Class: Fontisan::Woff2Font

Inherits:
Object
  • Object
show all
Defined in:
lib/fontisan/woff2_font.rb

Overview

Web Open Font Format 2.0 (WOFF2) font loader

This class manages WOFF2 font files and provides access to decompressed tables and transformed data.

Examples:

Reading a WOFF2 font

font = Woff2Font.from_file("font.woff2")
puts font.header.flavor
puts font.table_names

Defined Under Namespace

Classes: IOSource

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Woff2Font

Returns a new instance of Woff2Font.



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# File 'lib/fontisan/woff2_font.rb', line 90

def initialize
  @header = nil
  @table_entries = []
  @decompressed_tables = {}
  @parsed_tables = {}
  @io_source = nil
  @underlying_font = nil # Store the actual TrueTypeFont/OpenTypeFont
end

Instance Attribute Details

#decompressed_tables ⇒ Object

Allow both reading and setting for table delegation



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# File 'lib/fontisan/woff2_font.rb', line 88

def decompressed_tables
  @decompressed_tables
end

#header ⇒ Object

Allow both reading and setting for table delegation



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# File 'lib/fontisan/woff2_font.rb', line 88

def header
  @header
end

#io_source ⇒ Object

Allow both reading and setting for table delegation



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# File 'lib/fontisan/woff2_font.rb', line 88

def io_source
  @io_source
end

#parsed_tables ⇒ Object

Allow both reading and setting for table delegation



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# File 'lib/fontisan/woff2_font.rb', line 88

def parsed_tables
  @parsed_tables
end

#table_entries ⇒ Object

Allow both reading and setting for table delegation



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# File 'lib/fontisan/woff2_font.rb', line 88

def table_entries
  @table_entries
end

#underlying_font ⇒ Object

Allow both reading and setting for table delegation



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# File 'lib/fontisan/woff2_font.rb', line 88

def underlying_font
  @underlying_font
end

Class Method Details

.apply_transformations!(table_entries, decompressed_tables) ⇒ void

This method returns an undefined value.

Apply table transformations for glyf/loca/hmtx tables

Parameters:

  • table_entries (Array<Woff2TableDirectoryEntry>) —

    Table entries

  • decompressed_tables (Hash<String, String>) —

    Decompressed tables



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# File 'lib/fontisan/woff2_font.rb', line 518

def self.apply_transformations!(table_entries, decompressed_tables)
  # Find entries that need transformation
  glyf_entry = table_entries.find { |e| e.tag == "glyf" }
  hmtx_entry = table_entries.find { |e| e.tag == "hmtx" }

  # Get required metadata for transformations
  maxp_data = decompressed_tables["maxp"]
  hhea_data = decompressed_tables["hhea"]

  return unless maxp_data && hhea_data

  # Parse num_glyphs from maxp table
  # maxp format: version(4) + numGlyphs(2) + ...
  num_glyphs = maxp_data[4, 2].unpack1("n")

  # Parse numberOfHMetrics from hhea table
  # hhea format: ... + numberOfHMetrics(2) at offset 34
  number_of_h_metrics = hhea_data[34, 2].unpack1("n")

  # Check if this is a variable font by checking for fvar table
  variable_font = table_entries.any? { |e| e.tag == "fvar" }

  # Transform glyf/loca if needed
  # transform_length is only set when table is actually transformed
  # Check that transform_length exists and is greater than 0
  if glyf_entry&.instance_variable_defined?(:@transform_length) &&
      glyf_entry.transform_length&.positive?
    transformed_glyf = decompressed_tables["glyf"]

    if transformed_glyf
      result = Woff2::GlyfTransformer.reconstruct(
        transformed_glyf,
        num_glyphs,
        variable_font: variable_font,
      )
      decompressed_tables["glyf"] = result[:glyf]
      decompressed_tables["loca"] = result[:loca]
    end
  end

