text: // Copyright 2013 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // This is a duplicate of chromium's src/tools/imagediff/image_diff_png.cc
  // that has been modified to build in a pdfium environment, which itself
  // was duplicated as follows:
  
  // This is a duplicate of ui/gfx/codec/png_codec.cc, after removing code related
  // to Skia, that we can use when running layout tests with minimal dependencies.
  
  #include "testing/image_diff/image_diff_png.h"
  
  #include <stdlib.h>
  #include <string.h>
  
  #include <string>
  
  #include "third_party/base/compiler_specific.h"
  #include "third_party/base/logging.h"
  
  #ifdef USE_SYSTEM_ZLIB
  #include <zlib.h>
  #else
  #include "third_party/zlib/zlib.h"
  #endif
  
  #ifdef USE_SYSTEM_LIBPNG
  #include <png.h>
  #else
  #include "third_party/libpng16/png.h"
  #endif
  
  namespace image_diff_png {
  
  namespace {
  
  enum ColorFormat {
    // 3 bytes per pixel (packed), in RGB order regardless of endianness.
    // This is the native JPEG format.
    FORMAT_RGB,
  
    // 3 bytes per pixel, in BGR order regardless of endianness.
    FORMAT_BGR,
  
    // 4 bytes per pixel, in RGBA order in memory regardless of endianness.
    FORMAT_RGBA,
  
    // 4 bytes per pixel, in BGRA order in memory regardless of endianness.
    // This is the default Windows DIB order.
    FORMAT_BGRA,
  
    // 1 byte per pixel.
    FORMAT_GRAY,
  };
  
  // Represents a comment in the tEXt ancillary chunk of the png.
  struct Comment {
    std::string key;
    std::string text;
  };
  
  // Converts BGRA->RGBA and RGBA->BGRA.
  void ConvertBetweenBGRAandRGBA(const unsigned char* input,
                                 int pixel_width,
                                 unsigned char* output,
                                 bool* is_opaque) {
    for (int x = 0; x < pixel_width; x++) {
      const unsigned char* pixel_in = &input[x * 4];
      unsigned char* pixel_out = &output[x * 4];
      pixel_out[0] = pixel_in[2];
      pixel_out[1] = pixel_in[1];
      pixel_out[2] = pixel_in[0];
      pixel_out[3] = pixel_in[3];
    }
  }
  
  void ConvertBGRtoRGB(const unsigned char* bgr,
                       int pixel_width,
                       unsigned char* rgb,
                       bool* is_opaque) {
    for (int x = 0; x < pixel_width; x++) {
      const unsigned char* pixel_in = &bgr[x * 3];
      unsigned char* pixel_out = &rgb[x * 3];
      pixel_out[0] = pixel_in[2];
      pixel_out[1] = pixel_in[1];
      pixel_out[2] = pixel_in[0];
    }
  }
  
  void ConvertRGBAtoRGB(const unsigned char* rgba,
                        int pixel_width,
                        unsigned char* rgb,
                        bool* is_opaque) {
    for (int x = 0; x < pixel_width; x++) {
      const unsigned char* pixel_in = &rgba[x * 4];
      unsigned char* pixel_out = &rgb[x * 3];
      pixel_out[0] = pixel_in[0];
      pixel_out[1] = pixel_in[1];
      pixel_out[2] = pixel_in[2];
    }
  }
  
  }  // namespace
  
  // Decoder
  //
  // This code is based on WebKit libpng interface (PNGImageDecoder), which is
  // in turn based on the Mozilla png decoder.
  
  namespace {
  
  // Gamma constants: We assume we're on Windows which uses a gamma of 2.2.
  const double kMaxGamma = 21474.83;  // Maximum gamma accepted by png library.
  const double kDefaultGamma = 2.2;
  const double kInverseGamma = 1.0 / kDefaultGamma;
  
  class PngDecoderState {
   public:
    // Output is a vector<unsigned char>.
    PngDecoderState(ColorFormat ofmt, std::vector<unsigned char>* o)
        : output_format(ofmt),
          output_channels(0),
          is_opaque(true),
          output(o),
          row_converter(nullptr),
          width(0),
          height(0),
          done(false) {}
  
