Interesting approach, but like some others I'm wondering if this is the fastest and easiest way to do this kind of thing, especially since you are working with a tile based grid.

Probably a combination of 2d portals and raycasting would do the same trick, but more efficiently. I also think it would be easier to implement, and more flexible if you want to have moving obstacles. Most of this stuff is standard fare in even the simplest of 3d engines and well documented, the 2d case would actually be a simplification of those algorithms.

Nonetheless I think your solution is pretty clever and interesting, so kudos for that.