Class: Fontisan::Converters::OutlineConverter

Inherits:
Object
  • Object
show all
Includes:
ConversionStrategy
Defined in:
lib/fontisan/converters/outline_converter.rb

Overview

Strategy for converting between TTF and OTF outline formats

[‘OutlineConverter`](lib/fontisan/converters/outline_converter.rb) handles conversion between TrueType (glyf/loca) and CFF outline formats. This involves:

  • Extracting glyph outlines from source format

  • Converting to universal [‘Outline`](lib/fontisan/models/outline.rb) model

  • Building target format tables using specialized builders

  • Updating related tables (maxp, head)

  • Preserving all other font tables

  • Optionally preserving rendering hints

**Conversion Details:**

TTF → OTF:

  • Extract glyphs from glyf/loca tables

  • Convert TrueType quadratic curves to universal format

  • Build complete CFF table with CharStrings INDEX

  • Remove glyf/loca tables

  • Update maxp to version 0.5 (CFF format)

  • Update head table (clear indexToLocFormat)

OTF → TTF:

  • Extract CharStrings from CFF table

  • Convert CFF cubic curves to universal format

  • Build glyf and loca tables

  • Remove CFF table

  • Update maxp to version 1.0 (TrueType format)

  • Update head table (set indexToLocFormat)

Examples:

Converting TTF to OTF

converter = Fontisan::Converters::OutlineConverter.new
otf_font = converter.convert(ttf_font, target_format: :otf)

Converting OTF to TTF

converter = Fontisan::Converters::OutlineConverter.new
ttf_font = converter.convert(otf_font, target_format: :ttf)

Converting with hint preservation

converter = Fontisan::Converters::OutlineConverter.new
otf_font = converter.convert(ttf_font, target_format: :otf, preserve_hints: true)

Constant Summary collapse

SUPPORTED_FORMATS =

Supported outline formats

%i[ttf otf cff2].freeze

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from ConversionStrategy

#supports?

Constructor Details

#initialize ⇒ OutlineConverter

Initialize converter



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# File 'lib/fontisan/converters/outline_converter.rb', line 78

def initialize
  @font = nil
end

Instance Attribute Details

#font ⇒ TrueTypeFont, OpenTypeFont (readonly)

Returns Source font.

Returns:



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# File 'lib/fontisan/converters/outline_converter.rb', line 75

def font
  @font
end

Instance Method Details

#build_cff_table(outlines, font, _hints_per_glyph) ⇒ String

Build CFF table from outlines

Parameters:

  • outlines (Array<Outline>) —

    Glyph outlines

  • font (TrueTypeFont) —

    Source font (for metadata)

Returns:

  • (String) —

    CFF table binary data



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# File 'lib/fontisan/converters/outline_converter.rb', line 361

def build_cff_table(outlines, font, _hints_per_glyph)
  # Build CharStrings INDEX from outlines
  begin
    charstrings = outlines.map do |outline|
      builder = Tables::Cff::CharStringBuilder.new
      if outline.empty?
        builder.build_empty
      else
        builder.build(outline)
      end
    end
  rescue StandardError => e
    raise Fontisan::Error, "Failed to build CharStrings: #{e.message}"
  end

  # Apply subroutine optimization if enabled
  local_subrs = []

  if @optimize_cff
    begin
      charstrings, local_subrs = optimize_charstrings(charstrings)
    rescue StandardError => e
      # If optimization fails, fall back to unoptimized CharStrings
      warn "CFF optimization failed: #{e.message}, using unoptimized CharStrings"
      local_subrs = []
    end
  end

  # Build font metadata
  begin
    font_name = extract_font_name(font)
  rescue StandardError => e
    raise Fontisan::Error, "Failed to extract font name: #{e.message}"
  end

  # Build all INDEXes
  begin
    header_size = 4
    name_index_data = Tables::Cff::IndexBuilder.build([font_name])
    string_index_data = Tables::Cff::IndexBuilder.build([]) # Empty strings
    global_subr_index_data = Tables::Cff::IndexBuilder.build([]) # Empty global subrs
    charstrings_index_data = Tables::Cff::IndexBuilder.build(charstrings)
    local_subrs_index_data = Tables::Cff::IndexBuilder.build(local_subrs)
  rescue StandardError => e
    raise Fontisan::Error, "Failed to build CFF indexes: #{e.message}"
  end

