woff2/transform.cc

// Copyright 2013 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Library for preprocessing fonts as part of the WOFF 2.0 conversion.

#include "./transform.h"

#include <complex>  // for std::abs

#include "./buffer.h"
#include "./font.h"
#include "./glyph.h"
#include "./table_tags.h"

namespace woff2 {

namespace {

const int FLAG_ARG_1_AND_2_ARE_WORDS = 1 << 0;
const int FLAG_WE_HAVE_INSTRUCTIONS = 1 << 8;

void WriteBytes(std::vector<uint8_t>* out, const uint8_t* data, size_t len) {
  if (len == 0) return;
  size_t offset = out->size();
  out->resize(offset + len);
  memcpy(&(*out)[offset], data, len);
}

void WriteBytes(std::vector<uint8_t>* out, const std::vector<uint8_t>& in) {
  for (int i = 0; i < in.size(); ++i) {
    out->push_back(in[i]);
  }
}

void WriteUShort(std::vector<uint8_t>* out, int value) {
  out->push_back(value >> 8);
  out->push_back(value & 255);
}

void WriteLong(std::vector<uint8_t>* out, int value) {
  out->push_back((value >> 24) & 255);
  out->push_back((value >> 16) & 255);
  out->push_back((value >> 8) & 255);
  out->push_back(value & 255);
}

void Write255UShort(std::vector<uint8_t>* out, int value) {
  if (value < 253) {
    out->push_back(value);
  } else if (value < 506) {
    out->push_back(255);
    out->push_back(value - 253);
  } else if (value < 762) {
    out->push_back(254);
    out->push_back(value - 506);
  } else {
    out->push_back(253);
    out->push_back(value >> 8);
    out->push_back(value & 0xff);
  }
}

// Glyf table preprocessing, based on
// GlyfEncoder.java
// but only the "sbbox" and "cbbox" options are supported.
class GlyfEncoder {
 public:
  explicit GlyfEncoder(int num_glyphs)
      : sbbox_(false), cbbox_(true), n_glyphs_(num_glyphs) {
    bbox_bitmap_.resize(((num_glyphs + 31) >> 5) << 2);
  }

  bool Encode(int glyph_id, const Glyph& glyph) {
    if (glyph.composite_data_size > 0) {
      WriteCompositeGlyph(glyph_id, glyph);
    } else if (glyph.contours.size() > 0) {
      WriteSimpleGlyph(glyph_id, glyph);
    } else {
      WriteUShort(&n_contour_stream_, 0);
    }
    return true;
  }

  void GetTransformedGlyfBytes(std::vector<uint8_t>* result) {
    WriteLong(result, 0);  // version
    WriteUShort(result, n_glyphs_);
    WriteUShort(result, 0);  // index_format, will be set later
    WriteLong(result, n_contour_stream_.size());
    WriteLong(result, n_points_stream_.size());
    WriteLong(result, flag_byte_stream_.size());
    WriteLong(result, glyph_stream_.size());
    WriteLong(result, composite_stream_.size());
    WriteLong(result, bbox_bitmap_.size() + bbox_stream_.size());
    WriteLong(result, instruction_stream_.size());
    WriteBytes(result, n_contour_stream_);
    WriteBytes(result, n_points_stream_);
    WriteBytes(result, flag_byte_stream_);
    WriteBytes(result, glyph_stream_);
    WriteBytes(result, composite_stream_);
    WriteBytes(result, bbox_bitmap_);
    WriteBytes(result, bbox_stream_);
    WriteBytes(result, instruction_stream_);
  }

 private:
  void WriteInstructions(const Glyph& glyph) {
    Write255UShort(&glyph_stream_, glyph.instructions_size);
    WriteBytes(&instruction_stream_,
               glyph.instructions_data, glyph.instructions_size);
  }

  void WriteSimpleGlyph(int glyph_id, const Glyph& glyph) {
    int num_contours = glyph.contours.size();
    WriteUShort(&n_contour_stream_, num_contours);
    if (sbbox_) {
      WriteBbox(glyph_id, glyph);
    }
    // TODO: check that bbox matches, write bbox if not
    for (int i = 0; i < num_contours; i++) {
      Write255UShort(&n_points_stream_, glyph.contours[i].size());
    }
    int lastX = 0;
    int lastY = 0;
    for (int i = 0; i < num_contours; i++) {
      int num_points = glyph.contours[i].size();
      for (int j = 0; j < num_points; j++) {
        int x = glyph.contours[i][j].x;
        int y = glyph.contours[i][j].y;
        int dx = x - lastX;
        int dy = y - lastY;
        WriteTriplet(glyph.contours[i][j].on_curve, dx, dy);
        lastX = x;
        lastY = y;
      }
    }
    if (num_contours > 0) {
      WriteInstructions(glyph);
    }
  }

  void WriteCompositeGlyph(int glyph_id, const Glyph& glyph) {
    WriteUShort(&n_contour_stream_, -1);
    if (cbbox_) {
      WriteBbox(glyph_id, glyph);
    }
    WriteBytes(&composite_stream_,
               glyph.composite_data,
               glyph.composite_data_size);
    if (glyph.have_instructions) {
      WriteInstructions(glyph);
    }
  }

