I believe translating OpenCV code into RTL directly won't be any efficient. You need to implement your algorithms suitable to and taking advantage of an FPGA architecture. But maybe you need to do this for study purposes?
I searched online and found that equation (1) can be transformed into (2). But how ?
Pixel_ C = (int)(Pixel_A * alpha + Pixel_B * ( 1-alpha )); ---> (1)
Pixel_ C = (Pixel_A * alpha + Pixel_B * ( 32-alpha ) + 16)>>5; ---> (2)
This may be related to how OpenCV stores alpha data.