code: function sizeof(ttf) {
              ttf.support.glyf = [];
              var tableSize = 0;
              var hinting = ttf.writeOptions ? ttf.writeOptions.hinting : false;
              ttf.glyf.forEach(function (glyf) {
                  var glyfSupport = {};
                  glyfSupport = glyf.compound ? glyfSupport : getFlags(glyf, glyfSupport);
  
                  var glyfSize = glyf.compound
                      ? sizeofCompound(glyf, hinting)
                      : sizeofSimple(glyf, glyfSupport, hinting);
                  var size = glyfSize;
  
                  // 4字节对齐
                  if (size % 4) {
                      size += 4 - size % 4;
                  }
  
                  glyfSupport.glyfSize = glyfSize;
                  glyfSupport.size = size;
  
                  ttf.support.glyf.push(glyfSupport);
  
                  tableSize += size;
              });
  
              ttf.support.glyf.tableSize = tableSize;
  
              // 写header的indexToLocFormat
              ttf.head.indexToLocFormat = tableSize > 65536 ? 1 : 0;
  
              return ttf.support.glyf.tableSize;
          }
docs: 对glyf数据进行预处理，获取大小
  
  @param  {Object} ttf ttf对象
  @return {number} 大小