Is Doom 64 true 3D? (In terms of 3D structures)

[Guest Unregistered account]

So, this is a question that I've been wondering about for some time.

From what I understand, Doom 64 is a fork of the Doom engine which takes advantage of the hardware to create visually 3D structures, such horizontal beams and roofs you can see over.


(Sorry, these were the best I could find)


However, none of these apparently 3D structures ever appear in a way that allows the player to interact with them (I.E. walk above and below them).
Whenever stacked sectors appear, the Automap seems to show that it's just instant-moving floors and ceilings - which is what made me curious as to the true answer.

So... how did they do it? Is it some new floor-drawing algorithm that allows them to create flats in mid-air without the floor-fill style code turning it into a HOM? Or what?

[Chewyninja69]

Great question/analysis, unfortunately I know very little on the engine side of things. Sad face.

[LogicDeLuxe]

AFaik, this is only in rendering, but you usually can't actually walk on those beams.
And of course, if you can walk over and under a structure, it is instant moving sectors indeed, which keeps it from being multiplayer compatible.

[Maes]

Internally, the engine is still almost 100% pure vanilla Doom, so in terms of player mobility/interaction, there's virtually no change. The renderer might be "true 3D" in the sense that e.g. glBoom+ or any D3D/hardware accelerated port is "true 3D".

[scifista42]

Kapanyo said:

Is it some new floor-drawing algorithm that allows them to create flats in mid-air without the floor-fill style code turning it into a HOM?

Doom 64 has a hardware renderer, completely different from Doom's software one. Collision detection isn't much different from Doom's one, though.

[SaladBadger]

The 3d structures are actually given their look by the sky hack, but unlike vanilla doom, the sky hack in doom 64 causes nothing to be drawn, instead of a column of sky that is drawn in front of things. This means you can see things through that, but the 3d structures don't have a floor.

In the cases of the bridges you can go under or over, a macro is used to quickly reconfigure the bridge to what it needs to be. You can see this if you use noclip in doom 64 ex

[Voros]

They're fake. The very first example can be seen in the starting map, in the starting room, via that 4 circular lamp thing on the ceiling.

Kaiser explained it well in the Doom 64 Tech Bible: http://sourceforge.mirrorservice.org/d/do/doom64ex/docs/doom64_techbible.pdf

[Guest Unregistered account]

Thanks for your replies, everyone! It makes more sense now.

LogicDeLuxe said:

AFaik, this is only in rendering, but you usually can't actually walk on those beams.
And of course, if you can walk over and under a structure, it is instant moving sectors indeed, which keeps it from being multiplayer compatible.

I noted this in the OP.

[VGamingJunkie]

scifista42 said:

Doom 64 has a hardware renderer, completely different from Doom's software one. Collision detection isn't much different from Doom's one, though.

Sounds like 3D models imported into GZDoom, you can make very complex looking 3D models but you won't be able to interact with them in any kind of meaningful way due to lack of collision data.

[Koko Ricky]

Doom 64's engine just uses a modification of the original, so you're still dealing with a single two dimensional slice of X/Y coordinates that has height information via the Z axis. There are no fully enclosed 3D structures in Doom 64, not even Build-style slopes. It is being rendered in 3D, but the actual underlying geometry is only psuedo-3D.

[thereaverofdarkness]

There's no such thing as true 3D in a game, but most people agree that Quake makes a good reference point for comparison. 3D games almost always use the same basic perspective lines that Quake used, and this is also used by CGI to create 3D images. But many games before Quake experimented with a variety of styles which had their advantages and disadvantages.

Doom 64 appears to use the Dark Forces trick: it has the perspective lines pioneered by Doom, but allows sectors to be on top of other sectors in order to make platforms possible. In both Doom 64 and Dark Forces, these platform objects are uncommon, probably because they are CPU-intensive and may require extra bug-testing on each one just because it's easy to make a mistake and allow a situation in which the computer can't tell which sector the player is supposed to be in.

Someone above said that Doom 64 never allows you to stand on these platforms. Dark Forces did allow these areas to be traversed both above and below, but they usually did it with lifts or spiral staircases which probably allowed them to control the entrance points to either sector and keep them separated. Doom 64's platform sectors seem more open, perhaps that is why they are kept out of reach.

[Blastfrog]

You have it all wrong. The "3D" structures in Doom 64 are just lowered ceilings with the upper wall rendering cut off early / raised floors with the lower wall cut off early.

Dark Forces actually used something called portal rendering, which let different 2.5D layers connect horizontally (as in wall-to-wall, not floor-to-ceiling). The hovering bridges are actually 3D models.

[VGamingJunkie]

So a hybrid.

[Doomkid]

I should make another video like that one from a few weeks ago that addresses various console ports and source ports and such.. I first properly played Doom64 3-4 years ago and loved this clever trickery.

[VGamingJunkie]

It's a shame they couldn't simply have built it up as a portal engine in the same vein as Build, that would have allowed rooms over rooms without having to instantly raise floors, thus multiplayer compatibility wouldn't have been broken. Unless I'm mistaken, Duke 64 actually used a more polygonal 3D engine, just with traditional sprites for the actors.

[Koko Ricky]

Yeah, I think Build-esque features or even a polygonal + sprites engine (ala the Slavedriver engine) would have been really great, and with the N64's hardware it could have easily maintained a solid framerate. Interestingly, I remember years ago calculating how much detail would have been possible with 3D enemies and my rough estimate was pretty miserable: with Quake levels of polycounts there could be about 3-6 enemies on screen at once without much slowdown. Miserable. It's no wonder they went with sprites.

[VGamingJunkie]

Would voxel swapping have been feasible? I remember there was an attempt at a more 3D Doom homebrew for the DS and his proposed solution was polygonal models that swap with voxels at a distance to preserve the frame-rate. Not sure if the same could have been done for the N64, or if it could have even been done for the DS since the project seemed to have been canceled.

Probably better they used sprites, anyway, since they age better than models for the most part, and they were able to noticeably improve the sprite quality over the original on both Doom 64 and Duke 64.