When src is the same as desk, and a mask is provided, the expected behaviour could be to blend the dest inside the src where the mask are 255,255,255 instead of requiring the p (the centre) to be specified?

I had

src.shape   = 500,500
src_mask    = 500,500
dest.shape = 500,500

h, w = src_mask.shape[:2]

at this point I didn't see the use of the required argument p, as I expected the function to match the mask. But since it's a required argument, I provided (w//2, h//2) for p (the centre of everything). But instead of having the src aligned into dest, the resulting cloning was shifted up to the centre of the screen!