Advanced lift design techniques
Usually, Doom II lifts are restricted to raise (or lower) their floor height to the one from an adjacent sector at an higher or lower position. MAP30: Icon of Sin includes a lift that works without adjacent sectors, but is severely limited. What follows is a trick that allows you to have a sector that may raise and lower its ceiling and floor heights without needing to have an adjacent sector on the room to sets the desired height. These advanced lifts are very interesting because they allow plenty of advanced tricks, including spiral staircases and second floors.
This trick is done simply by creating a new dummy sector outside the map and giving it the same sector ID as the lift sector - this can be done easily in several modern editors (such as Doom Builder), which provide a simple option to instantly join several selected sectors into one sector. Then draw a new sector outside the map, adjacent to the lift sector. Set the new sector's floor height to be equal to the desired height, that is, the height to which the lift will rise.
- Note that the lift can be composed of multiple sectors, each rising to a different height; this allows for the creation of more detailed lifts, but should be used carefully - e.g. if one part of the lift is stopped from moving (by a player or a monster blocking it from fully raising), it will be "out of sync" with the rest of the lift for some time.
- By changing the floor/ceiling height of the new sector, you can change the lift's raising/lowering height during gameplay. This can be used e.g. to create a tripwire that opens a door with a monster ambush, but only functions after something else is done in the level, and can be passed safely before that.
- LIBRARY.WAD (file info) is an example of this trick.