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Creaphis

The Two Types of Glides

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Paska said:

(It's possible to have the angle 0.01 right even while recording, but requires using fist/chainsaw to monsters)

ahhh... so that's what was happening to me on pl2 map33. i kept getting the reversed slide and i couldn't figure out the why.

by the way i'm still rather surprised at your approach to the famous map21 glide. i mean vince's strafe-glide works nearly 100% if you don't overshoot the correct angle while turning right... and you can always teleport back and "restart", i would consider it faster/more reliable than a standard glide.

by the way.. how does the doom science explain the strafe glide and it's ridiculous prerequisites? :)

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dew said:

by the way i'm still rather surprised at your approach to the famous map21 glide. i mean vince's strafe-glide works nearly 100% if you don't overshoot the correct angle while turning right... and you can always teleport back and "restart", i would consider it faster/more reliable than a standard glide.


I don't know what you exactly mean with the vince's glide, but if it means this:
1. Teleport
2. Turn right for correct angle
3. Strafe50 through the bars
It never worked for me, so I had to find another way and I found two ways which the one I used was more reliable (thanks xepop :p).

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dew said:

by the way.. how does the doom science explain the strafe glide and it's ridiculous prerequisites? :)

My (possibly simplistic) understanding is:
The position in the tic before the glide needs to be close to the barriers.
The potential position in the next tic (if the movement is allowed) needs to be the other side of the barrier.

So you need to have started your movement from the right place, and need to be moving fast enough and in the right direction. For this type of glide, getting in position is the trickiest part, but the teleport in the lv21 case makes this easier.

Or were you asking something deeper and have I just stated the blindingly obvious?

Paska said:

It never worked for me, so I had to find another way and I found two ways which the one I used was more reliable (thanks xepop :p).

I've just done it three times out of three using exactly the method you describe (with zero vertical sensitivity), so perhaps you haven't been getting the angle right, or perhaps you're getting out of position. The angle is two "units" away anti-clockwise from facing north. If you have non-zero vertical sensitivity (as I presume you have), then this provides an easy way to get out of position. Of course, setting vertical sensitivity to zero is hopeless for other types of glides...

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Well, the hardest part of it is to actually press the three strafe50 buttons down at the same time. The way we do it in movies is slower, but works always. If I failed the first try with the normal style, I would have to wait all the fireballs etc anyway before I can try it second time.

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Grazza said:

I've just done it three times out of three using exactly the method you describe (with zero vertical sensitivity), so perhaps you haven't been getting the angle right, or perhaps you're getting out of position. The angle is two "units" away anti-clockwise from facing north. If you have non-zero vertical sensitivity (as I presume you have), then this provides an easy way to get out of position. Of course, setting vertical sensitivity to zero is hopeless for other types of glides...


I have zero vertical sensitivity but guess I used wrong angle because it worked :)

Paska said:

I found out that sometimes when you run to the wall you can run like "there was no wall". Atleast the weapon bobs like there was no wall. After this state has been achieved, guided glide never fails.


Here's 2 demos showing this. First demo shows guided glide working always and second is just nirvana glide done with this.

walless.zip

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Grazza said:

Of course, setting vertical sensitivity to zero is hopeless for other types of glides...

Ah, I've just understood something that had been puzzling me (specifically: why some guys have been turning sideways to do glides). Of course, you can do all these low-speed glides with zero vertical sensitivity, by using mouse-induced strafing.

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Something that I've suspected (and have been too lazy to confirm) is that the reason guided glides are still difficult is that it's actually harder than you'd think to get right next to a wall. While studying my west-to-east guideless glide demos, I noticed that as my y-coordinate slightly increased as I slowly approached the center of the gap from the south, my x-coordinate was such that there was always a tiny gap between me and the bars I was pushing directly into. I believe this can also be explained by what I know about Doom's movement code. When a player is moving directly into a wall that he's very close to, there comes a point where even the smallest possible forward movement is large enough to put the player inside the wall, meaning that the Doom engine will reject that movement and simply "slide" the player instead, in a direction parallel to the wall itself, so that the player remains just as far from the wall as when he started.

