fSwizzler->swizzle(dstRow, srcRow);
-            dstRow = SkTAddOffset<void>(dstRow, dstRowBytes);
-            srcRow += srcRowBytes;
-        }
-    } else {
-        storage.reset(requestedInfo.width() * SkSwizzler::BytesPerPixel(fSrcConfig));
-        uint8_t* srcRow = storage.get();
-        for (; row < requestedInfo.height(); row++) {
-            png_read_rows(fPng_ptr, &srcRow, png_bytepp_NULL, 1);
-            // FIXME: Only call IsOpaque once, outside the loop. Same for onGetScanlines.
-            fSwizzler->swizzle(dstRow, srcRow);
-            dstRow = SkTAddOffset<void>(dstRow, dstRowBytes);
-        }
-    }
-
-    // FIXME: do we need substituteTranspColor? Note that we cannot do it for
-    // scanline decoding, but we could do it here. Alternatively, we could do
-    // it as we go, instead of in post-processing like SkPNGImageDecoder.
-
-    if (setjmp(png_jmpbuf(fPng_ptr))) {
-        // We've already read all the scanlines. This is a success.
-        return kSuccess;
-    }
-
-    // read rest of file, and get additional comment and time chunks in info_ptr
-    png_read_end(fPng_ptr, fInfo_ptr);
-
-    return kSuccess;
-}
-
-uint32_t SkPngCodec::onGetFillValue(SkColorType colorType, SkAlphaType alphaType) const {
-    const SkPMColor* colorPtr = get_color_ptr(fColorTable.get());
-    if (colorPtr) {
-        return get_color_table_fill_value(colorType, colorPtr, 0);
-    }
-    return INHERITED::onGetFillValue(colorType, alphaType);
-}
-
-// Subclass of SkPngCodec which supports scanline decoding
-class SkPngScanlineDecoder : public SkPngCodec {
-public:
-    SkPngScanlineDecoder(const SkImageInfo& srcInfo, SkStream* stream,
-            SkPngChunkReader* chunkReader, png_structp png_ptr, png_infop info_ptr, int bitDepth)
-        : INHERITED(srcInfo, stream, chunkReader, png_ptr, info_ptr, bitDepth, 1)
-        , fSrcRow(nullptr)
-    {}
-
-    Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& options,
-            SkPMColor ctable[], int* ctableCount) override {
-        if (!conversion_possible(dstInfo, this->getInfo())) {
-            return kInvalidConversion;
-        }
-
-        const Result result = this->initializeSwizzler(dstInfo, options, ctable,
-                                                       ctableCount);
-        if (result != kSuccess) {
-            return result;
-        }
-
-        fStorage.reset(this->getInfo().width() * SkSwizzler::BytesPerPixel(this->srcConfig()));
-        fSrcRow = fStorage.get();
-
-        return kSuccess;
-    }
-
-    int onGetScanlines(void* dst, int count, size_t rowBytes) override {
-        // Assume that an error in libpng indicates an incomplete input.
-        int row = 0;
-        if (setjmp(png_jmpbuf(this->png_ptr()))) {
-            SkCodecPrintf("setjmp long jump!\n");
-            return row;
-        }
-
-        void* dstRow = dst;
-        for (; row < count; row++) {
-            png_read_rows(this->png_ptr(), &fSrcRow, png_bytepp_NULL, 1);
-            this->swizzler()->swizzle(dstRow, fSrcRow);
-            dstRow = SkTAddOffset<void>(dstRow, rowBytes);
-        }
-
-        return row;
-    }
-
-    bool onSkipScanlines(int count) override {
-        // Assume that an error in libpng indicates an incomplete input.
-        if (setjmp(png_jmpbuf(this->png_ptr()))) {
-            SkCodecPrintf("setjmp long jump!\n");
-            return false;
-        }
-        //there is a potential tradeoff of memory vs speed created by putting this in a loop. 
-        //calling png_read_rows in a loop is insignificantly slower than calling it once with count 
-        //as png_read_rows has it's own loop which calls png_read_row count times.
-        for (int row = 0; row < count; row++) {
-            png_read_rows(this->png_ptr(), &fSrcRow, png_bytepp_NULL, 1);
-        }
-        return true;
-    }
-
-private:
-    SkAutoTMalloc<uint8_t>      fStorage;
-    uint8_t*                    fSrcRow;
-
-    typedef SkPngCodec INHERITED;
-};
-
-
-class SkPngInterlacedScanlineDecoder : public SkPngCodec {
-public:
-    SkPngInterlacedScanlineDecoder(const SkImageInfo& srcInfo, SkStream* stream,
-            SkPngChunkReader* chunkReader, png_structp png_ptr, png_infop info_ptr,
-            int bitDepth, int numberPasses)
-        : INHERITED(srcInfo, stream, chunkReader, png_ptr, info_ptr, bitDepth, numberPasses)
-        , fHeight(-1)
-        , fCanSkipRewind(false)
-    {
-        SkASSERT(numberPasses != 1);
-    }
-
-    Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& options,
-            SkPMColor ctable[], int* ctableCount) override {
-        if (!conversion_possible(dstInfo, this->getInfo())) {
-            return kInvalidConversion;    
-        }
-
-        const Result result = this->initializeSwizzler(dstInfo, options, ctable,
-                                                       ctableCount);
-        if (result != kSuccess) {
-            return result;
-        }
-
-        fHeight = dstInfo.height();
-        // FIXME: This need not be called on a second call to onStartScanlineDecode.
