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Sigvatr

Things about Doom you just found out

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Buckshot said:

Strangely enough, the rifle DOOM guy appears to be holding is a HK G36.


Heckler & Koch G36, currently the default weapon of the German Bundeswehr, having a "temperature related accuracy issue" (supposedly already starting to spread during a hot summer, way below temperatures of frequent use).

Correctly predicted by an angle randomizer in DOOM. ;)

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Jaws In Space said:

I also hear the Arch-Vile say Arachnotron whenever it dies.

I always thought it sounded like it was screaming "OH GOD WHY." Kind of funny, considering Prince stated that it was made from a clip of a little girl saying "why" mixed in with some other random noises.

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I believe to remember that the Archvile cries "Why?" because it was planned as "The Medic" and doesn't understand why you don't want it to resurrect the KIA.

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Oops, MAP12 from doom2, where the floor lowers when you approach the cell pack behind the correct blue door. And floor stayed like this, it didn't lower.

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And it doesn't even have an action to it. What a bastard.

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joe-ilya said:

Oops, MAP12 from doom2, where the floor lowers when you approach the cell pack behind the correct blue door. And floor stayed like this, it didn't lower.

Just like in E3M1 and E3M9, the back sides of the bridge segments are untextured. If you just run around the trigger, but still close enough not to fall down, you'll get to see the glitch.

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In E2M4 when you take the first teleport the monsters in the destination room face the player but they won't wake up as long as you stay in the sector of the teleport or you don't shoot.

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LogicDeLuxe said:

joe-ilya said:

Oops, MAP12 from doom2, where the floor lowers when you approach the cell pack behind the correct blue door. And floor stayed like this, it didn't lower.
http://i.imgur.com/3vkdXvTl.png

Just like in E3M1 and E3M9, the back sides of the bridge segments are untextured. If you just run around the trigger, but still close enough not to fall down, you'll get to see the glitch.

Or when you trigger the line skip bug (doomwiki unluckily calls it "noclip bug"), which is probably what joe-ilya did in MAP12.

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So if you've done any Doom level editing you probably know about linedefs types 30 and 96: Raise By Shortest Lower Texture (or some similar name). Basically, the game looks through all the linedefs associated with the tagged sector, examines each sidedef on each 2S line, finds the height of the shortest lower texture, then raises the sector's floor by that amount. This is generally used along with a short step texture or something.

If you're very familiar with level editing, you may also know that for some reason, this action won't work when all the associated lower textures are 128 tall - the sector won't rise all the way up 128 units, but will stop short of it.

So naturally, this happens because there's a bug with this code. Here is how the code determines if it should examine a particular sidedef's lower texture:

if (side->bottomtexture >= 0)
Where the number there is the internal number of the texture. The problem is that it uses greater than or equal to zero instead of just greater than zero. And guess what happens if a sidedef doesn't actually have a lower texture set? You guessed it, this is equivalent to it being set to zero.

Alright, so what is the "zero" texture? Well because the textures are stored in an array, and because the programmers wanted texture #0 to be a signifier that a sidedef didn't have a texture, #0 is basically a "dummy" texture - one that is defined, but that is never intended to be used. In Doom it's called AASTINKY, and in Doom 2 it's the even more hardcore AASHITTY.

Anyways, so this all means that when a sidedef doesn't have a lower texture, i.e. its lower texture equals zero, the code for the floor raise action looks at AASHITTY / AASTINKY instead. And that's why the sector won't raise 128 units - because in all likelihood at least one associated sidedef has no lower texture, and thus the code notices the height of AASTINKY / AASHITTY, which is defined as less than 128, so it ends up being the shortest.

But there's one more quirk here: AASTINKY and AASHITTY aren't even the same height. The former is 72 units high, and the latter is 64 units. So that means if you load the exact same map in Doom and Doom 2, and reproduce this bug, you'll get the following game-dependent difference:

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@Linguica: The pillar on the right part of the gif doesn't rise smoothly like the one on the left. Is that normal?

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I wondered for a while why 128 seemed to be a magic number there despite not seeming to appear at all, and then it dawned on me: it isn't.

If I'm correct, the Doom and Doom 2 difference has the marginally interesting side effect of also causing incongruity with the 72-pixel high small doors; in Doom, the special will raise a floor with them as lower textures properly. In Doom 2, however, AASHITTY gets in the way of that.

Granted, the combination of that special and those textures are likely extremely rare, but it's still somewhat interesting to note that.

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axdoom1 said:

@Linguica: The pillar on the right part of the gif doesn't rise smoothly like the one on the left. Is that normal?

I just used Fraps to record video of each of them, it's not scientific.

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I actually had to modify AASHITTY for my WAD because I needed to raise a sky-hack floor with tag 667 (which works the same way) for part of an even more elaborate hack.

