After seeing DwainumB's wip yesterday, I decided to investigate for a few hours into the zipping glitch, and think I have a pretty good understanding on how it works.
How this game works movement-related is pretty wierd. There are two heights you can be at in the game, which translate to being on ground and being on elevated ground: I'll call these 'ground' and 'high ground' respectively. High ground is higher than ground, so if there's high ground next to ground, Lucas will jump from high ground to ground, and effectively change his 'height' from high ground to ground. The jump triggers the switch from high ground to ground.
Note that you can only jump either on ledges facing downwards or on corners. I have no idea why you cannot jump off ledges facing upwards.
Now, consider this situation:
This is probably the most important screen in the entire game, and for good reason. Black is ground, green are walls, and orange is high ground. Notice how high ground is just above a wall? This is what I outlined as the red section, and it is crucial. There are two things to understand before carrying on: the first is that walls cover both ground and high ground. In the case that you are on high ground,
ground also becomes walls, unlike what one would think; so the only way to progress into these 'walls' is to jump or use a slope. However, if walls cover both ground and high ground, how would it be possible to progress in this case? Flowers are actually a special case, in that they allow to walk over walls.
The thing with flowers is that they lower! And this is where the zipping glitch happens.. When Lucas walks on a flower, it will start to move, then dive back into the ground after a short amount of time. In the case that they lower, they turn from being high ground back into ground, and Lucas will do a special animation not found anywhere else in the game: he will fall.
What happens if he falls into a wall? This is where the madness begins. The programmers knew of this case, and so implemented a very half-assed zipping mechanic: if Lucas is detected to be into a wall, he gains a ton of backwards speed, and basta. The backwards speed is I assume a result of helping innocent players who entered a wall by accident, and 'push' them back this way. This way, it would also be impossible for an human player to zip on purpose, because it would require precise frame perfect imputs.
Except there's two problems with this zipping mechanic. The first is that it only
gives Lucas speed, and doens't force him to use it. This means, if there's no input, Lucas will stay lodged in his wall just fine. This is normally not a problem, because there's not a lot of places to go from being stuck in a wall; you can usually only do wall to wall movement, so there's not a lot to go to from the green spot.
The second problem is how the change from high ground to ground is controlled. Remember that Lucas will only transition from high ground to ground either if he jumps (initiated on walking to ground while on high ground while not facing up) or falling (special animation specific to flowers.) But what happens if we interrupt, or even skip the falling animation? It turns out there isn't any check for that, and so Lucas stays in high ground even though the ground beneath him. Game broken!
Pointing back to what we said earlier, while on high ground, ground becomes walls. We are effectively zipping onto the ground!! This makes the glitch extremely powerful, since you can essentially walk around freely on the entire map (and the whole game is on one single map.. in theory, I'll get back to that later.)
Specifically, once you are on high ground, since we don't have access to flowers anymore, the only way to fall back to ground is to either:
- jump, and we can't jump (since we can't stand still on high ground anymore while holding a direction.)
- walk onto a slope
- interact with water (as it affects both ground and high ground)
- interact with pits (same as water)
- interact with rocky terrain (no idea why this affects it..)
The only reason we would want to get back on high ground again would be to interrupt zipping (which is needed in a lot of cases.)
Now that we can walk freely around the map, what can we do? Well, not a whole lot. We can walk to the last area of the game, but no actors are spawned; we can walk to other areas, but only three are loaded when we zip in this specific spot (this, the dark forest, and the cactus garden.) Because this game is heavily checkpoint and event-based, we can't do anything at all! However, for loaded areas, all the terrain is fully fonctional (you can still die on water, fall into pits, etc.)
To add insult to injury, you can't interact with other actors at all! This means you can't just walk around the entire game at zipping speed, moving some ants along the way. A shame, but overall, the zipping glitch still remains its usefulness for faster movement, as long as a flower and a wall are accessible nearby.
