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.