The work around hardware limitations is amazing. I prefer fully polygonal 3D games but there is undoubtedly a charm in the 2.5D aesthetic.

It’s due to the technique used : *Y-shearing.* Heretic & Dark Forces also used it. True 3D needs to divide each coordinate by the Z to implement perspective projection, which is an “expensive” operation in computer performance terminology. It really only became feasible once graphics accelerators proliferated.

The funny thing is - we can achieve the "incorrect" look of Build Engine's "looking up" by using a tilt shift camera lens. The Build Engine does not simulate rotating the camera up or down like Quake does, but shifting the camera's frame up or down without changing the perspective.

Descent from 1995 was full 3D and was semi-playable on a 386 computer. It was more about optimisation and the features that the Duke team wanted to focus on, not the absolute lack of suitable hardware. Descent's mapwork was more ascetic, but on the other hand it had 3D enemy characters and some pretty solid effects. I also remember Quake running slightly smoother than Duke on my friend's 486, but I'm not sure what type that machine was exactly...

This just shows how these games were made with blood, sweat, tears, and sheer determination of will. It's incredible.

Keep in mind it's easier to notice when you are directly playing the game. A perfect way to make sure you can see the difference is in fact to play the anniversary version of nukem 3d, as you can toggle between classic and modern cameras

You can also look up and down with the mouse in Duke Nukem 3D if you press the U key.

This was the first game I ever tried to mod. Remember making maps then going to friends house on the weekend for a lan party and playing it with others. Used to make hugh pits that annoyed players... Where they would fall for a long time before being able to respawn. Remember vividly making sprites of mesh planes. Billboards is what I would say they are called today.

Btw quakes inability to display curvilinear or 5-point perspective is not due to its "perspective" but fov. Quake is not rendering 3 point perspective as it is not rendering one type of perspective as they all exist in a 3d space given it is true 3d. The only thing required to display curvilinear perspective is to widen the fov (which im sure is doable in quake), similar to changing from a long focal lens to a wider one, the nature of our worlds perspective doesn't change, just the parameters of the lens viewing it.

Great explanation! I recently showed how to program doom from scratch and it's a great thing to learn.

i was like, bruh it's like a VERY long vertical image that allows scrolling and then you actually said the same thing at the end was so satisfying

I love that automatically generated captions wrote 'consumer man' instead of 'Ken Silverman'.😂 Great video btw

Fascinating video! I always thought games like DN3D, Dark Forces, Shadow Warrior, and other games with the ability to look up and down felt unnatural but figured it was the limitations of the engine and never put more thought into it.

What I find interesting about this progression of technology is how certain things now make sense about the old days - when I first got into gaming, I had a crappy 486 with 8MBs of RAM (upgraded from 4). I bought Quake... it wouldn't run. I remember something about "floating point" being the issue; my CPU at the time couldn't handle the calculations a true 3D game needed. Now, knowing more about the technology later in life, it all makes more sense. At that point in history, one of the biggest changes... was mathematical; it wasn't a matter of brute force, of raw computational power, but about the type of computation being done. The type of mathematics being done.

Great vid! I've been looking for a comprehensive breakdown like that!

0:24 it's not ROR, just a bridge made of sprites :]

I never had an issue with the 2.5D version and found it somewhat easier to decode visually; I suspect because our brains do an autocorrect before we're aware of the distortion from real 3D, but not so readily on a screen where it's actually a flat image.

Wow, this was a fantastic video explaining the concept, and your visualizations were excellent. I'm glad KZfaq put this in my suggesteds.

The more you learn about duke nukem 3d, the more you are amazed of the cleverness of its creators

Duke nukem 3d was not the last 2.5d fps, when quake came out, no one had ever seen anything like it and it took at least a year for developers to scramble and make their own 3d engine. There where plenty of 2.5d games released later in 1996 into 97 and some from 98. In 1996 you had duke nukem 3d, strife, Chex quest, powerslave, and final doom and it’s 2 expansion packs, and in 1997 you had blood, shadow warrior, chasm the rift, hacx, red neck rampage, and outlaws. There where probably less 3d games released in this time then 2.5d, I can only think of quake, quake 2, and turok.

Wonderful explanation! An illustrator here: We need more points more farther we are. Very close, it's 1-point perspective. A bit far - 2-point. Up to fish-eye, 5-point, which is human eye vision.

0:24 - There is no ROR in Duke3D, you've shown a sprite bridge. In Duke3d you can have 2 sectors intersecting if you can't see both of them occupying the same vertical space. The game with ROR was Blood, but it is kind of limited, you can have only 2 sectors using the portal rendering.

