Props to him for coming up with the simplest way to explain this

Doesn't really explain it too well, BSP trees are what you use to decide what to render, then you run the actual rendering code that renders the walls that the BSP tree has decided are the ones that should be drawn.

Once someone had told me about not being able to have rooms above rooms in the doom engine I found the level design to be pretty amazing. There's lots of maps that have a lot of vertical sections when in reality it's flat, really nice design considering the limitations.

He sure does have an autistic acception of what 3D means.

PS : i just replayed some Duke 3D (build engine) and it has several parts where you moved over some other parts of the map so he was wrong when saying 2.5D engines cant make 1 part of a level under another.

You never actually do that in Duke3D, it's all smoke and mirrors. For example, in e1m2 when you drop down into the sewer, you actually fall into a hole and get teleported to another place in the map entirely. You can't fully look down the hole and see the bottom because of how broken looking up and down is in Build engine games - smoke and mirrors.

If you check the automap you can actually see the teleports happen, and how things you think are above or below your are actually off in some random corner of the map. If you noclip you can get to every room without going up or down.

And this guy isn't arguing the game is 2.5d, he's saying it's totally flat 2d. Clearly the game is being drawn in 3d though, and the gameplay does actually factor in height. His biggest argument is the enemy hitboxes having infinite height - from a shooting point of view the game could easily be top down. The problem for me is that isn't a limitation as much as a gameplay choice. They could probably have made you look up and down to shoot enemies at different elevations, but that would have sucked with keyboardlook. He totally neglected that angle, which is actually pretty important.

I'll always say Doom is a 3d game, it just doesn't have real 3d geometry.

Its exactly my thought. But i remember clearly some parts because i played it yesterday, where you are on platforms/decks where you are over other zones where you were just before. At the very begining of the http://legacy.3drealms.com/duke3d/walkthrough/e2m9.html Darkside map there is such platform behind the building where you progress, its not a big floor but its a floor nontheless, there is even on Lunar Reactor a moment where you are in a small air cooling tunel and there is a hole in the bottom of it if you blow it up, you can fall to the void if you go there without jetpack http://legacy.3drealms.com/duke3d/images/walk..._small.jpg

I was thinking about that video while playing and i thought what he said was not correct, there is other parts where there is even bridges that you go under and then over!

Well i think its enough discussion for a youtube vid :P

Oh yeah I know the bridge in the first example you gave. Those bridges aren't real level genometry I don't think. They might just be game entities, or it might be a weird hack in Build. I think I've heard of some tricks, at least for getting inside of spaces that are supported.

You are correct, the bridges are just entities. The Shadow Warrior version of the build engine was a little more sophisticated in its tricks (eg: same old water teleport trick but you set up cameras so you can see through them and make it look like level above level geometry) but also limited in the whole 'room above a room' aspect.

Though the engine allowed bizarre geometry like duke3d e2m10 and e3m10 to exist, which could never happen in a true 3D engine.

Source, at least for Portal, has seamless looking world portals that can simulate some pretty freaky geometry. I don't think you can say it can never happen in a true 3D engine, but it still just requires something weird and kind of dirty :p

Anyway did you say bizarre geometry? Because there's only one perfect example of that in Duke3D - e4m1

doom is 3d. this guy is a fuckin autist.

Doesn't have proper Z axis tho.

it doesn't change the fact that it's 3d

The map geometry somewhat is.

wasn't it a widely accepted fact that it's not 3D? it has no 3D objects, monsters are sprites ffs.

the world itself is kinda 3D.

In the files that came with the map maker for Wolfenstein 3D on how to use it, they had made it so there was data missing, like it had been stolen and not all the data had been found (it ended with something like "and to do....." as if the data was missing). It was possible to make rooms over each other, you just couldn't see both of the at the same time. I used this for a custom map that had the layout of my home when I played around with the map maker.