Monster Infighting

Monster infighting in Doom may sound simple on paper, but you'd be surprised by the amount of hidden and obscure mechanics.

Music:
Plug Ugly by Bucket
Infimum by Ribbiks

Patreon:

[CyberneticSheep]

When you hate yourself so much you start tearing yourself apart for hitting an explosive barrel

[redline]

"Get a load of these demons"
-Doomguy

[rodylermglez]

The justification John Romero gave for including infighting as a mechanic is my all time favourite game design quirk: "They are chaotic/evil!"

[mastergame]

"[...] It will start tearing itself apart."


*Brutal.*

[nightmaregats]

As soon as they see Doomguy, they realize that fighting amongst themselves is better.

[alicetretyakova]

About self-infighting: you didn't say everything. If monster without melee attack is targeted to themselves, they will shoot in the air in eastern direction, which is the zero angle

[valkarion]

1:55 it's good to know that even back in 93 no one took function argument naming seriously.

[ChusenOne]

that edgy baron trying to hurt himself got me

[mjc]

0:21 - Can we just take a moment to appreciate how awesome that orbiting missile manipulation was? **chef kiss**

[Clanker]

the way doom is programmed is amazing, it's nice to have someone that teach us about this, keep the great work decino.

[maxinecaulfield]

This is such a well designed game. It also makes sense that these hell creatures don't have any attachment to each other.

[christiancinnabars]

AI “infighting” is always my favorite part of games. Bonus points if there are special interactions the AI have with each other that isn’t ever done against the player.

[kaczan]

It's stunning that a game made over 20 years ago, that seems so simple on the surface, has so many complicated systema, like this or the randomness in animations. I also like that Archie has no threshold. It balances him out a bit.

[MoogleSan]

Baron of Hell: 'Trust Nobody, Not Even Yourself'

[tormuse]

4:44 If you really want to see something wild, try firing a single pistol shot at a Lost Soul while it's in the middle of a charge. (I'm serious, go try it!) It freezes, hovering in mid-air, continuing its charge animation forever, completely helpless, letting you walk up and punch it to death, unless you hit it with something that knocks it back into a wall or another enemy. (In which case it will only damage things that are in the direction it's currently moving, regardless of what direction it's facing)


I haven't looked at the source code, but I think the reason for the way Lost Souls behave (from what I've observed of the original game) is that when it charges, it becomes its own projectile. Every time it finishes a charge, it essentially becomes a new enemy, which is why it doesn't remember who it was in-fighting with after a single charge, and also probably why it doesn't make any sound when you get its attention. (Otherwise, it would be making that noise after every time it charges!)



This makes me think that a video explaining the Lost Soul behaviour could be interesting.

[DissedRedEngie]

Whenever you are having a bad day, remember that the barrel remembers who hurt it.

[neDoomedSpaceMarine]

Monster Infighting is such a delightfully fun feature. After all these years, making monsters start a big brawl where they just angrily tear each other apart, still makes me giggle like a fool.

[xjyo]

Highlighting the lines in the code was like reading and analyzing the rules of Death Note

[hi-i-am-atan]

Some extra notes:


1. The reason why making a sound previously in a room will prevent monsters from idling is because sound propagation is _permanent._ As soon as you press the fire button ( which, for most guns, means before they even _fire_ ), the "sound" spreads as far as it can given physical barriers and sound blocking lines, then marks all sectors that are touched with the firing player's id as their soundtarget. Then, whenever a monster calls A_Look ( the codepointer that, well, looks for a new target, called in every Spawn state ), it checks its current sector's soundtarget, and if there is one, it wakes up and starts chasing them. Notably, since soundtarget is only checked in A_Look, a monster that kills its current target with look around, see no players in vision range, go back to idle, check for a soundtarget, then immediately wake back up again. You can tell this from the fact that it makes its alert sound again.


2. Those hardcoded exceptions with the hell nobles and archviles are inherited by any actor that replaces them via Dehacked. Any actor that is internally a baron of hell will never be hurt by a projectile sourced to an actor that is internally a hell knight, and vice-versa, and the archvile's targeting idiosyncrasies will be adopted by anything that is internally an archvile. This doesn't go for hitscanners or lost souls being able to infight themselves, however, as those are caused by the effects of the hitscan and lost soul charge codepointers themselves.


3. Minor correction, but all vanilla Doom monsters call A_Chase twice per step ( one at the start of the animation frame, and one in the middle ). This means that it takes a minimum of 50 ( visual ) steps for a monster to be able to change targets, though it easily can be more if a monster starts an attack with its first A_Chase call per step. Except with the caco, though that's because it literally doesn't have a moving animation.

[Anonymous-]

Baron:I’m gonna kill you doom guy!
Revenant: *shoots baron*
Baron: But first....