Class: Fontisan::Hints::HintValidator

Inherits:
Object
  • Object
show all
Defined in:
lib/fontisan/hints/hint_validator.rb

Overview

Validates hint data for correctness and compatibility

This validator ensures that hints are well-formed and compatible with their target format. It performs multiple levels of validation:

  • TrueType instruction bytecode validation

  • PostScript hint parameter validation

  • Stack neutrality verification

  • Hint-outline compatibility checking

Examples:

Validate TrueType instructions

validator = HintValidator.new
result = validator.validate_truetype_instructions(prep_bytes)
if result[:valid]
  puts "Valid TrueType instructions"
else
  puts "Errors: #{result[:errors]}"
end

Validate PostScript hints

validator = HintValidator.new
result = validator.validate_postscript_hints(ps_dict)
puts result[:warnings] if result[:warnings].any?

Constant Summary collapse

MAX_BLUE_VALUES =

Maximum allowed values for PostScript hint parameters

14
MAX_OTHER_BLUES =

7 pairs

10
MAX_STEM_SNAP =

5 pairs

12

Instance Method Summary collapse

Instance Method Details

#validate_postscript_hints(hints) ⇒ Hash

Validate PostScript hint parameters

Checks for:

  • Valid parameter ranges

  • Proper pair counts for blue zones

  • Sensible stem width values

Parameters:

  • hints (Hash) —

    PostScript hint parameters

Returns:

  • (Hash) —

    Validation result with :valid, :errors, :warnings keys



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# File 'lib/fontisan/hints/hint_validator.rb', line 138

def validate_postscript_hints(hints)
  errors = []
  warnings = []

  # Validate blue_values
  if hints[:blue_values]
    blue_values = hints[:blue_values]
    if blue_values.length > MAX_BLUE_VALUES
      errors << "blue_values exceeds maximum (#{MAX_BLUE_VALUES}): #{blue_values.length}"
    end
    if blue_values.length.odd?
      errors << "blue_values must be pairs (even count): #{blue_values.length}"
    end
  end

  # Validate other_blues
  if hints[:other_blues]
    other_blues = hints[:other_blues]
    if other_blues.length > MAX_OTHER_BLUES
      errors << "other_blues exceeds maximum (#{MAX_OTHER_BLUES}): #{other_blues.length}"
    end
    if other_blues.length.odd?
      errors << "other_blues must be pairs (even count): #{other_blues.length}"
    end
  end

  # Validate stem widths
  [:std_hw, :std_vw].each do |key|
    if hints[key] && hints[key] <= 0
      errors << "#{key} must be positive: #{hints[key]}"
    end
  end

  # Validate stem snaps
  [:stem_snap_h, :stem_snap_v].each do |key|
    if hints[key]
      if hints[key].length > MAX_STEM_SNAP
        errors << "#{key} exceeds maximum (#{MAX_STEM_SNAP}): #{hints[key].length}"
      end
      if hints[key].any? { |v| v <= 0 }
        warnings << "#{key} contains non-positive values"
      end
    end
  end

  # Validate blue_scale
  if hints[:blue_scale]
    if hints[:blue_scale] <= 0
      errors << "blue_scale must be positive: #{hints[:blue_scale]}"
    end
    if hints[:blue_scale] > 1.0
      warnings << "blue_scale unusually large (>1.0): #{hints[:blue_scale]}"
    end
  end

  # Validate language_group
  if hints[:language_group]
    unless [0, 1].include?(hints[:language_group])
      errors << "language_group must be 0 (Latin) or 1 (CJK): #{hints[:language_group]}"
    end
  end

  {
    valid: errors.empty?,
    errors: errors,
    warnings: warnings,
  }
end

#validate_stack_neutrality(instructions) ⇒ Hash

Validate stack neutrality of instruction sequence

Ensures the instruction sequence leaves the stack in the same state as it started (net stack change of zero).