  # Transform hmtx if needed
  # transform_length is only set when table is actually transformed
  # Check that transform_length exists and is greater than 0
  if hmtx_entry&.instance_variable_defined?(:@transform_length) &&
      hmtx_entry.transform_length&.positive?
    transformed_hmtx = decompressed_tables["hmtx"]

    if transformed_hmtx
      decompressed_tables["hmtx"] = Woff2::HmtxTransformer.reconstruct(
        transformed_hmtx,
        num_glyphs,
        number_of_h_metrics,
      )
    end
  end
end

.build_sfnt_in_memory(header, table_entries, decompressed_tables) ⇒ String

Build SFNT binary structure in memory

Parameters:

Returns:

  • (String) —

    Complete SFNT binary data



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# File 'lib/fontisan/woff2_font.rb', line 624

def self.build_sfnt_in_memory(header, table_entries, decompressed_tables)
  sfnt_data = +""

  # Calculate offset table fields
  num_tables = table_entries.length
  entry_selector = (Math.log(num_tables) / Math.log(2)).floor
  search_range = (2**entry_selector) * 16
  range_shift = num_tables * 16 - search_range

  # Write offset table
  sfnt_data << [header.flavor].pack("N")
  sfnt_data << [num_tables].pack("n")
  sfnt_data << [search_range].pack("n")
  sfnt_data << [entry_selector].pack("n")
  sfnt_data << [range_shift].pack("n")

  # Calculate table offsets
  offset = 12 + (num_tables * 16) # Header + directory
  table_records = []

  table_entries.each do |entry|
    tag = entry.tag
    data = decompressed_tables[tag]
    next unless data

    length = data.bytesize

    # Calculate checksum
    checksum = Utilities::ChecksumCalculator.calculate_table_checksum(data)

    table_records << {
      tag: tag,
      checksum: checksum,
      offset: offset,
      length: length,
      data: data,
    }

    # Update offset for next table (with padding)
    offset += length
    padding = (Constants::TABLE_ALIGNMENT - (length % Constants::TABLE_ALIGNMENT)) %
      Constants::TABLE_ALIGNMENT
    offset += padding
  end

  # Write table directory
  table_records.each do |record|
    sfnt_data << record[:tag].ljust(4, "\x00")
    sfnt_data << [record[:checksum]].pack("N")
    sfnt_data << [record[:offset]].pack("N")
    sfnt_data << [record[:length]].pack("N")
  end

  # Write table data with padding
  table_records.each do |record|
    sfnt_data << record[:data]

    # Add padding
    padding = (Constants::TABLE_ALIGNMENT - (record[:length] % Constants::TABLE_ALIGNMENT)) %
      Constants::TABLE_ALIGNMENT
    sfnt_data << ("\x00" * padding) if padding.positive?
  end

  # Update checksumAdjustment in head table
  update_checksum_in_memory(sfnt_data, table_records)

  sfnt_data
end

.calculate_table_directory_size(table_entries) ⇒ Integer

Calculate size of table directory

Parameters:

Returns:

  • (Integer) —

    Size in bytes



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# File 'lib/fontisan/woff2_font.rb', line 579

def self.calculate_table_directory_size(table_entries)
  size = 0
  table_entries.each do |entry|
    size += 1 # flags byte

    # Tag (4 bytes if custom, 0 if known)
    tag_index = entry.flags & 0x3F
    size += 4 if tag_index == 0x3F

    # orig_length (UIntBase128) - estimate
    size += uint_base128_size(entry.orig_length)

    # transform_length if present
    if entry.transform_version && !entry.transform_version.nil?
      size += uint_base128_size(entry.transform_length)
    end
  end
  size
end

.decompress_tables(io, header, table_entries) ⇒ Hash<String, String>

Decompress tables from WOFF2 compressed data block

Parameters:

Returns:

  • (Hash<String, String>) —

    Map of tag to decompressed data



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# File 'lib/fontisan/woff2_font.rb', line 490

def self.decompress_tables(io, header, table_entries)
  # IO stream is already positioned at compressed data after reading table directory
  # No need to seek - just read from current position
  compressed_data = io.read(header.total_compressed_size)

