Windows

[Drakotsu]

Ive been wondering this for a while,
You know how on some maps there are windows, and you can see through them, but it IS a solid texture.
For example,
In mission_one_b6 at the starting point there is a window between the humans and the aliens start position, but you cant go through it, only see through it.
How do you do that?

Thanks for your help,
Drakotsu

[Knowitall66]

Shader on a detail brush.