  # Build Private DICT with Subrs offset if we have local subroutines
  begin
    private_dict_hash = {
      default_width_x: 1000,
      nominal_width_x: 0,
    }

    # If we have local subroutines, add Subrs offset
    # Subrs offset is relative to Private DICT start
    if local_subrs.any?
      # Add a placeholder Subrs offset first to get accurate size
      private_dict_hash[:subrs] = 0

      # Calculate size of Private DICT with Subrs entry
      temp_private_dict_data = Tables::Cff::DictBuilder.build(private_dict_hash)
      subrs_offset = temp_private_dict_data.bytesize

      # Update with actual Subrs offset
      private_dict_hash[:subrs] = subrs_offset
    end

    # Build final Private DICT
    private_dict_data = Tables::Cff::DictBuilder.build(private_dict_hash)
    private_dict_size = private_dict_data.bytesize
  rescue StandardError => e
    raise Fontisan::Error, "Failed to build Private DICT: #{e.message}"
  end

  # Calculate offsets with iterative refinement
  begin
    # Initial pass
    top_dict_index_start = header_size + name_index_data.bytesize
    string_index_start = top_dict_index_start + 100 # Approximate
    global_subr_index_start = string_index_start + string_index_data.bytesize
    charstrings_offset = global_subr_index_start + global_subr_index_data.bytesize

    # Build Top DICT
    top_dict_hash = {
      charset: 0,
      encoding: 0,
      charstrings: charstrings_offset,
    }
    top_dict_data = Tables::Cff::DictBuilder.build(top_dict_hash)
    top_dict_index_data = Tables::Cff::IndexBuilder.build([top_dict_data])

    # Recalculate with actual Top DICT size
    string_index_start = top_dict_index_start + top_dict_index_data.bytesize
    global_subr_index_start = string_index_start + string_index_data.bytesize
    charstrings_offset = global_subr_index_start + global_subr_index_data.bytesize
    private_dict_offset = charstrings_offset + charstrings_index_data.bytesize

    # Update Top DICT with Private DICT info
    top_dict_hash = {
      charset: 0,
      encoding: 0,
      charstrings: charstrings_offset,
      private: [private_dict_size, private_dict_offset],
    }
    top_dict_data = Tables::Cff::DictBuilder.build(top_dict_hash)
    top_dict_index_data = Tables::Cff::IndexBuilder.build([top_dict_data])

    # Final recalculation
    string_index_start = top_dict_index_start + top_dict_index_data.bytesize
    global_subr_index_start = string_index_start + string_index_data.bytesize
    charstrings_offset = global_subr_index_start + global_subr_index_data.bytesize
    private_dict_offset = charstrings_offset + charstrings_index_data.bytesize

    # Final Top DICT
    top_dict_hash = {
      charset: 0,
      encoding: 0,
      charstrings: charstrings_offset,
      private: [private_dict_size, private_dict_offset],
    }
    top_dict_data = Tables::Cff::DictBuilder.build(top_dict_hash)
    top_dict_index_data = Tables::Cff::IndexBuilder.build([top_dict_data])
  rescue StandardError => e
    raise Fontisan::Error,
          "Failed to calculate CFF table offsets: #{e.message}"
  end

  # Build CFF Header
  begin
    header = [
      1,    # major version
      0,    # minor version
      4,    # header size
      4,    # offSize (will be in INDEX)
    ].pack("C4")
  rescue StandardError => e
    raise Fontisan::Error, "Failed to build CFF header: #{e.message}"
  end

  # Assemble complete CFF table
  begin
    header +
      name_index_data +
      top_dict_index_data +
      string_index_data +
      global_subr_index_data +
      charstrings_index_data +
      private_dict_data +
      local_subrs_index_data
  rescue StandardError => e
    raise Fontisan::Error, "Failed to assemble CFF table: #{e.message}"
  end
end

#build_glyf_loca_tables(outlines, _hints_per_glyph) ⇒ Array<String, String, Integer>

Build glyf and loca tables from outlines

Parameters:

  • outlines (Array<Outline>) —

    Glyph outlines

Returns:

  • (Array<String, String, Integer>) —
    glyf_data, loca_data, loca_format


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# File 'lib/fontisan/converters/outline_converter.rb', line 520

def build_glyf_loca_tables(outlines, _hints_per_glyph)
  glyf_data = "".b
  offsets = []