    ColorFormat output_format;
    int output_channels;
  
    // Used during the reading of an SkBitmap. Defaults to true until we see a
    // pixel with anything other than an alpha of 255.
    bool is_opaque;
  
    // An intermediary buffer for decode output.
    std::vector<unsigned char>* output;
  
    // Called to convert a row from the library to the correct output format.
    // When NULL, no conversion is necessary.
    void (*row_converter)(const unsigned char* in,
                          int w,
                          unsigned char* out,
                          bool* is_opaque);
  
    // Size of the image, set in the info callback.
    int width;
    int height;
  
    // Set to true when we've found the end of the data.
    bool done;
  };
  
  void ConvertRGBtoRGBA(const unsigned char* rgb,
                        int pixel_width,
                        unsigned char* rgba,
                        bool* is_opaque) {
    for (int x = 0; x < pixel_width; x++) {
      const unsigned char* pixel_in = &rgb[x * 3];
      unsigned char* pixel_out = &rgba[x * 4];
      pixel_out[0] = pixel_in[0];
      pixel_out[1] = pixel_in[1];
      pixel_out[2] = pixel_in[2];
      pixel_out[3] = 0xff;
    }
  }
  
  void ConvertRGBtoBGRA(const unsigned char* rgb,
                        int pixel_width,
                        unsigned char* bgra,
                        bool* is_opaque) {
    for (int x = 0; x < pixel_width; x++) {
      const unsigned char* pixel_in = &rgb[x * 3];
      unsigned char* pixel_out = &bgra[x * 4];
      pixel_out[0] = pixel_in[2];
      pixel_out[1] = pixel_in[1];
      pixel_out[2] = pixel_in[0];
      pixel_out[3] = 0xff;
    }
  }
  
  // Called when the png header has been read. This code is based on the WebKit
  // PNGImageDecoder
  void DecodeInfoCallback(png_struct* png_ptr, png_info* info_ptr) {
    PngDecoderState* state =
        static_cast<PngDecoderState*>(png_get_progressive_ptr(png_ptr));
  
    int bit_depth, color_type, interlace_type, compression_type;
    int filter_type, channels;
    png_uint_32 w, h;
    png_get_IHDR(png_ptr, info_ptr, &w, &h, &bit_depth, &color_type,
                 &interlace_type, &compression_type, &filter_type);
  
    // Bounds check. When the image is unreasonably big, we'll error out and
    // end up back at the setjmp call when we set up decoding.  "Unreasonably big"
    // means "big enough that w * h * 32bpp might overflow an int"; we choose this
    // threshold to match WebKit and because a number of places in code assume
    // that an image's size (in bytes) fits in a (signed) int.
    unsigned long long total_size =
        static_cast<unsigned long long>(w) * static_cast<unsigned long long>(h);
    if (total_size > ((1 << 29) - 1))
      longjmp(png_jmpbuf(png_ptr), 1);
    state->width = static_cast<int>(w);
    state->height = static_cast<int>(h);
  
    // Expand to ensure we use 24-bit for RGB and 32-bit for RGBA.
    if (color_type == PNG_COLOR_TYPE_PALETTE ||
        (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8))
      png_set_expand(png_ptr);
  
    // Transparency for paletted images.
    if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
      png_set_expand(png_ptr);
  
    // Convert 16-bit to 8-bit.
    if (bit_depth == 16)
      png_set_strip_16(png_ptr);
  
    // Expand grayscale to RGB.
    if (color_type == PNG_COLOR_TYPE_GRAY ||
        color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
      png_set_gray_to_rgb(png_ptr);
  
