Mysteries of Doom

What are some things in Doom that haven't been explained yet? One example off the top of my head: linedef skips, I've never seen a good technical explanation of them.

Why the UAC has a bunch of secret passages, I mean they could be weapon caches but why would they be the same material as the surrounding walls. Which leads me to think that the UAC actually is a smuggling organization and sell their illegal cargo to the martians.

Has the empty secret room in E3M4 (House of Pain) ever been explained? I've always been curious about that little oddity.

RUSH said:

Has the empty secret room in E3M4 (House of Pain) ever been explained? I've always been curious about that little oddity.

Its obviously the room were prisoners wait to go through extreme pain(the 2 crushers with all the loot, that loot is actually the prisoners possessions that got squeezed out of them while they were getting crushed) Why else do you think it's called the house of pain?

Doominator2 said:

Why the UAC has a bunch of secret passages, I mean they could be weapon caches but why would they be the same material as the surrounding walls. Which leads me to think that the UAC actually is a smuggling organization and sell their illegal cargo to the martians.

U.A.C. = Universal Amphetamine Cartel?

My God, the truth is slowly revealing itself.

RUSH said:

Has the empty secret room in E3M4 (House of Pain) ever been explained? I've always been curious about that little oddity.

I'm thinking it's Petersen's way of messing with the player's head.

Or the Demons morphed it with their "own kind of reality" thing going on.

That's why I think the devs came up with that line, cus they knew their base looks little like a base.

What is with that random linedef in the void on MAP30? Some sort of nodebuilder strangeness or what?

The mystery of Thing236 in Map11 is one that runs infinitely deep.

Memfis said:

linedef skips, I've never seen a good technical explanation of them.

It's not a technical explanation, but according to dew when he was playtesting my maps is that orthogonal linedefs are easily skipped particularly if players are sr40/50 running, but by making the linedef non-orthogonal, as in not 90/180/270/360 degrees straight, the line cannot be skipped (or is very hard to skip). It would definitely be interesting to read a technical explanation for this.

Snakes said:

The mystery of Thing236 in Map11 is one that runs infinitely deep.

Oh, I didn't know that actually. pretty cool/strange.

Obsidian said:

What is with that random linedef in the void on MAP30? Some sort of nodebuilder strangeness or what?

Snakes said:

The mystery of Thing236 in Map11 is one that runs infinitely deep.

Likely the result of different layouts during development. As for the linedef, nodebuilders have no say in that kind of thing, it'd still be there no matter how they were built, or even if they weren't built at all.

Plutonia MAP12 has a single rogue Thing of type 0 (thing 225 at X: 1600 Y: -3104 ) which is invalid and yet is not caught by vanilla checks, due to priorities (gory details here). In some source ports this may cause crashes. I wonder how that ended up there...

It results in creating a "minus player" inside the engine (Player 1 is actually "player zero"). In vanilla, it's mostly asymptomatic. In other source ports it may give an outright crash or delayed glitches that are hard to track back to the source.

Joshy said:

It's not a technical explanation, but according to dew when he was playtesting my maps is that orthogonal linedefs are easily skipped particularly if players are sr40/50 running, but by making the linedef non-orthogonal, as in not 90/180/270/360 degrees straight, the line cannot be skipped (or is very hard to skip). It would definitely be interesting to read a technical explanation for this.

From what I've been told, lines at 45 degree angles are also pretty easily skippable, so odd angles somewhere in between are the way to go.

I'd have assumed its when you are moving fast enough, and your position is just right, you are on one side of the linedef in one frame and on the other side in the next frame. if this is the case, using sr40/50 means it is more likely to happen, but then you have to move more than the length from one corner of the player to the opposite one (since the player is square).

diagram

I thought same but according to 4shockblast it isn't that simple - http://www.doomworld.com/vb/post/1253684

It's also possible to skip lines by moving very slowly.

i never found an explanation as to why when you kill imps/zombies on high ledges, they sometimes fall forward towards the player. seen it happen very often myself.

Doom includes a lot of checks to ensure that movement -or rather, the intent of movement- does not result in trivially breaking bounds. Even if not perfect, it's definitively much more sophisticated in this respect than a CS freshman's first "bouncing ball" simulation program.

In some places, the checks are really kludgy -like sliding checks- or result in bugs like wallrunning, however it's very hard to defeat the standard movement routines.

However, while explicit checks might be hard to defeat, there's always the problem of limited precision and roundoff errors: if even the least significant digit of the player's X/Y coordinates ends up placing him on the wrong side of a linedef, even by 1/65536th of a map unit (the smallest possible), then the "impossible" will occur. Glides and similar exploits rely on modifying the player's X/Y position without Doom checking for it -this requires exploiting the finite-precision trigonometry, somehow, and finding "odd" angles that will cause X/Y position to be changed in a way that will elude checks.

For a clear-cut example of a linedef skip where the player is straddling the linedef for at least a tic and doesn't trigger it, there is my tv10-037.lmp (on TVR), at c. 0:29. Watch it in the automap with IDDT-IDDT and superslomo, and uncapped framerate off.

Probably if you check other linedef skips in this way, you'll find other examples. It seems there's something more complex (and momentum-related?) going on.

jmickle66666666 said:

if this is the case, using sr40/50 means it is more likely to happen, but then you have to move more than the length from one corner of the player to the opposite one (since the player is square).

Linedefs are being activated when the center of the object passes them. I don't think that boundaries matter in this case.

Why is there a barrel stuck halfway in the wall in MAP02? That one drives me mad to this day. Part of me loves it, but part of me wonders how it was missed when it's so obvious.

geekmarine said:

Why is there a barrel stuck halfway in the wall in MAP02? That one drives me mad to this day. Part of me loves it, but part of me wonders how it was missed when it's so obvious.

Don't forget the shotgun guy stuck in the wall.

The only reliable way I've found to skip a linedef is to place two special lines extremely close to each other (typically < 8 map units, maybe 4.) If you run at top speed -- not even sr40/50 -- the second lindef is usually skipped about 50% of the time.

geekmarine said:

Why is there a barrel stuck halfway in the wall in MAP02? That one drives me mad to this day. Part of me loves it, but part of me wonders how it was missed when it's so obvious.

I seem to remember someone saying the map was moved slightly to the side and the things were not moved in perfect alignment.

Clonehunter said:

Don't forget the shotgun guy stuck in the wall.

Oh yeah, I don't know why I forgot to mention him. I always felt so bad for the poor bastard. Never had a chance, AND he's trapped next to a barrel of highly volatile chemicals (what is that nukage in the barrels, anyway?).

Why some of the crushers and lifts are flagged to stop. Are they too loud when the player progresses the map? It's unnecessary and complicates multiplayer sometimes.

Vanilla Doom has a limit for moving platforms. I always though that was the reason, or at least the main reason.

Designers also may have thought that moving platforms would load the engine too much while unnecessarily working, when the player is elsewhere.

I'm not sure, but I've believed that the platform limit affects "halted" moving floors as well (talking about the infinitely up / down movement action), therefore it's useless to halt floors because of this limit.

EDIT: Maybe I've confused it. I know for sure though, that in vanilla, halted floors and crushers cannot be further operated using other linedef actions.

Heard about the limit of 30 moving platforms and didn't think about it in this occasion. I feel smart now.