Module: HexaPDF::Font::TrueType::Builder

Defined in:
lib/hexapdf/font/true_type/builder.rb

Overview

Builds a TrueType font file given a hash of TrueType tables.

Class Method Summary collapse

Class Method Details

.build(tables) ⇒ Object

Returns a TrueType font file representing the given TrueType tables (a hash mapping table names (strings) to table data).



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# File 'lib/hexapdf/font/true_type/builder.rb', line 43

def self.build(tables)
  search_range = 2**(tables.length.bit_length - 1) * 16
  entry_selector = tables.length.bit_length - 1
  range_shift = tables.length * 16 - search_range

  font_data = "\x0\x1\x0\x0".b + \
    [tables.length, search_range, entry_selector, range_shift].pack('n4')

  offset = font_data.length + tables.length * 16
  checksum = Table.calculate_checksum(font_data)

  # prepare head table for checksumming
  tables['head'][8, 4] = "\0\0\0\0"

  tables.each do |tag, data|
    table_checksum = Table.calculate_checksum(data)
    # tag, offset, data.length are all 32bit uint, table_checksum for header and body
    checksum += tag.unpack('N').first + 2 * table_checksum + offset + data.length
    font_data << [tag, table_checksum, offset, data.length].pack('a4N3')
    offset += data.length
  end

  tables['head'][8, 4] = [0xB1B0AFBA - checksum].pack('N')
  tables.each_value {|data| font_data << data}

  font_data
end