I have square layer, containing a circular image surrounded by white, and I need to envelope distort just the circle into a polygon shape. When I do Envelope Distort > Make with Top Object, however, the whole square shape of the image -- including the white "corners" -- is included in the distort.
Before and after (actual result):
How can I specify that I only want a circular portion of an image layer to be distorted to the edges of the polygon?
Before and after (desired result):