フォントのweight値を書き換える

fix-ttf-weight.rb

#!/usr/bin/env ruby

fail unless ARGV.length == 2
file = ARGV[0]
weight = ARGV[1].to_i

open(file, "r+b:ASCII-8BIT") do |io|
  ver, ntables, srange, eselector, rshift = io.read(12).unpack("Nn*")
  fail unless Math.log2(ntables).floor == eselector and
              (2**eselector)*16 == srange and
              ntables*16-srange == rshift

  header_pos = nil
  ntables.times do
    if io.read(4) == "OS/2"
      header_pos = io.pos - 4
      break
    end
    io.pos += 12
  end
  fail unless header_pos

  checksum, offset, length = io.read(12).unpack("N*")
  io.pos = offset + 4
  io.write([weight].pack("n"))

  io.pos = offset
  sum = 0
  (length/4.0).ceil.times { sum += io.read(4).unpack("N")[0] }
  sum &= 0xffffffff
  io.pos = header_pos + 4
  io.write([sum].pack("N"))
end