@party: Weaving thread

I spent this weekend at @party 2010, the first (and hopefully not last) demoparty of this name. The event was in the Town of Harvard, Massachusetts – a bit outside of Boston. I heard four live music performances, saw an early cut of Jason Scott’s almost-finished Get Lamp documentary, and saw and heard grafix, music, and demos (wild and windows) in the Saturday evening compos. There were great tunes, a truly excellent 4k windows demo, an incredible demo running on an Arduino, and much more. Many thanks to the organizer, Metoikos, and everyone who helped her out. And, a big thanks to the demoscene!

Working with two others and using the moniker “nom de nom,” I completed my first demoscene production: thread, a Commodore 64 demo that has fewer than 32 bytes of code. (There are no C64 demos this size or smaller on pouet.net, as far as I can tell.) This demo is a tribute to a BASIC program that generates random mazes, one that exists in one form in the C64 User’s Guide but has also circulated as a one-liner. Here’s a version of the program:

10 PRINT CHR$(205.5+RND(1)); : GOTO 10

I developed thread working in person first with Le Colonial of Atlanta, a sometime co-author of mine who also writes Atari VCS games. (He’s also known as Ian Bogost.) At the party itself, I was fortunate to encounter C64 expert rv6502 of MontrĂ©al, who joined me and did the heavy lifting in the second phase of this project.

After working one evening with Le Colonial in Cambridge, we had a 32 byte program that wasn’t exactly like the original, but did something pretty cool. When I checked it out on my actual C64 right before I left for the party, however, it didn’t work. The SID was initialized differently in the emulators I’d used than it was on the box itself – as it happened – and there was something odd happening with my video display as well.

I brought my C64 to the event rather half-heartedly, without any way of getting programs onto it other than typing them in and without a display. Alas, I wasn’t going to get away from the program that easily: Dr. Claw brought me a monitor to use and NO CARRIER loaned me a flash cart – and, later, a physical copy of the Commodore 64 Programmer’s Guide. rv6502 and I sat down to work further on the program. It turned out my C64’s video was different that of the emulators I used, but also different from Ferris’s actual C64 (which matched the behavior of the emulators I tried). So it wasn’t just an emulator failing to match the metal; the two different C64s apparently have different KERNAL code in ROM. Dumping my machine’s ROM and used that with my emulator would have solved that part of the mismatch.

I won’t try to go into all the details of developing this demo, but there were two particularly great things about the process at a high level. First, I got to collaborate with and learn from two others at different points. Second, I got to learn a lot more about the C64, including many things I wouldn’t have run up against if I hadn’t been working on something like this. I’m not talking about small differences between emulation and the hardware, which were a minor part of this experience, in the end. I mean finding excellent facilities of the 6502 and the C64 to work around those which weren’t doing what we wanted.

We’ve released thread in three versions: The canonical one, which has 31 bytes of code but is in a 33-byte PRG file, because the beginning memory location is stored in the first two bytes of PRG files. If this bothers you, there is a 28-byte version which fits into a 30-byte PRG file and has all the same colors, but displayed in a way that we think is not as pretty. We also include a simple, straightforward reimplementation of the BASIC program above: A 20-byte program in a 22-byte PRG file. I’d love to get this uploaded to pouet.net at some point, but I don’t know how. For now, here’s a zipfile with source and PRGs.

thread got 4th place in the Oldschool category at @party. After you load a PRG file in your emulator (or on your C64), you can run it by typing “SYS 4096”.

Finally, these are the 31 bytes of thread:

A9 80 8D 0F D4 8D 12 D4 A8 B1 F9 8D 86 02 AD 1B D4 29 01 69 6D 20 D2 FF E8 D0 ED E6 F9 50 E9

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