Class: Fontisan::Converters::OutlineConverter

Inherits:
Object
  • Object
show all
Includes:
CffTableBuilder, ConversionStrategy, GlyfTableBuilder, OutlineExtraction, OutlineOptimizer
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 OutlineOptimizer

#optimize_charstrings

Methods included from GlyfTableBuilder

#build_glyf_loca_tables

Methods included from CffTableBuilder

#build_cff_table

Methods included from OutlineExtraction

#extract_cff_outlines, #extract_ttf_outlines

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

#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 201

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)

  # 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 CharStrings from outlines
  charstrings = outlines.map do |outline|
    builder = Tables::Cff::CharStringBuilder.new
    if outline.empty?
      builder.build_empty
    else
      builder.build(outline)
    end
  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 CFF table from charstrings and local subrs
  cff_data = build_cff_table(charstrings, local_subrs, font)

  # 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 449

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 308

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 490

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 510

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 652

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 610

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_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 640

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 578

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

#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 415

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

#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 255

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 264

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 246

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 382

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 399

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 325

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 337

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 280

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 527

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 664

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