Class: Fontisan::TrueTypeFont

Inherits:
BinData::Record
  • Object
show all
Defined in:
lib/fontisan/true_type_font.rb

Overview

TrueType Font domain object using BinData

Represents a complete TrueType Font file using BinData’s declarative DSL for binary structure definition. The structure definition IS the documentation, and BinData handles all low-level reading/writing.

Extended from ExtractTTC to support table parsing for analysis.

Examples:

Reading and analyzing a font

ttf = TrueTypeFont.from_file("font.ttf")
puts ttf.header.num_tables  # => 14
name_table = ttf.table("name")  # Fontisan extension
puts name_table.english_name(Tables::Name::FAMILY)

Loading with metadata mode

ttf = TrueTypeFont.from_file("font.ttf", mode: :metadata)
puts ttf.loading_mode  # => :metadata
ttf.table_available?("GSUB")  # => false

Writing a font

ttf.to_file("output.ttf")

Constant Summary collapse

PAGE_SIZE =

Page size for lazy loading alignment (typical filesystem page size)

4096

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#io_source ⇒ Object

IO source for lazy loading



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# File 'lib/fontisan/true_type_font.rb', line 67

def io_source
  @io_source
end

#lazy_load_enabled ⇒ Object

Whether lazy loading is enabled



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# File 'lib/fontisan/true_type_font.rb', line 70

def lazy_load_enabled
  @lazy_load_enabled
end

#loading_mode ⇒ Object

Loading mode for this font (:metadata or :full)



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# File 'lib/fontisan/true_type_font.rb', line 64

def loading_mode
  @loading_mode
end

#page_cache ⇒ Object

Page cache for lazy loading (maps page_start_offset => page_data)



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# File 'lib/fontisan/true_type_font.rb', line 73

def page_cache
  @page_cache
end

#parsed_tables ⇒ Object

Parsed table instances cache (Fontisan extension)



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# File 'lib/fontisan/true_type_font.rb', line 61

def parsed_tables
  @parsed_tables
end

#table_data ⇒ Object

Table data is stored separately since it’s at variable offsets



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# File 'lib/fontisan/true_type_font.rb', line 58

def table_data
  @table_data
end

Class Method Details

.finalize(io) ⇒ Proc

Finalizer proc for closing IO

Parameters:

  • io (IO) —

    The IO object to close

Returns:

  • (Proc) —

    The finalizer proc



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# File 'lib/fontisan/true_type_font.rb', line 429

def self.finalize(io)
  proc { io&.close }
end

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

Read TrueType Font from a file

Parameters:

  • path (String) —

    Path to the TTF file

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

    Loading mode (:metadata or :full, default: :full)

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

    If true, load tables on demand (default: false for eager loading)

Returns:

Raises:

  • (ArgumentError) —

    if path is nil or empty, or if mode is invalid

  • (Errno::ENOENT) —

    if file does not exist

  • (RuntimeError) —

    if file format is invalid



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# File 'lib/fontisan/true_type_font.rb', line 87

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)

  # Validate mode
  LoadingModes.validate_mode!(mode)

  File.open(path, "rb") do |io|
    font = read(io)
    font.initialize_storage
    font.loading_mode = mode
    font.lazy_load_enabled = lazy

    if lazy
      # Keep file handle open for lazy loading
      font.io_source = File.open(path, "rb")
      font.setup_finalizer
    else
      # Read tables upfront
      font.read_table_data(io)
    end

    font
  end
rescue BinData::ValidityError, EOFError => e
  raise "Invalid TTF file: #{e.message}"
end

.from_ttc(io, offset, mode: LoadingModes::FULL) ⇒ TrueTypeFont

Read TrueType Font from TTC at specific offset

Parameters:

  • io (IO) —

    Open file handle

  • offset (Integer) —

    Byte offset to the font

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

    Loading mode (:metadata or :full, default: :full)

Returns:



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# File 'lib/fontisan/true_type_font.rb', line 124

def self.from_ttc(io, offset, mode: LoadingModes::FULL)
  LoadingModes.validate_mode!(mode)

  io.seek(offset)
  font = read(io)
  font.initialize_storage
  font.loading_mode = mode
  font.read_table_data(io)
  font
end

Instance Method Details

#close ⇒ void

This method returns an undefined value.

Close the IO source (for lazy loading)



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# File 'lib/fontisan/true_type_font.rb', line 413

def close
  @io_source&.close
  @io_source = nil
end

#family_name ⇒ String?

Get font family name

Returns:

  • (String, nil) —

    Family name or nil if not found



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# File 'lib/fontisan/true_type_font.rb', line 365

def family_name
  name_table = table(Constants::NAME_TAG)
  name_table&.english_name(Tables::Name::FAMILY)
end

#find_table_entry(tag) ⇒ TableDirectory?

