internal void removeSubInterface(TransparencySubInterface subInterface)
 {
     if (subInterfaces != null)
     {
         subInterfaces.Remove(subInterface);
     }
 }
 internal void addSubInterface(TransparencySubInterface subInterface)
 {
     if (subInterfaces == null)
     {
         subInterfaces = new List <TransparencySubInterface>();
     }
     subInterfaces.Add(subInterface);
     subInterface.setAlpha(getCurrentTransparency(activeTransparencyState));
 }