  # Decompress entire data block with Brotli
  decompressed_data = Brotli.inflate(compressed_data)

  # Split decompressed data into individual tables
  decompressed_tables = {}
  offset = 0

  table_entries.each do |entry|
    table_size = entry.transform_length || entry.orig_length
    table_data = decompressed_data[offset, table_size]
    offset += table_size

    decompressed_tables[entry.tag] = table_data
  end

  decompressed_tables
end

.from_file(path, mode: LoadingModes::FULL, lazy: false) ⇒ Woff2Font

Read WOFF2 font from a file and return Woff2Font instance

Parameters:

  • path (String) —

    Path to the WOFF2 file

  • mode (Symbol) (defaults to: LoadingModes::FULL) —

    Loading mode (:metadata or :full)

  • lazy (Boolean) (defaults to: false) —

    If true, load tables on demand

Returns:

Raises:

  • (ArgumentError) —

    if path is nil or empty

  • (Errno::ENOENT) —

    if file does not exist

  • (InvalidFontError) —

    if file format is invalid



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# File 'lib/fontisan/woff2_font.rb', line 307

def self.from_file(path, mode: LoadingModes::FULL, lazy: false)
  if path.nil? || path.to_s.empty?
    raise ArgumentError, "path cannot be nil or empty"
  end
  raise Errno::ENOENT, "File not found: #{path}" unless File.exist?(path)

  woff2 = new
  woff2.io_source = IOSource.new(path)

  File.open(path, "rb") do |io|
    # Read header to determine font flavor
    woff2.header = Woff2::Woff2Header.read(io)

    # Validate signature
    unless woff2.header.signature == Woff2::Woff2Header::SIGNATURE
      raise InvalidFontError,
            "Invalid WOFF2 signature: expected 0x#{Woff2::Woff2Header::SIGNATURE.to_s(16)}, " \
            "got 0x#{woff2.header.signature.to_i.to_s(16)}"
    end

    # Read table directory
    woff2.table_entries = read_table_directory_from_io(io, woff2.header)

    # Decompress table data
    woff2.decompressed_tables = decompress_tables(io, woff2.header,
                                                  woff2.table_entries)

    # Apply table transformations if present
    apply_transformations!(woff2.table_entries, woff2.decompressed_tables)

    # Build SFNT structure in memory
    sfnt_data = build_sfnt_in_memory(woff2.header, woff2.table_entries,
                                     woff2.decompressed_tables)

    # Create StringIO for reading
    sfnt_io = StringIO.new(sfnt_data)
    sfnt_io.rewind

    # Parse tables based on font type
    if woff2.truetype?
      font = TrueTypeFont.read(sfnt_io)
      font.initialize_storage
      font.loading_mode = mode
      font.lazy_load_enabled = lazy

      # Create fresh StringIO for table data reading
      table_io = StringIO.new(sfnt_data)
      font.read_table_data(table_io)

      # Store underlying font for table access delegation
      woff2.underlying_font = font
      woff2.parsed_tables = font.parsed_tables
    elsif woff2.cff?
      font = OpenTypeFont.read(sfnt_io)
      font.initialize_storage
      font.loading_mode = mode
      font.lazy_load_enabled = lazy

      # Create fresh StringIO for table data reading
      table_io = StringIO.new(sfnt_data)
      font.read_table_data(table_io)

      # Store underlying font for table access delegation
      woff2.underlying_font = font
      woff2.parsed_tables = font.parsed_tables
    else
      raise InvalidFontError,
            "Unknown WOFF2 flavor: 0x#{woff2.header.flavor.to_s(16)}"
    end
  end

  woff2
rescue BinData::ValidityError, EOFError => e
  raise InvalidFontError, "Invalid WOFF2 file: #{e.message}"
end

.read_table_directory_from_io(io, header) ⇒ Array<Woff2TableDirectoryEntry>

Read table directory from IO

Parameters:

Returns:



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# File 'lib/fontisan/woff2_font.rb', line 388

def self.read_table_directory_from_io(io, header)
  table_entries = []

  header.num_tables.times do
    entry = Woff2TableDirectoryEntry.new

    # Read flags byte with nil check
    flags_data = io.read(1)
    if flags_data.nil?
      raise EOFError,
            "Unexpected EOF while reading table directory flags"
    end

    flags = flags_data.unpack1("C")
    entry.flags = flags

    # Determine tag
    tag_index = flags & 0x3F
    if tag_index == 0x3F
      # Custom tag (4 bytes)
      tag_data = io.read(4)
      if tag_data.nil? || tag_data.bytesize < 4
        raise EOFError,
              "Unexpected EOF while reading custom tag"
      end

      entry.tag = tag_data.force_encoding("UTF-8")
    else
      # Known tag from table
      entry.tag = Woff2TableDirectoryEntry::KNOWN_TAGS[tag_index]
      unless entry.tag
        raise InvalidFontError, "Invalid table tag index: #{tag_index}"
      end
    end

    # Read orig_length (UIntBase128)
    entry.orig_length = read_uint_base128_from_io(io)

    # Determine if transformLength should be read
    # According to WOFF2 spec section 4.2:
    # - transformLength is ONLY present when table is actually transformed
    # - For glyf/loca: transformation is indicated by transform_version = 0
    # - For hmtx: transformation is indicated by transform_version = 1
    # - For all other tables: no transformation, no transformLength
    transform_version = (flags >> 6) & 0x03

    # transformLength is present when table is actually transformed
    # glyf/loca use version 0 for transformation, hmtx uses version 1
    has_transform_length = if ["glyf", "loca"].include?(entry.tag)
                             # For glyf/loca, version 0 means transformed
                             transform_version.zero?
                           elsif entry.tag == "hmtx"
                             # For hmtx, version 1 means transformed
                             transform_version == 1
                           else
                             false
                           end

    if has_transform_length
      entry.transform_length = read_uint_base128_from_io(io)
      entry.transform_version = transform_version
    end

    table_entries << entry
  end

  table_entries
end

.read_uint_base128_from_io(io) ⇒ Integer

Read variable-length UIntBase128 integer from IO

Parameters:

  • io (IO) —

    Open file handle

Returns:

  • (Integer) —

    The decoded integer value

Raises:



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# File 'lib/fontisan/woff2_font.rb', line 461

def self.read_uint_base128_from_io(io)
  result = 0
  5.times do
    byte_data = io.read(1)
    if byte_data.nil?
      raise EOFError,
            "Unexpected EOF while reading UIntBase128"
    end

    byte = byte_data.unpack1("C")

    # Continue if high bit is set
    if (byte & 0x80).zero?
      return (result << 7) | byte
    else
      result = (result << 7) | (byte & 0x7F)
    end
  end

  # If we're here, the encoding is invalid
  raise InvalidFontError, "Invalid UIntBase128 encoding"
end

.uint_base128_size(value) ⇒ Integer

Estimate size of UIntBase128 encoded value

Parameters:

  • value (Integer) —

    The value to encode

Returns:

  • (Integer) —

    Estimated size in bytes



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# File 'lib/fontisan/woff2_font.rb', line 603

def self.uint_base128_size(value)
  return 1 if value < 128

  bytes = 0
  v = value
  while v.positive?
    bytes += 1
    v >>= 7
  end
  [
    bytes,
    5,
  ].min # Max 5 bytes
end

.update_checksum_in_memory(sfnt_data, table_records) ⇒ void

This method returns an undefined value.

Update checksumAdjustment field in head table in memory

Parameters:

  • sfnt_data (String) —

    The SFNT binary data

  • table_records (Array<Hash>) —

    Table records with offsets



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# File 'lib/fontisan/woff2_font.rb', line 698

def self.update_checksum_in_memory(sfnt_data, table_records)
  # Find head table record
  head_record = table_records.find { |r| r[:tag] == Constants::HEAD_TAG }
  return unless head_record

  # Zero out checksumAdjustment field first
  head_offset = head_record[:offset]
  sfnt_data[head_offset + 8, 4] = "\x00\x00\x00\x00"

