Reference Manual - 0.9.25
IDirectFB   GetDisplayLayer

Retrieve an interface to a specific display layer.

GetDisplayLayer (
  IDirectFB   * thiz,
  DFBDisplayLayerID   layer_id,
  IDirectFBDisplayLayer   ** ret_interface
);

The default layer_id is DLID_PRIMARY. Others can be obtained using IDirectFB::EnumDisplayLayers().