Glitches in Lemmings (old thread)

[Dullstar]

I don't have the covox demo.  I actually found a glitch in one of my levels, but I decided its fine, since the intended solution would have to modified to fix it.  Besides, I'll say the three builders are there for people who don't realize that lemmings can fall any distance if it lands on an exit trigger area.

[Clam]

The level I mentioned isn't part of the covox demo (whatever that is. I haven't heard of it ). It's the last of the special ONML levels that came with the Lemmings Strategy Guide.

[Fleech]

The Covox demo is also knows as Save The Lemmings. I've just had a quick search and it's availalbe to download at Lemmings Universe if you're interested.

[ccexplore]

DOS/Amiga Lemmings

I've just started reading this thread thanks to the lack of communications on where the forums ended up at.  Just want to say that a few of the glitches you listed are specific to DOS.  I'll add details once I finish catching up.

[Clam]

Are they? I've never played the Amiga version so I thought they were pretty much the same.

@Fleech: I've downloaded the covox demo, and I still have no idea what you were talking about.

Back to glitches. A while back I found a few glitches with the left side of the map (which for most purposes acts as a solid wall). Like the blocker glitches, these could be used in levels which can't be solved in any other way. Does anyone else know about these?

[Fleech]

@Fleech: I've downloaded the covox demo, and I still have no idea what you were talking about.

My solution to the JackLemmings level was far from elegant and there is probably a simpler way to save 100%, which may be why what I've said makes no sense to you. In any case, getting stuck in the ceiling helped me at least.

[Clam]

Ohhh... you mean the invisible ceiling at the top of the map. Yeah, I can see how it could be useful on that level. And yes, there is a much easier way to get 100%. This requires the use of one or two turnaround tricks, which in themselves border on glitchiness (though they're probably better described as exploits of the game mechanics).

[ccexplore]

Are they? I've never played the Amiga version so I thought they were pretty much the same.

They are mostly the same.  Having gone through your list, the only two that doesn't work are the nuke glitch, the shrugger->climber glitch, and the direct drop.  Not on your list but another DOS-specific one is the trick on pausing the game to gain about 2 seconds (eliminated the time waiting for the lemming trapdoors to open).  I have to re-check the glitch on mining right one-way walls.

Back to glitches. A while back I found a few glitches with the left side of the map (which for most purposes acts as a solid wall). Like the blocker glitches, these could be used in levels which can't be solved in any other way. Does anyone else know about these?

I'm not aware of anything specifically glitchy about the left side.  In looking at the programming, it actually did a pretty consistent job of checking the left side of the map and treating it as a solid wall, but I suppose it's possible they forgot to do the check in certain cases.  I did use the left-side-acts-like-wall technique for my 100% solution to Wild 12 but that's about it.

[ccexplore]

I think I've pretty much covered the old thread (for the DOS version at least), except for Wicked 7.

Ok, the secret to Wicked 7:

The game keeps a map of interactive objects' trigger areas to check if a lemming walks into one.  The blocker's effects is actually done via trigger areas, a sort of "blocker's field" if you will.  Notably, the field is not tied directly to the blocker itself.

Normally, when you create a blocker, the game saves the original trigger areas at where the blocker is, then writes the "blocker's field" trigger areas into the map.  Then normally, when the blocker stops blocking (either the ground it stands on is removed, or it explodes), the game restores the original trigger areas into the map to remove the blocker's field.

Notice that the game assumes the blocker hasn't moved from the time it saves the original trigger areas and the time it restores them.  This assumption however is wrong:  when you explode a blocker, after the countdown goes to zero, it first transitions to a lemming that yells "Oh no" and shudders, before it finally explodes.  And the shuddering lemming will fall if you remove the ground it stands on.  Yet the blocker's field is only removed when the explosion happens.

As a result, when the blocker is moved this way, the game will "restore" the original trigger areas into the wrong place in the map (where the lemming ends up exploding, as opposed to where it was originally blocking).  So you get two effects:

1) the blocker field remains
2) the original trigger areas get transferred into the new position

My lose-4 solution to Wicked 7 make use of #1.