  # Build each glyph
  outlines.each do |outline|
    offsets << glyf_data.bytesize

    if outline.empty?
      # Empty glyph - no data
      next
    end

    # Build glyph data using GlyphBuilder class method
    glyph_data = Fontisan::Tables::GlyphBuilder.build_simple_glyph(outline)
    glyf_data << glyph_data

    # Add padding to 4-byte boundary
    padding = (4 - (glyf_data.bytesize % 4)) % 4
    glyf_data << ("\x00" * padding) if padding.positive?
  end

  # Add final offset
  offsets << glyf_data.bytesize

  # Build loca table
  # Determine format based on max offset
  max_offset = offsets.max
  if max_offset <= 0x1FFFE
    # Short format (offsets / 2)
    loca_format = 0
    loca_data = offsets.map { |off| off / 2 }.pack("n*")
  else
    # Long format
    loca_format = 1
    loca_data = offsets.pack("N*")
  end

  [glyf_data, loca_data, loca_format]
end

#convert(font, options = {}) ⇒ Hash<String, String>

Convert font between TTF and OTF formats

Parameters:

Options Hash (options):

  • :target_format (Symbol) —

    Target format (:ttf or :otf)

  • :optimize_cff (Boolean) —

    Enable CFF subroutine optimization (default: false)

  • :preserve_hints (Boolean) —

    Preserve rendering hints (default: false)

  • :preserve_variations (Boolean) —

    Keep variation data during conversion (default: true)

  • :generate_instance (Boolean) —

    Generate static instance instead of variable font (default: false)

  • :instance_coordinates (Hash) —

    Axis coordinates for instance generation (default: {})

Returns:

  • (Hash<String, String>) —

    Map of table tags to binary data



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# File 'lib/fontisan/converters/outline_converter.rb', line 93

def convert(font, options = {})
  @font = font
  @options = options
  @optimize_cff = options.fetch(:optimize_cff, false)
  @preserve_hints = options.fetch(:preserve_hints, false)
  @preserve_variations = options.fetch(:preserve_variations, true)
  @generate_instance = options.fetch(:generate_instance, false)
  @instance_coordinates = options.fetch(:instance_coordinates, {})
  target_format = options[:target_format] ||
    detect_target_format(font)
  validate(font, target_format)

  source_format = detect_format(font)

  # Check if we should generate a static instance instead
  if @generate_instance && variable_font?(font)
    return generate_static_instance(font, source_format, target_format)
  end

  case [source_format, target_format]
  when %i[ttf otf]
    convert_ttf_to_otf(font, options)
  when %i[otf ttf]
    convert_otf_to_ttf(font)
  when %i[cff2 ttf]
    # CFF2 to TTF - treat CFF2 similar to OTF for now
    convert_otf_to_ttf(font)
  when %i[ttf cff2]
    # TTF to CFF2 - for variable fonts
    convert_ttf_to_otf(font, options)
  else
    raise Fontisan::Error,
          "Unsupported conversion: #{source_format} → #{target_format}"
  end
end

#convert_otf_to_ttf(font) ⇒ Hash<String, String>

Convert OpenType/CFF font to TrueType

Parameters:

Returns:

  • (Hash<String, String>) —

    Target tables



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# File 'lib/fontisan/converters/outline_converter.rb', line 179

def convert_otf_to_ttf(font)
  # Extract all glyphs from CFF table
  outlines = extract_cff_outlines(font)

  # Extract hints if preservation is enabled
  hints_per_glyph = @preserve_hints ? extract_cff_hints(font) : {}

  # Build glyf and loca tables
  glyf_data, loca_data, loca_format = build_glyf_loca_tables(outlines,
                                                             hints_per_glyph)

  # Copy all tables except CFF
  tables = copy_tables(font, ["CFF ", "CFF2"])

  # Add glyf and loca tables
  tables["glyf"] = glyf_data
  tables["loca"] = loca_data

  # Update maxp table for TrueType
  tables["maxp"] = update_maxp_for_truetype(font, outlines, loca_format)

  # Update head table for TrueType
  tables["head"] = update_head_for_truetype(font, loca_format)

  # Convert and apply hints if preservation is enabled
  if @preserve_hints && hints_per_glyph.any?
    # Extract font-level hints separately
    hint_set = extract_cff_hint_set(font)

    unless hint_set.empty?
      # Convert PostScript hints to TrueType format
      converter = Hints::HintConverter.new
      tt_hint_set = converter.convert_hint_set(hint_set, :truetype)

