module TTFunk::Table::Cmap::Format04

Attributes

code_map[R]
language[R]

Public Class Methods

encode(charmap) click to toggle source

Expects a hash mapping character codes to glyph ids (where the glyph ids are from the original font). Returns a hash including a new map (:charmap) that maps the characters in charmap to a another hash containing both the old (:old) and new (:new) glyph ids. The returned hash also includes a :subtable key, which contains the encoded subtable for the given charmap.

# File lib/ttfunk/table/cmap/format04.rb, line 16
def self.encode(charmap)
  end_codes = []
  start_codes = []
  next_id = 0
  last = difference = nil

  glyph_map = { 0 => 0 }
  new_map =
    charmap.keys.sort.each_with_object({}) do |code, map|
      old = charmap[code]
      glyph_map[old] ||= next_id += 1
      map[code] = { old: old, new: glyph_map[old] }

      delta = glyph_map[old] - code
      if last.nil? || delta != difference
        end_codes << last if last
        start_codes << code
        difference = delta
      end
      last = code

      map
    end

  end_codes << last if last
  end_codes << 0xFFFF
  start_codes << 0xFFFF
  segcount = start_codes.length

  # build the conversion tables
  deltas = []
  range_offsets = []
  glyph_indices = []
  offset = 0

  start_codes.zip(end_codes).each_with_index do |(a, b), segment|
    if a == 0xFFFF
      # We want the final 0xFFFF code to map to glyph 0.
      # The glyph index is calculated as glyph = charcode + delta,
      # which means that delta must be -0xFFFF to map character code
      # 0xFFFF to glyph 0.
      deltas << -0xFFFF
      range_offsets << 0
      break
    end

    start_glyph_id = new_map[a][:new]

    if a - start_glyph_id >= 0x8000
      deltas << 0
      range_offsets << 2 * (glyph_indices.length + segcount - segment)
      a.upto(b) { |code| glyph_indices << new_map[code][:new] }
    else
      deltas << -a + start_glyph_id
      range_offsets << 0
    end

    offset += 2
  end

  # format, length, language
  subtable = [
    4, 16 + 8 * segcount + 2 * glyph_indices.length, 0
  ].pack('nnn')

  search_range = 2 * 2**(Math.log(segcount) / Math.log(2)).to_i
  entry_selector = (Math.log(search_range / 2) / Math.log(2)).to_i
  range_shift = (2 * segcount) - search_range
  subtable << [
    segcount * 2, search_range, entry_selector, range_shift
  ].pack('nnnn')

  subtable << end_codes.pack('n*') << "\0\0" << start_codes.pack('n*')
  subtable << deltas.pack('n*') << range_offsets.pack('n*')
  subtable << glyph_indices.pack('n*')

  { charmap: new_map, subtable: subtable, max_glyph_id: next_id + 1 }
end

Public Instance Methods

[](code) click to toggle source
# File lib/ttfunk/table/cmap/format04.rb, line 95
def [](code)
  @code_map[code] || 0
end
supported?() click to toggle source
# File lib/ttfunk/table/cmap/format04.rb, line 99
def supported?
  true
end

Private Instance Methods

parse_cmap!() click to toggle source
# File lib/ttfunk/table/cmap/format04.rb, line 105
def parse_cmap!
  length, @language, segcount_x2 = read(6, 'nnn')
  segcount = segcount_x2 / 2

  io.read(6) # skip searching hints

  end_code = read(segcount_x2, 'n*')
  io.read(2) # skip reserved value
  start_code = read(segcount_x2, 'n*')
  id_delta = read_signed(segcount)
  id_range_offset = read(segcount_x2, 'n*')

  glyph_ids = read(length - io.pos + @offset, 'n*')

  @code_map = {}

  end_code.each_with_index do |tail, i|
    start_code[i].upto(tail) do |code|
      if (id_range_offset[i]).zero?
        glyph_id = code + id_delta[i]
      else
        index = id_range_offset[i] / 2 +
          (code - start_code[i]) - (segcount - i)
        # Because some TTF fonts are broken
        glyph_id = glyph_ids[index] || 0
        glyph_id += id_delta[i] if glyph_id != 0
      end

      @code_map[code] = glyph_id & 0xFFFF
    end
  end
end