    // Deal with gamma and keep it under our control.
    double gamma;
    if (png_get_gAMA(png_ptr, info_ptr, &gamma)) {
      if (gamma <= 0.0 || gamma > kMaxGamma) {
        gamma = kInverseGamma;
        png_set_gAMA(png_ptr, info_ptr, gamma);
      }
      png_set_gamma(png_ptr, kDefaultGamma, gamma);
    } else {
      png_set_gamma(png_ptr, kDefaultGamma, kInverseGamma);
    }
  
    // Tell libpng to send us rows for interlaced pngs.
    if (interlace_type == PNG_INTERLACE_ADAM7)
      png_set_interlace_handling(png_ptr);
  
    // Update our info now
    png_read_update_info(png_ptr, info_ptr);
    channels = png_get_channels(png_ptr, info_ptr);
  
    // Pick our row format converter necessary for this data.
    if (channels == 3) {
      switch (state->output_format) {
        case FORMAT_RGB:
          state->row_converter = nullptr;  // no conversion necessary
          state->output_channels = 3;
          break;
        case FORMAT_RGBA:
          state->row_converter = &ConvertRGBtoRGBA;
          state->output_channels = 4;
          break;
        case FORMAT_BGRA:
          state->row_converter = &ConvertRGBtoBGRA;
          state->output_channels = 4;
          break;
        case FORMAT_GRAY:
          state->row_converter = nullptr;
          state->output_channels = 1;
          break;
        default:
          NOTREACHED();
          break;
      }
    } else if (channels == 4) {
      switch (state->output_format) {
        case FORMAT_RGB:
          state->row_converter = &ConvertRGBAtoRGB;
          state->output_channels = 3;
          break;
        case FORMAT_RGBA:
          state->row_converter = nullptr;  // no conversion necessary
          state->output_channels = 4;
          break;
        case FORMAT_BGRA:
          state->row_converter = &ConvertBetweenBGRAandRGBA;
          state->output_channels = 4;
          break;
        default:
          NOTREACHED();
          break;
      }
    } else {
      NOTREACHED();
      longjmp(png_jmpbuf(png_ptr), 1);
    }
  
    state->output->resize(state->width * state->output_channels * state->height);
  }
  
  void DecodeRowCallback(png_struct* png_ptr,
                         png_byte* new_row,
                         png_uint_32 row_num,
                         int pass) {
    PngDecoderState* state =
        static_cast<PngDecoderState*>(png_get_progressive_ptr(png_ptr));
  
    if (static_cast<int>(row_num) > state->height) {
      NOTREACHED();
      return;
    }
  
    unsigned char* base = NULL;
    base = &state->output->front();
  
    unsigned char* dest = &base[state->width * state->output_channels * row_num];
    if (state->row_converter)
      state->row_converter(new_row, state->width, dest, &state->is_opaque);
    else
      memcpy(dest, new_row, state->width * state->output_channels);
  }
  
  void DecodeEndCallback(png_struct* png_ptr, png_info* info) {
    PngDecoderState* state =
        static_cast<PngDecoderState*>(png_get_progressive_ptr(png_ptr));
  
    // Mark the image as complete, this will tell the Decode function that we
    // have successfully found the end of the data.
    state->done = true;
  }
  
  // Automatically destroys the given read structs on destruction to make
  // cleanup and error handling code cleaner.
  class PngReadStructDestroyer {
   public:
    PngReadStructDestroyer(png_struct** ps, png_info** pi) : ps_(ps), pi_(pi) {}
    ~PngReadStructDestroyer() { png_destroy_read_struct(ps_, pi_, NULL); }
  
   private:
    png_struct** ps_;
    png_info** pi_;
  };
  
  bool BuildPNGStruct(const unsigned char* input,
                      size_t input_size,
                      png_struct** png_ptr,
                      png_info** info_ptr) {
    if (input_size < 8)
      return false;  // Input data too small to be a png
  
    // Have libpng check the signature, it likes the first 8 bytes.
    if (png_sig_cmp(const_cast<unsigned char*>(input), 0, 8) != 0)
      return false;
  
    *png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!*png_ptr)
      return false;
  