This is why we must rely on "drift" (the tiny amount of sideways movement when moving in a direction that is nearly orthogonal) to get ourselves into position, even when performing guided glides. The standard procedure for these glides is to move against the guiding wall, face the gap (or face 90 degrees away from the gap if strafing in) and make small movements into the gap until the glide succeeds. What's going on "behind the scenes" is that, first, the player gets close to the guide wall by moving into it, but doesn't quite manage to touch it. Then, as the player makes slow forward movements against the wall with the gap, Doom takes the sideways component of each of these movement vectors and tries to slide the player. Every individual sideways vector will be either be larger than, smaller than or equal to the distance between the player and the wall. When the vector is larger than the distance to the wall, Doom rejects the resulting player position as illegal and thus the player doesn't move. When the vector is smaller, the player will slide that much closer to the guide wall. When the vector and the distance are the same size, the player finally ends up exactly next to the guide wall, and thus can move freely into the gap.

Because it's possible to move only a single "micro-unit" (see my previous post on guideless glides) with sideways movement vectors, it should be impossible for a guided glide to "fail." Success is just a matter of feeding the Doom engine tiny forward movements until the sideways components of these movements slide the player all the way to the guide wall. Then again, there might not be a reliable way to move only a single micro-unit to the right while recording in vanilla Doom, as the player can't face 0.01 degrees to the right of a map axis unless his angle has been altered by punching/chainsawing. This would imply that guided glides where the guide wall is on the right side of the gap are more difficult. If this is actually the case, then an alternate method to handle these glides would be to make small backward movements, away from the gap, until the sideways components of these movement vectors move the player all the way to the guide wall. Then, the player should be able to slide cleanly through the gap, as long as he doesn't break contact with the guide wall. The important thing is that the player reaches the wall; this doesn't have to happen right at the gap's entrance, but can happen anywhere along the length of the guide. Once the player is touching the guide, he can slide through the gap smoothly, as many times as he pleases.

This explains why Paska is able to glide repeatedly and easily in his first "walless" demo. However, there's something else going on in these demos that I can't account for; I have no idea where the momentum wobble is coming from. Simple walls like these are not usually wobble-friendly surfaces. Maybe once you're directly touching a wall it's possible to build up momentum against it, but even that only explains the wobble in the first demo. Anyways, I'd like to just clarify one more thing: the glide in Paska's "walless2" demo isn't a guided gap glide - it's a wobble glide, which works for the same reason that the "Nirvana glide" is possible in the first place. As far as the engine is concerned, the player is running from one legal position inside of the yellow key doors to another legal position outside of them. The player has enough momentum when just inside the doors for his next position to be completely outside of the doors one tic later. The only difference between this wobble glide in this demo and the usual Nirvana glide is that in the normal case, the player's momentum comes from a run-up, while in this case, the player is able to build up momentum by running directly against the yellow doors for some weird reason.

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Creaphis said:

This would imply that guided glides where the guide wall is on the right side of the gap are more difficult. If this is actually the case, then an alternate method to handle these glides would be to make small backward movements, away from the gap, until the sideways components of these movement vectors move the player all the way to the guide wall. Then, the player should be able to slide cleanly through the gap, as long as he doesn't break contact with the guide wall.


Thanks Creaphis, this works too easy :) I just had to try that MM2 map14 glide and it's perfect, just check the demo.

mm2glide.zip

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Question for glide experts.
In my UV-Max demo for TRIEX.WAD I've skipped secret in the sector 238 because I couldn't reach it. I still want to know is it possible with 'guideless glide' or maybe something else?

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haha... yes, that sector should be accessible with a guideless glide, however i see no appeal in even trying it. :) that has to be one of the dumbest secrets in the doom industry!

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most probably not, jonathan rimmer's lv16-023 dates to 7. 9. 1999

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Another geometry for the void glide? Maybe, but confirmation from other maps will be needed to make sure this isn't some map-specific glitch.

The new setting is a 45 degree angle between a west-east line and a southwest-northeast line. If I angle myself so that I am facing east-by-northeast (i.e. towards the vertex when lodged in it), and then move away (strafing right) and then use normal forward motion, I make the void glide fairly often.