      # Apply TrueType hints (writes fpgm/prep/cvt tables)
      applier = Hints::TrueTypeHintApplier.new
      tables = applier.apply(tt_hint_set, tables)
    end
  end

  tables
end

#convert_ttf_to_otf(font, _options = {}) ⇒ Hash<String, String>

Convert TrueType font to OpenType/CFF

Parameters:

  • font (TrueTypeFont) —

    Source font

  • options (Hash) —

    Conversion options (currently unused)

Returns:

  • (Hash<String, String>) —

    Target tables



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# File 'lib/fontisan/converters/outline_converter.rb', line 134

def convert_ttf_to_otf(font, _options = {})
  # Extract all glyphs from glyf table
  outlines = extract_ttf_outlines(font)

  # Extract hints if preservation is enabled
  hints_per_glyph = @preserve_hints ? extract_ttf_hints(font) : {}

  # Build CFF table from outlines and hints
  cff_data = build_cff_table(outlines, font, hints_per_glyph)

  # Copy all tables except glyf/loca
  tables = copy_tables(font, %w[glyf loca])

  # Add CFF table
  tables["CFF "] = cff_data

  # Update maxp table for CFF
  tables["maxp"] = update_maxp_for_cff(font, outlines.length)

  # Update head table for CFF
  tables["head"] = update_head_for_cff(font)

  # Convert and apply hints if preservation is enabled
  if @preserve_hints && hints_per_glyph.any?
    # Extract font-level hints separately
    hint_set = extract_ttf_hint_set(font)

    unless hint_set.empty?
      # Convert TrueType hints to PostScript format
      converter = Hints::HintConverter.new
      ps_hint_set = converter.convert_hint_set(hint_set, :postscript)

      # Apply PostScript hints (validation mode - CFF modification pending)
      applier = Hints::PostScriptHintApplier.new
      tables = applier.apply(ps_hint_set, tables)
    end
  end

  tables
end

#convert_variations(font, target_format) ⇒ Hash?

Convert variation data during outline conversion

Parameters:

Returns:

  • (Hash, nil) —

    Converted variation data or nil



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# File 'lib/fontisan/converters/outline_converter.rb', line 786

def convert_variations(font, target_format)
  return nil unless @preserve_variations
  return nil unless variable_font?(font)

  fvar = font.table("fvar")
  return nil unless fvar

  axes = fvar.axes
  converter = Variation::Converter.new(font, axes)

  # Get glyph count
  maxp = font.table("maxp")
  return nil unless maxp

  glyph_count = maxp.num_glyphs

  # Convert variation data for each glyph
  variation_data = {}
  glyph_count.times do |glyph_id|
    source_format = detect_format(font)

    data = case [source_format, target_format]
           when %i[ttf otf], %i[ttf cff2]
             # gvar → blend
             converter.gvar_to_blend(glyph_id)
           when %i[otf ttf], %i[cff2 ttf]
             # blend → gvar
             converter.blend_to_gvar(glyph_id)
           end

    variation_data[glyph_id] = data if data
  end

  variation_data.empty? ? nil : variation_data
end

#copy_tables(font, exclude_tags = []) ⇒ Hash<String, String>

Copy non-outline tables from source to target

Parameters:

Returns:

  • (Hash<String, String>) —

    Copied tables



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# File 'lib/fontisan/converters/outline_converter.rb', line 566

def copy_tables(font, exclude_tags = [])
  tables = {}

  font.table_data.each do |tag, data|
    next if exclude_tags.include?(tag)

    tables[tag] = data if data
  end

  tables
end

#detect_format(font) ⇒ Symbol

Detect font format from tables

Parameters:

Returns:

  • (Symbol) —

    Format (:ttf, :otf, or :cff2)

Raises:

  • (Error) —

    If format cannot be detected



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# File 'lib/fontisan/converters/outline_converter.rb', line 827

def detect_format(font)
  # Check for CFF2 table first (OpenType variable fonts with CFF2 outlines)
  if font.has_table?("CFF2")
    :cff2
  # Check for CFF table (OpenType/CFF)
  elsif font.has_table?("CFF ")
    :otf
  # Check for glyf table (TrueType)
  elsif font.has_table?("glyf")
    :ttf
  else
    raise Fontisan::Error,
          "Cannot detect font format: missing outline tables (CFF2, CFF, or glyf)"
  end
end

