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dummy sectors

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I'm trying to do some special effects in a wad I'm working on and
I'm having trouble with "dummy sectors". Just what do they do and
how do you set them up?

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Dummy sector is a sector you create outside of the playable part of the map (well, in most cases you do, that is), it does not have any impact on the gameplay, but it holds a few values that can be used by other sectors and specials as a reference. Even, or maybe especially in Vanilla doom compatibile maps.

Imagine you want to use a special that lowers the floor to the next adjacent floor. This basically searches which of the sectors "touching" the sector you've tagged with this special, has the next highest floor (dooh, feeling dizzy already?). If a tagged sector with floor height equal 128 is touching sectors with heights 32, 64, 24, and -12, the special (upon activating) will lower the floor from 128 to the value of 64.

Why am I explaining such basic stuff? Now imagine you'd like, for some reason, the floor to be lowered not to 64 but to 80. None of your sectors has this floor height, and for some another unknown reason, there is no possibility (or no sense) of applying such sector near your tagged one (the one with floor height 128, remember?).
Then you should create a dummy sector outside the map, so nobody will ever see it, and give it a floor height of 80. Then you place an isolated piece of the tagged sector (floor height 128) touching the dummy sector.

Now, since the sector with floor height 80 is still a valid sector to the game (although it'll never be visited), and it literally touches the tagged sector - even if it's just it's isolated part - it will also be taken into account when specials are calculating values like "next adjacent" or "highest neighbouring (...)", therefore you can move your flat heights to almost every value you desire, as long as you're smart.

Dummy sectors are of a great importance to various source ports as well. Boom / PRBoom / ZDoom / GZDoom have even mores specials that can use their dummy values (floor height, ceiling height, light value, floor texture, ceil texture... and so on).

Hope this helps.

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just my 2 cents:

first you need an editor with a sector merge/join button, such as doom builder. if you've not used this before it will make it so that two or more sectors are the same one.

the important part of that is to remember that a sector doesnt have to be all one piece, in a funny way they dont really exist - they only exist where the linedefs surrounding it say they do. so if you have 4 linedefs in a square and they all say "inside here is setor number XYZ" then that sector's defined floor/ceiling heights/textures will appear inside that square when you play the game. but there's nothing to say that ANOTHER set of lines that make up another square miles away can also say "in here is sector number XYZ". this is how 10-sector and 2-sector maps are possible.

so you could make a chess board, with black squares and white squares out of - not 64 individual sectors - but two sectors, each repeated in 32 different places with one being black and one white. once you've gotten your head around that then you're ready to use dummy sectors.

i tend to make mine 64x64 and outside the playable area of the map, like ellmo said: just because the player wont ever see them doesnt mean that they're not valid sectors.

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I have often thought that calling this approach "Dummy sector" to be a very poor choice by whoever coined the term. There is nothing "Dummy" about such sectors AT ALL, they are the same as any other.

In the original DOOM source there are linedefs which are created momentarily when needed which do not exist in the "real" map (these are used for various tasks such as resolving end of game specials like A_KeenDie). These are "Dummy lines" in a truer sense.

Similarly, in Doomsday's XG there are virtual sectors/lines which can do this kind of thing without needing actual architecture in the map. Those are more like what the term "Dummy" suggests.

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A better term might be "Control sectors", as they "control" the properties of something in the map, for instance the top and bottom heights and textures definining where a 3D floor is, the light inside it defining the light below the sector and the texture on the walls defining the texture on the outside of the block

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Dummy sectors are called dummy, not because they aren't real or they are imitating something. Think of a "crash test dummy", they're dummies too, but if it wasn't for them we wouldn't have gone far in car safety, would we?

Dummy sectors are real, but not shown. They don't break nor fix the architecture, but they are invaluable to the final effect. They serve control purpose to the map author, and an unknown (mostly imperceptible) purpose to the player - thus "dummy" is a perfect name, just as any other:
-control sectors
-remote sectors
-virtual sectors

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