Blurry window effect

Hi there,

Does anyone know how to re-create the blurry window effect you see in
the d2_coast map, where as you get closer to a window, the less blurry
the view gets, and as you step back the window gets more blurry?

Here are 2 screenshots to illustrate what I mean:

Is it a func_areaportalwindow entity, Bob?

I played around with func_areaportalwindow, and it seems like its very
close to the behavior I showed in the above examples, as I approach the
brush, it begins to fade away, the effect that is missing is the blurry
effect when the player is further away, what could control this?

I ran surfaceprop on the bursh and I got this:

] surfaceprop

Hit surface "glass" (entity func_breakable, model "*7" Translucent. ),
texture "maps/d2_coast_10/glass/glasswindow017a_-4873_-235_1417"

Is the blurr effect done using a special texture? a special model?

How can I find out how Valve did this effect?

[edit]

Could this effect be some type of overlay maybe?

Maybe a shader?

[/edit]