Watching Demo Factory (C64)

Let’s do something a little different and look at one of my own demos, specifically Demo Factory on the C64 from 1987. The original idea came about from a brainstorming session with friends and was intended to be a less than serious response to the plethora of bog standard demos around at the time which usually included a bitmapped picture, some music and a sprite-based ROL scroller in the border. We all found the idea of an automated factory churning these similar-looking demos out on a conveyor belt amusing so I set about programming, pausing only to work things out on paper first – something I haven’t bothered doing since – and to read up on how the hardware sprite priority registers worked from the C64 Programmer’s Reference Guide.

Looking back now the code itself is embarrassingly simple – even more so than I remembered it being in fact – but in my defence I was still learning assembly language and indeed the C64 at the time. The music is Rob Hubbard’s Hunter Patrol theme which arrived as a file he’d uploaded to Compunet that had the music located low in memory and started an IRQ to play it before dropping back to BASIC; my code calls that and executes behind it, using timing loops rather than actually waiting for a rasterline or anything sensible because I didn’t know better. I’m tempted to call this my first “real demo” because, despite there being a few releases prior to it including Past Shock, this was the first time I managed to get action on the screen with someone else’s music playing.

The “logic” was, if I recall correctly after three decades, that a parody didn’t have to be particularly well programmed because shonky code could be passed off as part of the joke; similarly, the lack of a scrolling message was absolutely part of the “protest” against bog standard demos and not in the slightest because I couldn’t get one working or anything like that… honest! There’s also a healthy whiff of irony and very probably hypocrisy about me of all people railing against the bog standard demo as a format since I’m incredibly fond of it as a format, was inspired to start coding demos by releases like Future Shock and have since programmed several releases over the years which stick to that tried and tested formula.

I’ve considered doing a remixed version of Demo Factory on a couple of occasions previously which would be an overhaul of the graphics and actually running from interrupt with all the benefits that would entail; it could perhaps animate all of the elements of the demo making machine that I wasn’t able to handle back in 1987 as well and, just for the sake of irony, would probably include a scrolling message as well…?

2 thoughts on “Watching Demo Factory (C64)

  1. Aw, ain’t that sweet. T.M.R wasn’t always a coding legend and had to start somewhere… 😉

    Seriously though, it’s decent stab at a demo for someone still learning and earns bonus points for the ‘irony’ within.

    That music brings back fond memories. I remember loading the game just for the music and leaving it playing while I got on with other things in the confines of my bedroom. Actually, that sounds a bit dubious…

    Great idea to do a remix! How about starting with something that looks identical to the original then slowly ‘upgrade’ parts of the screen to end up with something new and shiny?

  2. There’s a fair few people who’d say I’ve never been a coding legend… with me being probably the most likely culprit, now I think about it! =-)

    And as for Demo Factory 2018… we-ell, let’s just say “watch this space”?

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