Thursday, May 26, 2016

Doom Is, In Fact, 3D

So, with the release of the new Doom game, there's been some hubbub of people looking back on the old games.  One thing that caught my attention, was that there are people talking about the technical aspects of how Doom and Wolfenstein 3D makes them not 3D games.  Not really, anyway.


The comments section of the video kind of exploded with people arguing that there's little distinction given for why Doom isn't 3D and that the definition for what actually makes a game 3D isn't really given in a clear way.  Some people have attempted to defend the claims, but, in the end it just doesn't hold up.

Doom is a 3D game, and I can't believe I have to explain why.




1.) Introduction

Before games like Quake and Super Mario 64 arrived on the scene, 3D software was crazy limited.  Developers had to pull out all sorts of crazy tricks to make games 3D, and once they had done just that, they had a hard time figuring out how to make a 3D environment intuitive to a player using a controller or a mouse and a keyboard.  2D graphics made tons of sense, but a leap into 3D meant having to rethink everything.  Considering an entire dimension extra requires tons of thought.

It's because of this that Wolfenstein 3D ended up relatively simple, playing more like a top-down tactical shooter than taking advantage of any kind of 3D space.  (See: the last section of this post!)

New 3D tech means more dimensions to fill with Hitlers.
Not only was controlling a 3D landscape really difficult, but getting a computer to choke down the processes necessary to draw a 3D environment required some serious trickster antics.  Wolfenstein 3D did this via a method known as raycasting, where the player emits rays that draw columns of texture bits on the screen resized depending on how far they traveled to hit a wall.  It's a super nifty trick.

Moving into Doom, id Software opted to use a new method of drawing 3D environments using chunks of processed information known as sectors.  This method allowed for a more active Z-axis (up and down, in the programming world) as well as more complex level geometry.
Picture unrelated

2.) Dispelling the Idea that Doom is a "Top Down Shooter"

Doom plays fairly similarly to a top down run-n-gun arcade game at times.  This is due to its similarity to Wolfenstein 3D, which is a game that does not have an active Z variable determining anything at all within gameplay.  That similarity, however, ends at the control scheme.
The Doom 2 secret levels can count too.
As I mentioned in the introduction, this gives Doom, one of the first FPS games, and one of the absolute first FPS games to include an active third dimension, a gameplay feel that isn't overly complicated or intimidating to a gaming audience who were used to playing games like Commander Keen and The Legend of Zelda.  You couldn't drop them right into the third dimension with clunky controls on a keyboard and expect them to suddenly be okay with this.  You can't make one of the very first FPS games ridiculously complicated to control.
Unless you're System Shock: a game that was practically unplayably complicated but is still one of the best games ever made.
Now, the point has been made that, because the game uses an archaic form of 3D rendering and mostly plays like a 2D top down shooter, it should be considered as such and the third dimension presented in Doom should be treated as an illusion, just like any top-down game that has faked perspective and pretends to have differing heights.

I have many problems with this argument.

People actually argue that this ladder is as 3D as Doom

2.a) Your camera is three dimensional

Your environment in Doom is 3D.  You can observe it from three different dimensions and move across all three dimensions.  Let me demonstrate:
My goodness, it's Map01 from Doom 2.  I'm looking at this structure that protrudes from the ground on the Z axis, while having square dimensions on the X and Y axes.  But perhaps it's all just an illusion, and the game is only making me think that it treats this box as being 3D.  Let's check.
Hmm, I'm able to rotate around the structure, rotating my vision and seeing this structure from different angles.  Is this a ruse as well?  Perhaps it doesn't behave as a 3D object beyond appearances...
Well, I certainly can't move through the structure.  Its X and Y axes are determining that something is there to prevent my player character from moving straight through it.  So I know that it at the very least has 2D collision.  But, what if 2D collision is all that there is?  What if I can't move above it because the game is actually a 2D engine with some tricky rendering scheme that looks for all intents and purposes like there's a 3rd spacial dimension despite there not being any such thing?  Well, we'll have to test that!
I took an elevator upwards, above the height of the structure.  Perhaps this movement through 3D space is another illusion that should not be counted for some reason.  But wait, what's this that I'm about to do?
My God!  I have used my non-instantaneous descent from running straight off of the elevator to land directly atop the metal structure, determining that its height influences its interaction with the world around it.
Alright, so for those of you who aren't attempting to push that Doom is a 2D game out of some kind of stubborn refusal to admit that Doom is an early version of a 3D for some reason, that should really be enough for you to see that Doom is a 3D game.  Not only does it draw its world with three dimensions but it also allows its actors and world geometry to interact from three dimensions.  The player can explore three dimensions of the game world by using those three dimensions.