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So, the workaround is just to put your taller-than-dummy textures on both sides' lower textures, even the sides that will not be seen?

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Tag 667 not working as expected is a bug closely related to the one Linguica was talking about. It's easy to overlook forgetting to set all relevant lower textures. which can lead to the map being uncompletable. The bug is further masked by the fact that Boom changed tag 667's behavior — it ignores untextured lowers in its search for the shortest tex — and most later ports adopted this change.

MAP07 in the original release of Armadosia is one notable example of the above. The map was broken in vanilla / vanilla compat, and an empty lower texture on an invisible part of the linedef facing away from the tagged sector was the culprit.

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It takes "4 shots" of BFG to kill a cyberdemon at close range, but takes only "2 shots" to kill him at point blank range.
Likewise, It takes "2 shots" of BFG to kill a mastermind at close range, but takes only "1 shot" to kill him at point blank range.

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Linguica said:

So if you've done any Doom level editing you probably know about linedefs types 30 and 96: Raise By Shortest Lower Texture (or some similar name)....AASTINKY and AASHITTY...

(Wow, I like the new QUOTE tag :)
Nice research there, Linguica! It amazes me just how many quirky issues can arise in Doom. Let me present a semi-deep thought: (ramble a bit)

Many computer systems are built with exacting, "rigid" rules, as a result of top-down planning, expert research, etc. In those such systems, every possible interaction has been considered and studied right up front, leaving little room for surprises.

Then, there's the empirical design philosophy. Basically, you make some sort of container (a map), and some simple rules governing it (height, width, objects cannot cross walls, etc.). Next, get some images for the walls and floor - just enough to get something to display on the walls (think Alpha v0.2).

Then, you make some objects, and design their properties as needed. Throw some into a map, and adjust things as necessary until they move reasonably well, and look realistic.

Make some weapons, center them at the bottom of the screen, and animate them. Give them some properties as needed.

...Etc, etc.

In the empirical system, you make changes as the need arises. You adjust and tweak, until you have something fun and cool. With this type of system, you introduce the possibility of having a lot of subtle, hard-to-reproduce bugs. But, you also gain a lot of rare, interesting complex interactions. That's why we are STILL learning new things about Doom.

To me, the pre-planned design would have led to a more "plastic", predictable experience. But Doom was created more along the lines of the empirical philosophy. It's almost as if you took a bunch of strange monsters, and a marine and some weapons, and dropped them into a strange off-world environment, and forced them to interact.

Some of the most interesting interactions (and bugs) happened directly because of this "loose coupling", design-as-needed philosophy:

Voodoo-dolls, monster suicide/barrel suicide, zombie players, invincible ghosts, monster missiles triggering lifts, glides, etc. Had id designed more carefully, I claim that the game would be much less interesting today.

More towards the "Raise By Shortest Lower Texture" issue, Boom changing the way the shortest texture is calculated can definitely cause demos to go out of sync, so this "fix" is reverted during old demo playback. Maybe there are a few more of these inconsistencies waiting to be discovered - no one knows for sure. But dealing with these weird issues is a side-effect of having such an interesting game.

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Linguica said:

AASTINKY and AASHITTY aren't even the same height. The former is 72 units high, and the latter is 64 units. So that means if you load the exact same map in Doom and Doom 2, and reproduce this bug, you'll get the following game-dependent difference

Oh neat, I suppose if Freedoom had changed the height of those textures (looks like it hasn't) then the behavior of those linedefs in a map would be dependent on whether one played it with Freedoom or the original IWADs...

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After reading the "Favorite places within IWAD maps" thread I began noticing all sorts of tiny little cute details in the maps I thought I knew.

In MAP01's large brown room, the irregularly-shaped "stairs" leading up to the window have different ceiling heights from the rest of the room. Another thing I never paid attention to until now, is that the two lamps in that room actually have a ring of light around them. And in the blue room to the north, the four blocks with zombiemen on them light up the area around them, too.
Caring about such details... I really have no life.

Come to think of it, that brown room kinda looks like a jolly alien face showing its tongue: http://imgur.com/IAfGfJE

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In MAP01's large brown room, the irregularly-shaped "stairs" leading up to the window have different ceiling heights from the rest of the room

Always thought that that stairs is actually a part of the felt down ceiling. Also shape of the ceiling perfectly match to a shape of the stairs

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ABRACADABRA said:

Also shape of the ceiling perfectly match to a shape of the stairs

Because the simplicity of sector-based detailing makes it so.

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joe-ilya said:

The hell knight says "allah akbar" when he dies.

No.

It's a stock sound from a jaguar that you can hear in some other games too (Abuse and I believe Gothic, off the top of my head).

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ABRACADABRA said:

Always thought that that stairs is actually a part of the felt down ceiling.

There's something to it. Interesting. I never thought of that, I think.

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