  # Calculate file checksum
  checksum = 0
  sfnt_data.bytes.each_slice(4) do |bytes|
    word = bytes.pack("C*").ljust(4, "\x00").unpack1("N")
    checksum = (checksum + word) & 0xFFFFFFFF
  end

  # Calculate adjustment
  adjustment = (0xB1B0AFBA - checksum) & 0xFFFFFFFF

  # Write adjustment to head table
  sfnt_data[head_offset + 8, 4] = [adjustment].pack("N")
end

Instance Method Details

#cff? ⇒ Boolean

Check if font has CFF flavor

Returns:

  • (Boolean) 


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# File 'lib/fontisan/woff2_font.rb', line 113

def cff?
  return false unless @header

  [Constants::SFNT_VERSION_OTTO, 0x4F54544F].include?(@header.flavor)
end

#family_name ⇒ Object

Get font family name



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# File 'lib/fontisan/woff2_font.rb', line 257

def family_name
  name_table = table("name")
  name_table&.english_name(Tables::Name::FAMILY)
end

#find_table_entry(tag) ⇒ Object

Find table entry by tag



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# File 'lib/fontisan/woff2_font.rb', line 149

def find_table_entry(tag)
  @table_entries.find { |entry| entry.tag == tag }
end

#full_name ⇒ Object

Get full font name



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# File 'lib/fontisan/woff2_font.rb', line 269

def full_name
  name_table = table("name")
  name_table&.english_name(Tables::Name::FULL_NAME)
end

#has_table?(tag) ⇒ Boolean

Check if table exists

Returns:

  • (Boolean) 


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# File 'lib/fontisan/woff2_font.rb', line 144

def has_table?(tag)
  @table_entries.any? { |entry| entry.tag == tag }
end

#initialize_storage ⇒ Object

Initialize storage hashes



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# File 'lib/fontisan/woff2_font.rb', line 100

def initialize_storage
  @decompressed_tables ||= {}
  @initialize_storage ||= {}
end

#metadata ⇒ Object

Get metadata (if present)



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# File 'lib/fontisan/woff2_font.rb', line 238

def metadata
  return nil unless @header&.meta_length&.positive?
  return nil unless @io_source

  begin
    File.open(@io_source.path, "rb") do |io|
      io.seek(@header.meta_offset)
      compressed_meta = io.read(@header.meta_length)
      Brotli.inflate(compressed_meta)
    end
  rescue StandardError => e
    warn "Failed to decompress metadata: #{e.message}"
    nil
  end
end

#post_script_name ⇒ Object

Get PostScript name



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# File 'lib/fontisan/woff2_font.rb', line 275

def post_script_name
  name_table = table("name")
  name_table&.english_name(Tables::Name::POSTSCRIPT_NAME)
end

#preferred_family_name ⇒ Object

Get preferred family name



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# File 'lib/fontisan/woff2_font.rb', line 281

def preferred_family_name
  name_table = table("name")
  name_table&.english_name(Tables::Name::PREFERRED_FAMILY)
end

#preferred_subfamily_name ⇒ Object

Get preferred subfamily name



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# File 'lib/fontisan/woff2_font.rb', line 287

def preferred_subfamily_name
  name_table = table("name")
  name_table&.english_name(Tables::Name::PREFERRED_SUBFAMILY)
end

#subfamily_name ⇒ Object

Get font subfamily name



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# File 'lib/fontisan/woff2_font.rb', line 263

def subfamily_name
  name_table = table("name")
  name_table&.english_name(Tables::Name::SUBFAMILY)
end

#table(tag) ⇒ Object

Get parsed table object



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# File 'lib/fontisan/woff2_font.rb', line 186

def table(tag)
  # Delegate to underlying font if available
  return @underlying_font.table(tag) if @underlying_font

  # Fallback to parsed_tables hash
  # Normalize tag to UTF-8 string for hash lookup
  # Use dup to create mutable copy since force_encoding modifies in place
  tag_key = tag.to_s.dup.force_encoding("UTF-8")
  @parsed_tables[tag_key]
end

#table_data(tag = nil) ⇒ String, ...

