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didierbertrand

Intercepts overflow discussion

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yeah I guess it's "all ghost bug" , quite weird to see it in a map like that, usually it happens when you fight against hordes.

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Intercepts overflow. If you are playing in prboom+, I'd recommend turning off intercepts overflow emulation, especially if you are recording on wads like this that are prone to it. If you're using Doom2.exe or Chocolate-Doom, then a fair number of attempts to play this wad will end up in this type of way.

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Ah, thanks! Now I remember that I've heard about this bug before. But I didn't know that effect last even after restart. And that brings up another question: if I die on the level intentionally to reach the exit faster (for example, the exit is too far from the place where bug occurs, but very close to the starting point), will it be considered as a valid speeddemo?

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Memfis said:

But I didn't know that effect last even after restart.

I think you are right. It should not be applied after level restart. PrBoom+ does not reload blockmap after restarting on the same level and that's because you are still in noclip mode.

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Memfis said:

if I die on the level intentionally to reach the exit faster (for example, the exit is too far from the place where bug occurs, but very close to the starting point), will it be considered as a valid speeddemo?

The fundamental problem is that in most maps (including this one) it is physically impossible to exit when in this state. You can't press switches. You can't activate teleporter lines/exits. The only* way you can exit while in this state is to enter** a sector of the type "damage and exit if health <10%", such as in Doom e1m8. The only known demos where this was successfully used are on blacktwr.wad, which does indeed have such a sector. On maps that don't have this sector type, the all-ghosts bug unconditionally trashes the recording attempt.

* Just possibly there is some way to get a Romero head to take damage, but I wouldn't bet on it being a realistic idea, and again there are few maps that have one.

** Or to be in the void in an area that the engine considers to have the same sector properties - see my tv29 demo where I made use of that following a void glide, and couldn't actually enter the exit sector itself.

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I understood Memfis' question as about using multiple lives ; using the first life to go to a certain point where the intercepts overflow occur, getting killed quickly so he gets back to the start, and running straight to the exit on second life.

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Oh, probably. Well, in most maps that won't be possible, for the reasons I gave above. And if this is indeed a glitch in prboom+ (can't very easily test, since in Doom2.exe and Choc this demo crashes soon after the overflow), then the resulting demo would be primarily a port-bug demo (and a "death abuse" demo). And that's assuming you can find a map where it would be of use.

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Grazza said:

* Just possibly there is some way to get a Romero head to take damage, but I wouldn't bet on it being a realistic idea, and again there are few maps that have one.


That's brilliant idea!
PA30 with all ghost bug while arch-vile blast damage kills you and romero? :)

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You would need at least four archvile explosions to wipe away Romero's 250 hitpoints. Also, it would be hard to be in line-of-sight with an archvile and next to the Romero head at the same time - probably the only way to accomplish this would be to run full speed directly into the Icon of Sin's forehead while an archvile is charging an attack on you so that the attack completes before the player falls all the way down to Romero's level, but instead is still partially visible to the archvile through the Icon's brain-hole. Even then, you would probably need the archvile to be in the center of the highest (southernmost) platform. Considering that ghost monsters can freely walk over large drop-offs, it would be hard to keep an archvile in this position.

Despite all the roadblocks, I'm starting to think a pacifist MAP30 is actually possible. Triggering the intercepts overflow in the first place is simple enough (in theory): after starting the level, hide in the southwest corner of the map in this demo until large enough piles of telefragged corpses have developed. Then, fire a shot so it travels over a few of these piles. Theoretically, that should trigger the overflow. Then, it's a matter of waiting for archviles to spawn or walk into the right position so that the player can perform the stunt described in the above paragraph.

If it turns out to be impossible to survive enough vile-blasts to kill Romero, then a -solo-net demo with death-abuse (ie. respawning and continuing to play after a death) would still be a pretty significant milestone.

Note that I'm making a few assumptions about how the Doom engine works that could prove to be wrong. I'm assuming that triggering an intercepts overflow is as simple as I think it is, I'm assuming that ghost archviles will still target a ghost player, and I'm assuming that a ghost Romero will be damaged by splash damage with the all-ghost glitch in effect.