#detect_target_format(font) ⇒ Symbol

Detect target format as opposite of source

Parameters:

Returns:

  • (Symbol) —

    Target format



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# File 'lib/fontisan/converters/outline_converter.rb', line 847

def detect_target_format(font)
  source = detect_format(font)
  case source
  when :ttf
    :otf
  when :cff2
    :ttf
  else
    :ttf
  end
end

#extract_cff_hint_set(font) ⇒ HintSet

Extract complete PostScript hint set from font

Parameters:

Returns:

  • (HintSet) —

    Complete hint set



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# File 'lib/fontisan/converters/outline_converter.rb', line 989

def extract_cff_hint_set(font)
  extractor = Hints::PostScriptHintExtractor.new
  extractor.extract_from_font(font)
rescue StandardError => e
  warn "Failed to extract PostScript hint set: #{e.message}"
  Models::HintSet.new(format: :postscript)
end

#extract_cff_hints(font) ⇒ Hash<Integer, Array<Hint>>

Extract hints from CFF font

Parameters:

Returns:

  • (Hash<Integer, Array<Hint>>) —

    Map of glyph ID to hints



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# File 'lib/fontisan/converters/outline_converter.rb', line 947

def extract_cff_hints(font)
  hints_per_glyph = {}
  extractor = Hints::PostScriptHintExtractor.new

  # Get CFF table
  cff = font.table("CFF ")
  return {} unless cff

  # Get number of glyphs
  num_glyphs = cff.glyph_count

  # Extract hints from each CharString
  num_glyphs.times do |glyph_id|
    charstring = cff.charstring_for_glyph(glyph_id)
    next if charstring.nil?

    hints = extractor.extract(charstring)
    hints_per_glyph[glyph_id] = hints if hints.any?
  end

  hints_per_glyph
rescue StandardError => e
  warn "Failed to extract CFF hints: #{e.message}"
  {}
end

#extract_cff_outlines(font) ⇒ Array<Outline>

Extract outlines from CFF font

Parameters:

Returns:

  • (Array<Outline>) —

    Array of outline objects

Raises:



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# File 'lib/fontisan/converters/outline_converter.rb', line 327

def extract_cff_outlines(font)
  # Get CFF table
  cff = font.table("CFF ")
  raise Fontisan::Error, "CFF table not found" unless cff

  # Get number of glyphs
  num_glyphs = cff.glyph_count

  # Extract all glyphs
  outlines = []
  num_glyphs.times do |glyph_id|
    charstring = cff.charstring_for_glyph(glyph_id)

    outlines << if charstring.nil? || charstring.path.empty?
                  # Empty glyph
                  Models::Outline.new(
                    glyph_id: glyph_id,
                    commands: [],
                    bbox: { x_min: 0, y_min: 0, x_max: 0, y_max: 0 },
                  )
                else
                  # Convert CharString to outline
                  Models::Outline.from_cff(charstring, glyph_id)
                end
  end

  outlines
end

#extract_font_name(font) ⇒ String

Extract font name from name table

Parameters:

Returns:

  • (String) —

    Font name



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# File 'lib/fontisan/converters/outline_converter.rb', line 671

def extract_font_name(font)
  name_table = font.table("name")
  if name_table
    font_name = name_table.english_name(Tables::Name::FAMILY)
    return font_name.dup.force_encoding("ASCII-8BIT") if font_name
  end

  "UnnamedFont"
end

#extract_ttf_hint_set(font) ⇒ HintSet

Extract complete TrueType hint set from font

Parameters:

Returns:

  • (HintSet) —

    Complete hint set



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# File 'lib/fontisan/converters/outline_converter.rb', line 977

def extract_ttf_hint_set(font)
  extractor = Hints::TrueTypeHintExtractor.new
  extractor.extract_from_font(font)
rescue StandardError => e
  warn "Failed to extract TrueType hint set: #{e.message}"
  Models::HintSet.new(format: :truetype)
end

#extract_ttf_hints(font) ⇒ Hash<Integer, Array<Hint>>

Extract hints from TrueType font

Parameters:

Returns:

  • (Hash<Integer, Array<Hint>>) —

    Map of glyph ID to hints



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# File 'lib/fontisan/converters/outline_converter.rb', line 915

def extract_ttf_hints(font)
  hints_per_glyph = {}
  extractor = Hints::TrueTypeHintExtractor.new

