Class: Fontisan::Variation::Optimizer

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

Overview

Optimizes CFF subroutines for variable fonts

This class analyzes CharStrings in CFF2 variable fonts and optimizes blend operations by extracting common blend sequences into subroutines, deduplicating variation regions, and minimizing ItemVariationStore data.

Optimization strategies:

  1. Blend pattern extraction - Find repeating blend sequences
  2. Region deduplication - Merge identical variation regions
  3. ItemVariationStore optimization - Compact delta storage
  4. Subroutine reordering - Place frequent blends in low IDs

Examples:

Optimizing a variable font

optimizer = Fontisan::Variation::Optimizer.new(cff2_table)
optimized = optimizer.optimize
# => Optimized CFF2 table with reduced file size

See Also:

  • docs/SUBROUTINE_ARCHITECTUREdocs/SUBROUTINE_ARCHITECTURE.md
  • docs/CFF2_ARCHITECTUREdocs/CFF2_ARCHITECTURE.md

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(cff2, options = {}) ⇒ Optimizer

Initialize optimizer

Parameters:

  • cff2 (CFF2) —

    CFF2 table with blend operators

  • options (Hash) (defaults to: {}) —

    Optimization options

Options Hash (options):

  • :max_subrs (Integer) —

    Maximum subroutines (default: 65535)

  • :region_threshold (Float) —

    Region similarity threshold (default: 0.001)

  • :deduplicate_regions (Boolean) —

    Enable region deduplication (default: true)



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# File 'lib/fontisan/variation/optimizer.rb', line 38

def initialize(cff2, options = {})
  @cff2 = cff2
  @options = {
    max_subrs: 65535,
    region_threshold: 0.001,
    deduplicate_regions: true,
  }.merge(options)

  @stats = {
    original_size: 0,
    optimized_size: 0,
    blend_patterns_found: 0,
    subroutines_created: 0,
    regions_deduplicated: 0,
  }
end

Instance Attribute Details

#cff2 ⇒ CFF2 (readonly)

Returns CFF2 table being optimized.

Returns:

  • (CFF2) —

    CFF2 table being optimized



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# File 'lib/fontisan/variation/optimizer.rb', line 26

def cff2
  @cff2
end

#stats ⇒ Hash (readonly)

Returns Optimization statistics.

Returns:

  • (Hash) —

    Optimization statistics



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# File 'lib/fontisan/variation/optimizer.rb', line 29

def stats
  @stats
end

Instance Method Details

#analyze_blend_patterns ⇒ Array<BlendPattern>

Analyze blend patterns in CharStrings

Scans all CharStrings to find repeating blend operator sequences that can be extracted into subroutines.

Returns:

  • (Array<BlendPattern>) —

    Identified blend patterns



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# File 'lib/fontisan/variation/optimizer.rb', line 90

def analyze_blend_patterns
  patterns = []
  glyph_count = @cff2.glyph_count

  glyph_count.times do |glyph_id|
    charstring = @cff2.charstring(glyph_id)
    next unless charstring

    # Extract blend operator sequences
    blend_sequences = extract_blend_sequences(charstring)
    patterns.concat(blend_sequences)
  end

  # Group identical patterns
  grouped = group_patterns(patterns)
  @stats[:blend_patterns_found] = grouped.length

  grouped
end

#compact_variation_data(store) ⇒ Object

Compact variation data by removing unused entries

Parameters:

  • store (ItemVariationStore) —

    Variation store



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# File 'lib/fontisan/variation/optimizer.rb', line 247

def compact_variation_data(store)
  # Identify used variation indices from CharStrings
  used_indices = collect_used_variation_indices

  # Remove unused data
  store.item_variation_data.each do |data|
    data.compact_unused(used_indices)
  end
end

#coords_similar?(c1, c2) ⇒ Boolean

Check if coordinates are similar within threshold

Parameters:

  • c1 (Float) —

    First coordinate

  • c2 (Float) —

    Second coordinate

Returns:

  • (Boolean) —

    True if similar



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# File 'lib/fontisan/variation/optimizer.rb', line 225

def coords_similar?(c1, c2)
  (c1 - c2).abs <= @options[:region_threshold]
end

#deduplicate_regions ⇒ Object

Deduplicate variation regions

Merges regions that are functionally identical (within threshold).



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# File 'lib/fontisan/variation/optimizer.rb', line 155

def deduplicate_regions
  return unless @cff2.variation_store

  regions = @cff2.variation_store.region_list
  original_count = regions.length

  # Find duplicate regions
  unique_regions = []
  region_mapping = {}

  regions.each_with_index do |region, index|
    # Check if region matches any existing unique region
    match_index = find_matching_region(region, unique_regions)

    if match_index
      region_mapping[index] = match_index
    else
      region_mapping[index] = unique_regions.length
      unique_regions << region
    end
  end

  # Update references in ItemVariationStore
  update_region_references(region_mapping) if regions.length > unique_regions.length

  @cff2.variation_store.region_list = unique_regions
  @stats[:regions_deduplicated] = original_count - unique_regions.length
end

#extract_blend_sequences(charstring) ⇒ Array<BlendPattern>

Extract blend sequences from CharString

Parameters:

  • charstring (String) —

    Binary CharString data

Returns:

  • (Array<BlendPattern>) —

    Blend patterns found



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# File 'lib/fontisan/variation/optimizer.rb', line 114

def extract_blend_sequences(charstring)
  patterns = []
  operators = parse_charstring_operators(charstring)

  operators.each_with_index do |op, index|
    next unless blend_operator?(op)

