Four Island

Well folks, I really did it this time. My propensity for prolix loquaciousness and overly comprehensive tutorialization has aggrandized to a heretofore novel level. I was working on a post about the history of updates to The Witness and how they affected speedrunners, and it got so long that it overflowed the database column (it had a max of 64kb, which I hit at about 11k words). I've resized that field now, but I had been considering breaking out some of the content into a separate post anyway, and I took this as a sign that I should get on that.

Old Version has a bunch of cool quirks and glitches, but there's one trick in particular that I spent a disproportionate amount of time talking about. It makes use of a glitch that no one thought was useful, it prompted discussions about whether you could mess with game files during a run, and research had to be done into the game's internal workings, the results of which ended up being important beyond just this trick. And also I was "at the scene of the crime", as they say.

Today, I'm going to talk about Force Bridge Skip.

On April 4th, 2016, an update was pushed on Steam for the PC version of The Witness. It changed a handful of things, and notably patched out a useful skip in the 100% category. There's one thing that changed, however, that was kind of weird. It was known before it was patched, of course, but it's unknown how long it even took for us to notice that it had been patched, because it didn't seem like anything more than an amusing glitch. In fact, it wasn't until five years after it had been patched that we really understood what we had lost.

I'll stop being ominous. A week after the game came out, MousseMoose was playing around with the force bridges in the Mountain and came across something strange:

If you positioned yourself on a force bridge, then loaded into another save that was standing in front of the force bridge panel, clicked into the panel, and finally loaded back into the original save, the force bridge would disappear right beneath your feet.

At first, this sounds great! You progress through Mountain by starting at the top and going down the floors until you reach the bottom. If we could remove the floor beneath us while standing in the central column, we could skip Floor 1 and Floor 2, right?

Well, unfortunately, no. The Witness does not have gravity. The player is able to walk from surface to surface when they are at close enough heights, but it's impossible for the player to fall. If the player were to attempt to walk off a surface when the next surface is much lower than they are (e.g. on the Quarry Elevator), they are simply blocked instead. If you enter solve mode while noclipping, you are zipped to the nearest floor beneath you, but that's likely more a feature of noclip mode than it is a part of the game's physics engine. In general, The Witness expects you to always be standing on a walkable surface.

So what happens if the surface you're standing on gets removed? The game teleports you to a known safe location. There are a number of these throughout the island, usually outside the entrance to each area, so that the game can be sure it's not putting you behind a locked door or something. In fact, if you haven't opened the Tutorial Gate (which is only possible by noclipping out of Tutorial), the game will always place you inside Tutorial, right beside the gate, because if it placed you outside then you'd never be able to get back in.

Anyway, what this all means is that when you use this glitch in Mountain, you get teleported to the mountaintop, instead of to the bottom floor. Because of this, the glitch was dismissed, and the mechanics behind it were not studied for a long time.

Enter: me! On August 20th, 2021, I was experimenting with this glitch because I wanted to see if there was anything the earlier players had missed. I was interested in Floor 2, because the force bridge puzzle there is particularly complex. In order to get to the elevator, you need both bridges to be solved, and one of them has to point to the exit door. Ordinarily, configuring the bridges like this requires you to walk back and forth between the two sides of the room, inputting different bridge solutions. In total, the optimal solution solves Blue Bridge 3 times and Orange Bridge twice. I wanted to see if there was any way I could trick the game into pre-solving Orange Bridge, so that we could draw Blue Bridge directly to the exit without any back-and-forth.

Instead, I discovered this:

I solve Blue Bridge as per usual. When I get to the other side, I solve Multipanel, and then I load into another file where I'm standing in front of the Blue Bridge panel. I click into it and load back into the other save, just like in MousseMoose's video. The Blue Bridge disappears as expected, but here's the important part: the cable coming out of the Blue Bridge panel is still lit up. I then input an Orange Bridge solution that satisfies the whole panel and goes to the exit (the one used in 100% runs), and exit the floor, skipping three bridge solves and saving 15 seconds of solving and walking.