    *info_ptr = png_create_info_struct(*png_ptr);
    if (!*info_ptr) {
      png_destroy_read_struct(png_ptr, NULL, NULL);
      return false;
    }
  
    return true;
  }
  
  }  // namespace
  
  // static
  bool Decode(const unsigned char* input,
              size_t input_size,
              ColorFormat format,
              std::vector<unsigned char>* output,
              int* w,
              int* h) {
    png_struct* png_ptr = NULL;
    png_info* info_ptr = NULL;
    if (!BuildPNGStruct(input, input_size, &png_ptr, &info_ptr))
      return false;
  
    PngReadStructDestroyer destroyer(&png_ptr, &info_ptr);
    if (setjmp(png_jmpbuf(png_ptr))) {
      // The destroyer will ensure that the structures are cleaned up in this
      // case, even though we may get here as a jump from random parts of the
      // PNG library called below.
      return false;
    }
  
    PngDecoderState state(format, output);
  
    png_set_progressive_read_fn(png_ptr, &state, &DecodeInfoCallback,
                                &DecodeRowCallback, &DecodeEndCallback);
    png_process_data(png_ptr, info_ptr, const_cast<unsigned char*>(input),
                     input_size);
  
    if (!state.done) {
      // Fed it all the data but the library didn't think we got all the data, so
      // this file must be truncated.
      output->clear();
      return false;
    }
  
    *w = state.width;
    *h = state.height;
    return true;
  }
  
  // Encoder
  //
  // This section of the code is based on nsPNGEncoder.cpp in Mozilla
  // (Copyright 2005 Google Inc.)
  
  namespace {
  
  // Passed around as the io_ptr in the png structs so our callbacks know where
  // to write data.
  struct PngEncoderState {
    explicit PngEncoderState(std::vector<unsigned char>* o) : out(o) {}
    std::vector<unsigned char>* out;
  };
  
  // Called by libpng to flush its internal buffer to ours.
  void EncoderWriteCallback(png_structp png, png_bytep data, png_size_t size) {
    PngEncoderState* state = static_cast<PngEncoderState*>(png_get_io_ptr(png));
    size_t old_size = state->out->size();
    state->out->resize(old_size + size);
    memcpy(&(*state->out)[old_size], data, size);
  }
  
  void FakeFlushCallback(png_structp png) {
    // We don't need to perform any flushing since we aren't doing real IO, but
    // we're required to provide this function by libpng.
  }
  
  void ConvertBGRAtoRGB(const unsigned char* bgra,
                        int pixel_width,
                        unsigned char* rgb,
                        bool* is_opaque) {
    for (int x = 0; x < pixel_width; x++) {
      const unsigned char* pixel_in = &bgra[x * 4];
      unsigned char* pixel_out = &rgb[x * 3];
      pixel_out[0] = pixel_in[2];
      pixel_out[1] = pixel_in[1];
      pixel_out[2] = pixel_in[0];
    }
  }
  
  #ifdef PNG_TEXT_SUPPORTED
  
  inline char* strdup(const char* str) {
  #if defined(OS_WIN)
    return _strdup(str);
  #else
    return ::strdup(str);
  #endif
  }
  
  class CommentWriter {
   public:
    explicit CommentWriter(const std::vector<Comment>& comments)
        : comments_(comments), png_text_(new png_text[comments.size()]) {
      for (size_t i = 0; i < comments.size(); ++i)
        AddComment(i, comments[i]);
    }
  
