Class: Fontisan::Variation::DeltaApplier

Inherits:
Object
  • Object
show all
Includes:
TableAccessor
Defined in:
lib/fontisan/variation/delta_applier.rb

Overview

Applies variation deltas to glyph outlines

This class handles the complete delta application process for TrueType variable fonts using gvar table data:

  1. Parse base glyph outline points

  2. Match active tuple variations to coordinates

  3. Parse and decompress deltas

  4. Apply deltas: new_point = base + Σ(delta × scalar)

  5. Expand IUP (Inferred Untouched Points)

Reference: OpenType specification, gvar table

Examples:

Applying deltas to a glyph

applier = Fontisan::Variation::DeltaApplier.new(font, interpolator, region_matcher)
adjusted_points = applier.apply_deltas(glyph_id, coordinates)

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from TableAccessor

#clear_variation_cache, #clear_variation_table, #has_variation_table?, #require_variation_table, #variation_table

Constructor Details

#initialize(font, interpolator, region_matcher) ⇒ DeltaApplier

Initialize delta applier

Parameters:



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# File 'lib/fontisan/variation/delta_applier.rb', line 45

def initialize(font, interpolator, region_matcher)
  @font = font
  @interpolator = interpolator
  @region_matcher = region_matcher
  @delta_parser = DeltaParser.new
  @variation_tables = {}
end

Instance Attribute Details

#delta_parser ⇒ DeltaParser (readonly)

Returns Delta parser.

Returns:



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

def delta_parser
  @delta_parser
end

#font ⇒ Font (readonly)

Returns Font object.

Returns:

  • (Font) —

    Font object



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

def font
  @font
end

#interpolator ⇒ Interpolator (readonly)

Returns Coordinate interpolator.

Returns:



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# File 'lib/fontisan/variation/delta_applier.rb', line 32

def interpolator
  @interpolator
end

#region_matcher ⇒ RegionMatcher (readonly)

Returns Region matcher.

Returns:



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# File 'lib/fontisan/variation/delta_applier.rb', line 35

def region_matcher
  @region_matcher
end

Instance Method Details

#apply_deltas(glyph_id, coordinates) ⇒ Array<Hash>?

Apply deltas to a glyph at given coordinates

Parameters:

  • glyph_id (Integer) —

    Glyph ID

  • coordinates (Hash<String, Float>) —

    Design space coordinates

Returns:

  • (Array<Hash>, nil) —

    Adjusted points or nil if not applicable



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# File 'lib/fontisan/variation/delta_applier.rb', line 58

def apply_deltas(glyph_id, coordinates)
  gvar = variation_table("gvar")
  glyf = variation_table("glyf")
  return nil unless gvar && glyf

  # Get base glyph outline points
  base_points = extract_glyph_points(glyph_id, glyf)
  return nil if base_points.nil? || base_points.empty?

  # Get tuple variations for this glyph
  tuple_data = gvar.glyph_tuple_variations(glyph_id)
  return base_points if tuple_data.nil? || tuple_data[:tuples].empty?

  # Match active tuples to coordinates
  matches = @region_matcher.match_tuples(
    coordinates: coordinates,
    tuples: tuple_data[:tuples],
  )

  return base_points if matches.empty?

  # Apply each active tuple's deltas
  adjusted_points = base_points.dup
  matches.each do |match|
    apply_tuple_deltas(adjusted_points, match, tuple_data,
                       base_points.length)
  end

  adjusted_points
end

#extract_glyph_points(glyph_id, glyf) ⇒ Array<Hash>?

Extract outline points from glyph

Parameters:

  • glyph_id (Integer) —

    Glyph ID

  • glyf (Glyf) —

    Glyf table

Returns:

  • (Array<Hash>, nil) —

    Array of points with :x, :y, :on_curve



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# File 'lib/fontisan/variation/delta_applier.rb', line 94

def extract_glyph_points(glyph_id, glyf)
  # This is a simplified version - full implementation would parse
  # complete glyf table data including composite glyphs
  glyph_data = glyf.glyph_data(glyph_id)
  return nil if glyph_data.nil?

  # Parse glyph outline (simplified)
  # Real implementation would fully parse SimpleGlyph or CompositeGlyph
  []
end