Yeah patenting algorithms is fucking stupid. Any programmer could've come up with this method independently. When I was doing stencil shadows I got sick of nearclipping and capping shadow volumes and one day thought "heeeey.... wait a sec. why can't I precompute volume for decayed light source anyway?" Which led me to google search and discover that carmack (and creative) had elegant working solution of the same idea.
If a mediocre programmer like me can think of it, anyone can.