/*
* 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 "SkCodecPriv.h"
#include "SkColorPriv.h"
#include "SkColorTable.h"
#include "SkBitmap.h"
#include "SkMath.h"
#include "SkOpts.h"
#include "SkPngCodec.h"
#include "SkSize.h"
#include "SkStream.h"
#include "SkSwizzler.h"
#include "SkTemplates.h"
#include "SkUtils.h"
///////////////////////////////////////////////////////////////////////////////
// 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, nullptr);
}
}
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)
// 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.
// TODO: If we add support for non-native swizzles, we'll need to handle that here.
bool SkPngCodec::decodePalette(bool premultiply, int* ctableCount) {
int numColors;
png_color* palette;
if (!png_get_PLTE(fPng_ptr, fInfo_ptr, &palette, &numColors)) {
return false;
}
// Note: These are not necessarily SkPMColors.
SkPMColor colorPtr[256];
png_bytep alphas;
int numColorsWithAlpha = 0;
if (png_get_tRNS(fPng_ptr, fInfo_ptr, &alphas, &numColorsWithAlpha, nullptr)) {
// 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 = &SkPremultiplyARGBInline;
} else {
proc = &SkPackARGB32NoCheck;
}
for (int i = 0; i < numColorsWithAlpha; i++) {
// We don't have a function in SkOpts that combines a set of alphas with a set
// of RGBs. We could write one, but it's hardly worth it, given that this
// is such a small fraction of the total decode time.
colorPtr[i] = proc(alphas[i], palette->red, palette->green, palette->blue);
palette++;
}
}
if (numColorsWithAlpha < numColors) {
// The optimized code depends on a 3-byte png_color struct with the colors
// in RGB order. These checks make sure it is safe to use.
static_assert(3 == sizeof(png_color), "png_color struct has changed. Opts are broken.");
#ifdef SK_DEBUG
SkASSERT(&palette->red < &palette->green);
SkASSERT(&palette->green < &palette->blue);
#endif
#ifdef SK_PMCOLOR_IS_RGBA
SkOpts::RGB_to_RGB1(colorPtr + numColorsWithAlpha, palette, numColors - numColorsWithAlpha);
#else
SkOpts::RGB_to_BGR1(colorPtr + numColorsWithAlpha, palette, numColors - numColorsWithAlpha);
#endif
}
// Pad the color table with the last color in the table (or black) in the case that
// invalid pixel indices exceed the number of colors in the table.
const int maxColors = 1 << fBitDepth;
if (numColors < maxColors) {
SkPMColor lastColor = numColors > 0 ? colorPtr[numColors - 1] : SK_ColorBLACK;
sk_memset32(colorPtr + numColors, lastColor, maxColors - numColors);
}
// Set the new color count.
if (ctableCount != nullptr) {
*ctableCount = maxColors;
}
fColorTable.reset(new SkColorTable(colorPtr, maxColors));
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, encodedColorType;
png_get_IHDR(png_ptr, info_ptr, &origWidth, &origHeight, &bitDepth,
&encodedColorType, nullptr, nullptr, nullptr);
if (bitDepthPtr) {
*bitDepthPtr = bitDepth;
}
// Tell libpng to strip 16 bit/color files down to 8 bits/color.
// TODO: Should we handle this in SkSwizzler? Could this also benefit
// RAW decodes?
if (bitDepth == 16) {
SkASSERT(PNG_COLOR_TYPE_PALETTE != encodedColorType);
png_set_strip_16(png_ptr);
}
// Now determine the default colorType and alphaType and set the required transforms.
// Often, we depend on SkSwizzler to perform any transforms that we need. However, we
// still depend on libpng for many of the rare and PNG-specific cases.
SkColorType colorType = kUnknown_SkColorType;
SkAlphaType alphaType = kUnknown_SkAlphaType;
switch (encodedColorType) {
case PNG_COLOR_TYPE_PALETTE:
// 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) {
// TODO: Should we use SkSwizzler here?
png_set_packing(png_ptr);
}
colorType = kIndex_8_SkColorType;
// Set the alpha type depending on if a transparency chunk exists.
alphaType = png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS) ?
kUnpremul_SkAlphaType : kOpaque_SkAlphaType;
break;
case PNG_COLOR_TYPE_RGB:
if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) {
// Convert to RGBA if transparency chunk exists.
png_set_tRNS_to_alpha(png_ptr);
alphaType = kUnpremul_SkAlphaType;
} else {
alphaType = kOpaque_SkAlphaType;
}
colorType = kN32_SkColorType;
break;
case PNG_COLOR_TYPE_GRAY:
// Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel.
if (bitDepth < 8) {
// TODO: Should we use SkSwizzler here?
