This is a composition created for use in Resolume (etc) as an FFGL plug. It's designed to be used on a channel with a moving image and a lot of clear space (ie zero opacity). The feedback fills up in the clear space and then is automatically masked so that it has a "decay" and you can still see any background layers beneath.
I'd love some feedback (ha). I suspect this qualifies as a thoroughly noob composition. I'm sure there must be simpler ways of doing this.