Things about Doom you just found out

[scifista42]

But they didn't all die in one shot - that's what 42PercentHealth was talking about.

Edited April 12, 2017 by scifista42

[Dragonfly]

31 minutes ago, Slimz said:

Took 40 seconds to kill them.

Actually it took around 6 - 7 seconds.

[Tracer]

1 hour ago, 42PercentHealth said:

So they're illegal in most (all?) US states.

From Gun.laws.com :

 

"In the United States, it is illegal to posses a sawed off shotgun that has a barrel length of less than eighteen inches, unless the individual has obtained a taxed permit from the ATF. That permit requires a background check and payment of an excise tax for that weapon. However, each state has different laws which govern the types of weapons that residents are allowed to own and a state may forbid ownership of a sawed off shotgun, simply because of the ease with which it can be concealed."

[axdoomer]

If the Doom executable triggers an I_Error before it has called I_Init, it will lockup and the only thing to do is to restart your DOS machine.

 

This is because I_Error shutdowns systems inside the executable before it quits (sound, video, etc.), but if I_Init is not called first, then they are not started in the first place. This works, but where a problem takes place is in I_ShutdownSound. For some reason, the executable waits for 30/35 of a second after DMX before it shut it down. If I_Init wasn't called, then the timer in DMX wasn't even started and since the timer will never increment, the game locks up.

 

This bug affects Doom v1.9, but not Doom v1.2.

Edited April 12, 2017 by axdoomer

[kb1]

9 hours ago, axdoomer said:

If the Doom executable triggers an I_Error before it has called I_Init, it will lockup and the only thing to do is to restart your DOS machine.

 

This is because I_Error shutdowns systems inside the executable before it quits (sound, video, etc.), but if I_Init is not called first, then they are not started in the first place. This works, but where a problem takes place is in I_ShutdownSound. For some reason, the executable waits for 30/35 of a second after DMX before it shut it down. If I_Init wasn't called, then the timer in DMX wasn't even started and since the timer will never increment, the game locks up.

 

This bug affects Doom v1.9, but not Doom v1.2.

How did you discover this? (curiousity)

[Linguica]

9 minutes ago, kb1 said:

How did you discover this? (curiousity)

You've seen his PCDoom port, right? If anyone is interested in weird DOS engine minutiae it would be him.

[axdoomer]

19 minutes ago, Linguica said:

You've seen his PCDoom port, right? If anyone is interested in weird DOS engine minutiae it would be him.

I did not make PCDoom. It's @nukeykt's work. He's a God for all of the reverse engineering work that he's made on the vanilla Doom engine. I'm using his port as a base for mine.

 

His port has a wrapper and you can bind it to the illegal DMX leaks easily. You compile this with Open Watcom and this gives you a 100% accurate vanilla engine. (like if you had the original DOS source code)

Edited April 13, 2017 by axdoomer

[kb1]

12 hours ago, Linguica said:

You've seen his PCDoom port, right? If anyone is interested in weird DOS engine minutiae it would be him.

Yes, I saw of its existence, but not what it was (or I didn't comprehend what it was at the time). I am intrigued, now, though, and would love to know more. I've always wanted to have THE definitive source code and compiler, and be able to recreate doom.exe/doom2.exe as exactly as possible, at least as a novelty. And, just now looking at some posts, there are some neat as-of-yet-unknown facts, such as the exact pitch-shift calculation - fascinating stuff! I don't know how I missed this one. This is absolutely a Thing about Doom that I just found out! Nice. This deserves a closer look.

 

Is there a thread where both nukeykt's and axdoomer's ports are compared, or, at least described, like the first introduction threads?

Edited April 13, 2017 by kb1

[axdoomer]

There is no thread about these source ports. Here's some short descriptions. Nothing really special since most of them aim to be a doom.exe clone.

 

PCDoom by Nukeytk
-Uses the Apogee sound library. No PC Speaker support.
-Sound pitch
-Behaves like the original Doom v1.9 and Doom II executable
-Less faithful to vanilla Doom than its successor: PCDoom-v2

PCDoom-v2 by Nukeytk
-Uses the Apogee sound library. No PC Speaker support.
-No sound pitch
-Emulates the Final Doom executable.
-Various accuracy fixes from its predecessor, uses assembly for rendering code like vanilla.
-The most faithful source port out there, it's exactly like you're using the vanilla executable.

Doom Vanille by AXDOOMER
-Uses the Apogee sound library. No PC Speaker support.
-Optional sound pitch (enable with -sndpitch)
-Game can be chosen using "-iwad <iwadname>".