So this is, essentially, the 2.5d version of the "pan and scan" technique movies used to adjust 16:9 movies to 4:3 TV screens back before widescreen TVs were a thing. Basically, how pan and scan worked was a "focus frame" that matched the TV's 4:3 aspect ratio was placed on the 16:9 movie frame, which the editor could move (or "pan") around the larger frame to focus on essential bits of action. Whenever the focus frame moved, though, it created the same unnatural and offputting feeling of looking up and down in Duke Nukem 3D as the perspective didn't shift as predictably as a real camera movement would have. This offputting feeling was made worse if the focus frame was panned at the same time as the camera was moving as the perspective shift of the camera often would move contrary to the focus frame panning - a very poorly edited movie using pan and scan could even trigger someone who suffers from motion sickness and, rarely, even epilepsy. There's a very good reason why many of the more prolific and artistic filmmakers of the day said pan and scan ruined cinema for home viewing... It's still very interesting to see that similar techniques were developed for games of the same era.

Now that I look back at how this weird effect looked back in the day, It reminds me of how you scroll a pdf document with photos up and down lol. Its strange how they thought this could be a convincing solution for its time, it always looked weird but interesting.

Looking up and down was needed if you wanted to shoot a switch, because autoaiming did only apply for enemies.

As a former 3D game developer, something I’d like to clarify here is true 3D games don’t have perspective per se, they have projections. The reason straight lines must be rendered straight even though human vision is curvilinear is that you are seeing the game world through a flat monitor. The renderer’s job is to work out what colour light would come through a point of an imaginary rectangle towards a set of of imaginary eyes in the game world and set it to the corresponding pixel of the monitor that is in front of your real eyes in the real world. If anyone is interested in how all of this works, they should look at projection matrixes. It is all just matrix multiplication.

I didn't finish watching the video but I gotta correct you my friend. You need to aim up and down to effectively use splash weapons and the shrinker, also you need it to shoot at buttons to progress and to access secret s

I'm glad I watched this video. I already knew most of how it works, I think from a video by Decino, but seeing the screenshots stacked on top of each other to show that the camera scrolls was not something I realized!

- It's actually a lot simpler than that and has nothing to do with perspective at all. Looking up or down in _Quake_ actually TILTS the camera up and down, but in _Duke 3D,_ it PANS the camera up and down as if the player is standing or squatting. - Ken Silverman made the Build engine then disappeared. He played around with voxels, but never kept up with 3D games.

9:16 Glad to see Marathon mentioned! Though I feel that you failed to mention that the Marathon games did not have automatic vertical aim. You had to carefully aim up and down, which was quite tricky without a cross-hair. Sometimes it was impossible because you could only tilt your head a limited amount or the illusion would be ruined. As far as I can tell, Marathon was the first game with mouse-controlled free look. Many still played with keyboard only for the first few years though.

Yeah, mouselook in Build Engine games almost feel orthographic. Though, an actual orthographic camera in an FPS would be impossible to use, unless it was a sniping game.

5:09 I know that effect to well every time I check if something's bent it looks bent because of my eye even if it's not bent

I remember making maps for Duke3D. Trying to make a swimming pool was complicated because of the fake 3D perspective. But before Duke3D and Quake. There was Descent, which came out a year before both games, in 1995. Which was also fully 3D and fully traversable in any direction, at any time. Since you are piloting a spaceship which has sideways, forward/backward and up/down movements. But this full freedom of motion was hard to control for many at the time with only a keyboard. This was prior to a mouse being generally accepted input device for FPS games.

This could likely be remedied by skewing the final rendered image in post depending on the "angle" of the player camera. Of course, it won't be perfect, but it would likely be noticeably more realistic than the vertical scrolling method.

You gave some really great visualizations to explain the topic!

So, looking down in Duke 3D is, at certain extent, the same thing as crouching?

I remember getting real sick trying to look up in down in 2.5d games back then, so I never really did.😆 Always thought it was a cheap gimmick till Quake roared onto the scene

Fisheye cameras dont produce "5 point perspective" .. they produce "sinusoidal perspective". This means the lines going to the vanishing point are curved .. they are sine waves, whose amplitude varies according to their variance from the three straight "horizon" lines that go thru the dead center of the image. Each of the three sine waves goes thru two vanishing points beyond the edges of the frame .. or at least far from the center of the image. A vanishing point near the center of the frame must have its next vanishing point beyond the edge of the image .. unless it is some kinda panoramic 360 degree type view. First demonstrated in the works of MC Esher (1898 - 1972) EDIT .. actually I think we are talking about the same thing .. I just never bothered to consider there are 5 vanishing points before .. usually Id add in a separate vanishing point per object in the drawing, to best suit its orientation :)

I wonder how much heavier it would have been to distort the entire image so that when you look down, the top of the frame stretches wider, and when you look up, the bottom of the frame stretches wider...

Quake wasn't the very first fully polygonal game, by the way. Descent had geometry and enemies fully polygonal and Terminator Skynet and Future Shock had the same but with 2D weapons and VFX.

