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Linguica

Did you know if you fall onto a floor at -32768 units it turns into a portal

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Something similar happens when going in the x and y direction past 32767 (+ and -) units. It puts you at the other side of the map. But sometimes you get blocked (without noclip) by something I don't quite understand yet. Usually if the floor height on the other side is of equal height or lower it works (only tested it while I was in the void).

Edited by Dwaze

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I remember the first case happening when I was trying to make a rocket jump level as high as possible. Had to settle for a smaller sector height to avoid the issue.

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Interesting also is if you escape a portal using the movement keys, you will hit the floor and recover. But, if you allow your x/y momentum to carry you out of the portal, you'll become glued to the ceiling and unable to move, even with noclip.

 

EDIT: I made a mistake here, this is not due to momentum but is instead a consequence of Doom lacking a "terminal velocity" and eventually overflowing your Z momentum.

Edited by JadingTsunami : Fixing a mistake

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I don't get the second one, about the "equivalence principle" thing, or what's happening in the video. The third one confuses me too, how did he get in air if you can't aim a rocket down in vanilla?

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First one reminds me of a similar effect in SNES Doom using pro-action replay cheat code, but in this case you go through the ceiling and then appearing in the floor again and so on, if you deactivated the cheat code you could fall over the floor from ceiling.

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Wow, that's really interesting and nice found. As HorrorMovieGuy  mentioned i'm looking forward how creative people will turn this into awsome things.

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If anyone is curious what is going on with the portals, it's because -32768 is exactly the lowest value a floor can take in Doom. If you try to go lower than that, the value will wrap around to a big positive number.

 

So when Doom applies gravity to the player, -32768-"gravity" drops below -32768, which wraps around to a big positive number. Doom uses this big positive number as the player's height.

 

After "lowering" the player, Doom checks to see if you've hit the ceiling. Of course, now the player appears to be way above the ceiling, so the code snaps the player's height to match the ceiling. The cycle continues, creating the "portal" effect.

 

Curiously, you can have a safe, solid floor at -32768, if the adjacent floor that you descend from is exactly -32766. This is because Doom's initial gravity is -2, and the calculation -32766-2 = -32768 will not wrap around. Similarly, any drop that, when combined with Doom's gravity calculation results in exactly -32768 would be safe as well.

 

I suspect the latter could make a neat way for map-makers to use this effect. It won't work in engines like ZDoom, though.

 

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This is wonderful. The last one reminds me of a ZDaemon bug in deathmatch, if you set the "players cannot exit" DMflag but end up stuck in a "damaging floor exit", your health will simply drain down to 1% and you'll never actually die. It totally breaks certain DM maps, especially older ones where damaging floor exits weren't ultra uncommon.

 

I love little finds like this.

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I for one, cannot wait for the day that mappers will use this to simulate something like zero gravity or some wacky way to "jump" in a non-euclidian space. A pity something like this may not work in a modern source port.

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2 hours ago, TimeOfDeath666 said:

The portal thing also happens in masterjumps9y, the plasma-jumping map09, but instead you go through the ceiling and come up through the floor. The ceiling is at 32767 and floor is at 520.

Actually, it happens in all the sectors with that ceil height in the map. The other massive sector has floor at 0, but you also wrap around on the target platforms, one of which is mere 2000 units tall. With the immense plasmajump z-axis momentum you're almost guaranteed to have when hitting the ceil... you can loop around several times before regaining control, heh.

 

However I don't think this is the exact same glitch. I have tried to recreate the ceiling glitch in vanilla in the past, but it didn't work. I made the tallest sector possible (1 unit more and the entire sector overflows & becomes impassable), built stairs to the ceiling, added an archvile for the final boost... and nope, nothing. Maybe vanilla needs a magic overflow value as well?

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dew - Ok cool, haven't played that map in a while :)

Managed to recreate the ceiling portal in pr+ with -cl2 using Grain of Salt's vanilla plasma jumping dehacked while also using the immortal sector trick: ceilportal.wad (just stay against the wall and shoot)

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Huh this seems like something that should've been fairly obvious, im surprised it hasn't been discovered until now especially considering Doom is one of the most modded games ever.

 

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I remember the opposite happening years ago in Zandronum (or maybe even Skulltag), where the ceiling was at 32767 and something was thrusting me upwards, and I went through the ceiling like it wasn't there.

 

Bigbox is a gigantic empty sandbox map for testing / playing around with mods. It is a single room that is as big as a map can get in all 3 dimensions.

 

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Huh, that's pretty neat. I'm always amazed when I learn new tidbits about Doom all these years later.

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