Module: Fontisan::Ufo::Compile::Meta

Defined in:
lib/fontisan/ufo/compile/meta.rb

Overview

Builds the OpenType meta table.

The meta table stores font metadata as tagged data — longer-form strings than the name table supports. Common tags:

"dlng" — design languages (BCP-47 tags)
"slng" — supported languages

See Also:

Constant Summary collapse

VERSION = 
1
HEADER_SIZE = 
16
DATA_MAP_SIZE =

tag(4) + offset(4) + length(4)

12

Class Method Summary collapse

Class Method Details

.build(data:) ⇒ String?

Returns meta table bytes, or nil if no data.

Parameters:

  • data (Hash<String,String>) —

    tag → UTF-8 string value

Returns:

  • (String, nil) —

    meta table bytes, or nil if no data



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# File 'lib/fontisan/ufo/compile/meta.rb', line 21

def self.build(data:)
  return nil if data.nil? || data.empty?

  count = data.size
  data_offset = HEADER_SIZE + (count * DATA_MAP_SIZE)

  io = +""
  io << [VERSION, 0, count, data_offset].pack("NNNN")

  # Two iterations over the same data: the meta table has two
  # distinct output sections (data map entries then data values)
  # that cannot be interleaved. The map-entry section records
  # offsets that depend on the total size of the value section,
  # so the value section must be produced last.
  #
  # rubocop:disable Style/CombinableLoops
  offset = data_offset
  data.each do |tag, value|
    io << tag.ljust(4, " ")[0, 4]
    io << [offset, value.bytesize].pack("NN")
    offset += value.bytesize
  end
  data.each_value { |value| io << value.b }
  # rubocop:enable Style/CombinableLoops

  io
end