-        fSrcRowBytes = this->getInfo().width() * SkSwizzler::BytesPerPixel(this->srcConfig());
-        fGarbageRow.reset(fSrcRowBytes);
-        fGarbageRowPtr = static_cast<uint8_t*>(fGarbageRow.get());
-        fCanSkipRewind = true;
-
-        return SkCodec::kSuccess;
-    }
-
-    int onGetScanlines(void* dst, int count, size_t dstRowBytes) override {
-        // rewind stream if have previously called onGetScanlines,
-        // since we need entire progressive image to get scanlines
-        if (fCanSkipRewind) {
-            // We already rewound in onStartScanlineDecode, so there is no reason to rewind.
-            // Next time onGetScanlines is called, we will need to rewind.
-            fCanSkipRewind = false;
-        } else {
-            // rewindIfNeeded resets fCurrScanline, since it assumes that start
-            // needs to be called again before scanline decoding. PNG scanline
-            // decoding is the exception, since it needs to rewind between
-            // calls to getScanlines. Keep track of fCurrScanline, to undo the
-            // reset.
-            const int currScanline = this->nextScanline();
-            // This method would never be called if currScanline is -1
-            SkASSERT(currScanline != -1);
-
-            if (!this->rewindIfNeeded()) {
-                return kCouldNotRewind;
-            }
-            this->updateCurrScanline(currScanline);
-        }
-
-        if (setjmp(png_jmpbuf(this->png_ptr()))) {
-            SkCodecPrintf("setjmp long jump!\n");
-            // FIXME (msarett): Returning 0 is pessimistic.  If we can complete a single pass,
-            // we may be able to report that all of the memory has been initialized.  Even if we
-            // fail on the first pass, we can still report than some scanlines are initialized.
-            return 0;
-        }
-        SkAutoTMalloc<uint8_t> storage(count * fSrcRowBytes);
-        uint8_t* storagePtr = storage.get();
-        uint8_t* srcRow;
-        const int startRow = this->nextScanline();
-        for (int i = 0; i < this->numberPasses(); i++) {
-            // read rows we planned to skip into garbage row
-            for (int y = 0; y < startRow; y++){
-                png_read_rows(this->png_ptr(), &fGarbageRowPtr, png_bytepp_NULL, 1);
-            }
-            // read rows we care about into buffer
-            srcRow = storagePtr;
-            for (int y = 0; y < count; y++) {
-                png_read_rows(this->png_ptr(), &srcRow, png_bytepp_NULL, 1);
-                srcRow += fSrcRowBytes;
-            }
-            // read rows we don't want into garbage buffer
-            for (int y = 0; y < fHeight - startRow - count; y++) {
-                png_read_rows(this->png_ptr(), &fGarbageRowPtr, png_bytepp_NULL, 1);
-            }
-        }
-        //swizzle the rows we care about
-        srcRow = storagePtr;
-        void* dstRow = dst;
-        for (int y = 0; y < count; y++) {
-            this->swizzler()->swizzle(dstRow, srcRow);
-            dstRow = SkTAddOffset<void>(dstRow, dstRowBytes);
-            srcRow += fSrcRowBytes;
-        }
-
-        return count;
-    }
-
-    bool onSkipScanlines(int count) override {
-        // The non-virtual version will update fCurrScanline.
-        return true;
-    }
-
-    SkScanlineOrder onGetScanlineOrder() const override {
-        return kNone_SkScanlineOrder;
-    }
-
-private:
-    int                         fHeight;
-    size_t                      fSrcRowBytes;
-    SkAutoMalloc                fGarbageRow;
-    uint8_t*                    fGarbageRowPtr;
-    // FIXME: This imitates behavior in SkCodec::rewindIfNeeded. That function
-    // is called whenever some action is taken that reads the stream and
-    // therefore the next call will require a rewind. So it modifies a boolean
-    // to note that the *next* time it is called a rewind is needed.
-    // SkPngInterlacedScanlineDecoder has an extra wrinkle - calling
-    // onStartScanlineDecode followed by onGetScanlines does *not* require a
-    // rewind. Since rewindIfNeeded does not have this flexibility, we need to
-    // add another layer.
-    bool                        fCanSkipRewind;
-
-    typedef SkPngCodec INHERITED;
-};
-
-SkCodec* SkPngCodec::NewFromStream(SkStream* stream, SkPngChunkReader* chunkReader) {
-    SkAutoTDelete<SkStream> streamDeleter(stream);
-    png_structp png_ptr;
-    png_infop info_ptr;
-    SkImageInfo imageInfo;
-    int bitDepth;
-    int numberPasses;
-
-    if (!read_header(stream, chunkReader, &png_ptr, &info_ptr, &imageInfo, &bitDepth,
-                     &numberPasses)) {
-        return nullptr;
-    }
-
-    if (1 == numberPasses) {
-        return new SkPngScanlineDecoder(imageInfo, streamDeleter.detach(), chunkReader,
-                                        png_ptr, info_ptr, bitDepth);
-    }
-
-    return new SkPngInterlacedScanlineDecoder(imageInfo, streamDeleter.detach(), chunkReader,
-                                              png_ptr, info_ptr, bitDepth, numberPasses);
-}