    ~CommentWriter() {
      for (size_t i = 0; i < comments_.size(); ++i) {
        free(png_text_[i].key);
        free(png_text_[i].text);
      }
      delete[] png_text_;
    }
  
    bool HasComments() { return !comments_.empty(); }
  
    png_text* get_png_text() { return png_text_; }
  
    int size() { return static_cast<int>(comments_.size()); }
  
   private:
    void AddComment(size_t pos, const Comment& comment) {
      png_text_[pos].compression = PNG_TEXT_COMPRESSION_NONE;
      // A PNG comment's key can only be 79 characters long.
      if (comment.key.length() > 79)
        return;
      png_text_[pos].key = strdup(comment.key.substr(0, 78).c_str());
      png_text_[pos].text = strdup(comment.text.c_str());
      png_text_[pos].text_length = comment.text.length();
  #ifdef PNG_iTXt_SUPPORTED
      png_text_[pos].itxt_length = 0;
      png_text_[pos].lang = 0;
      png_text_[pos].lang_key = 0;
  #endif
    }
  
    const std::vector<Comment> comments_;
    png_text* png_text_;
  };
  #endif  // PNG_TEXT_SUPPORTED
  
  // The type of functions usable for converting between pixel formats.
  typedef void (*FormatConverter)(const unsigned char* in,
                                  int w,
                                  unsigned char* out,
                                  bool* is_opaque);
  
  // libpng uses a wacky setjmp-based API, which makes the compiler nervous.
  // We constrain all of the calls we make to libpng where the setjmp() is in
  // place to this function.
  // Returns true on success.
  bool DoLibpngWrite(png_struct* png_ptr,
                     png_info* info_ptr,
                     PngEncoderState* state,
                     int width,
                     int height,
                     int row_byte_width,
                     const unsigned char* input,
                     int compression_level,
                     int png_output_color_type,
                     int output_color_components,
                     FormatConverter converter,
                     const std::vector<Comment>& comments) {
  #ifdef PNG_TEXT_SUPPORTED
    CommentWriter comment_writer(comments);
  #endif
    unsigned char* row_buffer = NULL;
  
    // Make sure to not declare any locals here -- locals in the presence
    // of setjmp() in C++ code makes gcc complain.
  
    if (setjmp(png_jmpbuf(png_ptr))) {
      delete[] row_buffer;
      return false;
    }
  
    png_set_compression_level(png_ptr, compression_level);
  
    // Set our callback for libpng to give us the data.
    png_set_write_fn(png_ptr, state, EncoderWriteCallback, FakeFlushCallback);
  
    png_set_IHDR(png_ptr, info_ptr, width, height, 8, png_output_color_type,
                 PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,
                 PNG_FILTER_TYPE_DEFAULT);
  
  #ifdef PNG_TEXT_SUPPORTED
    if (comment_writer.HasComments()) {
      png_set_text(png_ptr, info_ptr, comment_writer.get_png_text(),
                   comment_writer.size());
    }
  #endif
  
    png_write_info(png_ptr, info_ptr);
  
    if (!converter) {
      // No conversion needed, give the data directly to libpng.
      for (int y = 0; y < height; y++) {
        png_write_row(png_ptr,
                      const_cast<unsigned char*>(&input[y * row_byte_width]));
      }
    } else {
      // Needs conversion using a separate buffer.
      row_buffer = new unsigned char[width * output_color_components];
      for (int y = 0; y < height; y++) {
        converter(&input[y * row_byte_width], width, row_buffer, NULL);
        png_write_row(png_ptr, row_buffer);
      }
      delete[] row_buffer;
    }
  
    png_write_end(png_ptr, info_ptr);
    return true;
  }
  
  }  // namespace
  
  // static
  bool EncodeWithCompressionLevel(const unsigned char* input,
                                  ColorFormat format,
                                  const int width,
                                  const int height,
                                  int row_byte_width,
                                  bool discard_transparency,
                                  const std::vector<Comment>& comments,
                                  int compression_level,
                                  std::vector<unsigned char>* output) {
    // Run to convert an input row into the output row format, NULL means no
    // conversion is necessary.
    FormatConverter converter = nullptr;
  
    int input_color_components, output_color_components;
    int png_output_color_type;
    switch (format) {
      case FORMAT_BGR:
        converter = ConvertBGRtoRGB;
        FALLTHROUGH;
  
      case FORMAT_RGB:
        input_color_components = 3;
        output_color_components = 3;
        png_output_color_type = PNG_COLOR_TYPE_RGB;
        discard_transparency = false;
        break;
  