This reveals the trick behind the glitch. When you're clicked into a panel and load into another save, you can hear the sound of the solve canceling after the load finishes. This carries forward to the force bridges: their panels make very distinct and continuous noises while you're clicked into them, and you can briefly hear it after the load finishes. It seems like the game doesn't kick you out of solve mode until the file has been loaded. In most cases, this doesn't really matter, because canceling a panel solve has no effect. It's not like you can unsolve panels.

Well, except for force bridges.

The force bridge panels are special. Drawing a line on a force bridge panel creates the force bridge in real time. Solving the panel locks the bridge into place, but if you cancel the solve instead, the bridge disappears. So, what's happening here is that the game loads you into the file, then realizes it has to cancel the solve you were drawing, and because it was a force bridge panel, it has to perform the panel's special logic upon solve canceling, which is to remove the bridge.

But then why does the panel's cable stay lit up, if the game is performing the full cancel logic in the loaded file? It's because the cable is deactivated when you start solving the force bridge panel. The bridge is immediately removed once you click in, and you'd have to input a valid solution in order to re-illuminate the cable. But you never start solving the panel in the loaded file, you only stop. And thus we can get away with only two bridge solves.

Of course, the only reason I'm talking about this is because it is no longer possible to do it as of April 4th. The game no longer does anything to cancel solves after loading a file. But it's still useful if you want to specifically do old version runs, which have their own categories on the leaderboard! They're less competitive because there's little reason to ever play on an old version, but you can still do it.

This discovery immediately sparked a conversation about loading saves during runs. In the past, the only run that involved loading saves was 100%/99.8%. Solving the Tutorial Gate EP traps you in the Easter Egg Ending, but if you reload your file, you will be back in Tutorial without the Hotel spawned, and you'll still have the point for solving that EP on your file. Similarly, the Wonkavator, which activates the game's regular ending, is a counted panel that is required for 100% solves, but reloading the file removes you from the ending while keeping the point for solving it.

The thing about both of those cases is that they involve loading the same file that you were already playing. In order to do Force Bridge Skip, you'd specifically need to be able to load a file that's standing in front of the Blue Bridge panel while your main file is standing on the Orange Bridge side. The video above uses a second save file created outside of the main run, which is controversial because then should the time taken to set up that second save be reflected on the timer? The skip wouldn't save time, then. Should players just be allowed to put a prepared file in the game's save directory? But that would make it not really a full game run.

There is another solution to this, though! What if you loaded another file that was created during the same run?

Save File Splitting

If you've ever played The Witness before, you've probably noticed that the game automatically and silently saves your progress. There isn't even a menu option for saving; the game just does it. You might also notice that you have multiple save files, even if you're still in your first playthrough. This is important.

We've known for a long time that the game splits your save files sometimes, and that if you compare two runs in the same category, the splits will often be in similar places. But we didn't understand why and when it did this. In theory, if we could get the game to split our save file right when we're standing in front of the Blue Bridge panel, we could use that file for Force Bridge Skip, with no external setup required. It wouldn't be very fun, though, if we had to rely on a mechanic we didn't understand to just randomly split our save file at the right place.

In response to this, darkid started digging into the game's internals. He was one of the earliest modders of The Witness, and is responsible for many of the low-level things we know about the game. And sure enough, it didn't take long for him to uncover the logic behind the autosaving feature. Here's what we learned:

1. Pausing triggers a save.
2. Entering one of the endings (by solving the Wonkavator or solving the Tutorial Gate EP) triggers a save.
3. An autosave is triggered every 60 seconds, unless you are in the middle of solving an EP, in which case the game waits until you're done.
4. While the game is saving, it checks your current "score" against the old one in the save file. Your score is the sum of your solved panels, EP's, and obelisks (the pillars that show the EP's you've found). If your score divided by 60 (rounded down) is greater than the old score divided by 60, then the game saves to a new file instead of overwriting the last one. You can imagine there are markers every 60 points, and passing one of them is what triggers the split.

