Reference Manual - 0.9.25
IDirectFBSurface   SetAlphaRamp

Set the alpha ramp for formats with one or two alpha bits.

SetAlphaRamp (
  IDirectFBSurface   * thiz,
  __u8   a0,
  __u8   a1,
  __u8   a2,
  __u8   a3
);

Either all four values or the first and the last one are used, depending on the format. Default values are: 0x00, 0x55, 0xaa, 0xff.