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Ahh, neat.

With regards to handling the presence of walls, that's a case where I see the utility of PIF versus displacement vectors and guessfactors as being significant. Guessfactors aren't really well-suited to the presence of walls. Displacement vectors allow you to handle walls occluding where they end up. PIF however allows you to handle not only walls occluding where they end up, but also handle ruling out paths which would be interrupted by walls.