components/pwg_encoder/pwg_encoder.cc

// 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.

#include "components/pwg_encoder/pwg_encoder.h"

#include <limits.h>
#include <string.h>

#include <algorithm>
#include <memory>

#include "base/big_endian.h"
#include "base/logging.h"
#include "components/pwg_encoder/bitmap_image.h"

namespace pwg_encoder {

namespace {

const uint32_t kBitsPerColor = 8;
const uint32_t kColorOrder = 0;  // chunky.

// Coefficients used to convert from RGB to monochrome.
const uint32_t kRedCoefficient = 2125;
const uint32_t kGreenCoefficient = 7154;
const uint32_t kBlueCoefficient = 721;
const uint32_t kColorCoefficientDenominator = 10000;

const char kPwgKeyword[] = "RaS2";

const uint32_t kHeaderSize = 1796;
const uint32_t kHeaderCupsDuplex = 272;
const uint32_t kHeaderCupsHwResolutionHorizontal = 276;
const uint32_t kHeaderCupsHwResolutionVertical = 280;
const uint32_t kHeaderCupsTumble = 368;
const uint32_t kHeaderCupsWidth = 372;
const uint32_t kHeaderCupsHeight = 376;
const uint32_t kHeaderCupsBitsPerColor = 384;
const uint32_t kHeaderCupsBitsPerPixel = 388;
const uint32_t kHeaderCupsBytesPerLine = 392;
const uint32_t kHeaderCupsColorOrder = 396;
const uint32_t kHeaderCupsColorSpace = 400;
const uint32_t kHeaderCupsNumColors = 420;
const uint32_t kHeaderPwgTotalPageCount = 452;
const uint32_t kHeaderPwgCrossFeedTransform = 456;
const uint32_t kHeaderPwgFeedTransform = 460;

const int kPwgMaxPackedRows = 256;

const int kPwgMaxPackedPixels = 128;

struct RGBA8 {
  uint8_t red;
  uint8_t green;
  uint8_t blue;
  uint8_t alpha;
};

struct BGRA8 {
  uint8_t blue;
  uint8_t green;
  uint8_t red;
  uint8_t alpha;
};

template <class InputStruct>
void EncodePixelToRGB(const void* pixel, std::string* output) {
  const InputStruct* i = reinterpret_cast<const InputStruct*>(pixel);
  output->push_back(static_cast<char>(i->red));
  output->push_back(static_cast<char>(i->green));
  output->push_back(static_cast<char>(i->blue));
}

template <class InputStruct>
void EncodePixelToMonochrome(const void* pixel, std::string* output) {
  const InputStruct* i = reinterpret_cast<const InputStruct*>(pixel);
  output->push_back(static_cast<char>((i->red * kRedCoefficient +
                                       i->green * kGreenCoefficient +
                                       i->blue * kBlueCoefficient) /
                                      kColorCoefficientDenominator));
}

std::string EncodePageHeader(const BitmapImage& image,
                             const PwgHeaderInfo& pwg_header_info) {
  char header[kHeaderSize];
  memset(header, 0, kHeaderSize);

  uint32_t num_colors =
      pwg_header_info.color_space == PwgHeaderInfo::SGRAY ? 1 : 3;
  uint32_t bits_per_pixel = num_colors * kBitsPerColor;

  base::WriteBigEndian<uint32_t>(header + kHeaderCupsDuplex,
                                 pwg_header_info.duplex ? 1 : 0);
  base::WriteBigEndian<uint32_t>(header + kHeaderCupsHwResolutionHorizontal,
                                 pwg_header_info.dpi.width());
  base::WriteBigEndian<uint32_t>(header + kHeaderCupsHwResolutionVertical,
                                 pwg_header_info.dpi.height());
  base::WriteBigEndian<uint32_t>(header + kHeaderCupsTumble,
                                 pwg_header_info.tumble ? 1 : 0);
  base::WriteBigEndian<uint32_t>(header + kHeaderCupsWidth,
                                 image.size().width());
  base::WriteBigEndian<uint32_t>(header + kHeaderCupsHeight,
                                 image.size().height());
  base::WriteBigEndian<uint32_t>(header + kHeaderCupsBitsPerColor,
                                 kBitsPerColor);
  base::WriteBigEndian<uint32_t>(header + kHeaderCupsBitsPerPixel,
                                 bits_per_pixel);
  base::WriteBigEndian<uint32_t>(
      header + kHeaderCupsBytesPerLine,
      (bits_per_pixel * image.size().width() + 7) / 8);
  base::WriteBigEndian<uint32_t>(header + kHeaderCupsColorOrder, kColorOrder);
  base::WriteBigEndian<uint32_t>(header + kHeaderCupsColorSpace,
                                 pwg_header_info.color_space);
  base::WriteBigEndian<uint32_t>(header + kHeaderCupsNumColors, num_colors);
  base::WriteBigEndian<uint32_t>(header + kHeaderPwgCrossFeedTransform,
                                 pwg_header_info.flipx ? -1 : 1);
  base::WriteBigEndian<uint32_t>(header + kHeaderPwgFeedTransform,
                                 pwg_header_info.flipy ? -1 : 1);
  base::WriteBigEndian<uint32_t>(header + kHeaderPwgTotalPageCount,
                                 pwg_header_info.total_pages);
  return std::string(header, kHeaderSize);
}

template <typename InputStruct, class RandomAccessIterator>
void EncodeRow(RandomAccessIterator pos,
               RandomAccessIterator row_end,
               bool monochrome,
               std::string* output) {
  // According to PWG-raster, a sequence of N identical pixels (up to 128)
  // can be encoded by a byte N-1, followed by the information on
  // that pixel. Any generic sequence of N pixels (up to 129) can be encoded
  // with (signed) byte 1-N, followed by the information on the N pixels.
  // Notice that for sequences of 1 pixel there is no difference between
  // the two encodings.