[Clam]

I know about those glitches (otherwise I couldn't have solved all of geoo's original levels), but I can't figure out how to apply them to Wicked 7. Still, I'm sure your explanation will be enlightening to some


And from your post it looks like you aren't aware of the left-wall glitches. The problem with the left wall is this:

When a lemming walks into a wall (any wall, not just the edge of the map), it actually goes into the wall slightly as it turns around. This is what allows you to dig out steel or one-way arrows by bashing in the opposite direction. At the left edge of the map, this means the lemming is actually positioned off the map for one frame. Beyond the edge of the map, the game doesn't detect terrain, so the lemming is actually walking on nothing for a moment. In most cases, the game handles this well - but there are exceptions .

This can be combined with another known glitch (one that has been mentioned in this thread) to produce an even more remarkable effect.

[ccexplore]

The problem with the left wall is this:

<snip>At the left edge of the map, this means the lemming is actually positioned off the map for one frame. Beyond the edge of the map, the game doesn't detect terrain, so the lemming is actually walking on nothing for a moment.</snip>

Hmm, I'm definitely not aware of that.  I'll need to review the code again to see the details, but I can definitely see how the game might've set the boundary for left-side turnaround off by one pixel, and neglect to check for falling in that case, allow you to walk on nothing for that frame.

Incidentally, have you verified that this works in DOS Lemmings (being played in DOSBox or directly)?  If this glitch only works in Lemmix, then it's something we should fix in Lemmix, given it was meant to clone DOS Lemming's game physics exactly.

[Clam]

Just checked. It doesn't work in DOS ONML.

[ccexplore]

Just checked. It doesn't work in DOS ONML.

I just checked the game's programming, and indeed it skips the checks for fall detection during the left-boundary turnaround for walkers, so what you said about the lemming walking on air at that frame is possible.  The question I think might hinge on the details of where exactly DOS Lemmings/ONML clips the terrain graphics at the level boundaries.  This is an area of the game's programming that I haven't fully investigated (because it's a pain), but I suppose the question will need to be answered at some point for Lemmix to match DOS Lemmings at the boundaries.  (It's not the first time; we had to fix Lemmix once to support with the ceiling-bash glitch, because it turns out that partially depends on the game reading pixels off the top of the map by actually reading from the topmost row of pixels on the map.)

Based on my theory, I think you should be able to make the glitch work even in Lemmings/ONML/CustLemm, if you explicitly "clip" the terrain yourself at the turnaround boundary, using eraser terrain pieces.

[Clam]

Aha. I've tested another level and observed the glitch behaviour. For the record:

Crazy 18 - Terrain extends off the edge of the map. Glitch observed in Lemmix, but not DOS.
Fun 23 - Terrain doesn't extend off the edge of the map. Glitch observed in Lemmix and DOS.

That seems to be consistent with what you've just said.

[Clam]

It's probably worth noting with regards to this glitch that it is possible to place steel areas off the left side of the map. I'm not aware of any level that does this though.

Interactive objects can't be positioned off the left side of the map (when you load the level it disappears, and actually ends up a LONG way off to the right), which takes away a potential use for the glitch. The best you can do here is to place the object on the map and (politely ) ask the player to load the level in Lemmix, move the object to the left and then start the playtest mode.

EDIT: OK, it IS possible to place objects out to and X position of -16, but no further. The point is that you can't place an exit far enough off screen that its trigger is off the screen. (You can get some mean hidden traps though ) However, if you place it like this in Lemmix and playtest it, the lemmings will exit as they turn around at the left wall.


I should also mention the falling blocker/bomber glitch, which I've forgotten thus far. When a lemming blocks or starts the "oh no" animation when there is no ground underneath it, it falls down. This is part of the trick where a miner falls through a piece of ground without breaking it, and also features in my backroute solution to a recent custom level.