How to Get ROP4 Mask bit?

I am working on printer driver sample which capture GDI call such as DrvBitBlt(), DrvTextOut() … etc. In DrvBitBlt i am getting ROP4 value as 0XF0F0. It mean to say that we need to use the brush object.

When I read the DrvBitBlt() ROP4 the documentation says:

The low byte specifies a Rop3 that should be calculated if the mask is one, and the high byte specifies a Rop3 that can be calculated and ap开发者_StackOverflow中文版plied if the mask is 0.

My question is where the mask value will be present. How go get the mask bit is 0 or 1.

The mask bits come from the third parameter to DrvBitBlt