    # Extract blend and surrounding context
    pattern = extract_pattern_context(operators, index)
    patterns << pattern if pattern
  end

  patterns
end

#extract_blend_subroutines(patterns) ⇒ Array<Subroutine>

Extract common blend sequences into subroutines

Parameters:

  • patterns (Array<BlendPattern>) —

    Blend patterns

Returns:

  • (Array<Subroutine>) —

    Created subroutines



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# File 'lib/fontisan/variation/optimizer.rb', line 133

def extract_blend_subroutines(patterns)
  # Filter patterns by frequency and savings
  candidates = patterns.select do |pattern|
    pattern[:frequency] >= 2 && pattern[:savings].positive?
  end

  # Convert patterns to format expected by SubroutineOptimizer
  # The optimizer expects objects with methods, but we have hashes
  # For now, just select and order them directly
  selected = candidates.sort_by { |p| -p[:savings] }
    .take(@options[:max_subrs])

  # Order by frequency for efficient encoding
  ordered = selected.sort_by { |p| -p[:frequency] }

  @stats[:subroutines_created] = ordered.length
  ordered
end

#find_matching_region(region, unique_regions) ⇒ Integer?

Find matching region within threshold

Parameters:

  • region (RegionAxisCoordinates) —

    Region to match

  • unique_regions (Array<RegionAxisCoordinates>) —

    Existing unique regions

Returns:

  • (Integer, nil) —

    Index of matching region or nil



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# File 'lib/fontisan/variation/optimizer.rb', line 189

def find_matching_region(region, unique_regions)
  unique_regions.each_with_index do |unique, index|
    return index if regions_match?(region, unique)
  end
  nil
end

#optimize ⇒ CFF2

Optimize CFF2 table

Performs all optimization passes and returns optimized table.

Returns:

  • (CFF2) —

    Optimized CFF2 table



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# File 'lib/fontisan/variation/optimizer.rb', line 60

def optimize
  @stats[:original_size] = estimate_table_size(@cff2)

  # Step 1: Analyze blend patterns across all CharStrings
  blend_patterns = analyze_blend_patterns

  # Step 2: Extract common blend sequences into subroutines
  subroutines = extract_blend_subroutines(blend_patterns)

  # Step 3: Deduplicate variation regions
  deduplicate_regions if @options[:deduplicate_regions]

  # Step 4: Optimize ItemVariationStore
  optimize_item_variation_store

  # Step 5: Rebuild CharStrings with subroutine calls
  rebuild_charstrings(subroutines)

  @stats[:optimized_size] = estimate_table_size(@cff2)
  @stats[:savings_percent] = calculate_savings_percent

  @cff2
end

#optimize_delta_encoding(store) ⇒ Object

Optimize delta encoding for efficiency

Parameters:

  • store (ItemVariationStore) —

    Variation store



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# File 'lib/fontisan/variation/optimizer.rb', line 260

def optimize_delta_encoding(store)
  store.item_variation_data.each(&:optimize_encoding)
end

#optimize_item_variation_store ⇒ Object

Optimize ItemVariationStore

Compacts delta storage by removing unused data and optimizing encoding.



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# File 'lib/fontisan/variation/optimizer.rb', line 232

def optimize_item_variation_store
  return unless @cff2.variation_store

  store = @cff2.variation_store

  # Remove unused variation data
  compact_variation_data(store)

  # Optimize delta encoding (use shortest representation)
  optimize_delta_encoding(store)
end

#rebuild_charstrings(subroutines) ⇒ Object

Rebuild CharStrings with subroutine calls

Parameters:

  • subroutines (Array<Subroutine>) —

    Subroutines to use



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# File 'lib/fontisan/variation/optimizer.rb', line 267

def rebuild_charstrings(subroutines)
  return if subroutines.empty?

  glyph_count = @cff2.glyph_count

  glyph_count.times do |glyph_id|
    charstring = @cff2.charstring(glyph_id)
    next unless charstring

    # Rewrite CharString to use subroutines
    optimized = rewrite_with_subroutines(charstring, subroutines)
    @cff2.set_charstring(glyph_id, optimized)
  end

  # Update subroutine index in CFF2
  @cff2.local_subr_index = subroutines
end

#regions_match?(r1, r2) ⇒ Boolean

Check if two regions match within threshold

Parameters:

  • r1 (RegionAxisCoordinates) —

    First region

  • r2 (RegionAxisCoordinates) —

    Second region

Returns:

  • (Boolean) —

    True if regions match



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# File 'lib/fontisan/variation/optimizer.rb', line 201

def regions_match?(r1, r2)
  return false unless r1.axis_count == r2.axis_count

  r1.axis_count.times do |i|
    coords1 = r1.region_axes[i]
    coords2 = r2.region_axes[i]

    # Compare start, peak, end coordinates
    return false unless coords_similar?(coords1.start_coord,
                                        coords2.start_coord)
    return false unless coords_similar?(coords1.peak_coord,
                                        coords2.peak_coord)
    return false unless coords_similar?(coords1.end_coord,
                                        coords2.end_coord)
  end

  true
end

#statistics ⇒ Hash

Get optimization statistics

Returns:

  • (Hash) —

    Statistics about optimization



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# File 'lib/fontisan/variation/optimizer.rb', line 288

def statistics
  @stats
end