Physics Objects on the Boundary of Death

...at least that's what the overly dramatic line in my TODO.txt said.

It's hot today and I'm feeling less than entirely energetic, but I wanted to make at least some progress on Rktcr before taking my laptop off to air-conditioned environs to wait out the afternoon.

So I finally fixed up the level vignetting so that objects falling out of the level border are masked out. (Before is on the left.) The code to do this is a complete hack, but I was feeling lazy and wanted to avoid writing convex/half-plane clipping code, so I ended up opting for a bit of extra overdraw and calling it good enough.

This ticks off another of the myriad little things that need to get done in Rktcr, and brings the game a (tiny) bit closer to release.