Class: Fontisan::FontWriter

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

Overview

FontWriter handles writing font binaries from table data

This class assembles a complete font binary from individual table data, including:

  • Writing the sfnt header (offset table)
  • Building the table directory
  • Writing table data with proper 4-byte alignment
  • Calculating all checksums
  • Updating the head table's checksumAdjustment field

Reference: OpenType spec section on font file structure

Examples:

Write font from tables

tables = {
  'head' => head_data,
  'hhea' => hhea_data,
  'maxp' => maxp_data,
  'hmtx' => hmtx_data,
  'cmap' => cmap_data
}
binary = FontWriter.write_font(tables)
File.binwrite('subset.ttf', binary)

Write to file directly

FontWriter.write_to_file(tables, 'subset.ttf')

Constant Summary collapse

TRUETYPE_TABLE_ORDER =

OpenType/TrueType table ordering (recommended order)

%w[
  head hhea maxp OS/2 hmtx LTSH VDMX hdmx cmap fpgm prep cvt
  loca glyf kern name post gasp PCLT DSIG
].freeze
OPENTYPE_TABLE_ORDER =

OpenType/CFF table ordering (recommended order)

%w[
  head hhea maxp OS/2 name cmap post CFF CFF2
].freeze

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(tables_hash, sfnt_version: 0x00010000) ⇒ FontWriter

Initialize writer with table data

Parameters:

  • tables_hash (Hash<String, String>) —

    Map of table tag to binary data

  • sfnt_version (Integer) (defaults to: 0x00010000) —

    Font sfnt version



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# File 'lib/fontisan/font_writer.rb', line 94

def initialize(tables_hash, sfnt_version: 0x00010000)
  @tables = tables_hash
  @sfnt_version = sfnt_version
end

Class Method Details

.detect_sfnt_version(tables_hash) ⇒ Integer

Detect sfnt version based on table presence

Parameters:

  • tables_hash (Hash<String, String>) —

    Map of table tag to binary data

Returns:

  • (Integer) —

    Detected sfnt version



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# File 'lib/fontisan/font_writer.rb', line 63

def self.detect_sfnt_version(tables_hash)
  if tables_hash.key?("CFF ") || tables_hash.key?("CFF2")
    0x4F54544F # 'OTTO' for OpenType/CFF
  else
    0x00010000 # 1.0 for TrueType
  end
end

.write_font(tables_hash, sfnt_version: nil) ⇒ String

Write complete font binary from table data

Examples:

binary = FontWriter.write_font(tables_hash)
binary = FontWriter.write_font(tables_hash, sfnt_version: 0x4F54544F)

Parameters:

  • tables_hash (Hash<String, String>) —

    Map of table tag to binary data

  • sfnt_version (Integer, nil) (defaults to: nil) —

    Font sfnt version (0x00010000 for TrueType, 0x4F54544F for OpenType/CFF). If nil, auto-detects based on tables.

Returns:

  • (String) —

    Complete font binary



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# File 'lib/fontisan/font_writer.rb', line 53

def self.write_font(tables_hash, sfnt_version: nil)
  # Auto-detect sfnt version if not provided
  sfnt_version ||= detect_sfnt_version(tables_hash)
  new(tables_hash, sfnt_version: sfnt_version).write
end

.write_to_file(tables_hash, path, sfnt_version: nil) ⇒ Integer

Write font binary to file

Examples:

FontWriter.write_to_file(tables_hash, 'output.ttf')

Parameters:

  • tables_hash (Hash<String, String>) —

    Map of table tag to binary data

  • path (String) —

    Output file path

  • sfnt_version (Integer, nil) (defaults to: nil) —

    Font sfnt version. If nil, auto-detects.

Returns:

  • (Integer) —

    Number of bytes written



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# File 'lib/fontisan/font_writer.rb', line 80

def self.write_to_file(tables_hash, path, sfnt_version: nil)
  binary = write_font(tables_hash, sfnt_version: sfnt_version)

  # Create parent directories if they don't exist
  dir = File.dirname(path)
  FileUtils.mkdir_p(dir) unless Dir.exist?(dir)

  File.binwrite(path, binary)
end

Instance Method Details

#write ⇒ String

Write the complete font binary

Returns:

  • (String) —

    Complete font binary



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# File 'lib/fontisan/font_writer.rb', line 102

def write
  # Order tables according to format
  ordered_tags = order_tables

  # Calculate table offsets
  table_entries = calculate_table_entries(ordered_tags)

  # Build font binary
  font_data = String.new(encoding: Encoding::BINARY)

  # Write offset table (sfnt header)
  font_data << write_offset_table(table_entries.size)

  # rubocop:disable Style/CombinableLoops
  # Write table directory (ALL entries first)
  table_entries.each do |entry|
    font_data << write_table_entry(entry)
  end

  # Write table data (ALL data after directory)
  table_entries.each do |entry|
    font_data << entry[:data]
    font_data << entry[:padding]
  end
  # rubocop:enable Style/CombinableLoops

  # Calculate and update head table checksum adjustment
  update_checksum_adjustment!(font_data, table_entries)

  font_data
end