Game developer and modder , perhaps best-known for the SilentPatches he's released for various games including Grand Theft Auto: San Andreas, has stumbled across (and fixed) a bug that's been lying dormant for two decades. And while this manifestation was, apparently, triggered by a new build of Windows 11, it's been there the whole time.
Silent received a "rather specific bug report" relating to SilentPatch, in which a user noted that after updating their Windows 11 to version 24H2, the Skimmer plane disappears completely from [[link]] the game. It can't be spawned using the trainer tool, nor does it appear on its usual spawn points.
Our programming hero notes this wasn't an isolated complaint, and he's been receiving comments about the missing Skimmer since November last year. One user set up a virtual machine (VM) running Windows 11 23H2, confirmed that the plane spawned OK, then updated the VM to Windows 11 24H2 and the plane disappeared. As this user put it, why "a small feature update in 2024 breaks a random plane in a 2005 game is anyone’s guess."
I'll ha' that
Needless to say GTA: San Andreas has no means of actually showing this extraordinary event, instead showing "a famous 'burn-in effect' known to occur when the camera gets launched into infinity or close to it. Funny enough, you can still kind of make out the shape of the plane even though the animations give up completely to the inaccuracies of the floating point values."
Silent began investigating the issue and hit upon an "obviously enormous" numerical value for the plane's rotor blade speed, but what caused the plane to shoot up such an unimaginable distance? "There are two possibilities," explains Silent:
- The plane spawns high up in the sky already.
- The plane spawns at ground level and then shoots up in the next frame.
At this point Silent starts going into the details of functions, Z coordinates, bounding boxes, and a dozen other pieces of terminology. If I tried to stitch together an explanation, I'd probably get bits of it wrong and it would look like gibberish anyway. For the more code-inclined, you can feast on Silent's workings in his .
The long-and-short is that Silent identifies a corrupted Z value (spawn coordinates), and guesses that this is resulting in either the collision file being read incorrectly ("highly unlikely, but not impossible given that this issue could potentially have been an OS bug") or "the bounding box is read correctly, but then it’s updated with an outrageously incorrect value."
This leads Silent to further analysis of the bounding box and Z coordinate, and the realisation that when a specific vehicle is spawned for the first time, the game updates the Z coordinate to reflect the car's natural suspension height. Yes, we are still talking about a plane.
"This is where things went wrong first," writes Silent, before launching into a detailed analysis of how the suspension lines are computed, and where he finally identified the problem: In vehicles.ide, the Skimmer has fewer parameters than other planes, making it resemble the entries for boats instead. It's the only plane missing parameters for its front and rear wheels."Does re-adding those parameters fix the seaplane? Unsurprisingly, it does!" he writes.
Having identified the problem, which somehow involves the game thinking the plane is a boat, our man then goes full Sherlock to identify why Rockstar's coders missed it.
"I have a likely explanation for why Rockstar made this specific mistake in the data to begin with—in Vice City, Skimmer was defined as a boat, and therefore did not have those values defined by design! When in San Andreas they changed Skimmer’s vehicle type to a plane, someone forgot to add those now-required extra parameters. [[link]] Since this game seldom verifies the completeness of its data, this mistake simply slipped under the radar.
"In the case of this rabbit hole, the discovery of this fix only raised more questions—why did this break only now? What made the game work fine despite this issue for over twenty years, before a new update to Windows 11 suddenly challenged the status quo?"
"This was the most interesting bug I’ve encountered for a while."
Silent
Surprisingly enough, this particular version of Windows 11 is actually not responsible. He identifies the ultimate problem as being an "actual floating point value that was sitting on the stack in [[link]] exactly the right spot.
"I then inspected vehicles.ide for TopFun—the vehicle defined directly before Skimmer. Sure enough, its wheel scale is 0.7!" he wrote. "This is the exact proof I needed—notice that in the Windows 10 run, some of the local variables are even still visible to the human eye (like the normal vehicle class), while in Windows 11, they are completely gone. It’s also worth pointing out that even in Windows 10, the very next local variable after the wheel scales has been overwritten by LeaveCriticalSection, which means the game was 4 bytes away from hitting this exact bug years earlier! The luck at display here is insane."
So even though Windows 11 24H2 brought this bug to light, "the real issue here is the game relying on undefined behavior (uninitialized local variables)." The bug could've popped up on Windows 10, or 7, or XP, or even Windows 98—the math just didn't end up that way."
Ever the completionist, Silent goes on to look through the code on other San Andreas releases, and finds that the original Xbox version of the game included a fix not dissimilar to his own. This fix was included in other San Andreas releases, including GTA: The Definitive Edition.
"This was the most interesting bug I’ve encountered for a while," writes Silent. "I initially had a hard time believing that a bug like this would directly tie to a specific OS release, but I was proven completely wrong. At the end of the day, it was a simple bug in San Andreas and this function should have never worked right, and yet, at least on PC it hid itself for two decades."
In a flourish I can only admire, Silent ends by explaining why his fix is slightly more accurate than Rockstar's equivalent, and uses the discovery to reinforce some good coding principles like validating your input data: "San Andreas was notoriously bad at this." Meow!
In Tom Wolfe's book The Right Stuff, which focuses on the remarkable test pilots who worked on the early stages of the space program, he poses a question: "What is it, I wondered, that makes a man willing to sit up on top of an enormous roman candle, such as a Redstone, Atlas, Titan or Saturn rocket, and wait for someone to light the fuse?"
In the microcosm of San Andreas, a man called Silent wondered what made CJ enter a plane and then instantaneously launch "1.087 quadrillion light-years up in the sky." The real answers are all above, and . But the other answer is in the absurdity of these things working at all, the countless co-dependent calculations and things that can go wrong in something so seemingly simple as making a vehicle appear in the world. Now you see it: Now you're in another galaxy.