AVJ32 style "3d floors"?

This trick amazed me. Somehow I haven't noticed it until just recently. Two days ago I watched the new demo on this map and thought "oh wow, it's a very convincing 3d floor in vanilla! I want to put stuff like this in my maps!":


But I found it very difficult to replicate and I don't at all understand when it works and when it doesn't, what the limitations are, etc... If someone with better knowledge could write a simple explanation, preferably bundled with some WAD examples, I would be most grateful.

You can get avj.wad here... - http://www.doomworld.com/idgames/index.php?id=16322

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@andrewj: It's Arch-vile Jump MAP32.

@Memfis: I've taken a look, it's a very smart trick. It's made up of a combination of two tricks that I think you already know about, I'll deal with them one at a time.

First up, the ceiling of the overhang. You know how insta-lift monster traps work? Those traps where the monsters are in a really low pit and they get instantly raised up to reveal the monsters? Those traps prevent you from seeing the walls of the pits by leaving them untextured, what happens is that the nearby floor flat "bleeds" out onto where the walls of the pits would normally be rendered. What's happening here is that all of the walls in this area are untextured, and so the ceiling flat coming from the nearby tunnels is being drawn over the entire area. To demonstrate this, here's what happens if you remove the trick that renders the walls in this area (which I'll get to next).



Notice that the entire area above is drawn with the ceiling flat. This is because it is bleeding across all of the untextured walls. Also the area the monsters are standing on is totally invisible, but we'll get to that next.

OK, so now the walls. All of the walls in this area are midtextures on two-sided linedefs. Go try something out in DoomBuilder. Make a square room, then draw a linedef in the middle of the room and add a midtexture on it. Now align this midtexture so half of it is below the floor. Now load this up in a software renderer such as PrBoom+. What you'll see is that the entire texture is drawn, even the half that should be cut off by the floor. The reason for this is that because midtextures on two-sided linedefs can be partially transparent, they're drawn later than the rest of the level geometry when it comes to drawing the scene (for example, any monsters behind some bars need to be drawn before the bars are drawn so that the texture is drawn in front of them).

Now open this level in doombuilder and look at the sector the monsters are standing on here. Notice that they have a GSTONE midtexture, but this texture has an offset of -256 (so it is drawn below the floor height of the sector). These midtextures are drawn late during the rendering of this scene and they are carefully aligned so that they cover the bleeding flat in just the right places. Try changing these alignments and it should become clear.

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This is mindblowing. I must use it one day. Thank you both Memfis for coming up with that and Melon for the explanation which (to my own surprise) I understood. Excellent!

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It actually works okay in GZDoom too. (Well, as long as you're not looking up too much.)

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Thanks! Takes me forever to find the correct vertical offsets but at least I know how it is done now. Props to termrork for coming up with the idea.

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There's also two pairs of superimposed linedefs - 552 above 479 and 758 above 442, with 442 & 479 facing sector 74 and the other pair facing sector 90. I'm not sure if they've something to do with the false ceiling in sector 90, or sectors 102 & 104.

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It breaks when you get close to the fake ceiling (like most tricks of this type). With some care it could be very effective.

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SiD Map 01 and BTSX E1M22 (the last hub) have a variation of the same trick.

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It's a pretty awesome trick despite being so simple. I first saw it about two years ago in Roger Ritenour's Phobos, and I've been overusing it in my maps ever since - check CC4 Map14 and Interception Map28 for examples.

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I'm trying my best to understand this without actually downloading the wad (I'm using a public computer right now)

Are those monsters raised up there purely for show? I mean, it looks like you can't actually get up there. Can they attack the player from up there? Also are you able to walk under it? Do you bump into invisible walls or anything? Is the movement of the monsters up there impaired?

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40oz said:

Are those monsters raised up there purely for show? I mean, it looks like you can't actually get up there. Can they attack the player from up there? Also are you able to walk under it? Do you bump into invisible walls or anything? Is the movement of the monsters up there impaired?

No. Not without cheating. Yes. Yes, but not under the monsters for obvious reasons. None that I noticed. Yes, apart from the obvious walls there's impassable lines in front of the barons and revenants, plus monster blocking lines to separate them.

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