Get decompressed table data

Parameters:

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

    The table tag (optional)

Returns:

  • (String, Hash, nil) —

    Table data if tag provided, or hash of all tables if no tag



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# File 'lib/fontisan/woff2_font.rb', line 162

def table_data(tag = nil)
  # If no tag provided, return all tables
  if tag.nil?
    # First try underlying font's table data if available
    if @underlying_font.respond_to?(:table_data)
      return @underlying_font.table_data
    end

    # Fallback to decompressed_tables
    return @decompressed_tables.dup
  end

  # Tag provided - return specific table
  # First try underlying font's table data if available
  if @underlying_font.respond_to?(:table_data)
    underlying_data = @underlying_font.table_data[tag]
    return underlying_data if underlying_data
  end

  # Fallback to decompressed_tables
  @decompressed_tables[tag]
end

#table_names ⇒ Object

Get list of table tags



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# File 'lib/fontisan/woff2_font.rb', line 154

def table_names
  @table_entries.map(&:tag)
end

#to_otf(output_path) ⇒ Object

Convert to OTF



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# File 'lib/fontisan/woff2_font.rb', line 218

def to_otf(output_path)
  unless cff?
    raise InvalidFontError,
          "Cannot convert to OTF: font is not CFF flavored"
  end

  # Build SFNT and create OpenTypeFont
  sfnt_data = self.class.build_sfnt_in_memory(@header, @table_entries,
                                              @decompressed_tables)
  sfnt_io = StringIO.new(sfnt_data)

  # Create actual OpenTypeFont and save for table delegation
  @underlying_font = OpenTypeFont.read(sfnt_io)
  @underlying_font.initialize_storage
  @underlying_font.read_table_data(sfnt_io)

  FontWriter.write_to_file(@underlying_font.tables, output_path)
end

#to_ttf(output_path) ⇒ Object

Convert to TTF



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# File 'lib/fontisan/woff2_font.rb', line 198

def to_ttf(output_path)
  unless truetype?
    raise InvalidFontError,
          "Cannot convert to TTF: font is not TrueType flavored"
  end

  # Build SFNT and create TrueTypeFont
  sfnt_data = self.class.build_sfnt_in_memory(@header, @table_entries,
                                              @decompressed_tables)
  sfnt_io = StringIO.new(sfnt_data)

  # Create actual TrueTypeFont and save for table delegation
  @underlying_font = TrueTypeFont.read(sfnt_io)
  @underlying_font.initialize_storage
  @underlying_font.read_table_data(sfnt_io)

  FontWriter.write_to_file(@underlying_font.tables, output_path)
end

#truetype? ⇒ Boolean

Check if font has TrueType flavor

Returns:

  • (Boolean) 


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# File 'lib/fontisan/woff2_font.rb', line 106

def truetype?
  return false unless @header

  [Constants::SFNT_VERSION_TRUETYPE, 0x00010000].include?(@header.flavor)
end

#units_per_em ⇒ Object

Get units per em



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# File 'lib/fontisan/woff2_font.rb', line 293

def units_per_em
  head = table("head")
  head&.units_per_em
end

#valid? ⇒ Boolean

Check if font is valid

Returns:

  • (Boolean) 


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# File 'lib/fontisan/woff2_font.rb', line 134

def valid?
  return false unless @header
  return false unless @header.signature == Woff2::Woff2Header::SIGNATURE
  return false unless @header.num_tables == @table_entries.length
  return false unless has_table?("head")

  true
end

#validate_signature! ⇒ Object

Validate WOFF2 signature



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# File 'lib/fontisan/woff2_font.rb', line 127

def validate_signature!
  unless @header && @header.signature == Woff2::Woff2Header::SIGNATURE
    raise InvalidFontError, "Invalid WOFF2 signature"
  end
end

#variable_font? ⇒ Boolean

Check if font is a variable font

Returns:

  • (Boolean) —

    true if font has fvar table (variable font)



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# File 'lib/fontisan/woff2_font.rb', line 122

def variable_font?
  has_table?("fvar")
end