# The Two Types of Glides

In zdaemon I have, in several instances, witnessed players void gliding during deathmatch

I went to test a situation like this with xdre:
One wall is going directly north-east and second is going directly north. Then I placed 2 players to form a "wall" to test if it's possible to do the void glide.
| = wall going directly north
/ = wall going directly north-east
oo = two players forming a wall
g = guy trying to go to the void
... = space

...|
oo|
g/
/

For some reason, guy trying to go to the void bounced from the wall to south-west with speed of 29.120328. The strange part is that it kept going with that speed, even with WT tics inserted :P It stopped when he hit a wall.

When the void glide succeed with normal walls, the distance moved is over 60. I think I got it as high as 67.93.

how exactly am i supposed to push the button from the outside in e2m6?

odysseyofnoises said:

how exactly am i supposed to push the button from the outside in e2m6?

This is exactly what I'm trying to figure out. I've spend over 3 hours try to get the switch to activate, and nothing has happened. Getting outside of the map was the easy part -- and that wasn't even easy.

ive managed to get it two times when testing, but now ive been trying for hours and cant get it... i got to the void quickly though

Just look perpendicular to the wall and slide to the correct position. Correct position in this case is that you can barely see the button. That's the easiest way I think.

Fastest way should be to use some other angles, but I think that would require some calculations or extreme amount of luck.

looper: i've experienced this type of elastic mega-collision too, even when using just walls. i actually got it to work (almost, kinda) reliably and i remember gusta talking about exploiting a similar (the same?) effect for a speed trick in some future map of his.

here, if you move the barrels around a little, you'll get the elastic effect eventually. :P

Looper said:

For some reason, guy trying to go to the void bounced from the wall to south-west with speed of 29.120328. The strange part is that it kept going with that speed, even with WT tics inserted :P It stopped when he hit a wall.

Whoops! Probably because the doomguy was midair (and hit the ground at the same tic as he hit the wall)... silly me. Although the deceleration was kind of slow but I guess it was still normal :p

I admit that he looks like John Cleese, huehuehue.

Regarding pressing the e2m6 exit switch from the void (and other such cases), the main point to understand is that this isn't a normal switch trick. You can't press it through the wall. This type of linedef will "eat" use-key presses. You need to press the end of the exit linedef itself, and obviously from the correct side. For this, you need to approach it pretty much as in a glide, and align yourself perfectly with it, and be pressing use at exactly the right moment so that you are in contact with the linedef but infinitessimally on the correct side of it. As I say, it is just like a glide, except that at the critical moment you press the switch rather than slide through a gap.

This is one reason why void glides are only useful in a narrow range of circumstances - the exit linedef needs to touch the void directly and the player needs enough room to slide up to it.

Other demos that use this:
http://doomedsda.us/wad1501.html (my nomo - there's no void glide here, but there is a linedef that eats use-key presses)

This is one "hidden" feature that makes xepop's p2m6 so impressive - to the untrained eye it looks like a normal switch trick (and that he executes it a little uncleanly), whereas it is something requiring precision that he accomplishes very quickly.

Maybe old news but I noticed that in Resurgence beta1 map30 I'm able to do a classic guided glide without positioning myself "properly". Instead of 0° angle I can use something like 23°, didn't know that was possible. Recorded with -complevel 2 so that I could use -longtics.

resur-glide.zip

I'm working on a 2002ado.wad TAS demo and stopped on E1M5 because I decided to test Memfis' idea of a void glide. Is any of these glides possible?
I tried all of these, but I only got a wobble on two of them and nothing else (the momentum I gained on wobbling was not enough, it goes up to ~17 and stops, -turbo 255 didn't help as well).
P.S.: There is a test demo in an attachment.

ClumsyDoomer said:

I'm working on a 2002ado.wad TAS demo and stopped on E1M5 because I decided to test Memfis' idea of a void glide. Is any of these glides possible?

http://i.imgur.com/iYr2Yln.png
http://i.imgur.com/yVzGhJg.png

Yes. I did the rightmost one; i'm not aware of being able to void glide except in that precise configuration (90 degree angle, corner facing east). I did it -complevel 3 in normal play.

kraflab said:

I'm not aware of being able to void glide except in that precise configuration (90 degree angle, corner facing east).

You're a bit out of date there. dew and myself spotted some additional possibilities a few years back. I used the idea later when I eventually found a map where it was useful.

And there is the brand new revelation that the adjoining wall can even be north-south (i.e. 135 degree angle). See this post (and earlier/later posts). Still not clear how much of a speed boost and/or obstruction is necessary for that to work.

