def self.encode(charmap)
end_codes = []
start_codes = []
next_id = 0
last = difference = nil
glyph_map = { 0 => 0 }
new_map = charmap.keys.sort.inject({}) do |map, code|
old = charmap[code]
glyph_map[old] ||= next_id += 1
map[code] = { :old => old, :new => glyph_map[old] }
delta = glyph_map[old] - code
if last.nil? || delta != difference
end_codes << last if last
start_codes << code
difference = delta
end
last = code
map
end
end_codes << last if last
end_codes << 0xFFFF
start_codes << 0xFFFF
segcount = start_codes.length
deltas = []
range_offsets = []
glyph_indices = []
offset = 0
start_codes.zip(end_codes).each_with_index do |(a, b), segment|
if a == 0xFFFF
deltas << 0
range_offsets << 0
break
end
start_glyph_id = new_map[a][:new]
if a - start_glyph_id >= 0x8000
deltas << 0
range_offsets << 2 * (glyph_indices.length + segcount - segment)
a.upto(b) { |code| glyph_indices << new_map[code][:new] }
else
deltas << -a + start_glyph_id
range_offsets << 0
end
offset += 2
end
subtable = [4, 16 + 8 * segcount + 2 * glyph_indices.length, 0].pack("nnn")
search_range = 2 * 2 ** (Math.log(segcount) / Math.log(2)).to_i
entry_selector = (Math.log(search_range / 2) / Math.log(2)).to_i
range_shift = (2 * segcount) - search_range
subtable << [segcount * 2, search_range, entry_selector, range_shift].pack("nnnn")
subtable << end_codes.pack("n*") << "\0\0" << start_codes.pack("n*")
subtable << deltas.pack("n*") << range_offsets.pack("n*") << glyph_indices.pack("n*")
{ :charmap => new_map, :subtable => subtable, :max_glyph_id => next_id+1 }
end