An Arrow Through The Code? Jet Set Willy's Weird Bug Explained

#Speccy
One of the strangest and most intractable bugs in classic gaming laid bare. The glitch that made ZX Spectrum smash hit Jet Set Willy a lot harder than it should have been.

Music:

Space Navigator
Yellow Flamingo

Sarah, The Instrumentalist

Sleeplessness

The Bothers Records

Background image:
Paweł Czerwiński

Jet Set Willy Map

Pavero

[dfactotum]

I know I'm a bit late here, but just a note about the collision detection: the way that worked in JSW was that the game checked when it was drawing the enemy sprite to see if it intersected anything on the screen. Since the normal setup was that the enemies would never overlap the scenery this was fine--the only thing they could possibly touch was the player sprite. The corrupted guardian data could move the guardian into a position where they were overlapping something else as soon as you entered the room, though, which is why you instantly died.

[akumjh]

The title turned out to be far more literal than I expected.

[globus]

As someone who didn't get any further than BASIC programming it was great to have this explained so simply - cheers!

[immortalsofar]

My first assembler program on the C64 was a simple, petscii pong game - replacing the ball with a space for animation. Every now and then, this would knock a block out of the wall and, hitting that spot again, would send the ball ploughing through memory leaving a trail of spaces behind it, ricocheting off any bytes of memory that happened to coincide with a wall block. At this point, it would either hit zero page and crash the machine or hit the VIC chip, make a farting sound and crash the machine (a sound effect I used in my next game). That certainly became a feature - hitting that spot became the whole point of the game!

[trippymchippy]

I remember the days of typing 500 lines of basic from 'Sinclair Weekly' in order to land the 'V' on the '=' and avoid the '*''s... amazing stuff...
And then came Zombie Zombie - mind blown ;)

[tomkrawec]

Extremely informative video, only drawback is not playing enough of the JSW intro music at the start.

[MajoradeMayhem]

"... what passes for the Speccy's GPU..."
I love your snark, hah

[Domarius]

Jet Set Willy to Cave Story: "I used to be an indie game like you. But then I took an arrow to the code."

[Tomsonic]

As a 5 year old, I was absolutely TERRIFIED of the giant face in the Chapel and Priest's Hole, and remember my dad showing me how it had vanished one time when we were playing. Little did I know what would happen when I tried to get to the Kitchen...

[chrislambe]

1984 - It is not a bug it's a feature. Love it.

[elektronkim]

I never forget my first game project with some ZX-Spectrum assembler. I let some Basic code run for making a road. The assembler was the car with keys for left and right movements, collision checks and drawing the road again. It was 20 lines of each and felt so speedy. A good road could be dumped to tape and reloaded. One mistake in the assembler gave a full crash and reset the ZX-Spectrum. Bad code would always send the execution address to ROM address 0 eventually with maybe 32768 instructions of random nature. At 7 MHz that's a split second.

[LordmonkeyTRM]

"Our bugs are features" sounds familiar...great video as always.

[Becka_Harper]

The CPC version alongside Elite was my gaming life for a very long time. I still have very fond memories of hundreds of hours spent playing it.

[ChrisWalshZX]

Great description of The Attic Bug. I knew a rogue arrow was the cause but not about the two areas of Guardian Data. Clearly, if you were to enter and leave when the arrow hasn't traveled much, the amount of "damage" would be less. Thanks

[nagualdesign]

1984 was the year I first learned how to program. Great days.

Anyone else reading the words "Google" out of the worm at 7:40?

[MrMegaManFan]

It’s lovely that home enthusiasts fixed it but absolutely horrid that the publisher lied to people about it being intentionally designed that way. These days that would bring on a massive lawsuit!

[PearFinch]

Fascinatingly, there’s a Jet Set Willy cameo on FL Studio.

[matthewrease]

When you said an arrow I thought it was going to be an issue with a pointer in memory but no you meant a literal around lol. That's fantastic...

[Mark-prug]

A classic game which I never completed until decades later via a CPC emulator.