The Quad-Sectioned Military Door - from id Software's E2M1

The QuakeLab - http://www.in2nett.com/stevefu/QuakeLab

        TEXTURES:

        TECH02_7 - The main faces of the door segments.
        TECH02_6 - The edges of the door segments.

        ENTITIES:

        func_door

        WHAT TO DO:

        Start by making a rectangular brush 96 units high, 128 units wide,
        and 16 units thick. If your editor is equipped with a clipping
        plane tool (a tool that acts like a pair of scissors), use that to
        cut from corner to corner of this rectangular brush, copying and
        positioning as necessary to get the four segments. Individually
        designate each door segment as a func_door and adjust the 'lip'
        value to your liking. The demo MAP uses a lip value of -1. Assign
        the door segments a 'sounds' value of '2' and adjust the 'speed'
        to your liking. Assign each segment an appropriate 'angle' value
        so that the top one goes up, the bottom one goes down, etc.

        Position the door segments in between the areas you wish to
        connect.

        NOTE: Lip values are read from the corner-edge of the wall next
        to the door. Setting the lip to higher negative values will cause
        the door to retract even further, while setting it to a high
        positive value should make it retract less.

        The door is done. The next part is the problematic one since it
        involves making the 'sockets' for the door segments to fill when
        they open. If you didn't do this, it would appear that the door
        segments were retracting into solid walls and that appears
        unconvincing.

        It would be best to position the door segments in their opened,
        separated positions, and then add brushes to create the necessary
        cavities for the door segments. An automatic brush-to-room tool in
        most editors will speed up the process greatly.

        That's it. Just be careful not to make leaks when making the
        door cavities.

        OPTIONS:

        Appearances of quad-segment doors are up to the builder. This is
        probably the most complicated sort of door you can make in that
        the next logical step would be to have more door segments, some of
        which would move diagonally; this is not possible due to the
        single angle setup. We have tried using a 'mangle' field such as
        the one used to control the direction of an intermission camera,
        but this did not work.