code: function Animation(duration, metas) {
              this._d = Math.round(duration * 60 / 1000);
              this._m = metas || {};
              this._c = [];
              this._l = 1;
              this._p =
                  this._h =
                      this._w = false;
              this._i = C2D.ACenter.a(this);
          }
docs: 构造函数。