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printz

Vanilla Doom trick to obtain Boom-like deep water

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I got this report on Perdition Gate not looking correct in Eternity but managing to do so in PrBoom+ or Crispy Doom. Looking in the editor I saw that it uses a strange network of overlapped linedefs to achieve something in vanilla Doom that can be officially done in Boom (transfer-heights deep water).

 

Normally so far we would get vanilla Doom deep water having just the "depth" effect, not also the ability to dive underwater.

 

Here are editor screenshots showing the overlapping linedefs, as well as screenshots showing the sectors referenced by them.

 

Sector #72 (the one referenced by the short linedef) is the illusionary one, with heights -600 -600 both for floor and ceiling, both with FWATER3. It's only referenced by outer linedefs.

 

Sector #74 seems to be the real one, fully closed and spanning what you see in the editor as the FWATER3 flats.

 

To make matters even more interesting, the inner linedefs (those residing inside the water sector) point to sector #74 on both sides, but they're not connected to the large linedef pointing to #74 from the outer wall.

 

I wonder how much can this effect be redone in other vanilla-compatible mods. It's too bad that Eternity can't render that. I wonder if it's caused by Cardboard. It really looks like something difficult to fix. I wish I knew how to fix it.

Captură de ecran din 2018.02.25 la 12.58.06.png

Captură de ecran din 2018.02.25 la 12.58.09.png

Captură de ecran din 2018.02.25 la 13.01.38.png

Captură de ecran din 2018.02.25 la 13.01.40.png

Edited by printz : Added mention about the inner lines.

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3 hours ago, printz said:

I wonder if it's caused by Cardboard.

Yeah. It's one of Graf's favorite things, a weird exploit of vanilla glitches; if you change how the renderer works it stops working. You'd have to write heuristics to detect the exploit and then explicitly simulate it by rerouting it through the transfer height effect.

 

Likewise, don't expect this level to work in any OpenGL renderer.

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4 hours ago, alowe said:

Need in game video to understand it better

You can look in the page I linked to.

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36 minutes ago, printz said:

You can look in the page I linked to.

Looking at the images in that link I'm not seeing anything unusual. Just a water texture applied to a floor. If there's a hidden pit this is nothing unusual either. I as hoping you had discovered an effect not seen before and just wanted to understand what it is.

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4 hours ago, Linguica said:

Hmm, the 2 floors wad doesn't have a room above a room (well not directly above). It also has a problem in that it sometimes blocked me from entering the middle section.

 

The underground effect is a cool effect and I guessed straight away how it was done before checking it in the editor. Despite knowing this and despite having probably done this a few times and thinking it was a glitch, I've never used this effect. Very nice atmospheric effect - I like.

 

The cross example I've done several times but this one is done better. My versions have telltale signs if you look close enough that destroy the illusion but this example is more robust. Not sure I'll ever use it though since all the places I could have used it I've done in other ways, but it's technically better than what I've done.

 

The underwater one is a bit weird. Normally when selecting a sector (in the editor) it highlights the sector the mouse is over. But in this wad example different sectors are selected while the mouse is moving within the same sector (and I don't mean the joined control sectors). This is also something I've accidentally done before and considered a glitch and found it was caused when some lines that make a sector refer to indexes other than that sector. This is the example I'm probably going to learn the most from.

 

Nice examples and thanks for the link.

 

Edit:

I should have read the textfile first and now understand that the 2 floors example was a stage in development that the cross example perfected.

 

Edit: Edit:

Oh, and I checked it with ZDoom and DB2 (incase people wondered WTF I was talking about with editor behaviour).

Edited by alowe

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ZDoom doesn't always render vanilla tricks correctly, so don't use it to check out these example levels. For popular vanilla levels ZDoom resorted to use hardcoded corrections or conversions.

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On 2/25/2018 at 5:41 AM, alowe said:

Need in game video to understand it better

 

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Wow, neat video! Pretty awesome, especially for vanilla!

 

I can't find a Perdition's Gate with a MAP31, or pg-raw.wad - can anyone please provide a link?

 

It should be possible to set up some debug stuff in a working port, and Eternity, that dumps out render info for a single frame, to figure out what the differences are.

 

But, even if you figure out the render differences, and you also devise a way to switch the render to "Vanilla Mode", it may be difficult for the computer to detect that it's time to switch modes. The computer would have to be able to detect, with 100% accuracy "Hey, this is one of those "bad" geometry setups where I need to switch to Vanilla mode.", and then "Ok, now I can switch back.".

 

Because you're dealing with "bad" geometry, who's to say what the correct way to render it is? I guess one could say "when in doubt, use Vanilla's method." But, when you have a completely new renderer that gracefully renders things like portals, and perfect polyobjects, it may not be so easy to go back and do things the Vanilla way. Goodness, what an ordeal.

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7 minutes ago, kb1 said:

I can't find a Perdition's Gate with a MAP31, or pg-raw.wad - can anyone please provide a link?

You can find it on Tom Mustaine's site IIRC.

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6 hours ago, Gez said:

You can find it on Tom Mustaine's site IIRC.

Yes, the website, and the ZIP file, thank you. Wow, there's lot of DOS stuff in the ZIP. The Good Ol' Days, I guess :)

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This one's really an interesting effect. But can someone explain how GZDoom's hardware renderer manages to glitch less than its software renderer? That seems a bit odd to me. In ZDoom 2.8.1 is looks as intended.

 

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10 hours ago, Jerry.C said:

This one's really an interesting effect. But can someone explain how GZDoom's hardware renderer manages to glitch less than its software renderer? That seems a bit odd to me. In ZDoom 2.8.1 is looks as intended.

 

The problem with all ports is they let you tip the view up and down. This destroys the illusion. In vanilla, because you're fixed to look straight ahead, it works as originally intended.

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