-Emulates the correct executable according to the IWAD used

-Emulation of alternative Final Doom executable can be forced using "-alt".
-Add support for newschool deathmatch 3.0 (-dm3) 

-Won't crash if Demo4 is not found. Also brings other changes.
-Based on PCDoom-v2 but remove assembly from source code. No Joystick support because of this. 
-Fixes various game lockups, like the I_Error bug or OS corruption when a WAD has more than 4046 lumps.

 

DoomNew by Frank Sapone (who worked on Daikatana)
-Uses the DMX library (Frank received it from John Romero as a gift for his work)
-Support for DEH patches
-The author also made Heretic for DOS with support for VR goggles.

 

Hopefully, Paul Radek will release the DMX source code soon. Nukeytk as been able to contact him and Radek should be releasing the DMX source code once he's cleaned it up, if he's really going to do it...

 

All of these sound ports are compiled with Open Watcom which is the open version of the original compiler used for Doom. (except maybe DoomNew)
The great thing with using the Watcom compiler is that you don't have to write code to emulate Doom's behavior, it's all emulated by itself because the Watcom compiler produces code that's like the original. (e.g. overflows should behave the same because the layout of the code will be the same inside the executable.)

Edited April 17, 2017 by axdoomer
doom vanille updated

[axdoomer]

I've just found this inaccessible area on Plutonia MAP15: 

 

 

From the inside:

 

 

There is no mention of it on the DoomWiki. On don't know what it's supposed to represent or why it's there because it doesn't add anything visually to the level. From the closest point of view that you can get normally, you are still very far and all you see is that there may be a black room. 

 

EDIT: Huh, it's just a room which contains enemies to teleport....   :-(

Edited April 16, 2017 by axdoomer

[RjY]

15 hours ago, axdoomer said:

EDIT: Huh, it's just a room which contains enemies to teleport....   :-(

Yeah one or other of the Casalis liked to put their monster teleporter holding areas in full view of the playable part of the map. There is another example on pl27.

[axdoomer]

I just found out that there are some PC speaker sounds in the IWAD that Doom doesn't play. They are: posact, bgact, dmact, dmpain, popain, sawidl.

 

The sounds are there and work, but there is a check in the engine when sounds are played that checks if the sound is one of them and if it is, then it's not played. The two reasons are that they may be too annoying  ("act" sounds) or may cut other sounds like gun shots ("pain" sounds). I will let you guess about "sawidl" (chainsaw idle sound). 

[DoctorNuriel]

I only just now discovered the pillar containing a chaingun on Refueling Base... damn.

[Scotty]

I had no idea that, on the E2 intermission screen, the Tower of Babel gets 'built' as you progress through the episode.

[leodoom85]

Well, just find out that Doom is harder than I thought if you play it with only the pistol.... :P

[drygnfyre]

1 hour ago, Scotty said:

I had no idea that, on the E2 intermission screen, the Tower of Babel gets 'built' as you progress through the episode.

Fortress of Mystery is also only visible on the map when you actually reach it. (Although the blood spot indicating a cleared map remains).

[Dragonfly]

1 hour ago, Scotty said:

I had no idea that, on the E2 intermission screen, the Tower of Babel gets 'built' as you progress through the episode.

I never realised this either, just checked it out, very cool! Definitely something that should have been more emphasised somehow.

 

[axdoomer]

Today I have found out that a hitscan error occurs on E3M6. When you shoot through the air, bullets can get blocked. See this video. It previously saw it occurred on Doom 2 map12, but the cause seemed more obvious because it occurred along the four long walls which make the square box of the map. 

 

 

Seems like it's caused by the linedef #0 which is duplicated to another location on the map. I have drawn a green line where I know it occurs. Seems like Doom as some trouble checking hitscan collisions against long linedefs and it moves the linedef somewhere else. It may be an overflow. It happens more frequently when linedef #0 is too long because the engine always check for collisions against this linedef due to a bug. 

 

 

I've updated the DoomWiki article, but it may not be displayed yet because it needs to be approved by an admin first. (I forgot to login, so the changes were made as an anonymous user) 

Edited April 24, 2017 by axdoomer

[NecrumWarrior]

I just found out about the cone of hitscan damage that the BFG9000 deals after impacting. I assumed that it had radiated from the projectile, not the player. My play has improved directly as a result.

[drygnfyre]

It wasn't until I joined this forum and discovered DoomWiki that I even really knew how the BFG worked. For a long time, I figured it just created a very large blast zone, like a gigantic rocket launcher. But it's not that at all.

 

(However, I have read that some source ports can make changes to the BFG to have it work that way).

[NecrumWarrior]

4 minutes ago, drygnfyre said:

It wasn't until I joined this forum and discovered DoomWiki that I even really knew how the BFG worked. For a long time, I figured it just created a very large blast zone, like a gigantic rocket launcher. But it's not that at all.