Find a table entry by tag

Parameters:

  • tag (String) —

    The table tag to find

Returns:



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# File 'lib/fontisan/true_type_font.rb', line 303

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

#full_name ⇒ String?

Get full font name

Returns:

  • (String, nil) —

    Full name or nil if not found



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# File 'lib/fontisan/true_type_font.rb', line 381

def full_name
  name_table = table(Constants::NAME_TAG)
  name_table&.english_name(Tables::Name::FULL_NAME)
end

#has_table?(tag) ⇒ Boolean

Check if font has a specific table

Parameters:

  • tag (String) —

    The table tag to check for

Returns:

  • (Boolean) —

    true if table exists, false otherwise



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# File 'lib/fontisan/true_type_font.rb', line 286

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

#head_table ⇒ TableDirectory?

Get the head table entry

Returns:



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# File 'lib/fontisan/true_type_font.rb', line 310

def head_table
  find_table_entry(Constants::HEAD_TAG)
end

#initialize_storage ⇒ void

This method returns an undefined value.

Initialize storage hashes (Fontisan extension)



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# File 'lib/fontisan/true_type_font.rb', line 138

def initialize_storage
  @table_data = {}
  @parsed_tables = {}
  @loading_mode = LoadingModes::FULL
  @lazy_load_enabled = false
  @io_source = nil
  @page_cache = {}
end

#post_script_name ⇒ String?

Get PostScript name

Returns:

  • (String, nil) —

    PostScript name or nil if not found



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# File 'lib/fontisan/true_type_font.rb', line 389

def post_script_name
  name_table = table(Constants::NAME_TAG)
  name_table&.english_name(Tables::Name::POSTSCRIPT_NAME)
end

#preferred_family_name ⇒ String?

Get preferred family name

Returns:

  • (String, nil) —

    Preferred family name or nil if not found



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# File 'lib/fontisan/true_type_font.rb', line 397

def preferred_family_name
  name_table = table(Constants::NAME_TAG)
  name_table&.english_name(Tables::Name::PREFERRED_FAMILY)
end

#preferred_subfamily_name ⇒ String?

Get preferred subfamily name

Returns:

  • (String, nil) —

    Preferred subfamily name or nil if not found



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# File 'lib/fontisan/true_type_font.rb', line 405

def preferred_subfamily_name
  name_table = table(Constants::NAME_TAG)
  name_table&.english_name(Tables::Name::PREFERRED_SUBFAMILY)
end

#read_metadata_tables_batched(io) ⇒ void

This method returns an undefined value.

Read metadata tables using page-aware batching

Groups adjacent tables within page boundaries and reads them together to maximize filesystem prefetching and minimize random seeks.

Parameters:

  • io (IO) —

    Open file handle



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# File 'lib/fontisan/true_type_font.rb', line 185

def read_metadata_tables_batched(io)
  # Typical filesystem page size (4KB is common, but 8KB gives better prefetch window)
  page_threshold = 8192

  # Get metadata tables sorted by offset for sequential access
  metadata_entries = tables.select { |entry| LoadingModes::METADATA_TABLES_SET.include?(entry.tag) }
  metadata_entries.sort_by!(&:offset)

  return if metadata_entries.empty?

  # Group adjacent tables within page threshold for batched reading
  i = 0
  while i < metadata_entries.size
    batch_start = metadata_entries[i]
    batch_end = batch_start
    batch_entries = [batch_start]

    # Extend batch while next table is within page threshold
    j = i + 1
    while j < metadata_entries.size
      next_entry = metadata_entries[j]
      gap = next_entry.offset - (batch_end.offset + batch_end.table_length)

      # If gap is small (within page threshold), include in batch
      if gap <= page_threshold
        batch_end = next_entry
        batch_entries << next_entry
        j += 1
      else
        break
      end
    end

    # Read batch
    if batch_entries.size == 1
      # Single table, read normally
      io.seek(batch_start.offset)
      tag_key = batch_start.tag.dup.force_encoding("UTF-8")
      @table_data[tag_key] = io.read(batch_start.table_length)
    else
      # Multiple tables, read contiguous segment
      batch_offset = batch_start.offset
      batch_length = (batch_end.offset + batch_end.table_length) - batch_start.offset

      io.seek(batch_offset)
      batch_data = io.read(batch_length)

      # Extract individual tables from batch
      batch_entries.each do |entry|
        relative_offset = entry.offset - batch_offset
        tag_key = entry.tag.dup.force_encoding("UTF-8")
        @table_data[tag_key] = batch_data[relative_offset, entry.table_length]
      end
    end

    i = j
  end
end

#read_table_data(io) ⇒ void

This method returns an undefined value.