  # Get required tables
  head = font.table("head")
  maxp = font.table("maxp")
  loca = font.table("loca")
  glyf = font.table("glyf")

  # Parse loca with context
  loca.parse_with_context(head.index_to_loc_format, maxp.num_glyphs)

  # Extract hints from each glyph
  maxp.num_glyphs.times do |glyph_id|
    glyph = glyf.glyph_for(glyph_id, loca, head)
    next if glyph.nil? || glyph.empty?

    hints = extractor.extract(glyph)
    hints_per_glyph[glyph_id] = hints if hints.any?
  end

  hints_per_glyph
rescue StandardError => e
  warn "Failed to extract TrueType hints: #{e.message}"
  {}
end

#extract_ttf_outlines(font) ⇒ Array<Outline>

Extract outlines from TrueType font

Parameters:

Returns:

  • (Array<Outline>) —

    Array of outline objects



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# File 'lib/fontisan/converters/outline_converter.rb', line 286

def extract_ttf_outlines(font)
  # Get required tables
  head = font.table("head")
  maxp = font.table("maxp")
  loca = font.table("loca")
  glyf = font.table("glyf")

  # Parse loca with context
  loca.parse_with_context(head.index_to_loc_format, maxp.num_glyphs)

  # Create resolver for compound glyphs
  resolver = Tables::CompoundGlyphResolver.new(glyf, loca, head)

  # Extract all glyphs
  outlines = []
  maxp.num_glyphs.times do |glyph_id|
    glyph = glyf.glyph_for(glyph_id, loca, head)

    outlines << if glyph.nil? || glyph.empty?
                  # Empty glyph - create empty outline
                  Models::Outline.new(
                    glyph_id: glyph_id,
                    commands: [],
                    bbox: { x_min: 0, y_min: 0, x_max: 0, y_max: 0 },
                  )
                elsif glyph.simple?
                  # Convert simple glyph to outline
                  Models::Outline.from_truetype(glyph, glyph_id)
                else
                  # Compound glyph - resolve to simple outline
                  resolver.resolve(glyph)
                end
  end

  outlines
end

#generate_static_instance(font, source_format, target_format) ⇒ Hash<String, String>

Generate static instance from variable font

Parameters:

  • font (TrueTypeFont, OpenTypeFont) —

    Variable font

  • source_format (Symbol) —

    Source format

  • target_format (Symbol) —

    Target format

Returns:

  • (Hash<String, String>) —

    Static font tables



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# File 'lib/fontisan/converters/outline_converter.rb', line 752

def generate_static_instance(font, source_format, target_format)
  # Generate instance at specified coordinates
  fvar = font.table("fvar")
  fvar ? fvar.axes : []

  generator = Variation::InstanceGenerator.new(font,
                                               @instance_coordinates)
  instance_tables = generator.generate

  # If target format differs from source, convert outlines
  if source_format == target_format
    instance_tables
  else
    # Create temporary font with instance tables
    temp_font = font.class.new
    temp_font.instance_variable_set(:@table_data, instance_tables)

    # Convert outline format
    case [source_format, target_format]
    when %i[ttf otf]
      convert_ttf_to_otf(temp_font, @options)
    when %i[otf ttf], %i[cff2 ttf]
      convert_otf_to_ttf(temp_font)
    else
      instance_tables
    end
  end
end

#optimize_charstrings(charstrings) ⇒ Array<Array<String>, Array<String>>

Optimize CharStrings using subroutine extraction

Parameters:

  • charstrings (Array<String>) —

    Original CharString bytes

Returns:

  • (Array<Array<String>, Array<String>>) —
    optimized_charstrings, local_subrs


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# File 'lib/fontisan/converters/outline_converter.rb', line 685

def optimize_charstrings(charstrings)
  # Convert to hash format expected by PatternAnalyzer
  charstrings_hash = {}
  charstrings.each_with_index do |cs, index|
    charstrings_hash[index] = cs
  end

  # Analyze patterns
  analyzer = Optimizers::PatternAnalyzer.new(
    min_length: 10,
    stack_aware: true,
  )
  patterns = analyzer.analyze(charstrings_hash)

  # Return original if no patterns found
  return [charstrings, []] if patterns.empty?

  # Optimize selection
  optimizer = Optimizers::SubroutineOptimizer.new(patterns,
                                                  max_subrs: 65_535)
  selected_patterns = optimizer.optimize_selection

