abbreviate title based on utf8 characters

lua/dyn_menu.lua

@@ -32,11 +32,27 @@ local function escape_codec(str)
  else return str end
 end
 
+-- from http://lua-users.org/wiki/LuaUnicode
+local UTF8_PATTERN = '[%z\1-\127\194-\244][\128-\191]*'
+
+-- return a substring based on utf8 characters
+-- like string.sub, but negative index is not supported
+local function utf8_sub(s, i, j)
+ local t = {}
+ local idx = 1
+ for match in s:gmatch(UTF8_PATTERN) do
+ if j and idx > j then break end
+ if idx >= i then t[#t + 1] = match end
+ idx = idx + 1
+ end
+ return table.concat(t)
+end
+
 -- abbreviate title if it's too long
 local function abbr_title(str)
  if not str or str == '' then return '' end
  if o.max_title_length > 0 and str:len() > o.max_title_length then
- return str:sub(1, o.max_title_length) .. '...'
+ return utf8_sub(str, 1, o.max_title_length) .. '...'
  end
  return str
 end