Basically, the horizontal cheat is so good that it makes you EXPECT a similar vertical cheat, that sadly isn't there.

Duke wasn't support room above room, untill Shadow Warrior updated engine, who empliment some sort of portal effects (we got translussive water, upper flors etc) , but in duke 3d no room above rooms, what you see there, 0:20, is 4 stretched sprites that put together.

Later on, DooM-Engine games can do the same look up/down, with the same limit, such as Heretic, and HeXeN. Still no slopes, or room-over-room abilities. HeXeN did bring in tricks to make sectors deform, like swinging doors, for example.

You actually can see 2.5d games using proper 3d perspective today. Most notably through modern source ports for doom. These source ports permit free looking and even full free aiming. One thing that does immediately become apparent is that the sprites really are 2d objects. The most extreme example is trying to look at them when they are directly below you on a ledge they become barely visible. The way the world is rendered also still looks a little weird. Though you can see why besides the hardware limitations of the time up and down looking wasn't utilized.

5 cents: the bridge in E1M1 isn't really a room over room, it's a bunch of horizontal and vertical sprites. As such, it's destructible.

duke nukem vertical camera movement looks like you are scrilling up a single picture

I already knew the technique but I really enjoyed watching the video nonetheless. Your explanation are very well-written and easy to comprehend!

Excellent video man! Very understandable, very clear examples and very smart way of visualizing the explanation. Keep 'em coming!

I have to say, I never had a huge problem with how Build Engine games handled looking up and down. Like when someone pointed it out I was like 'yeah that is a bit odd' but it didn't hurt the game for me.

I kinds like the distorted perspective but that’s probably the nostalgia. I do think modern ports for Duke or Doom that use 3 point perspective look off too. Mostly because it makes it much more obvious the sprites arr just flat billboards.

Awesome video. Cool to see you take off time from running the Cyber 8 channel to do some retro gaming stuff, lol.

It's so strange seeing that effect. When I first saw it, I could have sworn the perspective shifted in the opposite direction to what it should, but in reality, my eyes are so used to seeing the normal perspective changes that I genuinely couldn't figure out what was going on.

You are an amazing youtuber! I’ve watched your playstation graphics video and this video and you have an amazing ability at describing these retro graphics

I remember spending a lot of time with the level editor for Duke Nukem 3D, but I never published any maps. You had to plan and work around the limitations, which in a way had its charm. In a top view you would draw and divide shapes that would be your walls, doors, floor height levels, crates and so on. Then in a 3D view you could select areas and raise the floor and/or lower the ceiling. So you could never have a floor or a platform that you could be both under and above. To create a mirror you needed a secret room behind the mirror that was at least as large as the room the player would be in infront of the mirror. And you would just set a special texture on walls and ceilings to show the skybox so it looked like you were outside, but you are always in a "closed box".

Only 2k subs??? Underrared channel

This is a really good explanation of what my issue is with some doom source ports aswell Thanks!

As somebody said: Quake is like Chingischan, every fps game has a little bit of Quake in its blood.

Quake wasn't the first 3D game, though. I remember playing X-Wing on DOS, which used true 3D graphics. Looking it up, it seems X-Wing was released in 1993, as opposed to Quake's 1996. I'm sure there were other older 3D games as well, though obviously the graphics would have been more primitive. This suggests to me that we knew how to do it before computers were powerful enough to handle something like Quake. Games less intense graphically than Quake could get away with using 3D graphics on less powerful hardware, though it wouldn't look as visually impressive. This also explains some of the weirdness in looking up and down in Dark Forces, which was a Doom clone.

Instead of tilting the camera they're using a tilt-shift lens

so Duke Nukem 3D POV camera moves like an elevator when looking up and down while Quake and shooters after it moves the POV camera on angles

shoutouts for perfectly describing what 1, 2 and 3 point perspective means

you could have compared Duke Nukem with the software renderer vs one of the opengl renderers available in 25th anniversary edition or world tour edition, side-by-side. Instead of two different games.

put in simpler terms, duke nukem is rendered as a long vertical screen, like on a phone. looking up and down scrolls that vertical screen up and down, making it fit in a rectangle monitor.

0:26 I could watch a full video on how room over room worked in vanilla Duke Nukem 3D and how the level designers used those tricks to create an immersive world.

Just stumbled upon your channel. Great content! I love these types of explainers. Subscribed!

Amazing work!