Void Glide (no exit) on The Final Assault Map01

tfa_void.zip

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Another geometry for the void glide? Maybe, but confirmation from other maps will be needed to make sure this isn't some map-specific glitch.


Hi, I found something that I thought was important but... it turned out not to be a factor. I thought the y-coordinate of the east-west line might matter because of how blockmap boundaries are handled, but when I moved the line it made no difference.

Rebuilding the nodes made no difference either. It looks like this will work in any map it appears in.

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i made a quick test and it seems that any angle between 45 and 90 degrees will work as long as the "bottom" wall is rotated by exactly 45 degrees to the axes. the node does not need to lie on the 32-unit grid, grazza's example scenario makes the void glide easy with any offset. i couldn't lock myself into the, um, pre-glide jackhammer at angles over 90 and the walls don't let you near the node with angles under 45, i think.

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sorry for doubleposting, here's proof of concept. the node is not on the 32-unit grid, the angle is slightly over 45 degrees. i aim at the node, move forward to slide in and strafe right to slide back to retry.

i chose this particular demo because it is actually an oddity. i didn't move during the glide itself. after i got locked in the jackhammer, i let go of the controls, but i wasn't losing any momentum and got pushed through. to top it off, during testing (sadly not recording) i had a similar scenario, but i pressed backwards during the jackhammer and a massive elastic collision threw me FAR across the room.

voidtest.zip

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Wow. Maybe new category for void demos wasn't such a bad idea, I guess.

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Jeez.

Yeah, if the DoomedSDA put the words "void glide" in a small font underneath all demos with void glides, I'd be happy with that, so that it'd still be obvious what the fastest non-void-glide demo is. The truth is that I'd rather not feel obligated to search every level for possible void glides just to record a competitive speed demo, especially if the in-level route is fun/interesting/whatever.

If we're talking about Compet-n categories however (and we obviously are), the point was raised last time that there's a long history of troublesome tricks being discovered that gradually get accepted into the fold. This might still not affect too many maps in the IWADs and official PWADs, and for the maps it does affect it could be seen as a blessing - a second wind for speedrunners - that could let us push a few records down even farther, in the year 2011.

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The number of maps this is liable to impact, even if dew is spot on (which seems very plausible to me), remains extremely small, for reasons discussed earlier.

This new insight might increase the possibilities for breaking back into maps.

Creaphis said:

I'd rather not feel obligated to search every level for possible void glides just to record a competitive speed demo

Generally, a very quick glance at the automap is enough to see that it isn't relevant (first thing to look at is the exit). Checking for things like 32-unit glides is a much more time-consuming task, and AV jumps require a far more detailed investigation. So in terms of time spent planning a Speed route, checking for void glides should on average be less than 1%.

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I found it strange that if I replaced the 'top' wall with things like lanterns and tried to go to the void I eventually got stuck. I couldn't move in any direction, but I had momentum because my weapon was bobbing (and if I used noclip, then I left like a rocket).

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Grazza said:

The number of maps this is liable to impact, even if dew is spot on (which seems very plausible to me), remains extremely small, for reasons discussed earlier.

yes. i actually spent more time looking for abusable maps than experimenting with the trick and the result is: the vast majority of mappers was prescient. they didn't use the 45° rotated bottom wall at all and if they used it, they didn't design a sharp angle at the top side. i've checked all the iwad maps and i think there's no way to abuse this new knowledge. if you find just one map, i will congratulate you on correcting me. :)

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Ok, I've managed to watch Doomguy's momentum values when the glide is performed. When one gets stuck in the wall (Dew calls it the Jackhammer), one's momentum values alternate each tick between ~27 and ~32 in the east and north directions. 32 is enough acceleration to skip right over the top line, if the new position is valid. The valid position check comes first, so the code to look for blocking lines is skipped. Well, that's the theory.

I can't figure out why the momentum maxes out, but anywhere the jackhammer is achievable, it should be possible to skip a blocking line.

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dew said:

yes. i actually spent more time looking for abusable maps than experimenting with the trick and the result is: the vast majority of mappers was prescient. they didn't use the 45° rotated bottom wall at all and if they used it, they didn't design a sharp angle at the top side. i've checked all the iwad maps and i think there's no way to abuse this new knowledge. if you find just one map, i will congratulate you on correcting me. :)

Well it's not just that very few maps have the necessary geometry to reach the void. The main things are:
1) In most cases the exit cannot be used from the void.
2) There is no viable route via the void from the point where you enter it to get anywhere near the exit.

