Module: Fontisan::Ufo::Compile::Cff2

Defined in:
lib/fontisan/ufo/compile/cff2.rb

Overview

Builds the OpenType CFF2 table from UFO glyphs.

CFF2 is simpler than CFF1: no Name INDEX, String INDEX, Encoding, or Charset. The Top DICT references CharStrings and a Font DICT INDEX (which wraps at least one Font DICT pointing to a Private DICT).

Layout (static font, single Font DICT, empty Private DICT):

Header (5 bytes)
Top DICT (variable — offsets to CharStrings + Font DICT INDEX)
Global Subr INDEX (4 bytes — empty)
CharStrings INDEX (variable)
Font DICT INDEX (variable — wraps one Font DICT)
Font DICT: DICT with Private operator [0, 0] (empty Private)

The Top DICT offsets depend on the Top DICT's own size — a circular dependency resolved with fixed-point iteration (the same pattern as the CFF1 builder).

See Also:

Constant Summary collapse

CHARSTRINGS_OPERATOR =

CFF2 Top DICT operator encodings.

17
VARIATION_STORE_OPERATOR =

0x11

24
FONT_DICT_INDEX_OPERATOR =

0x18

[12, 36].freeze
PRIVATE_OPERATOR =

0x12

18

Class Method Summary collapse

Class Method Details

.build(_font, glyphs:, variation_store: nil) ⇒ String

Returns CFF2 table bytes.

Parameters:

  • font (Fontisan::Ufo::Font)
  • glyphs (Array<Fontisan::Ufo::Glyph>) —

    in gid order

  • variation_store (String, nil) (defaults to: nil) —

    ItemVariationStore bytes for variable CFF2 fonts. When present, embedded between the GlobalSubr INDEX and CharStrings INDEX, and referenced from the Top DICT via operator 24.

Returns:

  • (String) —

    CFF2 table bytes



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# File 'lib/fontisan/ufo/compile/cff2.rb', line 41

def self.build(_font, glyphs:, variation_store: nil)
  charstrings = glyphs.map { |g| charstring_for(g) }
  global_subr_index = empty_global_subr_index
  font_dict = build_font_dict(private_size: 0, private_offset: 0)
  font_dict_index = Tables::Cff2::IndexBuilder.build([font_dict])
  vs_bytes = variation_store&.b

  # Fixed-point iteration: encode Top DICT, compute offsets, repeat.
  top_dict = encode_top_dict(
    charstrings_offset: 0, font_dict_index_offset: 0,
    variation_store_offset: vs_bytes ? 0 : nil
  )
  layout = compute_layout(top_dict:, charstrings:, global_subr_index:,
                          font_dict_index:, variation_store: vs_bytes)

  10.times do
    top_dict = encode_top_dict(
      charstrings_offset: layout[:charstrings_offset],
      font_dict_index_offset: layout[:font_dict_index_offset],
      variation_store_offset: layout[:variation_store_offset],
    )
    next_layout = compute_layout(top_dict:, charstrings:, global_subr_index:,
                                 font_dict_index:, variation_store: vs_bytes)
    break if same_offsets?(layout, next_layout)

    layout = next_layout
  end

  assemble(layout:)
end