I have a patch that make width & height variations on quads.

I would like to apply these variations only in a zone defined by a matrix (this could be mouse drawing or camera tracking).

I tryed a solution with jit.alphablend to define the zone, but this seems not the way for quads.

How can to tell to quads: "move (apply expression) in that zone only" ?

I tryed a solution with jit.alphablend to define the zone, but this seems not the way for quads. 

Zone-tracking 2 quads-movement