The fact that there are score markers every 60 points is noteworthy, because that's actually another thing that changed in the April 4th update! Before that version, the markers were every 120 points instead. It's a shame that this changed in the same update that made Force Bridge Skip impossible, so we can't take advantage of it in Legacy runs, but that's the way game patches go.

Regardless, this discovery was key to making Force Bridge Skip usable in runs! To explain how this works, let's take a look at All Lasers. Doing the standard route using Single Latch Skip and Stair Snipe results in a solve count of 230 right as we're standing in front of the Blue Bridge panel.¹ This is, by some beautiful coincidence, very close to a point barrier (240).

The idea is that we'd blink the pause menu while standing in front of Blue Bridge, in order to force a save and reset the autosave timer. We'd then have 60 seconds to solve Blue Bridge, walk across, and then do Multipanel, which is six solves. Ideally, we would have between 240 and 246 points upon solving the last Multipanel,² so that we could pause the game and force another save, and because we'd crossed a point barrier, it'd be in a new file, allowing us to load into the file where we're standing in front of Blue Bridge.

The problem is that 230 solves + 7 is 237. We'd need to walk into Mountain Floor 2 with three extra points in order to successfully split our save. Luckily, there are a handful of ways we can do this!

• There's two panels that you can snipe while waiting on the Desert Elevator. The timing to get them is pretty tight, but there's no risk of losing time.
• In Mill, there's a set of four linked panels that control a ramp and lift. Solving one of them automatically solves the others, although there is one that is not activated at first and can't be solved until you do the Lower Row panel set. We don't do the Lower Row in the stair snipe route, but still, solving just one of these would get us all 3 extra points. After you solve the Upper Row, you have to wait a second for the Control Room 1 panel to turn on, and you also happen to be standing right next to two of the linked panels. It's not technically free to do this because the time it takes for the panel to turn on is pretty short, but it's still an extremely efficient way to get those extra solves.
• There's an EP that's free to get while you're waiting on the boat from Quarry to Treehouse. It is almost no effort to do, and wastes no time regardless of whether you're successful, so most All Lasers runners will do it just to pass time on the boat.
• There's a very simple panel (almost a straight line) on the mountaintop called the River panel and it's in view when you're standing behind the statues, giving you a couple of seconds in which to solve it while waiting for the mountaintop seal to open. This window is longer than the one for the Mill linked panels, but it's still not great, and it's only one point.
• If you're fast enough, you can solve the Purple Bridge EP while you're waiting for the stairs to Blue Bridge to descend. This is quite literally the last moment you could possibly get an extra solve in!

You only need three extra points with this route,³ so there's no reason to do all of these. The easiest method is to just get the Mill linked panels. If you want to make sure you don't waste any time, however, you can get at least one of the Desert panels, the boat EP, and then the Purple Bridge EP if you didn't get both Desert panels.

And it works! The Legacy All Lasers world record successfully gets through Mountain Floor 2 with only two bridge solves. The extra solves it gets are the first of the two Desert panels, the linked Mill panels, the boat EP, and then the River panel for some reason, for a total of 6 extra points. It ends up with 236 points before solving Blue Bridge and 243 points after Multipanel, and since the 240 point barrier gets crossed, it splits the file. Horray! It should be noted that only three extra points were needed, and the linked Mill solve definitely lost time, but that just means there's room for improvement. (I'm criticizing my own run, so it's okay).

So, that's All Lasers. What about 7 Lasers, then? Unfortunately, things don't work out as well. The standard Legacy 7 Lasers route ends up with 98 solves before Blue Bridge and 105 after Multipanel, which is 15 away from the 120 point barrier. Unlike All Lasers, there aren't many places where you can get free solves. There's no boat and no Desert Elevator. You can still get the Purple Bridge EP right before Blue Bridge. The only other place you have some waiting time is at the mountaintop while you're waiting for Swamp laser to go up. There's 5 extra points that can be gotten up there, but you'd be hard pressed to get them all without losing any time, especially on Old Version. And even that would still leave you with 9 more required points. There's nowhere else to get free points, and no reroutes that wouldn't likely lose more time than Force Bridge Skip would save. Alas.

