getOffset = function(axis) {
            var delta = that.getDelta(e)
                , wheelDir = that.args.wheelDir;

            if(wheelDir) {
                delta[wheelDir] = delta[wheelDir === "x" ? "y" : "x"];
                delta[wheelDir === "x" ? "y" : "x"] = 0;
            }
            return that.state[axis] + delta[axis] * that.args.wheelSpeed;
        }
Mouse wheel event handle
@param {[type]} e [description]
@param {[type]} that [description]
@return {[type]} [description]