png_set_expand_gray_1_2_4_to_8(png_ptr);
}
if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) {
png_set_tRNS_to_alpha(png_ptr);
// We will recommend kN32 here since we do not support kGray
// with alpha.
colorType = kN32_SkColorType;
alphaType = kUnpremul_SkAlphaType;
} else {
colorType = kGray_8_SkColorType;
alphaType = kOpaque_SkAlphaType;
}
break;
case PNG_COLOR_TYPE_GRAY_ALPHA:
// We will recommend kN32 here since we do not support anything
// similar to GRAY_ALPHA.
colorType = kN32_SkColorType;
alphaType = kUnpremul_SkAlphaType;
break;
case PNG_COLOR_TYPE_RGBA:
colorType = kN32_SkColorType;
alphaType = 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;
}
SkColorProfileType profileType = kLinear_SkColorProfileType;
if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sRGB)) {
profileType = kSRGB_SkColorProfileType;
}
if (imageInfo) {
*imageInfo = SkImageInfo::Make(origWidth, origHeight, colorType, alphaType, profileType);
}
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, nullptr);
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);
// suggestedColorType was determined in read_header() based on the encodedColorType
const SkColorType suggestedColorType = this->getInfo().colorType();
switch (suggestedColorType) {
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: {
const uint8_t encodedColorType = png_get_color_type(fPng_ptr, fInfo_ptr);
if (PNG_COLOR_TYPE_GRAY_ALPHA == encodedColorType ||
PNG_COLOR_TYPE_GRAY == encodedColorType) {
// If encodedColorType is GRAY, there must be a transparent chunk.
// Otherwise, suggestedColorType would be kGray. We have already
// instructed libpng to convert the transparent chunk to alpha,
// so we can treat both GRAY and GRAY_ALPHA as kGrayAlpha.
SkASSERT(encodedColorType == PNG_COLOR_TYPE_GRAY_ALPHA ||
png_get_valid(fPng_ptr, fInfo_ptr, PNG_INFO_tRNS));
fSrcConfig = SkSwizzler::kGrayAlpha;
} else {
if (this->getInfo().alphaType() == kOpaque_SkAlphaType) {
fSrcConfig = SkSwizzler::kRGB;
} else {
fSrcConfig = SkSwizzler::kRGBA;
}
}
break;
}
default:
// We will always recommend one of the above colorTypes.
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));
SkASSERT(fSwizzler);
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;
}
const int width = requestedInfo.width();
const int height = requestedInfo.height();
const int bpp = SkSwizzler::BytesPerPixel(fSrcConfig);
const size_t srcRowBytes = width * bpp;
// 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 (row == height) ? kSuccess : 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? Chromium uses png_process_data.
*rowsDecoded = row;
return (row == height) ? kSuccess : kIncompleteInput;
}
// FIXME: We could split these out based on subclass.
void* dstRow = dst;
if (fNumberPasses > 1) {
storage.reset(height * srcRowBytes);
uint8_t* const base = storage.get();
for (int i = 0; i < fNumberPasses; i++) {
uint8_t* srcRow = base;
for (int y = 0; y < height; y++) {
png_read_row(fPng_ptr, srcRow, nullptr);
srcRow += srcRowBytes;
}
}
// Now swizzle it.
uint8_t* srcRow = base;
for (; row < height; row++) {
fSwizzler->swizzle(dstRow, srcRow);
dstRow = SkTAddOffset<void>(dstRow, dstRowBytes);
srcRow += srcRowBytes;
}
} else {
storage.reset(srcRowBytes);
uint8_t* srcRow = storage.get();
for (; row < height; row++) {
png_read_row(fPng_ptr, srcRow, nullptr);
fSwizzler->swizzle(dstRow, srcRow);
dstRow = SkTAddOffset<void>(dstRow, dstRowBytes);
}
}
// 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) const {
const SkPMColor* colorPtr = get_color_ptr(fColorTable.get());
if (colorPtr) {
return get_color_table_fill_value(colorType, colorPtr, 0);
}
return INHERITED::onGetFillValue(colorType);
}
// 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_row(this->png_ptr(), fSrcRow, nullptr);
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;
}
for (int row = 0; row < count; row++) {
png_read_row(this->png_ptr(), fSrcRow, nullptr);
}
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_row(this->png_ptr(), fGarbageRowPtr, nullptr);
}
// read rows we care about into buffer
srcRow = storagePtr;
for (int y = 0; y < count; y++) {
png_read_row(this->png_ptr(), srcRow, nullptr);
srcRow += fSrcRowBytes;
}
// read rows we don't want into garbage buffer
for (int y = 0; y < fHeight - startRow - count; y++) {
png_read_row(this->png_ptr(), fGarbageRowPtr, nullptr);
}
}
//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);
}