'Depth Dependent Halos' for Wireframe rendering

'Depth Dependent Halos' is something I read on the UDK site a while ago, it's for their 'new' (by now pretty old...) wireframe rendering that increases readability of the lines for complex scenes. I was kind of wondering how they accomplished this and wanted to try this out myself (I was working on a wireframe-mode anyway, so it was the right time to experiment)

This is the effect I am trying to replicate. Black halos are drawn around the wireframe lines to provide a better understanding of depth differences between these lines.

I went through a few different approaches and ended up with a small post-processing shader that applies the halo around the wireframe lines. It took a few iterations to get the desired results, but I did end up with something that is pretty close to what I am looking for...

The first step was to create my regular wireframe and letting the post-processor create a small single pixel halo around these lines using a different color. The second step (still have to start on this one) will require a depth-buffer and use the depth information to determine if the outline/halo should be drawn with halos being drawn on top of lines underneath them, creating discontinuities between lines that intersect and are underneath others.

Some of the iterations I went through:

Trying to find out the correct pixel offset and coloring by finding edges and applying a different color to each direction (up/down/left/right in screen-space)

This is the current state of the code, and resembles the desired effect (of step 1) quite closely.

I have also been working on some additional scene navigation features. These are best shown in a video, but since I currently get my connection through a painfully slow USB stick - that will have to wait...

bonus image...(this result was less then expected, but looks pretty cool)