But people will not let things go, so I need to continue on.

2.b) The Player Interacts in 3D

Now, I've already displayed how the player moves through 3D space in 2.a but I want to address one argument in general.  Le'ts go back to Zelda for a moment.
Notice how the height of the aerial positioning of the crazy chicken cyclone doesn't prevent the chickens from hitting Link.  This is something that happens a lot in 2d Legend of Zelda games.  One of the most infamous examples is that you can swing your sword to the side and hit a bat flying far above you just because the sprites line up.

Somehow people compared this to Doom and think that this makes the argument that Doom is a 2D game in the same way that The Legend of Zelda games of old were 2D.  The arguments put forth to supplement this example are incredibly lazy and flimsy.

The main idea is that, just as the faux third dimension of Link to the Past shows that it is an illusion through objects' ability to interact with each other ignoring the Z axis, Doom also has interactions that ignore the Z axis which show that the Z axis is an illusion.

The problem is: Doom's interactions don't actually ignore the Z axis.
I'd be a dick to pretend that there's no reason for anybody to argue that the game ignores the Z axis.  The major argument comes from the game's auto aim, which automatically adjusts for Z axis for an enemy that you are aiming at on both the X and Y axis.  Here's an example:
So that douche is attacking me from above, obviously aiming down at me to fire.  Now, do I need to aim my weapon upwards to attack him?
Nope.  Got to kill him outright.  The game automatically lets the bullet move upwards to the enemy, almost as though... there's no Z axis being processed?
Well, I already proved in 2.a that the game takes place in a 3D environment, but some may think that this auto aiming is proof of the seams showing through.  Let me explain in two examples how you'd be wrong to think that.

Let's approach this situation a different way.
With cheats.
So, let's first show how the game's auto aiming applies to projectile based weapons.  I gave myself a rocket launcher using cheats and fired at the same zombieman.
Following the rising particle trail allowed by the sourceport I'm using, you can somewhat make out the trajectory of the launched rocket which auto aims to the zombie man.  This means that the rocket had to travel, along the Z axis, from the player's gun toward the zombie.  That means that the developers of the game actually had to program the autoaim by determining what the Z axis movement from the player's Z position to the zombie's Z position would be given the X and Y movement.  This goes to further prove my point that the auto aim was just another aspect that the developers added into the game to make the gameplay less complicated and more accessible to audiences newly becoming comfortable with a 3D environment.  This is not an example of the Z axis being a facade.

Just in case you think that this is just the work of the sourceport, I also took some screenshots from vanilla Doom 2 to show you what I'm talking about.



The rocket flies upwards at a trajectory that had to be carefully planned by an algorithm that takes into account the player's X, Y, and Z position in relation to the enemy's X, Y, and Z positions.  And it's not just the rocket launcher that does this.  Here's an example from the Plasma Rifle:
This demonstrates that you can actually see that the projectiles further in the distance are risen higher than the ones closer to the player.  It gives a great visual of the Z axis movement of the autoaimed projectiles.

But wait, you might be thinking, there's still the hitscan weapons like the pistol, shotgun, and chaingun!  You showed us that when you fire the bullet immediately hits the guy up high.  Doesn't that demonstrate that the hitscan ignores Z axis?

Nope.  Check out what happens when I fire the Super Shotgun at Mister Zombie Man.



I reloaded the save file and killed him 3 separate times to demonstrate this to you.
Notice how the scatter of the bullet puffs all appear where they would if the gun were to aim upward toward the zombie man rather than if the game were to ignore that there were a Z axis.  If the game were to ignore that there were a Z axis, only the bullets that actually line up with the Zombie Man on the X and Y axes would be elevated at all.  But no, the entire scatter is elevated (with the scatter intercepted earlier by the walls perpendicular to the zombie man showing bullet puffs at a lower elevation than those that manifest behind him, due to the angle of the shot) because the game has to adjust for the auto aiming that is there as a conscious decision on the part of the developers to make the game more accessible to an audience unfamiliar with 3D games.

Also, one more thing:
The lower bullets in the scatter are intercepted by the lower geometry.  There should no longer be any doubt in your mind that the auto aiming and the Z position of projectiles require a programmed third dimension, at the very least in the form of a variable, to function in the way that they do in Doom.

