Partial boolean clipping between two scan Lines ...How..?

[Ignorant]

I want the results of a bollean op only between 2 Scan Lines defines as YL,YH,YH>YL..
The boolean op result blow YL is NOT relevent.
The boolean op result above YH is NOT relevent.
It is NOT possible in the case to do boolean op over the entire region and then clip the result as resource requirements do not allow that.
.I know how to easily early terminate clipping at YH.
I have attached a png file .The image on the right is what I want.

      My requirement is to late start at YL without doing a boolean clipping in the region below y <=YL.