Designers wanted to give the player the ability to toggle seeing through walls so they could understand their progress and goals.  At the time, I was given to believe transparent model drawing was a scary thing and attempted to provide alternate solutions to the problem rather than actually tackle it.  This was the start of the (at the time) solution: glow outline silhouettes.

The idea was to do them like Left 4 Dead where certain objects of interest could be outlined in a glowing color, and that outline would not be occluded by any world geometry.  This was the first step, to outline objects.  You’ll notice that that’s all that’s happening here; you can’t limit what’s being outlined, you can’t specify color, and they don’t glow.  It might even look like they’re occluded by geometry, but in keeping with the aesthetic of Left 4 Dead, they were cumulative.  It can just be hard to tell that that’s what’s going on.

This image was taken on 10/10/12.