Grazza said:

You're a bit out of date there. dew and myself spotted some additional possibilities a few years back. I used the idea later when I eventually found a map where it was useful.

And there is the brand new revelation that the adjoining wall can even be north-south (i.e. 135 degree angle). See this post (and earlier/later posts). Still not clear how much of a speed boost and/or obstruction is necessary for that to work.

Ah interesting. I wish this kind of information was summarized and placed in some centralized location. Most of the common things are easy to get to but it seems like there are tons of things either hidden in various places or even undocumented altogether.

I think you made the wrong glide because you were too high above that slime area. :D I was talking about sector 20.
So, I've tried all of these glides and ALMOST succeeded on the fourth one (that corner between linedefs 207 and 208). Momentum went up to 28 and didn't want to increase anymore. With -turbo 255, momentum increases up to ~29 and drops to ~27.
As for others... I've never made a void glide before, so I don't know how they work. No one of the others worked for me, but it's too early to say that they're impossible.

I couldn't manage to slip into the void at any of those spots, although the switch seemed to really want to let me in.

So you've found a corner that looks like a magical door into the void, eh? Always idclip to the other side and check the void landscape first, it will save you a lot of time and grief. There may be a "void hill" on the other side at the height of your void corner, meaning you have no free space to glide into.

Wait a minute. Is this glide pointless then? It's impossible to run directly to the exit button because of height difference + it's impossible to "teleport" between map boundaries because a slimy sector kills you before you reach the southern border of the map.
Okay then. At least I've learned something about void glides. :D

The first thing to check if you are thinking of a void glide is whether the exit can be activated even if you reach an arbitrary position in the void. Most maps can be instantly discarded on that basis before you even start looking for possible void-glide locations.

Has anyone ever, like, formally documented the movement / collision code in Doom, and calculated the actual conditions necessary for tricks like the void glide to work?

RjY blesses us with code analysis every now and then when ppl cannot figure something out, usually it's not about collision though. There's one such post in this very thread. Sadly, all the useful info is scattered all over the subforum, and gets lost and dusted after a while. I've seen one nifty post about collision by some other person, which i, of course, cannot find at the moment. It involved some form of an explanation about the mechanics behind clipping through certain walls. Hopefully someone remembers where to find it.

That said, it would be amazing to have everything documented and stored in one place. And complete collision code documentation would be very useful for pretty much every speedrunner. Except for Looper, who already knows everything about the engine quirks anyway :p

I know something, but I don't have any summarized/generalized facts. Just random theories inside of my head, made from testing all kind of different things.

Guess: There's an in-between frame check for collision (or everytime player hits a wall?), but it doesn't work properly when going north/east (sign error?), so it goes double speed (wallrun). When there's a diagonal wall like the one used to get to the void, player gets twice the error, one because the player is going north and one because the player is going east. That's why the max distance moved in single tic is (probably) (60²+60²)^0.5 = ~85. The sign error might cause the ludicrous momentum change sometimes, but it's all guess D:

lol ugh, trying to understand the collision code is a nightmare

P_PlayerThink()
P_MovePlayer()
P_Thrust()
P_RunThinkers()
P_MobjThinker()
P_XYMovement()
P_TryMove()
P_CheckPosition()
P_SlideMove()
P_PathTraverse()
P_BlockLinesIterator()
P_TraverseIntercepts()
PTR_SlideTraverse()
P_HitSlideLine()



I often see questions about glides (getting through a 32-unit wide gap), and there is random information all over the place which makes it difficult to get the basics for speedrunning purposes. I'd like to have some place to refer to when this question pops up, so here's a summary of the stuff I know about 32 unit glides. This is all non-TAS methods.

There are several different types of glides in doom:
Guideless glides in west, south, north and east direction.
Guided glides with the wall on your left in same directions as above.
Guided glides with the wall on your right in same directions as above.

as well as special type of glides like:
Torch glide on map 19 of Doom 2 (not 32 units)
glide between the bars in map 22 of doom 2
glide between the middle opening on map 21 of doom 2 (not 32 units)
Void glide on E2M6 of doom 1 (no gap)

All those glides should be possible with -longtics, which is the default turning resolution if you are not recording any demos. Since glides are primarily used for speedrunning the command -record is used, which enables -shorttics by default.

For -shorttics there are much fewer possible angles and which you can face (lower turning resolution). If you don't understand what I mean above then trying -record or -shorttics should make the difference obvious. This is an advantage when dealing with most types of glides, while possibly a disadvantage for some. I first learned how to glide without using -shorttics, which is very difficult to do, but possible.

So, before attempting to do glides, use -record or -shorttics command as launch parameter. Once you understand how the glides work you can try to do it without -shorttics if you intend to use it outside of demo recording.

