function setValuesFromMousePosition (e) {
      const barW = bar.w // local copies for YUI compressor
      const barH = bar.h
      let locX = e.pageX - offset.l
      let locY = e.pageY - offset.t
      // keep the arrow within the bounds of the bar
      if (locX < 0) locX = 0
      else if (locX > barW) locX = barW
      if (locY < 0) locY = 0
      else if (locY > barH) locY = barH
      val.call(that, 'xy', {
        x: ((locX / barW) * rangeX) + minX,
        y: ((locY / barH) * rangeY) + minY
      })
    }
Calculate mouse position and set value within the current range.
@param {Event} e
@returns {void}