There's a couple of other categories we could look at, but they don't fare much better. 100%, for instance, has many route variations that you can play around with, and the numbers don't work out for any of them.⁴ Here's a comparison of some categories and routes, including the only one that works:

Route	Score before Blue Bridge	Nearest point barrier	Difference
7 Lasers	98	120	15 more needed
All Lasers with Single Latch Skip and Stair Snipe	230	240	3 more needed
All Panels	424	480	49 more needed
100% w/o Eclipse Skip, deferred Town and Theatre	502	480	23 too many
100% with Eclipse Skip	547	600	46 more needed

If the score threshold was 60 it would be easier to work something out with the limited stuff we can move around, but such is the curse of the April 4th update.

I think Force Bridge Skip is pretty cool, but it doesn't see much use because it only really works in Legacy All Lasers. darkid and I ran the category for a little bit while we were figuring out the trick and developing the route, and our times are amusingly over 4 minutes faster than anyone else on that leaderboard. Legacy categories aren't very popular because New Version is just better. There is one other made-up category that uses this trick, but once again, that's a tale for another blog post.

There's one last thing I need to talk about. At the beginning of the post, I mentioned that this trick had ramifications beyond just Legacy. The reason for that is the research into save file splitting. Knowing how to deterministically split your save file isn't really useful for normal runs, but it's a great tool to have in your arsenal when searching for more complicated tricks. And as it turns out, less than a year later, save file splitting ended up being a critical part of the biggest single time save in the entire game: Eclipse Skip!

You can read more about Eclipse Skip in the post I linked, but the basic rundown is that we needed to use multiple save files to get a Theatre video into a weird state. This is why it's fortunate that they changed the save split threshold to 60 points instead of 120. The Eclipse Skip route heads to Theatre and starts splitting save files as early as it possibly can in the run, and the player happens to get up to 60 points fairly close to the entrance to Theatre. If we had to wait until 120 points instead, it would make the route a lot more awkward. Of course, Eclipse Skip saves such a ridiculous amount of time that it would be worth any amount of re-routing to pull it off, but we're still glad that it worked out the way it did.

And that's the full scoop on Force Bridge Skip! I hope you enjoyed this slightly vainglorious trip down Speedrunning History Lane. I'll hopefully have my full report on updates to The Witness out soon, so keep an eye out for that!

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1. You can see in the screenshot above that the second file is right before the end of Mountain Floor 1, and I have a solve count of 224. Adding the two unsolved panels in the screenshot and the five Rainbow panels on the next floor would result in a solve count of 231. What gives? Well, I actually solved two extra panels in this run -- the Desert panels I mention a couple of paragraphs later. Subtracting those gives 229. The remaining difference is because the run I did was on New Version, and there's an extra panel you solve in All Lasers on Old Version that you don't in New Version. You'll see what I mean when I talk about Jungle Wall Skip. ↩

2. The reason we don't want more than 246 points after Multipanel is because it would mean we'd have at least 240 points before solving Blue Bridge, and thus the file wouldn't split. ↩

3. Doing Double Latch Skip instead of Single skips a panel, so you'd need four extra points instead of three. If you don't do Latch Skip at all, it adds three panels (including the two Desert panels mentioned as freebies), so you'd only need one extra point. Interestingly, Stair Snipe is almost required: not doing it adds 10 points (the six Lower Row panels, plus the full four linked Mill panels), which would place you at 240 points before solving Blue Bridge. If you didn't want to do Stair Snipe, you'd have to either do Double Latch Skip or Jungle Wall Skip, or leave Mill or Jungle via the slow routes. Just some unnecessary fun facts. ↩

4. It would be pretty strange if we could do Force Bridge Skip in 100%, because 100% requires you to get Blue Bridge EP, and thus you need to be on Floor 3 with Blue Bridge pointing to the exit at some point. This wouldn't actually be a problem though, because going from orange to blue takes the same number of bridge solves as going from blue to orange (4 solves), and thus we would still be saving three bridge solves using the skip. ↩