Read table data for all tables

In metadata mode, only reads metadata tables. In full mode, reads all tables. In lazy load mode, doesn’t read data upfront.

Parameters:

  • io (IO) —

    Open file handle



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

def read_table_data(io)
  @table_data = {}

  if @lazy_load_enabled
    # Don't read data, just keep IO reference
    @io_source = io
    return
  end

  if @loading_mode == LoadingModes::METADATA
    # Only read metadata tables for performance
    # Use page-aware batched reading to maximize filesystem prefetching
    read_metadata_tables_batched(io)
  else
    # Read all tables
    tables.each do |entry|
      io.seek(entry.offset)
      # Force UTF-8 encoding on tag for hash key consistency
      tag_key = entry.tag.dup.force_encoding("UTF-8")
      @table_data[tag_key] = io.read(entry.table_length)
    end
  end
end

#setup_finalizer ⇒ void

This method returns an undefined value.

Setup finalizer for cleanup



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# File 'lib/fontisan/true_type_font.rb', line 421

def setup_finalizer
  ObjectSpace.define_finalizer(self, self.class.finalize(@io_source))
end

#subfamily_name ⇒ String?

Get font subfamily name (e.g., Regular, Bold, Italic)

Returns:

  • (String, nil) —

    Subfamily name or nil if not found



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# File 'lib/fontisan/true_type_font.rb', line 373

def subfamily_name
  name_table = table(Constants::NAME_TAG)
  name_table&.english_name(Tables::Name::SUBFAMILY)
end

#table(tag) ⇒ Tables::*?

Get parsed table instance (Fontisan extension)

This method parses the raw table data into a structured table object and caches the result for subsequent calls. Enforces mode restrictions.

Parameters:

  • tag (String) —

    The table tag to retrieve

Returns:

  • (Tables::*, nil) —

    Parsed table object or nil if not found

Raises:

  • (ArgumentError) —

    if table is not available in current loading mode



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# File 'lib/fontisan/true_type_font.rb', line 329

def table(tag)
  # Check mode restrictions
  unless table_available?(tag)
    if has_table?(tag)
      raise ArgumentError,
            "Table '#{tag}' is not available in #{@loading_mode} mode. " \
            "Available tables: #{LoadingModes.tables_for(@loading_mode).inspect}"
    else
      return nil
    end
  end

  return @parsed_tables[tag] if @parsed_tables.key?(tag)

  # Lazy load table data if enabled
  if @lazy_load_enabled && !@table_data.key?(tag)
    load_table_data(tag)
  end

  @parsed_tables[tag] ||= parse_table(tag)
end

#table_available?(tag) ⇒ Boolean

Check if a table is available in the current loading mode

Parameters:

  • tag (String) —

    The table tag to check

Returns:

  • (Boolean) —

    true if table is available in current mode



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# File 'lib/fontisan/true_type_font.rb', line 294

def table_available?(tag)
  return false unless has_table?(tag)
  LoadingModes.table_allowed?(@loading_mode, tag)
end

#table_names ⇒ Array<String>

Get list of all table tags (Fontisan extension)

Returns:

  • (Array<String>) —

    Array of table tag strings



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# File 'lib/fontisan/true_type_font.rb', line 317

def table_names
  tables.map(&:tag)
end

#to_file(path) ⇒ Integer

Write TrueType Font to a file

Writes the complete TTF structure to disk, including proper checksum calculation and table alignment.

Parameters:

  • path (String) —

    Path where the TTF file will be written

Returns:

  • (Integer) —

    Number of bytes written

Raises:

  • (IOError) —

    if writing fails



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# File 'lib/fontisan/true_type_font.rb', line 252

def to_file(path)
  File.open(path, "wb") do |io|
    # Write header and tables (directory)
    write_structure(io)

    # Write table data with updated offsets
    write_table_data_with_offsets(io)

    io.pos
  end

  # Update checksum adjustment in head table
  update_checksum_adjustment_in_file(path) if head_table

  File.size(path)
end

#units_per_em ⇒ Integer?

Get units per em from head table (Fontisan extension)

Returns:

  • (Integer, nil) —

    Units per em value



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# File 'lib/fontisan/true_type_font.rb', line 354

def units_per_em
  head = table(Constants::HEAD_TAG)
  head&.units_per_em
end

#valid? ⇒ Boolean

Validate format correctness

Returns:

  • (Boolean) —

    true if the TTF format is valid, false otherwise



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# File 'lib/fontisan/true_type_font.rb', line 272

def valid?
  return false unless header
  return false unless tables.respond_to?(:length)
  return false unless @table_data.is_a?(Hash)
  return false if tables.length != header.num_tables
  return false unless head_table

  true
end