Should we join sectors?

If I'm understanding the question correctly.. If you have two sectors with identical properties (same floor and ceiling heights, lighting level and textures) it makes sense to combine them into one sector if you're worried about visplane overflows or HOMs. I've done this a few times in the past to get maps running in vanilla Doom.

I said, unless you know what you are doing. The problems start when mappers join sectors in separate parts of the map and then wonder why the monsters get alerted, or why some moving lifts act oddly.

Joining sectors to achieve a desired effect is fine. Joining sectors to save some resources should be avoided. For the render engine a sector is just a container for property settings, it will never affect what the renderer does internally, that's only decided by subsectors.

Joining sectors can be a handy tool for pulling off tricks involving dummy sectors, such as moving floors to unnatural positions or teleporting swarms of monsters without using sound tunnels. It can also be handy for consolidating pieces of the map that you KNOW have the same ceiling and floor values. Like Graf said, it doesn't actually affect render limits if you are paying attention to those things. It doesn't impact performance, and generally wouldn't be noticed by players. But when you decide to change the height of an entire area, you may be thankful that you decided to consolidate all those loose sectors.

I generally find merging sectors to be much more useful than simply joining them. This feature takes two adjacent sectors and actually merges them together into one cohesive sector. It can be an easy way to experiment with the geometry of your map without too much effort.

Short answer: Sector joining is a tool that you may find handy in your map design, but it isn't ever a requirement.

To add some technical detail to this, there are a few things you should know before you start merging sectors willy nilly:

* In vanilla-ish Doom engines, the sound effect for a sector (door open, floor move, etc) is spawned by taking a bounding box around the entire sector and spawning the sound at the center of that box. So if you have 2 sectors on opposite ends of a map that are merged and they move, the sound for them will emanate from a seemingly random unrelated point in between them.

* Similarly, this bounding box is used for some other calculations involving clipping and movement, and it can (and does) lead to weird, seemingly inexplicable problems with moving sectors where the engine incorrectly thinks that some solid object is blocking the sector from moving when in fact it shouldn't.

The answer should be a clear 'no'. There's some caveats to observe here which can render the map broken if not carefully considered.

Unless you KNOW what merging sectors entails, better skip it.

This won't lift any render limit AT ALL!

Joining makes editing those sectors later WAY easier.

I could have sworn it did, but I'd listen to Graf. I've done this quite a few times in the past with no consequence, but I guess it was to have light strobes matching or something, can't really think of any other reason yet I've found myself needing to do it a lot in the past.

Either way, if you're using PrBoom, you're going to have to use a lot of sectors for it to crash or result in HOMs. If it gets to that point, I recommend simply mapping in Boom format but running the wad in ZDoom unless demo compatibility is important to you.

24 minutes ago, Graf Zahl said:

The answer should be a clear 'no'.

Unless you don't want a set of bars opened locally to be SUPER-FUCKING LOUD. That said, I'm terrible for joining sectors just because I kinda want to drag a bunch of (say) ceiling heights around in DB's visual mode without flying around selecting them all...

I wouldn't do that, because joined sectors are sound connected, so, unless you don't use sound block lines or these sectors are in the same "area", that would mess with waking up monsters you don't want.

Windows bordering the same area, generally. Although I join like crazy for purposeful sound propagation (teleport traps, etc).

Then again, I don't make large maps. Doubt I'm gonna break anything, ever.

Can't you group sectors in doombuilder, so you can easily select all of them?

And yeah, I agree with Pavera, there's lots of cool tricks to use with joining sectors, so it's certainly handy

13 minutes ago, Pavera said:

I generally find merging sectors to be much more useful than simply joining them. This feature takes two adjacent sectors and actually merges them together into one cohesive sector. It can be an easy way to experiment with the geometry of your map without too much effort.

I've been a bit confused by this distinction. So far I've always used merging instead of joining, so I'm not really sure what joining is for. I thought it might be a way to move two sectors together while still allowing them to have different ceiling and floor flats, but when I tried that, it changed the flats as though I had done a merge. What does joining allow you to do that merging doesn't?

I was under the impression that the only difference between merge/join is that one causes the editor to remove 2S linedefs that would have both sides in the same sector after the combining is done, and the other leaves those intact.

Yup, that's the difference.

1 hour ago, Doomkid said:

If you have two sectors with identical properties (same floor and ceiling heights, lighting level and textures)

You forget tags

I am myself merging the sectors when I want to copy properties, cause its quick. But then I click conture of vertexes to make it split again. I wonder if there is not a schortcut for auto-split of contures that arent together, it would save some time.

Btw - offtopic but close - is it true that when I will triangulate sectors myself and not let the engine do it, I will not have slime trails?

This is a LONG time ago so things may have changed, but in Skulltag I made a DM map which chugged to 1fps in certain areas because of the (ridiculous) minute sector detail in the ceiling. Thing is, once I joined all matching sectors it ran smooth as butter. Any explanation for the cause of that? Was skulltag just shittily coded (despite it's ZDoom origins)?

1 hour ago, NinjaLiquidator said:

Btw - offtopic but close - is it true that when I will triangulate sectors myself and not let the engine do it, I will not have slime trails?

The engine (or node builder) doesn't triangulate anything. The BSP builder (note that BSP building isn't triangulation) may split some segs, though. If you manage to make a map such that the BSP builder will not split any seg, then there will not be slime trails. But just making a map out of triangles doesn't guarantee that this will be achieved. See https://doomwiki.org/wiki/Doom_rendering_engine#Node_building

There is no intrinsic advantages to merging sectors.

• Limits: there is a maximum number of sectors; however this maximum value is also the same as the maximum number of sides and the maximum number of lines. Consider: every sector has at least three lines, usually more (potentially, a lot more), and every line has at least one side. You'll reach the sidedef limit long before you reach the sector limit.
• Performances: the engine already merges together visplanes with identical characteristics (flat and light level) when the geometry allows it, so you don't gain anything by making them the same sector.
• Side-effects: see Linguica's post.

It's possible to want to merge sectors because you want to use a side effect, such as propagating monster alert (perhaps to a monster pen for a teleport ambush), or silencing a moving floor (by moving its sound origin far away from the playable area of the map). If you do merge distant sectors, be aware that if you get something like a lift that won't move up or a door that won't open, it might be because of the merged sectors.

Think about a situation like this:

Now, lets say we have a very large and detailed map. Many times a situation similar to the one depicted in that GIF happens. Merging/joining sectors saves lots of time and effort while building the map.

If we have literaly hundreds of sectors in this same situation that were deliberately merged/joined to save building time and effort, will this have any negative side effect while nodebuilding/playing? Is there any advantage, engine-wise (doom.exe and/or boom.exe), i.e. more framerate, whatever?

Not really. As far as nodebuilding goes, they still will be different subsectors, so it shouldn't have an impact on performances.

1 hour ago, Yokai said:

If we have literaly hundreds of sectors in this same situation that were deliberately merged/joined to save building time and effort, will this have any negative side effect while nodebuilding/playing? Is there any advantage, engine-wise (doom.exe and/or boom.exe), i.e. more framerate, whatever?

If it has a negative effect it will be when playing the map. I only can repeat myself: If you do not know what sector merging entails, only do it if it provides an effect you want, never to reduce sectors and never to make it easier to assign properties.

In the situation depicted on the gif, using joined sectors shouldn't have any negative effect. Only if, for example, the sector in between the 2 arches is a door, and it is closed, and the map relies on an assumption that sound will not propagate through the door until it opens, then the sound will propagate through the closed door anyway, via the joined sectors.