Believe me, if I found any maps where it was feasible to exit by going via the void, I would post a demo, whether or not it was faster than the regular route. I've checked many of the well-known wads, and found nothing apart from TVR map29. Though that was before this new insight, so I was just looking for the 90 degree case.

[Much later edit: found one!]

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How could one return from the void? I don't think getting stuck in the wall is possible on the back of a one-sided line (although I haven't tested this). I think one would need two-sided lines on the border of the map to slide along.

Hmm, I wonder if it would be possible to add sidedefs to lines in pwads with the correct geometry without desynching old demos. I'll check on this today sometime, whether at least in theory, places to re-enter the map can be engineered in existing pwads with old demos.

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Re-entering the map requires the same geometry as you need to break out of it (as seen from outside). This has been demonstrated by kimo_xvirus earlier in this thread (bottom of page 2).

I haven't so far found any maps where this idea can be employed.

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Thanks, Grazza. I'm interested in learning more about these glides, and I'll post here if I learn anything useful.

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I've recently found this awesome thread again and spent some time studying it. Looper's demos that show how guided glides never fail when you enter a "walless" wobbling state caught my attention, so i've run some tests yesterday, and hopefully they will be useful for someone sometime.
What i've found so far:
1) If you get perfectly close (i.e. 0.000000 distance away) to a 1-sided west-east wall, standing north of it, you'll be able to start wobbling against it and gain momentum. Same thing works against south-north walls from the eastern side. It doesn't work from other sides - the wobble never starts.

2) The wobble is similar to thing-wobbling / corner-wobbling (like xepop does in his built run often. See lift on map03 or keyed doors on map06 in 20uv-813.lmp). The difference is that your momentum is capped by 15.00 (i.e. 1/2 max speed) and gets immediately reset to zero once it tries to go over this cap.

3) It is possible to maintain a wallrun and push into a wall at the same time, thus gaining an orthogonal momentum slowly and doubling your running speed as usual.

4) It is possible to achieve this state at any point of the wall, the only requirement is a perfect coordinate. In unassisted gameplay this can be achieved by doing a glide between the wall and some object that's 32 unit away from it (like Looper did in one of his demos in this thread). In TAS it's possible to just use bruteforce. Some maps also place player1's start near a wall, such as map03 of Doom2, so that you can start wobbling immediately.

The use is probably very limited.

First obvious use is to jump over gaps in places where there's not enough room to build up your speed otherwise (and no rocketlauncher). This is demonstrated in walless_test002.wad: first demo is a quick built run, and in the second demo i play around a bit by showing a stuttering effect, and then successfully jumping over the gap (note that even a non-built demo is technically a TAS, since i used auto-sr50).

Second use is more complicated and could not be beneficial at all. The idea is to wallrun and build some orthogonal momentum to cut the corner quicker and continue a wallrun in the next room. It would be great if someone researched this better, because i suck at building :) This could shave off a precious tic (or a few) in places where it's usually faster to cut the corner by running at an angle instead of wallrunning. Rough demonstration can be found in walless_test001.wad, but note that i didn't try hard to optimize everything and was just showing a concept. I also suggest watching the demo in xdre.

Also you can use it to build up speed while waiting for a lift to raise up. It could be beneficial for future trajectory to avoid wobbling against a corner, and just wobble against some other spot of the wall.

Any suggestions concerning applications of this wallwobbling thing? Originally i wanted to build a singleplayer 13sec demo in map03 using this trick, but apparently it's not possible with this momentum-cap. I didn't test though, so i could be wrong.

walless_tests.zip

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Interesting. So, we have yet another effect that only works parallel to certain map axes. I can't keep all this stuff straight in my head anymore.

Are thing- and corner-wobbles also limited to 15 max momentum in the south and west directions?

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Creaphis said:

Are thing- and corner-wobbles also limited to 15 max momentum in the south and west directions?


No, but you can't do corner wobble to south nor west, I think.

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