  # Optimize ordering
  selected_patterns = optimizer.optimize_ordering(selected_patterns)

  # Return original if no patterns selected
  return [charstrings, []] if selected_patterns.empty?

  # Build subroutines
  builder = Optimizers::SubroutineBuilder.new(selected_patterns,
                                              type: :local)
  local_subrs = builder.build

  # Build subroutine map
  subroutine_map = {}
  selected_patterns.each_with_index do |pattern, index|
    subroutine_map[pattern.bytes] = index
  end

  # Rewrite CharStrings
  rewriter = Optimizers::CharstringRewriter.new(subroutine_map, builder)
  optimized_charstrings = charstrings.map.with_index do |charstring, glyph_id|
    # Find patterns for this glyph
    glyph_patterns = selected_patterns.select do |p|
      p.glyphs.include?(glyph_id)
    end

    if glyph_patterns.empty?
      charstring
    else
      rewriter.rewrite(charstring, glyph_patterns, glyph_id)
    end
  end

  [optimized_charstrings, local_subrs]
rescue StandardError => e
  # If optimization fails for any reason, return original CharStrings
  warn "Optimization warning: #{e.message}"
  [charstrings, []]
end

#otf_to_ttf ⇒ Hash<String, String>

Convert OpenType/CFF font to TrueType

Returns:

  • (Hash<String, String>) —

    Target tables

Raises:



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# File 'lib/fontisan/converters/outline_converter.rb', line 234

def otf_to_ttf
  raise Fontisan::Error, "No font loaded" unless @font

  convert_otf_to_ttf(@font)
end

#supported_conversions ⇒ Array<Array<Symbol>>

Get supported conversions

Returns:

  • (Array<Array<Symbol>>) —

    Supported conversion pairs



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# File 'lib/fontisan/converters/outline_converter.rb', line 243

def supported_conversions
  [
    %i[ttf otf],
    %i[otf ttf],
    %i[cff2 ttf],
    %i[ttf cff2],
  ]
end

#ttf_to_otf ⇒ Hash<String, String>

Convert TrueType font to OpenType/CFF

Returns:

  • (Hash<String, String>) —

    Target tables

Raises:



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# File 'lib/fontisan/converters/outline_converter.rb', line 225

def ttf_to_otf
  raise Fontisan::Error, "No font loaded" unless @font

  convert_ttf_to_otf(@font)
end

#update_head_for_cff(font) ⇒ String

Update head table for CFF format

Parameters:

Returns:

  • (String) —

    Updated head table binary data



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# File 'lib/fontisan/converters/outline_converter.rb', line 640

def update_head_for_cff(font)
  font.table("head")
  head_data = font.table_data["head"].dup

  # For CFF fonts, indexToLocFormat is not relevant
  # but we'll set it to 0 for consistency
  # indexToLocFormat is at offset 50 (2 bytes)
  head_data[50, 2] = [0].pack("n")

  head_data
end

#update_head_for_truetype(font, loca_format) ⇒ String

Update head table for TrueType format

Parameters:

  • font (OpenTypeFont) —

    Source font

  • loca_format (Integer) —

    Loca format (0=short, 1=long)

Returns:

  • (String) —

    Updated head table binary data



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# File 'lib/fontisan/converters/outline_converter.rb', line 657

def update_head_for_truetype(font, loca_format)
  font.table("head")
  head_data = font.table_data["head"].dup

  # Set indexToLocFormat at offset 50 (2 bytes)
  head_data[50, 2] = [loca_format].pack("n")

  head_data
end

#update_maxp_for_cff(_font, num_glyphs) ⇒ String

Update maxp table for CFF format

Parameters:

  • font (TrueTypeFont) —

    Source font

  • num_glyphs (Integer) —

    Number of glyphs

Returns:

  • (String) —

    Updated maxp table binary data



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# File 'lib/fontisan/converters/outline_converter.rb', line 583

def update_maxp_for_cff(_font, num_glyphs)
  # CFF uses maxp version 0.5 (0x00005000)
  # Structure: version (4 bytes) + numGlyphs (2 bytes)
  [Tables::Maxp::VERSION_0_5, num_glyphs].pack("Nn")
end

#update_maxp_for_truetype(font, outlines, _loca_format) ⇒ String

Update maxp table for TrueType format

Parameters:

