code: public int getRenderIndexFromRealIdx(final int realIdx) {
          if (columnMapping == null || realIdx == -1) {
              return realIdx;
          }
  
          for (final Entry<Integer, Integer> entry : columnMapping.entrySet()) {
              if (entry.getValue().equals(realIdx)) {
                  return entry.getKey();
              }
          }
  
          return realIdx;
      }
docs: Provides the render column index based on the real index
  
  @param realIdx
  @return