Second thing you will need is vertical mouse movement, this is not always required, but even when it is not it may have an advantage. Also different sensitivities can have an effect, too high and you can't do a west directed glide, too low and you need to use more vertical mousemovement to move forward which makes it more likely that you end up turning left\right instead.

The two first things you need to do is to find the correct angle and the correct position for the glide to work.
The correct angle is when you are facing the gap and walking\running against the wall, but only moving slowly towards the left.
The correct position is when you are not moving any further to the left. For a guided glide with the wall to your left you will have the wall to stop you.

For a guideless glide there are 2 directions in which you will stop, west and south. So when you are close to the gap in the west direction you walk (not run) into the gap until you stop moving forward. In the case of a south directed glide you need to take a step back and walk forward again. If you don't do that then there is a chance you will just continue further to the left and go past the gap.

Once you have stopped moving forward you need to use vertical mouse movement. The reason for this is because you will be able to do much slower forward movement than normal (like walk with W or up arrow) that is necessary (in some rare cases you go straight through before you stop) for the glide to work. For west directed glides the slowest possible speed (MF1) should be necessary, for south directed glides you need a slightly higher speed (MF2). The lowest possible speed for strafe on + mouse turn is SL2\SR2 which means vertical mouse movement is not necessary for south direction. I am not sure what speed is needed for east and north directed glides, but using the smallest possible speed and then increasing it should be the best method (I think it's MF2).

All the glides listed above are possible, there are different methods that if performed correctly will get you through the gap. So there is no randomness involved, but how fast you are able to get through depends on how quickly you can get the right angle, correct position and apply the correct amount of vertical mouse movement.

We here look at the correct angle, position and vertical mouse movement speed for most types of glides using -shorttics.
Direction: for example west directed means going east to west (right to left) direction as from looking on the minimap while facing the 32-unit gap, and wall to your left\right is when you are facing the 32-unit gap.

Guided glides with the wall to the left:
These are easy to do with the method described above. Some examples are Map 16 (east) and 21 (west) of doom 2 and map 21 (west) and 23 (north) of plutonia. Since map 16 is east directed it is slightly more difficult to do than map 21 which is west, but with practice they should take almost no time besides finding the correct angle.

The easiest type of glide is a guided west directed glide with the wall on your left while facing the gap. This type can be found on map 21 of doom 2. I would recommend if you haven't done a glide before to do map 21 of doom 2, which is through the closest teleporter and 45 degrees turn to the left.

Alternative method for East and North directions:
I recently discovered another way to do these glides during 30nm attempts. You need to be facing 45 or so degrees to the right compared to the usual angle if you are doing an east directed glide, then you SR50 along the wall (wallrun) into the gap. You should then be wobbling back and forth a lot, by using vertical mouse movement very slowly backwards (MB1) you will then go straight through after a short while (you will wobble less just when you are about to get it, if you don't wobble at all you used MB2 or higher, see 30nm2721 for example).

Guided glides with the wall to the right:
These types of glides are useless for all the IWADs, since there exists guided with the wall to the left instead for all of them afaik.

Either way, west and South directed glides are also somewhat easy to do with the above method. For an east directed glide you need to use a different technique, lv14-014 (map 14 of doom 2 uv-speed) shows this trick (no glide, different trick). You have to aim 1 tic to the left of being parallel with the wall and use continuous vertical mouse movement while you turn 1 tic to the right. This will get you close to the wall (by strafing against the wall you will notice that your gun wobbles a lot if you did it correctly) which will allow you do go through east directed guided glides with the wall to the right. North directed glides with the wall to your right are not possible afaik, unless you use melee attack (see below). You can find this glide on map 16 of doom 2, but it's useless since there's an east directed guided glide with the wall to your left. (I never do these types of glides and so I might be wrong here, I just quickly checked it at some point)

Guideless glides (all 4 of these types can be found in the same place on map 19 of plutonia):
From running plutonia I have discovered consistent method for how to do south directed and north directed glides. It also turns out east directed glides can be done consistent as well, but are really precise and therefore hard to do.

West directed glide is the easiest of these, and the method for it is described above, just apply the 3 steps: Position, angle and vert. mouse movement. Map 2 of doom 2 and map 8 of plutonia has this type of glide.

South directed glide can be difficult to do, also described above. Map 9,13 of plutonia has this type of glide.

North directed glides might be very difficult to learn. Once you notice a very thin line kind of move out of place on the left side you apply a very small amount of vertical mouse movement and the glide should work every time. However, it can be very difficult to not move past the gap when you try to get in the right spot. I think MF2 tics are needed to get through, but MF1 tics doesn't move you out of the gap, so by using a small amount of vertical mouse movement you eventually go from doing MF1 to MF2 which then gets you through.

