ttf-bitmap.cpp

#include <sstream>
#include <iostream>

#include <assert.h>
#include <stdint.h>

#include <ft2build.h>
#include FT_FREETYPE_H

int32_t
load_bitmap_char(FT_Face face,
		 FT_ULong char_code,
		 uint8_t * buf)
{
  FT_Error error;
  FT_UInt glyph_index = FT_Get_Char_Index(face, char_code);

  error = FT_Load_Glyph(face, glyph_index, FT_LOAD_DEFAULT);
  if (error) {
    std::cerr << "FT_Load_Glyph " << FT_Error_String(error) << '\n';
    return -1;
  }

  assert(face->glyph->format == FT_GLYPH_FORMAT_BITMAP);
  //printf("num_grays %d\n", face->glyph->bitmap.num_grays);
  //printf("pitch %d\n", face->glyph->bitmap.pitch);
  //printf("width %d\n", face->glyph->bitmap.width);
  //printf("char_code %lx rows %d\n", char_code, face->glyph->bitmap.rows);
  //assert((face->glyph->bitmap.rows % 8) == 0);
  //assert(face->glyph->bitmap.width / face->glyph->bitmap.pitch == 8);

  for (int y = 0; y < (int)face->glyph->bitmap.rows; y++) {
    uint8_t * row = &face->glyph->bitmap.buffer[y * face->glyph->bitmap.pitch];
    uint8_t row_out = 0;
    for (unsigned int x = 0; x < face->glyph->bitmap.width; x++) {
      if (x % 8 == 0) row_out = 0;
      const uint8_t bit = (row[x / 8] >> (7 - (x % 8))) & 1;
      //std::cerr << (bit ? "█" : " ");
      row_out |= (bit << (7 - (x % 8)));
      if (x % 8 == 7 || x == (face->glyph->bitmap.width - 1))
        buf[(y * face->glyph->bitmap.pitch) + (x / 8)] = row_out;
    }
    //std::cerr << "|\n";
  }

  // 'pitch' is bytes; 'width' is pixels
  return face->glyph->bitmap.rows * face->glyph->bitmap.pitch;
}

template <typename T>
constexpr inline T
parse_num(decltype(std::hex)& format, const char * s)
{
  T n;
  std::stringstream ss;
  ss << format << s;
  ss >> n;
  return n;
}

int main(int argc, char *argv[])
{
  FT_Library library;
  FT_Face face;
  FT_Error error;

  if (argc != 5) {
    std::cerr << "usage: " << argv[0] << " [start-hex] [end-hex] [font-file-path] [output-file-path]\n\n";
    std::cerr << "   ex: " << argv[0] << " 3000 30ff ipagp.ttf font.bin\n";
    return -1;
  }

  auto start = parse_num<uint32_t>(std::hex, argv[1]);
  auto end = parse_num<uint32_t>(std::hex, argv[2]);
  auto font_file_path = argv[3];
  auto output_file_path = argv[4];

  error = FT_Init_FreeType(&library);
  if (error) {
    std::cerr << "FT_Init_FreeType\n";
    return -1;
  }

  error = FT_New_Face(library, font_file_path, 0, &face);
  if (error) {
    std::cerr << "FT_New_Face\n";
    return -1;
  }

  error = FT_Select_Size(face, 0);
  if (error) {
    std::cerr << "FT_Select_Size: " << FT_Error_String(error) << ' ' << error << '\n';
    return -1;
  }

  assert(end > start);

  uint32_t pixels_per_glyph = (face->size->metrics.height * face->size->metrics.max_advance);
  assert(pixels_per_glyph % 8 == 0);
  uint32_t bytes_per_glyph = pixels_per_glyph / 8;
  uint32_t num_glyphs = (end - start) + 1;
  uint8_t buf[bytes_per_glyph * num_glyphs];

  uint32_t bitmap_offset = 0;
  for (uint32_t char_code = start; char_code <= end; char_code++) {
    int32_t bitmap_size = load_bitmap_char(face,
					   char_code,
					   &buf[bitmap_offset]);
    if (bitmap_size < 0) {
      std::cerr << "load_bitmap_char error\n";
      return -1;
    }

    bitmap_offset += bitmap_size;
    assert(bitmap_offset < (sizeof (buf)));
  }
  std::cerr << "bitmap_offset: 0x"  << std::dec << bitmap_offset << '\n';

  FILE * out = fopen(output_file_path, "w");
  if (out == NULL) {
    perror("fopen(w)");
    return -1;
  }
  fwrite(reinterpret_cast<void*>(&buf), bitmap_offset, 1, out);
  fclose(out);
}