So, gameplay-wise, the aiming is set up to be easier on people who aren't too familiar with 3D gameplay, but that doesn't mean that either the gameplay nor the weapons ignore the Z axis, but rather very deliberately compensate for it in order to provide a more intuitive experience.

So far, so good.  Let's cover one more base.

2.c) The player must use the Z axis to progress/reach certain areas

So, I've covered how the Z axis draws the environment and affects how the player's movement interacts with the world in 2.a and I covered how combat and the auto aim prove that there is an active Z axis in 2.b.  Let's take a look at one last thing here: the way that the Z axis actively affects the flow of a level and guides gameplay in a meaningful way.

For this, we must look no further than Doom 2's Map03.


Hey look it's some stuff I can't reach.  It's too high (you know, on the Z axis, the THIRD DIMENSION).


Hey look it's some more stuff, I'll try to reach it.


First let me move down the stairs on the Z axis (THE THIRD DIMENSION) to go check.


I'll be damned.  This stuff is too high as well.  If only this game didn't have a third dimension then this would not be an obstacle.  However, this game does have a third dimension, and as a result the level geometry prevents me from proceeding until I accomplish something else.


After flipping a switch, a bridge raised that allowed me to reach what was previously unreachable due to its height.  I have to be careful, however, as I can easily be knocked off of the bridge by an enemy attack and fall down along the Z axis into a pit.


Once reaching the teleporter, I am teleported into the area I showed before where I could not previously reach because it was too high up.  Heights were not just an active part of the gameplay, but actually formed the theme of the level!  I wonder if the level will continue this theme?


The final part of the level displays a ravine.  Goodness, what happens if I fall into this pit?


I am attacked by the demons within the pit and can not get out because the walls are too high (along the Z axis ((WHICH IS THE THIRD DIMENSION))).


Walls within the ravine lower, revealing sectioned off demons who were only unable to reach me because heightened walls stood between us.


After finding a switch that lowers an elevator, I am able to ride it to conquer the last (and tallest) height in the level, completing this level's theme.  Surely this is a one-off and the rest of Doom won't bother with heights right?


Oh hey look the very next level, I need to press a button to lower a key card which is clearly visible but high out of reach.


Oh hey look some items that I can only get if I find a way to get on top of those crates because right now they are high up and out of reach.


Oh hey look the final boss of the entire game is a puzzle of mastering all three dimensions by avoiding enemy fire on various cliffs which you use as elevators to reach a switch that you pull which activates a central elevator column which you must use to perfectly align yourself on the Z axis to deal a well placed rocket into the brain of a giant demon.

I think I can conclusively say that, yes, the game relies on all three dimensions for gameplay.

2.d) You can tell that the game is 2d because the player can't look up or down

When viewing the code for Doom, or even playing it with certain mods, it's apparent that the camera can be turned up or down in Doom.  The result is distorted unfortunately because John Carmack didn't really program the Z angle perspective on the camera to do up or down very well.  The result looks very similar to if you look down on a panoramic photo or Google Street View.  Shit just gets crazy stretched out.

This is from Strife, a Doom engine game that unlocks the ability to look up or down
This is an artifact from the Doom engine both 1) being a really primitive way to draw 3D and 2) there being a lack of focus on looking up or down as neither were considered necessary parts of the game (upward and downward movement would have only resulted in more complicated, slow gameplay and keyboard layouts, the same concerns that resulted in the auto-aiming).

In summary, the game looks 3D, has 3D collisions, has 3D aiming, and has 3D level design.  The game is, by its entire design and concept, a 3D game.  In its essence it behaves and looks like a 3D game, which, for me, is all that it takes for somebody to label a game 3D.  I mean, all that a game is is visuals, sound, and interaction.  If all of the above is 3D, then that takes the cake.  The game is 3D.  It does everything that a game is supposed to do, which is draw the illusion of a 3D world, just like modern 3D games do.

3.) But John, the game's 3D is a mere illusion

What in the Hell is that even supposed to mean?  It's a video game.  Everything is an illusion.  Almost all of the colors you see on your screen are an illusion made by blending pixels.  Saying that the 3D in Doom is an illusion is accurate, but it's accurate to say that about every game ever made.  Even games on VR are just made using two 2D images that show the same 2D screens at slightly different angles.  

Where the Hell do people draw the line to make a statement like this meaningful?

3.a) "It was made in a 2D editor, so it's just a 2D game drawing a 3D image"


Sometimes somebody gives an argument that's so atrocious that you feel bad that you can't directly make the person who made said argument feel stupid.