      case FORMAT_RGBA:
        input_color_components = 4;
        if (discard_transparency) {
          output_color_components = 3;
          png_output_color_type = PNG_COLOR_TYPE_RGB;
          converter = ConvertRGBAtoRGB;
        } else {
          output_color_components = 4;
          png_output_color_type = PNG_COLOR_TYPE_RGB_ALPHA;
          converter = nullptr;
        }
        break;
  
      case FORMAT_BGRA:
        input_color_components = 4;
        if (discard_transparency) {
          output_color_components = 3;
          png_output_color_type = PNG_COLOR_TYPE_RGB;
          converter = ConvertBGRAtoRGB;
        } else {
          output_color_components = 4;
          png_output_color_type = PNG_COLOR_TYPE_RGB_ALPHA;
          converter = ConvertBetweenBGRAandRGBA;
        }
        break;
  
      case FORMAT_GRAY:
        input_color_components = 1;
        output_color_components = 1;
        png_output_color_type = PNG_COLOR_TYPE_GRAY;
        discard_transparency = false;
        break;
  
      default:
        NOTREACHED();
        return false;
    }
  
    // Row stride should be at least as long as the length of the data.
    if (row_byte_width < input_color_components * width)
      return false;
  
    png_struct* png_ptr =
        png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!png_ptr)
      return false;
    png_info* info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr) {
      png_destroy_write_struct(&png_ptr, NULL);
      return false;
    }
  
    PngEncoderState state(output);
    bool success =
        DoLibpngWrite(png_ptr, info_ptr, &state, width, height, row_byte_width,
                      input, compression_level, png_output_color_type,
                      output_color_components, converter, comments);
    png_destroy_write_struct(&png_ptr, &info_ptr);
  
    return success;
  }
  
  // static
  bool Encode(const unsigned char* input,
              ColorFormat format,
              const int width,
              const int height,
              int row_byte_width,
              bool discard_transparency,
              const std::vector<Comment>& comments,
              std::vector<unsigned char>* output) {
    return EncodeWithCompressionLevel(input, format, width, height,
                                      row_byte_width, discard_transparency,
                                      comments, Z_DEFAULT_COMPRESSION, output);
  }
  
  // Decode a PNG into an RGBA pixel array.
  bool DecodePNG(const unsigned char* input,
                 size_t input_size,
                 std::vector<unsigned char>* output,
                 int* width,
                 int* height) {
    return Decode(input, input_size, FORMAT_RGBA, output, width, height);
  }
  
  // Encode a BGR pixel array into a PNG.
  bool EncodeBGRPNG(const unsigned char* input,
                    int width,
                    int height,
                    int row_byte_width,
                    std::vector<unsigned char>* output) {
    return Encode(input, FORMAT_BGR, width, height, row_byte_width, false,
                  std::vector<Comment>(), output);
  }
  
  // Encode an RGBA pixel array into a PNG.
  bool EncodeRGBAPNG(const unsigned char* input,
                     int width,
                     int height,
                     int row_byte_width,
                     std::vector<unsigned char>* output) {
    return Encode(input, FORMAT_RGBA, width, height, row_byte_width, false,
                  std::vector<Comment>(), output);
  }
  
  // Encode an BGRA pixel array into a PNG.
  bool EncodeBGRAPNG(const unsigned char* input,
                     int width,
                     int height,
                     int row_byte_width,
                     bool discard_transparency,
                     std::vector<unsigned char>* output) {
    return Encode(input, FORMAT_BGRA, width, height, row_byte_width,
                  discard_transparency, std::vector<Comment>(), output);
  }
  
  // Encode a grayscale pixel array into a PNG.
  bool EncodeGrayPNG(const unsigned char* input,
                     int width,
                     int height,
                     int row_byte_width,
                     std::vector<unsigned char>* output) {
    return Encode(input, FORMAT_GRAY, width, height, row_byte_width, false,
                  std::vector<Comment>(), output);
  }
  
  }  // namespace image_diff_png
  