Honestly, I don't remember issues with Duke Nukem 3D's way to do it (it was kinda weird, but generally felt okay, as if you're really just inspecting a flat photo or picture, or a page of text, so my brain accepted it fine, but Quake's way to di it, when teh camera rotates in one spot, creating something like the "fish eye effect", distorting walls and objects almost makes me dizzy. My brain just refuses to percieve this as "normal", because in real life when you look at things, you only clearly see that small area of the whole picture, much like in Duke Nukem 3D, and the rest of the picture is not so clear, so you don't see any distortions (also because they don't happen in solid objects), but when you "bow down" in Quake and the top end of the walls and boxes starts getting closer, as if they are falling at you, this makes me feel that something is not right, like if I'm very drunk and hallucinating.

The weird sense of things visibly warping into that surreal "correct-ish" perspective shape is from shifting the aspect of the overdrawn pixels to fake the perspective via shearing (iirc calculated against the horizon in the case of Build). You can get this same effect emulated in EDuke32's 3D renderer (Polymost) by setting the console variable `r_yshearing` to 1. Set back to 0 disable. It works with modern Build games like Ion Fury as well.

Well done, I'll always watch a duke3d vid.

"Might not be obvious" DUUUUUDE the camera just pans. WTF?! How can one NOT notice, that the camera doesn't rotate?

Nicely explained! Thank you, for well made video.

You can see the warping of the edges of your vision if you make a C with left hand (or a backward C with your right) and move it close to your face at the very edge of your peripheral vision while staring at a fixed point. It's really weird!

The doom engine did have looking up and down but only in Heretic and Hexen which both use the Doom Engine just modified by Raven Software. However the rendering of the modified Doom engine at the time in 1994 and 1995 had the same rendering as the Build Engine just without slopes and overlapping sectors. Hexen did have wavy effects in both Dark Crucible and Darkmare but still didn’t have slopes.

I remember playing the Demo of DN3D more or less when it came out, and noticing that looking up and down looked *odd* but not really knowing why- it's so good to know why now!

0:08 The technique in question is called raycasting.

Unintentional asmr, subscribed.

Everyone forgets about Ultima Underworld that came out just before Wolfenstein

8:56 It seems to be sliding by layers (near objects slide faster than far objects slide slower), not just scrolling of static view.

wow, probably this is why i have motion sickness from doom and duke3d engines, i almost die playing blood. but new fps i play just fine

A game with proper perspective projection that works acceptably even on an 486SX is Descent.

Very well explained, thanks man!

I used to make maps in Duke Nukem, and I'm sure you couldn't do floors above floors. Not properly, anyway. In the example in the video, I think the platform was achieved by placing sprites I'm the right orientation with collision on. I hope I'm right, because I had to make lots of compromises in my maps.

Informative video, really good editing work.

The look up and down is more like tippy toe and crouching.

When you look up/down on Duke Nuken it appears as if the game just offsets the image up/down, i.e., just slides it vertically.

I like those old engines because of how "direct" they are. What you see is what you get. You can see a wall somewhere, and indeed there is a wall with exactly the same shape. And all the monsters automatically inhabitate almost any world you can draw for them. In modern games with modern graphics the correspondence between visible and playable is lost. I can see houses and borders around them, these are all visually complex structures, but the real borders are still simple, it is just the player cannot see directly the "true" simplified level geometry. This can be exploited. Some indie game can run real Build engine for game logic and use another engine to render decorated level. Indie games are known to suffer from bad fight mechanic. Really bad. There are lots of custom maps for DN3D, and they are played better than many starter's indie games. Indie game developer can use Build to obtain passable enemies and fight mechanic

Ooh Marathon, I loved that on my Macintosh Performa. It had 2-3 titles if i remember correctly.

I like how you explain everything making it clear that they used tricks and stuff but still doing it with respect, like "yes, it wasn't true 3D but it was still ground breaking for its time"

Why didn't they just tilt the rendered image plane like a wall and render it tilted like the walls in the left right direction when you look up and down?

When we released the Duke Nukem World Tour, we made it true 3d.

Having played through Dark Forces with a free mouse aim mod but not an engine port, you do get used to the weird Z perspectives, but in turn real life will feel weird when you're done gaming.

Duke 3D was a mix between polygon 3D Graphics and Bitmap Sprites. Sprites were 2D and used to for the monsters, items, weaponry and ammo. They could of allowed a true look up/down like Quake but things would of looked laughable flat.

I feel like the 2 point perspective is more accurate to real life, looking up and down irl doesnt make objects seem closer

"2.5 D technology" dude just making things up

This is so fascinating. These games were before my time, and I always just kind of assumed by watching them (mostly Doom) that it was a true 3D environment and they saved on processing power by just making everything out of sprites instead of 3D models. I guess I didn't totally understand that true 3D just wasn't feasible in those times. Even though I've never played these games I find myself so fascinated by their inner workings.

looking up-down looks more like move camera by 1 axis up/down, not like rotation over axis

1:54 "Dook Nuookum. "

Don’t forget about Maze wars, the Actual 1st FPS 1974

Thanks, John Carmack.

How i see it is that its very nostalgic