public void createData()
 {
     m_data = new SpaceGraphData();
     m_data.OnRootChanged          = onRootChanged;
     m_data.OnHoverItemChanged     = onHilightChanged;
     m_data.OnSelectedItemsChanged = onHilightChanged;
 }
 //-----------------------------------------------------------------------------------------
 void onHilightChanged(SpaceGraphData _data)
 {
     Invalidate();
 }
 //-----------------------------------------------------------------------------------------
 void onRootChanged(SpaceGraphData _data)
 {
     Inactivate();
 }