DirectFB Reference Manual
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.