  • font (OpenTypeFont) —

    Source font

  • outlines (Array<Outline>) —

    Glyph outlines

  • loca_format (Integer) —

    Loca format (0 or 1)

Returns:

  • (String) —

    Updated maxp table binary data



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# File 'lib/fontisan/converters/outline_converter.rb', line 595

def update_maxp_for_truetype(font, outlines, _loca_format)
  # Get source maxp
  font.table("maxp")
  num_glyphs = outlines.length

  # Calculate statistics from outlines
  max_points = 0
  max_contours = 0

  outlines.each do |outline|
    next if outline.empty?

    contours = outline.to_truetype_contours
    max_contours = [max_contours, contours.length].max

    contours.each do |contour|
      max_points = [max_points, contour.length].max
    end
  end

  # Build maxp v1.0 table
  # We'll use conservative defaults for instruction-related fields
  [
    Tables::Maxp::VERSION_1_0, # version
    num_glyphs,                  # numGlyphs
    max_points,                  # maxPoints
    max_contours,                # maxContours
    0,                           # maxCompositePoints
    0,                           # maxCompositeContours
    2,                           # maxZones
    0,                           # maxTwilightPoints
    0,                           # maxStorage
    0,                           # maxFunctionDefs
    0,                           # maxInstructionDefs
    0,                           # maxStackElements
    0,                           # maxSizeOfInstructions
    0,                           # maxComponentElements
    0,                           # maxComponentDepth
  ].pack("Nnnnnnnnnnnnnnn")
end

#validate(font, target_format) ⇒ Boolean

Validate font for conversion

Parameters:

Returns:

  • (Boolean) —

    True if valid

Raises:

  • (ArgumentError) —

    If font is invalid

  • (Error) —

    If conversion is not supported



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# File 'lib/fontisan/converters/outline_converter.rb', line 259

def validate(font, target_format)
  raise ArgumentError, "Font cannot be nil" if font.nil?

  unless font.respond_to?(:tables)
    raise ArgumentError, "Font must respond to :tables"
  end

  unless font.respond_to?(:table)
    raise ArgumentError, "Font must respond to :table"
  end

  source_format = detect_format(font)
  unless supports?(source_format, target_format)
    raise Fontisan::Error,
          "Conversion #{source_format} → #{target_format} not supported"
  end

  # Check that source font has required tables
  validate_source_tables(font, source_format)

  true
end

#validate_source_tables(font, format) ⇒ Object

Validate source font has required tables

Parameters:

Raises:

  • (Error) —

    If required tables are missing



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# File 'lib/fontisan/converters/outline_converter.rb', line 864

def validate_source_tables(font, format)
  case format
  when :ttf
    unless font.has_table?("glyf") && font.has_table?("loca")
      raise Fontisan::MissingTableError,
            "TrueType font missing required glyf or loca table"
    end
    # Also verify tables can actually be loaded
    unless font.table("glyf") && font.table("loca")
      raise Fontisan::MissingTableError,
            "TrueType font missing required glyf or loca table"
    end
  when :cff2
    unless font.has_table?("CFF2")
      raise Fontisan::MissingTableError,
            "CFF2 font missing required CFF2 table"
    end
    unless font.table("CFF2")
      raise Fontisan::MissingTableError,
            "CFF2 font missing required CFF2 table"
    end
  when :otf
    unless font.has_table?("CFF ") || font.has_table?("CFF2")
      raise Fontisan::MissingTableError,
            "OpenType font missing required CFF or CFF2 table"
    end
    # Verify at least one can be loaded
    unless font.table("CFF ") || font.table("CFF2")
      raise Fontisan::MissingTableError,
            "OpenType font missing required CFF or CFF2 table"
    end
  end

  # Common required tables
  %w[head hhea maxp].each do |tag|
    unless font.has_table?(tag)
      raise Fontisan::MissingTableError,
            "Font missing required #{tag} table"
    end
    # Verify table can actually be loaded
    unless font.table(tag)
      raise Fontisan::MissingTableError,
            "Font missing required #{tag} table"
    end
  end
end

#variable_font?(font) ⇒ Boolean

Check if font is a variable font

Parameters:

Returns:

  • (Boolean) —

    True if font has variation tables



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# File 'lib/fontisan/converters/outline_converter.rb', line 1001

def variable_font?(font)
  font.has_table?("fvar")
end