third_party/WebKit/Source/platform/image-encoders/PNGImageEncoder.cpp

/*
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#include "platform/image-encoders/PNGImageEncoder.h"

#include "platform/graphics/ImageBuffer.h"
#include "wtf/PtrUtil.h"
#include <memory>

#include "zlib.h"

namespace blink {

PNGImageEncoderState::~PNGImageEncoderState() {
  png_destroy_write_struct(&m_png, &m_info);
}

static void writeOutput(png_structp png, png_bytep data, png_size_t size) {
  static_cast<Vector<unsigned char>*>(png_get_io_ptr(png))->append(data, size);
}

std::unique_ptr<PNGImageEncoderState> PNGImageEncoderState::create(
    const IntSize& imageSize,
    Vector<unsigned char>* output) {
  if (imageSize.width() <= 0 || imageSize.height() <= 0)
    return nullptr;

  png_struct* png = png_create_write_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0);
  png_info* info = png_create_info_struct(png);
  if (!png || !info || setjmp(png_jmpbuf(png))) {
    png_destroy_write_struct(png ? &png : 0, info ? &info : 0);
    return nullptr;
  }

  // Optimize compression for speed.
  // The parameters are the same as what libpng uses by default for RGB and RGBA
  // images, except:
  // The zlib compression level is set to 3 instead of 6, to avoid the lazy
  // Ziv-Lempel match searching.
  png_set_compression_level(png, 3);

  // The zlib memory level is set to 8.  This actually matches the default, we
  // are just future-proofing.
  png_set_compression_mem_level(png, 8);

  // The zlib strategy is set to Z_FILTERED, which does not match the default.
  // Avoid the zlib strategies Z_HUFFMAN_ONLY or Z_RLE.
  // Although they are the fastest for poorly-compressible images (e.g.
  // photographs), they are very slow for highly-compressible images (e.g. text,
  // drawings or business graphics)
  png_set_compression_strategy(png, Z_FILTERED);

  // The delta filter is PNG_FILTER_SUB instead of PNG_ALL_FILTERS, to reduce
  // the filter computations.
  png_set_filter(png, PNG_FILTER_TYPE_BASE, PNG_FILTER_SUB);

  png_set_write_fn(png, output, writeOutput, 0);
  png_set_IHDR(png, info, imageSize.width(), imageSize.height(), 8,
               PNG_COLOR_TYPE_RGB_ALPHA, 0, 0, 0);
  png_write_info(png, info);

  return wrapUnique(new PNGImageEncoderState(png, info));
}

void PNGImageEncoder::writeOneRowToPng(unsigned char* pixels,
                                       PNGImageEncoderState* encoderState) {
  png_write_row(encoderState->png(), pixels);
}

void PNGImageEncoder::finalizePng(PNGImageEncoderState* encoderState) {
  png_write_end(encoderState->png(), encoderState->info());
}

static bool encodePixels(const IntSize& imageSize,
                         const unsigned char* inputPixels,
                         Vector<unsigned char>* output) {
  std::unique_ptr<PNGImageEncoderState> encoderState =
      PNGImageEncoderState::create(imageSize, output);
  if (!encoderState.get())
    return false;

  unsigned char* pixels = const_cast<unsigned char*>(inputPixels);
  const size_t pixelRowStride = imageSize.width() * 4;
  for (int y = 0; y < imageSize.height(); ++y) {
    PNGImageEncoder::writeOneRowToPng(pixels, encoderState.get());
    pixels += pixelRowStride;
  }

  PNGImageEncoder::finalizePng(encoderState.get());
  return true;
}

bool PNGImageEncoder::encode(const ImageDataBuffer& imageData,
                             Vector<unsigned char>* output) {
  if (!imageData.pixels())
    return false;

  return encodePixels(imageData.size(), imageData.pixels(), output);
}

}  // namespace blink