First of all, the editor is just the blueprint.  You have to designate height to all of that geometry that you build for both the floor and the ceiling.  You also have to designate a Z position for the wall textures so they are properly aligned.  When you look at this:
If you were to say that that blueprint can only correspond to a two dimensional house with no height then you would be an idiot.  The same goes for the editor for Doom.  You draw the blueprints that way because that's just the easiest way (at the time) to write the information that Doom interprets when building the game.

Oh but wait, it gets better.  See, there's always multiple ways to attack a stupid argument.

Behold Doom Builder:

That's right.  A 3D editor that builds levels compatible with Doom.  So, does that make Doom 3D now?  Does that make only the levels made using the 3D editor 3D and all of the rest are 2D?

It becomes abundantly clear after thinking just the bare minimum amount of thought to be considered alive that this argument is monumentally stupid.  

3.b) Are the levels saved in a 3D format?

This is really just a spin-off of the last section, but bear with me.  Let's delve even deeper into it for one last attack, because I feel that this one is actually pretty integral to the entire debate.

Do you know what the code for a level in Doom looks like in raw format?


That's just the linedefs file of one of the maps.  What does a more modern map file look like when you look at the raw?


These are map files in the format at which the game can interpret them.  While they're interpreting, do you know what they look like?


Because the bullshit resource files don't matter to your computer.  They're broken down into bits to be processed and what the player gets is output based on interpreted machine code every time.

Everything is a lie!
Because of this, you can say that no games are 3D and I won't bat an eye.  Of course they're not.  They're two dimensional images with sound playing, fed to you by your computer depending on conditions set up by your input and advanced calculations.  

Pictured above: a rather complex calculation
Where I have a problem is where you say that Doom specifically isn't 3D.  By singling out Doom (and the other games made on the Doom engine) you are drawing the line that other games are 3D but for some stupid, trivial reason that's practically non-sequitur to the whole concept of whether or not something is 3D you think Doom isn't 3D enough to be 3D.

Doom is as 3D as a game needs to be to be a 3D game and then some.  The editor used is irrelevant to this concept.

Intermission

If you're still with me at this point, you've probably managed to dodge the bottles I've been throwing in my rage.  You have to understand, for me this is an entirely pointless concept with completely meaningless definitions but people are actually defending it and that drives me insane.  It demonstrates, to me, that some people have this bizarre need to validate silly concepts using nothing but non-arguments.

Since you've been such a trooper, have a kitten.


3.c) This game doesn't use the same rendering software as modern 3D engine X

Okay.  Lots of 3D engines, including modern ones, use their own software and 3D rendering methods.  Which one is the only one you consider legit?

The one 3D software to rule them all!
Doom was a primitive 3D engine that took a lot of shortcuts to work on primitive computers.  You know what?  It did just what it set out to do crazy well.  It made a 3D environment with 3D gameplay and 3D object interactions that is processed at ridiculously low requirements.  If you're going to suggest to me that something has to have higher requirements or has to lack the kind of heavy optimization that allowed Doom to run on older computers to be 3D then I'm going to have to ask you to substantiate that claim.  There is no substance to such an assertion and it really just puts the bar as high or low as your personal tastes.  This is no way to argue.

4.) Small things where the Z-Axis is Ignored

There are a couple things that, for the sake of fairness, I'd like to bring up.  You see, there are a couple legitimate areas in the game where the Z Axis is ignored, but people don't bring it up in arguments because most of the people arguing that Doom is not 3D don't know what they're talking about.  So, I'd like to show a couple examples of clear instances where the Z Axis is not taken into account, and then I will explain why they don't cause my position to falter.

4.a) Interactive Walls Don't Care About the Z Axis


The video says it all.  Regardless of your Z position relative to the Z position of a switch, you can still press it as long as the X and Y coordinates are accounted for.

4.b) Enemy Melee Doesn't Care About the Z Axis



Returning to Map03 on Doom 2, you can see that the Demons at the end of the level don't give a crap if you're standing on the top of the high ledge.  If your X and Y is close enough to their X and Y, they'll detect you as being close enough to enter their Melee state, and in their Melee state their Melee attack will count you as being close enough to take the damage.

4.c) Splash Damage

I'm including this because I actually really thought that this one was true.  But, on experimentation, it turns out that Splash Damage is actually dependent on the Z axis.

So I gave myself cheats and decided to point-blank rocket the ledge that this guy is standing on.


Nope, he's still standing strong.  Considering that the Zombieman only has 20 health points and a rocket can drop over 100 health points, I've really got to conclude that the splash damage is taking the Z axis into account.