EDIT: A few more thoughts have come to me:
-Another assumption I made is that, when the all-ghosts bug is in effect, the player can move can move as if the noclipping cheat was turned on. If the movement of ghost players is actually more restricted than that then this is probably impossible.
-A big problem when recording under the original .exe will be the visible sprite limit, because a few hundred monsters will have to get telefragged before 128 of them will lie along the same straight line. The best way to solve this problem may be to bring some co-op partners along just so that it's more likely that someone will be able to see when an archvile is in the right position. Another advantage of this approach is that when one player is too low on health to suffer another archvile-blast, he can trade places with someone else.

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I understood Memfis' question as about using multiple lives

Yes, that's what I meant. :)

And if this is indeed a glitch in prboom+ (can't very easily test, since in Doom2.exe and Choc this demo crashes soon after the overflow)

I would like to test it. Is there any fail-safe way to get all-ghosts bug? I've tried to shoot at ~170 cacodemons with BFG, but doom2.exe crashed.

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Memfis said:

I would like to test it. Is there any fail-safe way to get all-ghosts bug? I've tried to shoot at ~170 cacodemons with BFG, but doom2.exe crashed.

Easiest way to trigger an intercepts overflow that I know is to play Nuts.wad on Nightmare!. It happens quite often then. However, playing it back on Doom2.exe can be painfully slow, and it is also likely to crash.

The simplest way to test would be to choose one of the other demos with an overflow (see the thread I linked to) and to use prboom+ (and -recordfromto) to join the demo after the overflow, and then record whatever you want to test (e.g. whether the all-ghosts behaviour persists after restaring the level). Then see if plays back the same way with Doom2.exe.

Creaphis: Ghost players cannot move very freely (they are not "noclipping"). They are restricted by height differences - more so than normal players, in fact. Try playing Doom2 map04 as a ghost player - I found that the only way to reach the exit was to go all the way through the void. (Note that the ghost effect in that case was generated in a different way, so there might be subtle differences.) But I'm not at all sure that explosion damage works at all once the all-ghosts bug has been triggered. That leaves you with only melee attacks (they can hurt the player) and telescratching, but I don't think these attacks can be misdirected (i.e. they either hit the intended target or miss completely). I think Paska was probably joking, and should mention that by even entertaining the idea, I was more covering my ass in case there was some way. I don't like to dismiss anything as "impossible" unless it is a cast-iron certainty. You can test some of this stuff in the way I described in the precious paragraph.

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I was thinking that players made into ghosts by the all-ghosts bug have fewer movement restrictions than crushed zombie players, but I guess I don't have any grounds for assuming so. I suppose I could test this stuff but I was kind of hoping I could coax someone else into doing the dirty work for me. :)

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I suggest Eugene's pl15-odd.lmp if you want to investigate this further. The demo itself suggests a few conclusions, while if you wish to join it with -recordfromto, the overflow occurs about 48 seconds in, and there are plenty of height differences and archies (and other monsters), and you have the rocket launcher.

I'd love to see a pa30 done in this way, but I think you might conclude there is no way it will happen.

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Grazza said:

Creaphis: Ghost players cannot move very freely (they are not "noclipping"). They are restricted by height differences

I don't see height as a problem in map30 since you can go void and trigger all-ghosts bug there and run around universe to get to romero, then even if arch-vile wont hit you, how about lost soul charge hitting romero? I think it's melee attack which would hit.

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To test some of these ideas, I modified Nuts.wad, putting a bunch of Romero heads, lost souls and a pain elemental near the start position.

It's quite easy to create an intercepts overflow by playing on Nightmare and running as if you were going for a normal pacifist speedrun. More often than not, you get an overflow in the first room without needing to fire a shot. On UV, it can happen too, but is less likely.

I haven't been able to get the lost souls to harm the Romero heads after the overflow occurs. They just charge straight through him.

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