Watching Logo Demo (Plus/4)

Logo Demo from 1990 prominently features, as the name suggests, a large logo which was actually won in competition by a previous release of the programmer! Plus/4 scene stalwarts Muffbusters ran a 20 blocks democompo a little earlier in that year where the prize on offer for the winner was a bespoke logo drawn by group member Jeva and it was developer CSM who took the top spot with his release 20 Blocks. Two of the other three entries appear to have been lost to the mists of time, but third place was taken by a demo also called 20 Blocks which was a rough around the edges port of Moz(IC)art’s Luminous from the C64.

Along with that large, golden logo taking pride of place at the top of the screen and an area below it occupied by some blue colour splits – that routine is important, so we’ll cover it in more detail soon – there’s also a long scrolling message and the visuals are accompanied by a fairly short but still jolly piece of converted music which burbles away to itself in the background. The original SID version of the tune is credited to the Maniacs Of Noise in the scroller, but isn’t a piece I recognise even after spending a fruitless but nonetheless entertaining hour trawling through the relevant folders of the High Voltage SID Collection.

The entry for Logo Demo at Plus/4 World reliably informs us that the colour splitting routine CSM created was actually a significant piece of demoscene history for the machine, being the first time that abybody had managed to vertically split the border colour register so that there’s a different set of colours on each side of the screen. There’s also some neat multicolour character use to handle the transition of colours on the screen itself, which allows the split to swing smoothly back and forth… although I can’t help thinking that the colour tables themselves could have taken greater advantage of the platform’s 121 colour palette. That niggle aside though, this is a fun release which features a decent tune, some tidy graphics and a groundbreaking effect on the Plus/4.

Demo Factory 2018 (C64)

Okay, so between writing the first draft of Saturday’s post rambling about the development of Demo Factory and actually pushing it out to the world I found myself pondering ways to rework it and… well, sort of accidentally wrote a complete, upgraded version! Demo Factory 2018 has been through a few iterations since that first build, but the final code was finished in the early hours of this morning. The music this time is from the game Ninja Rabbits and was composed by Sean Connolly, whilst the general layout of the screen was based on the original 1976 release with some tweaks to add new features. After that, everything else was pretty much built from scratch.

In some respects at least this version works in the same way as the original Demo Factory, relying on the C64’s hardware-based sprite to background priority register for the disks – that’s why one of the character multicolours is black in both versions, those parts of the graphics can never have a higher priority than the sprites so the moving floppies are actually passing in front of those parts of the background – but the sprite-based part of the scroller has to work differently, with the left hand character being a sprite that’s being masked in software so it can pass behind the black part of the pipe regardless of the letter’s current colour.

Although there’s one highlighted effect running in the box labelled “VFX” there are also two starfield-like routines, the animating “SFX” cone and a couple of other, smaller elements which are mostly being refreshed every frame – the moving arrows are shifted every second frame because they don’t look as pretty moving faster and things like flashing lights change only when needed – and that lot are all handled with either character redefinition or simply changing the screen or colour RAM. The only hardware sprites in use are the eight floppies which are either on or sitting by the lower conveyor, the last three characters of the scroller as it falls from the upper belt and one expanded sprite which displays the character that’s just about to appear for the scroll.

I did consider saving Demo Factory 2018 for the CSDb intro competition if it happens this year – the highest byte of memory used is $3FFF since the upper and lower borders are open and the ghostbyte needed to be zeroed so the code is small enough and it does technically feature a logo – but it feels more appropriate to put it out now alongside my fevered ramblings about the original. The source code has been cleaned up and can be squinted at courtesy of GitHub for those who might be so inclined.

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…?