I was planning on making a HWA zoom system and then i read this -
I made a quick example to show the bug i think they were talking about. What happens is that if a object reaches the edge of the frame it distorts across the remaining part. The shader says to use a 1 pixel gap so that would probably fix though.
As well as demonstrating this problem though it's a simple working example for anyone that want to know how to do a HWA zoom.