So, after several days of setting up my fancy pre-lighting renderer, I discovered that — bam-badum! — the reason it wasn’t working was it was a technique designed for graphics cards more expensive than my (quite expensive) computer.
Thank you, book. I should have understood from the outset that I don’t deserve to be a game developer unless I can pawn my GPU for a car. I bow before you in your infinite wisdom, and realize now that the fault lies with my aspirations.
So… there goes depth mapping, and with it shadows. Either I figure out a hack (doubtful), or else it goes in the bin and the concept is redesigned to something I can implement with what I have at hand. Mind you, once I have a testbed 360 up and running, I’ll be able to compile to that.