getDescriptor(x, y) {
        const {
          left, top, height, width,
        } = ReactDOM.findDOMNode(this).getBoundingClientRect();
        const { rippleCentered: centered, rippleSpread: spread } = this.props;
        return {
          left: centered ? 0 : x - left - (width / 2),
          top: centered ? 0 : y - top - (height / 2),
          width: width * spread,
        };
      }
Find out a descriptor object for the ripple element being created depending on
the position where the it was triggered and the component's dimensions.

@param {Number} x Coordinate x in the viewport where ripple was triggered
@param {Number} y Coordinate y in the viewport where ripple was triggered
@return {Object} Descriptor element including position and size of the element