Reference Manual - 1.0.1
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.
要么所有四个值被使用，要么第一个和最后一个值被使用，依赖这个格式。默认值是：0x00, 0x55, 0xaa, 0xff 。

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