But what the Hell?  I'll try it again.

Yeah he's still running strong.

I tried this on both the Zdoom source port and on the vanilla game.  I really, really thought that if they didn't care to make enemy melee Z axis dependent then they would have overlooked splash damage, but that's not the case.  This one surprised even me.

Edit:

Now, it's come to my attention that the problem with this example is the linedef (the ledge) blocking the splash damage.  However, if a rocket were to explode far above an enemy, it would deal splash damage as though it were very close to it.

4.d) Why these oversights don't bother me

Doom is a 3D game, but is made using a ton of shortcuts.  Just as a dirt road is still a road, despite lacking the asphalt, Doom meets the criteria for being 3D.  The two oversights that I found don't detract from this because they are, on their own, isolated incidents of a third dimension being ignored.


One of the crazy things about a game engine is that, as long as you program the ability for exception into an engine, you can have a 3D world that defies its own rules if it saves on processing time.


In Doom, you can view the world in full 3D.  To that end they created a world that will work with a computer's ability to process 3D at the time.  There were limitations, but that doesn't stop it from being a 3D game.  It only keeps it from being uninhibited by the limitations of computers at the time.


Saying that the Z axis doesn't exist despite all of the things that it does do because of the things that it doesn't do would be the same as if I were to say that nothing in the game that isn't on screen at the time is being processed because the BFG is programmed to only damage that which is on screen.

Image credit: Melon on Steam.
So far I've demonstrated that the Z axis is an incredibly active part of the game.  Don't discount an entire active dimension within the game engine just because there are a couple exceptions which are either intentionally left in for computational purposes (the melee described in 4.b) or because the developers overlooked something that they never would have accounted for (the height check on wall mounted buttons in 4.a).  

5.) Little things to rub your nose in it


Finally, let's just get down to some random examples of the game acting 3D because I really don't want to ever have to revisit this after I write this damn dissertation on why a clearly 3D game is 3D.

5.a) Things can stack up

Doom has all sorts of crazy moments where there's tons of enemies and projectiles both on the ground and flying through the air.  The important thing about the third dimension here is that it allows for enemies like Lost Souls (the flying fire skull guys that charge at you) and Cacodemons (the big red cyclops meatball things that shoot fireballs at you from the sky) use their flight to bring a new dimension of chaos into each battle.  

If you have a Cacodemon flying overhead shooting fireballs down at you over the Imps, they essentially act like artillery fire.  At the right angle, their shots fly over the imps and hit you, but at the wrong angle they might catch an imp in the cross fire and you end up with a Cacodemon-Imp race war and you can choose to only deal with the stragglers.
Infighting remains one of the best things about Doom
The important thing to point out here is that you can have multiple objects (projectiles, enemies, decorations, the player) all taking up the same space in X and Y coordinates, but unless the Z coordinates line up with their programmed height they will not collide.  That is active 3D.

Note: the problem of Z-clipping is being brought to my attention, but during my tests on Doom 2 on DOS I clearly got to see enemies and projectiles fly over eachother without colliding.  If, perhaps, I am missing something here, then that's alright.  Given that this is just another extra thing I'm throwing out and most of my most major arguments have already given, I'd have no issue chocking this bit up to the same kind of thing that I mention in 4.d

5.b) Enemies Understand Difference in Height

So, first thing's first: enemies can understand differences in height.  Let's take a look at Doom 2's Map10 really fast.

Demons are a ground-based enemy.  They're all up on this platform with me.  In the distance is a slime reservoir.  Since I'm a filthy cheat and have God Mode enabled, I think I'll step into the slime.
As you can see, there's quite a noticeable ledge leading down into the slime.  How do enemies react to this?
Well, Lost Souls have no problem flying over to me.  They don't drop in height at all because they're flying enemies.  The demons, however, noticing that there's not really a dramatic drop-off, will step down to my level to try to eat my rock hard abs while I sit in the slime.  It's also worth mentioning that they have no problem stepping back up to my height from that ledge.

So, you might be thinking, they can drop down a short height.  What's the big deal?

Well, let's take a look at another scenario.

