luatexja.load_module('base');      local ltjb = luatexja.base
luatexja.load_module('jfont');     local ltjf = luatexja.jfont

local round = tex.round
local floor = math.floor
local attr_curjfnt = luatexbase.attributes['ltj@curjfnt']
local attr_jchar_class = luatexbase.attributes['ltj@charclass']
local attr_yablshift = luatexbase.attributes['ltj@yablshift']
local attr_ykblshift = luatexbase.attributes['ltj@ykblshift']

local ltjf_font_metric_table = ltjf.font_metric_table
local ltjf_find_char_class = ltjf.find_char_class

local unity=65536
local function print_scaled(s)
   local out=''
   local delta=10
   if s<0 then
      out=out..'-'; s=-s
   end
   out=out..tostring(floor(s/unity)) .. '.'
   s=10*(s%unity)+5
   repeat
      if delta>unity then s=s+32768-50000 end
      out=out .. tostring(floor(s/unity))
      s=10*(s%unity)
      delta=delta*10
   until s<=delta
   return out
end
local function set_valign(fmtable, fn)
   local fi = fonts.hashes.identifiers[fn]
   if not fi.ascender then fi = fi.parameters end
   local mt = fmtable.char_type[0]
   local ma = mt.height / (mt.height + mt.depth) * (fi.ascender + fi.descender)
   fmtable.down_offset = round(fi.ascender - ma)
   print('loading :', fn, print_scaled(fmtable.down_offset)
      .. ' / ' .. print_scaled(fi.size))
   return fmtable
end
luatexbase.add_to_callback("luatexja.define_jfont", 
			   set_valign, "ltj.valign.define_jfont", 1)
--  既に読み込まれているフォントに対しても，同じことをやらないといけない
for fn, v in pairs(ltjf_font_metric_table) do
   ltjf_font_metric_table[fn] = set_valign(v, fn)
end

local function get_valign (fstable, fmtable, jchar_class) 
   local d = fmtable.down_offset or 0
   fstable.down = fstable.down + d
   return fstable
end

luatexbase.add_to_callback("luatexja.set_width", 
			   get_valign, "ltj.valign.define_jfont", 1)