A Trick from the Land Beyond the Wobbles

Here's a simple demo but with an interesting trick:

Grenian (use gren_old.wad) by William Green, UV Speed in 0:25. [Note: doesn't work with the later version of this wad that is in the standard archives.]

I'll quote from the text-file:

This is a fairly simple demo, but illustrates what I think is a new, or at least little-documented, trick.

The trick occurs near the start of the demo, and enables me to get the blue key without getting stuck (the platform it is on is meant to lower, trapping the player, but I manage to avoid triggering it). Note that this is not a simple case of strafe-running over a linedef. I have not managed to do so at all with -nomonsters - it seems to be the interaction with the monsters that makes it possible.

I'll call this trick a "thing wobble". It may well be related to the well-known idea of "thing-running", whereby a wallrun-like effect is achieved in a west-to-east direction by running along a row of "things" (e.g. the barrels in Doom2 map23). However, there is more to it than that, and I think this trick has wider applications. (It may also be related to the form of grab seen in, e.g., Ultimate Doom E4M1.)

I believe the effect is as follows: when the player is running hard up against a "thing", the engine calculates his momentum as if he were actually running. Thus when the thing ceases to be in the way (e.g. it moves, or the player slides off it), the player's speed is as if he has had a run-up, rather than as if he had started off from stationary. Added to that, there is the possibility of a "thing-run" effect, if the direction is right.

Therefore in this demo, it is as if I have achieved a wallrunned S50 with a run-up - and this gives me enough speed to skip the linedef. (There is a similar set-up in this map with the red key - there I have been able, very occasionally, to get the same effect with -nomonsters using a actual wallrunned S50 with run-up, but my success rate is actually worse than for the blue key trick.)

I have included in the zip two other demos where similar effects are relevant. In C232P030 I make use of the thing wobble (though that jump can actually be made with just S50, I think), and MW11-036 is a weird demo that I still don't understand, but I manage to avoid triggering a linedef while wobbling up against a monster, so maybe it is related. (It could be more closely related to the E4M1 grab though - with quirks in the positioning system causing the engine to fail to see the player crossing the line.)

So, what are the possible applications of this trick? In addition to skipping linedefs, jumps off ledges could be done in this way. There is no scope for a run-up in that case, so a jump that would otherwise be impossible (or need rocket assistance) could be achieved using a thing wobble. The "thing" can take the form of a monster, a "thing"-based piece of decoration - or a coop partner.

I'd be interested to hear if this idea has been previously documented or consciously exploited, and if anyone can shed more light on the mechanics of it.

I haven't seen the demos yet, but from your description this may open up possibilities for a number of tricks throughout the IWADs and numerous major PWADs... I'm thinking especially along the lines of rocket jumps that are avoided because they cause too much damage, or single-map runs where a rocket jump is impossible (no RL) or unfeasible (RL too remote). And of course this would be easiest to implement in co/op I guess?

Anyway, congratulations on a potentially highly significant discovery!

Grazza said:

I'd be interested to hear if this idea has been previously documented or consciously exploited, and if anyone can shed more light on the mechanics of it.

I've known about this for a long time. At most it just makes jumps that were already possible with ST50 easier. One example was the ev07 jump across the lava.

EDIT: incidentally, this is also part of the mechanics behind the map19 candle glide. Once I was able to break the trick down and repeat it easily, I found it helped to move against the candles to gain speed, then push against the crack between the candles and the wall. When you repeat this enough, you'll squeeze through in no time.

I believe this trick helps with the lv13 keygrab, which is very difficult.

yeah, I think the torch has something to do with it too

interesting engine trick!

Interesting to hear that this effect is in the knowledge of specialists like Vile and Xit - and surprising that it hasn't therefore been more widely discussed (or exploited?). I'll certainly be on the lookout for more maps where it is relevant.

Here's another one. Not quite the same idea, but no doubt related.

Biowar map02 UV Pacifist/Speed in 0:09.

It involves a "wobble", but near a gap rather than a thing (a "jaws wobble"?). And I don't slide off it, but under it, since I die at that point. In the first gametic after death, from a standing start I travel 24 units. That's more than the maximum (23) that is possible from strafe-50 running under normal circumstances.

The momentum-preserving/accumulating effect of the wobble is essential for the trick to work, as the slide would be too long otherwise (barring some other weird effect kicking in).

The "jaws wobble" effect is fairly standard, as you tend to get it when you try a bars glide. But here I'm only interested in getting the wobble (the gap either side is only 24 units, so there's no glide possible), and I'm not even in the gap.

I think this is pretty weird. ;)

BTW, I suppose this trick could be done with just strafe-50 running and an absolutely perfectly timed hit from the sergeant. But that would just be sooo clichéd (not to mention difficult).

Rather recently as I was watching some COMPET-N demos I had been reminded of this thread. One place where this is used well is on Map23, to jump from one ledge to the other, crossing over the first room of the map.

The barrel run has been known for a long time, and is similar to a wall run. You're right that it can be initiated with a thing glide, rather than a standard run-up, and this was the case in Adam Hegyi's lv23-045 (current UV Speed record). He doesn't say in his text-file whether he deliberately did this.

AFAIK, the map23 jump can't be done with just a thing glide - you need the full row of barrels to get across (and the fact that they are in a west->east line is presumably also vital for it to work).

Ah, I wasn't paying attention to the fact that the Barrels below were still in place. But still, I'd dare say the wobble and thing-running may well be pretty much the same effect, except in the latter case the slight touch of many things in a row produces the speed gain, whereas in the first case the momentum is obtained by more friction against one thing.

