Class: Fontisan::Tables::Cff::OffsetRecalculator

Inherits:
Object
  • Object
show all
Defined in:
lib/fontisan/tables/cff/offset_recalculator.rb

Overview

Recalculates CFF table offsets after structure modifications

When the Private DICT size changes (e.g., adding hint parameters), all offsets in the CFF table must be recalculated. This class computes new offsets based on section sizes.

CFF Structure (sequential layout):

  • Header (fixed size)
  • Name INDEX
  • Top DICT INDEX (contains offsets to CharStrings and Private DICT)
  • String INDEX
  • Global Subr INDEX
  • CharStrings INDEX
  • Private DICT (variable size)
  • Local Subr INDEX (optional, within Private DICT)

Key offsets to recalculate:

  • charstrings: Offset from CFF start to CharStrings INDEX
  • private: [size, offset] in Top DICT pointing to Private DICT

Class Method Summary collapse

Class Method Details

.calculate_offsets(sections) ⇒ Hash

Calculate offsets for all CFF sections

Parameters:

  • sections (Hash) —

    Hash of section_name => binary_data

Returns:

  • (Hash) —

    Hash of offset information



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# File 'lib/fontisan/tables/cff/offset_recalculator.rb', line 30

def self.calculate_offsets(sections)
  offsets = {}
  pos = 0

  # Track position through CFF structure
  pos += sections[:header].bytesize
  pos += sections[:name_index].bytesize

  # Top DICT INDEX starts here
  offsets[:top_dict_start] = pos
  pos += sections[:top_dict_index].bytesize

  pos += sections[:string_index].bytesize
  pos += sections[:global_subr_index].bytesize

  # CharStrings INDEX offset (referenced in Top DICT)
  offsets[:charstrings] = pos
  pos += sections[:charstrings_index].bytesize

  # Private DICT offset and size (referenced in Top DICT)
  offsets[:private] = pos
  offsets[:private_size] = sections[:private_dict].bytesize

  offsets
end

.update_top_dict(top_dict, offsets) ⇒ Hash

Update Top DICT with new offsets

Parameters:

  • top_dict (Hash) —

    Top DICT data

  • offsets (Hash) —

    Calculated offsets

Returns:

  • (Hash) —

    Updated Top DICT



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# File 'lib/fontisan/tables/cff/offset_recalculator.rb', line 61

def self.update_top_dict(top_dict, offsets)
  updated = top_dict.dup
  updated[:charstrings] = offsets[:charstrings]
  updated[:private] = [offsets[:private_size], offsets[:private]]
  updated
end