A brush that triggers an event only once, then is ignored.

This can be used to spawn a monster, end a level (in conjunction with a target_changelevel), start or stop machines, open or close doors, etc. Any entity that can be targeted can be set off by trigger_once.

1.Firstly, create a good sized room (300x300x300) and place a info_player_start in there. Separate the room in half with another wall, but leave a 128x128 doorway in the middle. Place a light on both sides of the middle wall so you can see what the heck is goin on in there.

2.Create a normal door in the opening and give it a "targetname" of "door" and a "wait" of "-1" so it stays open after triggering.

3.Create another brush that crosses the length of the room where the player will walk through it. Give this brush the TRIG texture (its in all of the e*u* texture sets).

4.Apply the trigger_once entity to this new brush. This will automatically cause it to not be drawn in the game. Give it a "target" of "door".

5.Compile and run the map. When you cross the trigger brush the door will open and stay open.

Here's an example map (the one shown in the picture above) showing a trigger_once.

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