Parameters:

  • instructions (String) —

    Binary instruction bytes

Returns:

  • (Hash) —

    Result with :neutral, :stack_depth, :errors keys



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# File 'lib/fontisan/hints/hint_validator.rb', line 214

def validate_stack_neutrality(instructions)
  return { neutral: true, stack_depth: 0, errors: [] } if instructions.nil? || instructions.empty?

  errors = []
  stack_depth = 0
  bytes = instructions.bytes
  index = 0

  begin
    while index < bytes.length
      opcode = bytes[index]
      index += 1

      case opcode
      when 0x40 # NPUSHB
        count = bytes[index]
        index += 1 + count
        stack_depth += count

      when 0x41 # NPUSHW
        count = bytes[index]
        index += 1 + (count * 2)
        stack_depth += count

      when 0xB0..0xB7 # PUSHB[0-7]
        count = opcode - 0xB0 + 1
        index += count
        stack_depth += count

      when 0xB8..0xBF # PUSHW[0-7]
        count = opcode - 0xB8 + 1
        index += count * 2
        stack_depth += count

      when 0x1D, 0x1E, 0x1F # SCVTCI, SSWCI, SSW
        stack_depth -= 1

      when 0x44, 0x70 # WCVTP, WCVTF
        stack_depth -= 2
      end
    end
  rescue StandardError => e
    errors << "Error analyzing stack: #{e.message}"
  end

  {
    neutral: stack_depth == 0,
    stack_depth: stack_depth,
    errors: errors,
  }
end

#validate_truetype_instructions(instructions) ⇒ Hash

Validate TrueType instruction bytecode

Checks for:

  • Valid instruction opcodes

  • Correct parameter counts

  • Stack neutrality

Parameters:

  • instructions (String) —

    Binary instruction bytes

Returns:

  • (Hash) —

    Validation result with :valid, :errors, :warnings keys



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# File 'lib/fontisan/hints/hint_validator.rb', line 42

def validate_truetype_instructions(instructions)
  return { valid: true, errors: [], warnings: [] } if instructions.nil? || instructions.empty?

  errors = []
  warnings = []

  begin
    bytes = instructions.bytes
    stack_depth = 0
    index = 0

    while index < bytes.length
      opcode = bytes[index]
      index += 1

      case opcode
      when 0x40 # NPUSHB
        count = bytes[index]
        index += 1
        if index + count > bytes.length
          errors << "NPUSHB: Not enough bytes (need #{count}, have #{bytes.length - index})"
          break
        end
        stack_depth += count
        index += count

      when 0x41 # NPUSHW
        count = bytes[index]
        index += 1
        if index + (count * 2) > bytes.length
          errors << "NPUSHW: Not enough bytes (need #{count * 2}, have #{bytes.length - index})"
          break
        end
        stack_depth += count
        index += count * 2

      when 0xB0..0xB7 # PUSHB[0-7]
        count = opcode - 0xB0 + 1
        if index + count > bytes.length
          errors << "PUSHB[#{count - 1}]: Not enough bytes"
          break
        end
        stack_depth += count
        index += count

      when 0xB8..0xBF # PUSHW[0-7]
        count = opcode - 0xB8 + 1
        if index + (count * 2) > bytes.length
          errors << "PUSHW[#{count - 1}]: Not enough bytes"
          break
        end
        stack_depth += count
        index += count * 2

      when 0x1D, 0x1E, 0x1F # SCVTCI, SSWCI, SSW
        if stack_depth < 1
          errors << "#{opcode_name(opcode)}: Stack underflow"
        end
        stack_depth -= 1

      when 0x44, 0x70 # WCVTP, WCVTF
        if stack_depth < 2
          errors << "#{opcode_name(opcode)}: Stack underflow (need 2 values)"
        end
        stack_depth -= 2

      else
        warnings << "Unknown opcode: 0x#{opcode.to_s(16).upcase} at offset #{index - 1}"
      end
    end

    # Check stack neutrality
    if stack_depth != 0
      warnings << "Stack not neutral: #{stack_depth} value(s) remaining"
    end

  rescue StandardError => e
    errors << "Exception during validation: #{e.message}"
  end

  {
    valid: errors.empty?,
    errors: errors,
    warnings: warnings,
  }
end