  void WriteBbox(int glyph_id, const Glyph& glyph) {
    bbox_bitmap_[glyph_id >> 3] |= 0x80 >> (glyph_id & 7);
    WriteUShort(&bbox_stream_, glyph.x_min);
    WriteUShort(&bbox_stream_, glyph.y_min);
    WriteUShort(&bbox_stream_, glyph.x_max);
    WriteUShort(&bbox_stream_, glyph.y_max);
  }

  void WriteTriplet(bool on_curve, int x, int y) {
    int abs_x = std::abs(x);
    int abs_y = std::abs(y);
    int on_curve_bit = on_curve ? 0 : 128;
    int x_sign_bit = (x < 0) ? 0 : 1;
    int y_sign_bit = (y < 0) ? 0 : 1;
    int xy_sign_bits = x_sign_bit + 2 * y_sign_bit;
    if (x == 0 && abs_y < 1280) {
      flag_byte_stream_.push_back(on_curve_bit +
                                  ((abs_y & 0xf00) >> 7) + y_sign_bit);
      glyph_stream_.push_back(abs_y & 0xff);
    } else if (y == 0 && abs_x < 1280) {
      flag_byte_stream_.push_back(on_curve_bit + 10 +
                                  ((abs_x & 0xf00) >> 7) + x_sign_bit);
      glyph_stream_.push_back(abs_x & 0xff);
    } else if (abs_x < 65 && abs_y < 65) {
      flag_byte_stream_.push_back(on_curve_bit + 20 +
                                  ((abs_x - 1) & 0x30) +
                                  (((abs_y - 1) & 0x30) >> 2) +
                                  xy_sign_bits);
      glyph_stream_.push_back((((abs_x - 1) & 0xf) << 4) | ((abs_y - 1) & 0xf));
    } else if (abs_x < 769 && abs_y < 769) {
      flag_byte_stream_.push_back(on_curve_bit + 84 +
                                  12 * (((abs_x - 1) & 0x300) >> 8) +
                                  (((abs_y - 1) & 0x300) >> 6) + xy_sign_bits);
      glyph_stream_.push_back((abs_x - 1) & 0xff);
      glyph_stream_.push_back((abs_y - 1) & 0xff);
    } else if (abs_x < 4096 && abs_y < 4096) {
      flag_byte_stream_.push_back(on_curve_bit + 120 + xy_sign_bits);
      glyph_stream_.push_back(abs_x >> 4);
      glyph_stream_.push_back(((abs_x & 0xf) << 4) | (abs_y >> 8));
      glyph_stream_.push_back(abs_y & 0xff);
    } else {
      flag_byte_stream_.push_back(on_curve_bit + 124 + xy_sign_bits);
      glyph_stream_.push_back(abs_x >> 8);
      glyph_stream_.push_back(abs_x & 0xff);
      glyph_stream_.push_back(abs_y >> 8);
      glyph_stream_.push_back(abs_y & 0xff);
    }
  }

  std::vector<uint8_t> n_contour_stream_;
  std::vector<uint8_t> n_points_stream_;
  std::vector<uint8_t> flag_byte_stream_;
  std::vector<uint8_t> composite_stream_;
  std::vector<uint8_t> bbox_bitmap_;
  std::vector<uint8_t> bbox_stream_;
  std::vector<uint8_t> glyph_stream_;
  std::vector<uint8_t> instruction_stream_;
  bool sbbox_;
  bool cbbox_;
  int n_glyphs_;
};

}  // namespace

bool TransformGlyfAndLocaTables(Font* font) {
  Font::Table* transformed_glyf = &font->tables[kGlyfTableTag ^ 0x80808080];
  Font::Table* transformed_loca = &font->tables[kLocaTableTag ^ 0x80808080];

  int num_glyphs = NumGlyphs(*font);
  GlyfEncoder encoder(num_glyphs);
  for (int i = 0; i < num_glyphs; ++i) {
    Glyph glyph;
    const uint8_t* glyph_data;
    size_t glyph_size;
    if (!GetGlyphData(*font, i, &glyph_data, &glyph_size) ||
        (glyph_size > 0 && !ReadGlyph(glyph_data, glyph_size, &glyph))) {
      return FONT_COMPRESSION_FAILURE();
    }
    encoder.Encode(i, glyph);
  }
  encoder.GetTransformedGlyfBytes(&transformed_glyf->buffer);

  const Font::Table* head_table = font->FindTable(kHeadTableTag);
  if (head_table == NULL || head_table->length < 52) {
    return FONT_COMPRESSION_FAILURE();
  }
  transformed_glyf->buffer[7] = head_table->data[51];  // index_format

  transformed_glyf->tag = kGlyfTableTag ^ 0x80808080;
  transformed_glyf->length = transformed_glyf->buffer.size();
  transformed_glyf->data = transformed_glyf->buffer.data();

  transformed_loca->tag = kLocaTableTag ^ 0x80808080;
  transformed_loca->length = 0;
  transformed_loca->data = NULL;

  return true;
}

} // namespace woff2