  // We encode every largest sequence of identical pixels together because it
  // usually saves the most space. Every other pixel should be encoded in the
  // smallest number of generic sequences.
  // NOTE: the algorithm is not optimal especially in case of monochrome.
  while (pos != row_end) {
    RandomAccessIterator it = pos + 1;
    RandomAccessIterator end = std::min(pos + kPwgMaxPackedPixels, row_end);

    // Counts how many identical pixels (up to 128).
    while (it != end && *pos == *it) {
      ++it;
    }
    if (it != pos + 1) {  // More than one pixel
      output->push_back(static_cast<char>((it - pos) - 1));
      if (monochrome)
        EncodePixelToMonochrome<InputStruct>(&*pos, output);
      else
        EncodePixelToRGB<InputStruct>(&*pos, output);
      pos = it;
    } else {
      // Finds how many pixels there are each different from the previous one.
      // IMPORTANT: even if sequences of different pixels can contain as many
      // as 129 pixels, we restrict to 128 because some decoders don't manage
      // it correctly. So iterating until it != end is correct.
      while (it != end && *it != *(it - 1)) {
        ++it;
      }
      // Optimization: ignores the last pixel of the sequence if it is followed
      // by an identical pixel, as it is more convenient for it to be the start
      // of a new sequence of identical pixels. Notice that we don't compare
      // to end, but row_end.
      if (it != row_end && *it == *(it - 1)) {
        --it;
      }
      output->push_back(static_cast<char>(1 - (it - pos)));
      while (pos != it) {
        if (monochrome)
          EncodePixelToMonochrome<InputStruct>(&*pos, output);
        else
          EncodePixelToRGB<InputStruct>(&*pos, output);
        ++pos;
      }
    }
  }
}

const uint8_t* GetRow(const BitmapImage& image, int row, bool flipy) {
  return image.GetPixel(
      gfx::Point(0, flipy ? image.size().height() - 1 - row : row));
}

template <typename InputStruct>
std::string EncodePageWithColorspace(const BitmapImage& image,
                                     const PwgHeaderInfo& pwg_header_info) {
  bool monochrome = pwg_header_info.color_space == PwgHeaderInfo::SGRAY;
  std::string output = EncodePageHeader(image, pwg_header_info);

  // Ensure no integer overflow.
  CHECK(image.size().width() < INT_MAX / image.channels());
  int row_size = image.size().width() * image.channels();

  int row_number = 0;
  while (row_number < image.size().height()) {
    const uint8_t* current_row =
        GetRow(image, row_number++, pwg_header_info.flipy);
    int num_identical_rows = 1;
    // We count how many times the current row is repeated.
    while (num_identical_rows < kPwgMaxPackedRows &&
           row_number < image.size().height() &&
           !memcmp(current_row,
                   GetRow(image, row_number, pwg_header_info.flipy),
                   row_size)) {
      num_identical_rows++;
      row_number++;
    }
    output.push_back(static_cast<char>(num_identical_rows - 1));

    // Both supported colorspaces have a 32-bit pixels information.
    // Converts the list of uint8_t to uint32_t as every pixels contains 4 bytes
    // of information and comparison of elements is easier. The actual
    // Management of the bytes of the pixel is done by pixel_encoder function
    // on the original array to avoid endian problems.
    const uint32_t* pos = reinterpret_cast<const uint32_t*>(current_row);
    const uint32_t* row_end = pos + image.size().width();
    if (!pwg_header_info.flipx) {
      EncodeRow<InputStruct>(pos, row_end, monochrome, &output);
    } else {
      // We reverse the iterators.
      EncodeRow<InputStruct>(std::reverse_iterator<const uint32_t*>(row_end),
                             std::reverse_iterator<const uint32_t*>(pos),
                             monochrome, &output);
    }
  }
  return output;
}

}  // namespace

// static
std::string PwgEncoder::GetDocumentHeader() {
  std::string output;
  output.append(kPwgKeyword, 4);
  return output;
}

// static
std::string PwgEncoder::EncodePage(const BitmapImage& image,
                                   const PwgHeaderInfo& pwg_header_info) {
  // pwg_header_info.color_space can only contain color spaces that are
  // supported, so no sanity check is needed.
  std::string data;
  switch (image.colorspace()) {
    case BitmapImage::RGBA:
      data = EncodePageWithColorspace<RGBA8>(image, pwg_header_info);
      break;

    case BitmapImage::BGRA:
      data = EncodePageWithColorspace<BGRA8>(image, pwg_header_info);
      break;

    default:
      LOG(ERROR) << "Unsupported colorspace.";
      break;
  }
  return data;
}

}  // namespace pwg_encoder