Class: Fontisan::Optimizers::CharstringRewriter

Inherits:
Object
  • Object
show all
Defined in:
lib/fontisan/optimizers/charstring_rewriter.rb

Overview

Rewrites CharStrings by replacing repeated patterns with subroutine calls. Uses position-aware replacement to handle multiple patterns per glyph without offset corruption.

Examples:

Basic usage

builder = SubroutineBuilder.new(patterns, type: :local)
builder.build
subroutine_map = patterns.each_with_index.to_h { |p, i| [p.bytes, i] }
rewriter = CharstringRewriter.new(subroutine_map, builder)
rewritten = rewriter.rewrite(charstring, patterns_for_glyph)
valid = rewriter.validate(rewritten)

See Also:

  • docs/SUBROUTINE_ARCHITECTUREdocs/SUBROUTINE_ARCHITECTURE.md

Instance Method Summary collapse

Constructor Details

#initialize(subroutine_map, builder) ⇒ CharstringRewriter

Initialize rewriter with subroutine map and builder

Parameters:

  • subroutine_map (Hash<String, Integer>) —

    pattern bytes => subroutine_id

  • builder (SubroutineBuilder) —

    builder for creating calls



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# File 'lib/fontisan/optimizers/charstring_rewriter.rb', line 22

def initialize(subroutine_map, builder)
  @subroutine_map = subroutine_map
  @builder = builder
end

Instance Method Details

#rewrite(charstring, patterns) ⇒ String

Rewrite a CharString by replacing patterns with subroutine calls Sorts patterns by position (descending) to avoid offset issues when replacing multiple patterns in the same CharString.

Parameters:

  • charstring (String) —

    original CharString bytes

  • patterns (Array<Pattern>) —

    patterns to replace in this CharString

Returns:

  • (String) —

    rewritten CharString with subroutine calls



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# File 'lib/fontisan/optimizers/charstring_rewriter.rb', line 34

def rewrite(charstring, patterns)
  return charstring if patterns.empty?

  # Build list of all replacements: [position, pattern]
  replacements = build_replacement_list(charstring, patterns)

  # Remove overlapping replacements
  replacements = remove_overlaps(replacements)

  # Sort by position (descending) to avoid offset corruption
  replacements.sort_by! { |pos, _pattern| -pos }

  # Apply each replacement
  rewritten = charstring.dup
  replacements.each do |position, pattern|
    subroutine_id = @subroutine_map[pattern.bytes]
    next if subroutine_id.nil?

    call = @builder.create_call(subroutine_id)

    # Replace pattern with call at position
    rewritten[position, pattern.length] = call
  end

  rewritten
end

#validate(charstring) ⇒ Boolean

Validate rewritten CharString for structural correctness For now, performs basic validation. Future: full CFF parsing.

Parameters:

  • charstring (String) —

    CharString to validate

Returns:

  • (Boolean) —

    true if valid, false otherwise



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# File 'lib/fontisan/optimizers/charstring_rewriter.rb', line 66

def validate(charstring)
  return false if charstring.nil? || charstring.empty?

  # Basic validation: check for return operator at end
  # and reasonable length
  return false if charstring.empty?

  # More comprehensive validation can be added later
  true
end