You need to apply some vertical mouse movement before you start moving forward into the correct position. If you don't do that then you will move slightly to the right when you try to do the final step, but then you can just move forward to the line moves again so it's not a big deal. So you very carefully tap move forward until you see the change, and then you start to use vertical mouse movement. If done correctly, it works 100% of the time, after some practice this type of glide is not much more difficult than a south directed glide. Map 13 of plutonia and E4M4 has this type of glide.

East directed glide, same as above, except here you move forward until you see a line segment move out of place on the right side. Once that happens you need to take a step back and move forward and use vertical mouse movement.

East directed glides are difficult to describe any further, but since it's useless for IWADs I won't even bother, the setup for it is slow so for short IL's where it could be useful it would be best to just randomly try to get the right position and use vertical mouse movement. Perdgate 7 and 15 has this type of glide.

Special type of glides:
Map 22 of Doom 2 (bars glide): There is 1 specific angle that will get you through easily, make sure to take a step back and use run forward + strafe left. I also have an alternative method here, but it's hard to describe so I won't. See 30uv1959 for example, credits to Looper for the method.
Map 19 of Doom 2 (torch glide): Face the gap, take a step back and run forward + strafe left, there are several angles which will get you through.
Map 21 of Doom 2 (SR50 glide): Using a specific angle you can SR50 through the gap, not very useful. Some IL probably uses this trick.
Doom 1 E2M6 (Void glide): There are several angles which this glide works, some are better than others. Then running back and forwards will get you through eventually.

Alternative to vertical mouse movement:
Another possibility is to take a step back and go forward, repeat until you get through. This should work for west and south directed glides, though I am not 100% sure because I don't use it as this method is completely random and thus slower. Speed does not matter (as far as I noticed) so to get through as quick as possible you just have to minimize the time between each bump.

And that's as much as I can be bothered to describe glides, some questions like what is the correct angle to use for void glide could be answered by watching demos. If anything is incorrect feel free to correct me or if you have anything to add then please do.

One last thing, using melee(fist,chainsaw) on a monster will make a change so that when you move against the wall at any angle you will not be moving slowly towards the left. You can also return to the initial "angle" by furter attacking with melee, or you can even move slowly towards the right so that east\north glides are easy instead of west\south, either way just try to punch\chainsaw monsters and attempt to glide to see what I mean.

ZeroMaster010 said:

Guided glides with the wall to the right:
These types of glides are useless for all the IWADs, since there exists guided with the wall to the left instead for all of them afaik.

Either way, west and South directed glides are also somewhat easy to do with the above method. For an east directed glide you need to use a different technique, lv14-014 (map 14 of doom 2 uv-speed) shows this trick (no glide, different trick). You have to aim 1 tic to the left of being parallel with the wall and use continuous vertical mouse movement while you turn 1 tic to the right. This will get you close to the wall (by strafing against the wall you will notice that your gun wobbles a lot if you did it correctly) which will allow you do go through east directed guided glides with the wall to the right. North directed glides with the wall to your right are not possible afaik, unless you use melee attack (see below). You can find this glide on map 16 of doom 2, but it's useless since there's an east directed guided glide with the wall to your left. (I never do these types of glides and so I might be wrong here, I just quickly checked it at some point)

Any glide with the wall to the right is possible like Doom 2 map 14 by gliding in the opposite direction from the gap. If the wall is north or east from the player, though, there will be no boost against the wall, so you won't be able to know when you are at the .000000 coordinate.

I also forgot to mention that -record and -longtics is a possibility, but it's not used by anyone that records demos so it might be best to avoid it. In that case north directed glides with the wall to the right are possible.

As you said, you won't be able to know when you are at the correct position (.000000 coordinate), so possible but not any known consistent method I suppose would be more correct.

This nicely sums up how completely out of hand our naming conventions got. Glides everywhere despite describing entirely different tricks, heh. Also that's a lot of text!

If somebody feels qualified, I'd love to see this information end up at http://doomwiki.org/wiki/Glide with explanations of the various techniques that are all grouped under this name, with as much technical accuracy as possible.

The reason that article doesn't exist already is that nobody with a full understanding of the phenomena has ever considered contributing it, and none of us regular contributors are amongst that group, myself included.

I think void glide and impassable line glide deserve a different name. Technically they are not glides, are they?

ClumsyDoomer said:

I think void glide and impassable line glide deserve a different name. Technically they are not glides, are they?

You mean fence glide like in Doom2 map10 @exit room? :-P