 

(However, I have read that some source ports can make changes to the BFG to have it work that way).

The original function actually encourages more aggressive play so I think I like it better. It's great to shove the BFG in another Revenant's face to murder it, 2-for-1.

[drygnfyre]

Just now, NecrumWarrior said:

The original function actually encourages more aggressive play so I think I like it better. It's great to shove the BFG in another Revenant's face to murder it, 2-for-1.

Well, technically, the original BFG's function was it was just a bigger plasma gun. But it "looked like Christmas," so they changed it. And again, there are source ports out there that can restore that behavior, too.

 

Speaking of the BFG, one thing I also found out was because of how it works, you can actually still hit someone with it even if you're facing away from them or even in an entirely different room. Mainly due to the slight delay in its firing.

[Arctangent]

4 minutes ago, drygnfyre said:

Speaking of the BFG, one thing I also found out was because of how it works, you can actually still hit someone with it even if you're facing away from them or even in an entirely different room. Mainly due to the slight delay in its firing.

... No, it's due to what NecrumWarrior just said. The tracers radiate from you, not the projectile. Additionally, they're fired in the direction the projectile is facing - so if you shoot the BFG exactly east, the tracers will fire exactly east, no matter where you're facing when the projectile actually explodes.

[NecrumWarrior]

1 minute ago, Arctangent said:

... No, it's due to what NecrumWarrior just said. The tracers radiate from you, not the projectile. Additionally, they're fired in the direction the projectile is facing - so if you shoot the BFG exactly east, the tracers will fire exactly east, no matter where you're facing when the projectile actually explodes.

That is also useful information. Thanks.

 

And by original function I mean the one that shipped with Doom, not the beta version.

[Albertoni]

7 minutes ago, drygnfyre said:

But it "looked like Christmas," so they changed it. [...]

 

Speaking of the BFG, one thing I also found out was because of how it works, you can actually still hit someone with it even if you're facing away from them or even in an entirely different room.

I believe the real reason for it being cut were performance issues, actually. Having 100+ shots in the screen would quickly run you towards the sprite limit.

 

You might also not know about the silent BFG trick, where you'd use a wall to make a grunt just after firing it. Since in MP each player can only make one sound at a time, you'd essentially take away the single hope the other players had of avoiding a BFG.

[galileo31dos01]

Pinkies/Spectres (and Nightmare Spectres) are way more annoying in the PSX version than in the PC version, I don't why honestly

[Avoozl]

Pinkies were like the new Revenants in PSX Doom considering how crippled the actual Revenants were.

Edited April 27, 2017 by Avoozl

[Angry Saint]

TIL At one point in development, the Spider Mastermind was going to have a magic attack that likely would've held the player in place, leaving them vulnerable to the demon's normal chaingun attack. This is a frame for it. Sorry if someone already posted.

 

 

but actually a spiderdemon magic attack similar to the archvile one would be interesting...

[Graf Zahl]

On 25.3.2017 at 8:18 PM, Linguica said:

When I was writing up my Doom movement bible this was the one thing I was not able to sufficiently research (not without a LOT of effort). Wall running on a diagonal wall involves an entirely different mechanism than "normal" wall running and it's far more finicky - it relies on the same overestimation of slide movement used in void glides, and the rounding of angles so the game never tries to place the player inside a wall. Since it involves several different calculations piling on top of each other there was no easy way to systematically test it that I could find.

 

Straferun south along that angled wall and you will pretty consistently see a speed boost comparable to a "normal" wallrun. Also since you are going south it can't be the same mechanism as the normal wallrun since you don't get the doubled movement calculations from a southward run.

 

Sorry for digging out this old post, I must have missed it a month ago.

 

This was something I debugged and fixed in ZDoom 13 years ago. What happens here is simply that the engine uses the rather coarse sine table to calculate a movement vector from a line's angle. And if that line's angle happens to be in the place of the current sine value's range with the largest deviation from the real value for the given angle it just fails to calculate a usable vector. Depending on whether it points towards the wall or away from it you either get the acceleration or the bumpy movement.

 

Using linear algebra and P_InterceptVector instead of the trig tables makes the bug completely go away as does using a precise sin/cos function. This is entirely a math imprecision, not some faulty algorithm.

 

https://forum.zdoom.org/viewtopic.php?p=63238#p63238

 

[axdoomer]

The Arch-Vile will attack a dead monster if the monster had launched a projectile that hit the Arch-Vile after its death and while the Arch-Vile is attacking the player. This will make the Arch-Vile change its target to the monster's corpse and it will jump a bit in the air like the attack does to the player.