In the gap-wallow scenario, how can you be sure the extra boost isn't an effect of the Demon's attack? They definitely push you a bit when they hurt you.

myk said:

But still, I'd dare say the wobble and thing-running may well be pretty much the same effect, except in the latter case the slight touch of many things in a row produces the speed gain, whereas in the first case the momentum is obtained by more friction against one thing.

I speculated in the initial post in this thread that the effects are related. However, they don't seem to be the same. The thing run effect only appears to be west->east. The momentum-conserving/accumulating effect of the wobble works in other directions too (it's north->south in the Biowar example).

myk said:

In the gap-wallow scenario, how can you be sure the extra boost isn't an effect of the Demon's attack? They definitely push you a bit when they hurt you.

In the text-file I wrote: "I get plenty of momentum from the combination of strafe-50, and shotgun blast and a few demon bites." So I am saying it has an effect. Indeed, you slide a bit towards the exit if the demon kills you while you are just standing there normally. I imagine there is some limit on exactly how much momentum can be accumulated in this way, and I would guess that the effect from monster hits dies off as it normally would.

To clarify: I do not believe there is any thing-run effect in the Biowar demo.

My understanding of what is going on is like this: The wobble helps you preserve any momentum you would be building up if you were actually running while this was going on (rather than having your movement blocked). So the strafe-50 and the monster hits give you momentum which is released when you are actualy able to move. I'm not sure if you would move off at 23 units per gametic (i.e. max unassisted strafe-50 speed) if you were dead though - I don't know in which gametic it starts regarding you as a corpse (and thus unable to run).

In the case of the combined wobble and thing glide, there is the momentum accumulation effect and the thing-run effect. If the drection were north->south, then I imagine you'd only get the momentum accumulation effect, and so move off at a slightly lower speed.

To clarify further: what I find most weird here is what I get the wobble against.

On reflection, I would tend to think that the two effects are completely separate, but they often occur at the same time in practice.

I couldn't say myself for a certain lack of experience doing thing-glides in various places, but would Adam be saying the thing-glide works only in a west to east direction, or simply that the boost was a different thing than a wall-glide, since it didn't occur in the usual direction?

My theory is that the momentum gain is due purely to friction against the Barrels (since the player slams onto them.)

Going back to the gap-wobble, yeah... I should have read your text file more carefully. So this is showing that the wobble is not exclusively in relation to things?

In your glide you stay clear of the walls? Wouldn't gliding against the walls slow you down?

I ask because perhaps it is "just" a momentum retention for strafe-50 plus the Demon's bite, where the Player is suddenly relieved of any obstructions (as opposed to some other weird quirk.)

Adam's post here contains more information: "essentially the same as a 2s wall west->east wallrun". From that it sounds like it could work for south->north too (this would be easy enough to test). It seems to be a one-way thing though - try it in map23 with nomonsters (at ground level to make it easier, and to remove the wobble effect), and you'll see that east->west doesn't work.

Yes, my new wobble clearly isn't against a "thing", since there are only walls and barriers in front of me. You often see a wobble of this type when a standard bars glide (through a 32-unit gap) is almost working, or when attempting an E4M1-type grab. That it has momentum-retaining properties doesn't come as a great surprise, but I don't recall it being demonstrated before. (I'd guess that if you examined some glides that weren't executed smoothly {e.g. map22 in 30nm1849}, you'd find the player emerged with a "surprising" amount of speed, but I don't recall this being commented on, or put to use for an additional trick.)

myk said:
I ask because perhaps it is "just" a momentum retention for strafe-50 plus the Demon's bite, where the Player is suddenly relieved of any obstructions (as opposed to some other weird quirk.)

I don't think momentum is retained unless you're wobbling. Try it: just run into the barrier and keep strafe-50ing until you're killed, and see how far you slide when you don't get a wobble (it's pretty clear if you're wobbling or not, though quite often you get just a slight wobble, with a correspondingly shorter death slide).

Yeah, I wasn't very clear there; I meant no unusual circumstances other than the wobble (which causes the friction) and nature of the actions involved (particular movement speed and the damage.)

The Barrel glide does seem to function from east to west, but for me it appeared easier (and perhaps more effective) from west to east. Isn't there a clear burst of speed on the last try before I quit.?

It also lets you to the other ledge from either side of the Barrels going east (trying from above.)

myk said:

The Barrel glide does seem to function from east to west, but for me it appeared easier (and perhaps more effective) from west to east. Isn't there a clear burst of speed on the last try before I quit?

I found some time to analyse this. In the last east->west traverse, the maximum distance you travel in a single gametic is 26 units. Assuming Dashiva was right about 23 being the maximum from unassisted strafe-50 (and I don't doubt that he was), then there appears to be some effect of some sort. However, based on this evidence it is much smaller than the west->east effect. On an earlier west->east traverse, you had some gametics where you travelled 37 units (there may be some with more - I didn't analyse the whole demo), while Adam Hegyi's lv23-045 features some with 40 units per gametic (can we abbreviate this to upgt?).

Anyway, the fact that there appears to be an east->west effect (even if slight) is interesting. I had thought on a few occasions that was so (e.g. in Nuts.wad, running along the line of imps), but presumed it must have been an optical illusion of some sort.

It also lets you to the other ledge from either side of the Barrels going east (trying from above.)

OK - worth verifying but not surprising, since wallrunning works whether you are facing into or out from the wall, be it on your left or right.