An apparatus comprising means for: causing display of at least one world-locked volumetric object having at least one non-viewable region; determining a change in a user's viewing position relative to the at least one world-locked volumetric object; determining if the change in the user's viewing position relative to the at least one world-locked volumetric object will cause display of at least a portion of the at least one non-viewable region of the at least one world-locked volumetric object; and if it is determined that the change in the user's viewing position will cause display of at least a portion of the at least one non-viewable region, cause the at least one world-locked volumetric object to be user-locked.