Map28: The Spirit World.  The first thing you do is drop off a short cliff that's covered in Demons and Pain Elementals (meatballs that vomit Lost Souls).  If the Z axis is all a facade, perhaps it should be revealed when the ground-bound enemies abruptly jot down to my level to chase me.
But they never do.  The drop is too dramatic for them to risk.  The only enemies who brave the drop are Lost Souls because they can fly.
Looking back on my example from Map03, you can also see why this is programmed into the enemies.  Demons, like the ones far away there, stay on the other side of the gap and wait for me.  The demons in the boxes below stay in their boxes instead of climbing over them to reach me.  This is all simple stuff to maintain the integrity of the level design, but is semi-complicated 3D awareness on the part of the enemy AI that should not be overlooked when questioning whether or not Doom is a 3D game.

5.c) Elevators Matter

I quickly touched on this in 2.a, but I'm just going to flesh this bit out some more to be thorough in my explanation.  Elevation in Doom is an incredibly dynamic and important aspect of the game.  Elevators move along the Z axis at a speed that is relevant to the game. 
Doom 1's E1M4 is a pretty solid example of a level where elevation is used in dynamic ways.  It includes some enemies on high in the first area who you can kill with your guns but, since they are higher up than you, you can't raid them for ammo.  Bummer.  Also, keep an eye on that blue Soul Sphere in the distance.  It's too high up for you to grab, but it'll come into play soon!
First great example is this room that you walk into.  The moment you walk in, that elevator lifts up.  You know that it moves up or down, how will you get up there?
Bingo, the switch!  The switch lowers the elevator.  With the elevator lowered, you can jump onto it and then ride it upward, using level interaction for dynamic movement across the Z axis!  3D movement and level design, YES!
Success!  But wait, this level is full of examples like this.
There's this secret area here where you find the place where you can reach the Soul Sphere you were eyeballing in the introductory courtyard area.
Okay, so we know that switches control elevators, but this one is already down and won't go up.  The switch is also in a down position.  It only makes sense that the player should flip the switch up and then ride the elevator upward to the soul sphere.
Flipping the switch, but taking your time, makes you miss the slowly rising lift and you miss your one and only shot at grabbing that Soul Sphere.  You had to be faster than that!
This is what you would see if you got onto the lift in time, you clod!  In a fairly subtle way, the Z axis movement of the elevator was turned into its own challenge.  Doom uses stuff like this for traps and secrets all the time.  The speed of elevation is integral to finding certain secrets and an active part of the game.
A similar situation arises here where you can ride that lift in the distance to get up onto that overlooking area, where there is precious loot and a clearer shot at murdering all of those Zombiemen.
So you can hop on the lift (if you aren't paying close enough attention, an enemy can also hop on and ride with you, so chock that up to additional enemy AI understanding height differences).
And here we are, rising up to the new area.  If you aren't careful, however, you can fall off and not have an opportunity to get back up here!  Elevators can be used as one-way trips in levels.  That's another great dynamic use of the third dimension.  Let's look at just one more.
What the Hell?  There's a gap between me and the exit!  How do I get over there?  Is there... a teleporter?  No?  Is there... hmmm... a secret passage?  No?  How in the...
Yeah, no.  This is fucking impossible.  I can't get over there when there's a gap like this.  It's like a million miles long!
Well, fret not!  By wrapping around the level to an area with a Yellow key, you can press a switch that was so close but so far that raises those differently tiled floors to create a bridge!
An elevator acting as a rising bridge?  What is this dark magic?!
Why, navigation of dynamic and interactive 3D space was necessary to solve this level!  And it's not just a picture of a bridge appearing and a "Can cross" variable activating either.  It's the game's built in Z-axis, the player's height variable, the world geometry's Z speed and elevation all coming together to create a dynamic third dimension that can be used in a plethora of interesting 3D puzzles!

5.d) The Crusher

Aside from the mechanism itself, the following is not a sequence specifically scripted only for this one instance.  Any time world geometry crushes down unrelentingly on an enemy this happens:
I really hope I don't have to explain this one to you.

6.) Conclusion

Doom is 3D from its design to its subtle interactions down to the code in the levels and enemy AI.  

Doom runs on a super scaled back 3D engine.  It has seams where you can see the man behind the curtain, it has some rendering glitches, it has some places where the third dimension is outright ignored.  But, if after all that I've shown you, you still insist that this isn't enough to consider Doom's engine its own 3D environment, even if a very limited one, then you're going to have to operationally define what 3D means to you an reconcile that with what Doom is.  
But, really, if you try to strike me down now, I will become more powerful than you can possibly imagine.

If you think this was overkill, I just wanted to make sure I had my bases covered.  Sometimes, if tons of people are trying to make a silly argument, the best you can do is stop them at every single angle.  It's to round them up and play some crowd control.  Just like in Doom.
Thanks for reading.

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