Cocos2d-x开发---字幕效果

utfstrlen = function(str)  
        local len = #str;
        local left = len;
        local cnt = 0;
        local arr={0,0xc0,0xe0,0xf0,0xf8,0xfc};
        while left ~= 0 do
            local tmp=string.byte(str,-left);
            local i=#arr;
            while arr[i] do
                if tmp>=arr[i] then
                    left=left-i;
                    break;
                end;
                i=i-1;
            end;
            cnt=cnt+1;
        end;
        return cnt;
    end;

local lenNowDec = utfstrlen(nowDec);
local lenDes = utfstrlen(desc);

if lenNowDec < lenDec then
     --截取，重新设置
     local str =utf8sub(desc,lenNowDec + 1);
     self.captionLabel:setString(str);
end;

utf8sub = function(str, startChar, numChars)
      local startIndex = 1;
      while startChar > 1 do
          local char = string.byte(str, startIndex);
          startIndex = startIndex + DataSheetMgr.chsize(char);
          startChar = startChar - 1;
      end

      local currentIndex = startIndex;

      while numChars > 0 and currentIndex <= #str do
        local char = string.byte(str, currentIndex);
        currentIndex = currentIndex + DataSheetMgr.chsize(char);
        numChars = numChars -1;
      end;
      return str:sub(startIndex, currentIndex - 1);
end;