ui/src/main/java/ucar/nc2/ui/widget/SuperComboBox.java
protected int getItem( int pixel) {
      if (nitems < 2)
        return 0;

      int eff_width = b.width - 2*arrow_size;   // effective width
      double fitem = ((double) (pixel-arrow_size)*(nitems-1)) / eff_width;
      int item =  (int)(fitem+.5);
      item = Math.max( Math.min(item, nitems-1), 0);
      return item;
    }
protected int getItem( int pixel) {
      if (nitems < 2)
        return 0;

      int eff_width = b.width - 2*arrow_size;   // effective width
      double fitem = ((double) (pixel-arrow_size)*(nitems-1)) / eff_width;
      int item =  (int)(fitem+.5);
      item = Math.max( Math.min(item, nitems-1), 0);
      return item;
    }
return item selected by this pixel position