Code Notes – HDM Demo 1

It’s that time again dear reader (or thereabouts, your correspondent is aiming for one of these or a Release Notes post every second Thursday but was a little tied up yesterday) and it seemed like an interesting idea to branch out somewhat so, rather than covering a C64 demo, this third instalment in the Code Notes series is heading over to the author’s other former stomping ground, the Amstrad CPC. And, after a few hours of  pootling around at the CPC Rulez database, a candidate was selected; it does step away from the mid to late 1980s and wasn’t developed in the United Kingdom, but still seemed, to your correspondent at least, to be an interesting production to examine.


HDM Demo 1 by Happy DemoMaker

An Amstrad CPC demo released in 1991
Programming by Arkad
Graphics by THM
Music by various

Since the intention with this series was keep things at least relatively simple by examining one-part or at least one-file demos, what appears to be a first release from the wonderfully-named CPC crew Happy DemoMaker seems as good a starting point as any, offering up a couple of scrolling messages, some colour splits, a static picture and some stolen music. According to the upper scroller this demo took a month to write and was released during September 1991.HDM Demo 1 (Amstrad CPC)HDM Demo 1 utilises the Amstrad CPC’s mode 1 (which is a 320 by 200 pixel bitmapped screen with four colours by default) and there are three actual effects in play; the first is at the top where we have a routine which has the computer waiting for the start of each scanline in that area before setting two of the colour registers; there are static “colour bars” being fed to the background and a routine which draws a different set of colours to both background and logo whilst it patrols up and down. The second effect are the two scrolling messages which your correspondent assumes are using Z80 LDIR commands to move the relevant chunks of screen memory at one byte per frame before writing the next piece of character data in at the right hand side.

And between said scrollers are the mostly static graphics, specifically a picture of a CF2 floppy disk which is labelled “Copiez Moi”[1] and a Happy DemoMaker logo which is bookended by a couple of heads that loosely resemble Sentinel One from the 1980s cartoon series Space Sentinels. Pressing keys 1 to 5 both selects different pieces of extracted game music and alters the otherwise static message placed below the aforementioned logo as well and the final effect is a couple of bars below the CF2 where the lengths are being set depending on what is currently being played by two of the CPC’s AY sound channels.

HDM Demo 1 isn’t the pinnacle of user-developed code for the Amstrad CPC any more than Planet Invasion was for the C64, but your correspondent is focusing more on these releases because they’re the “meat and two veg” of the demo scene. Productions like these are representative of the bedroom coder since they’re usually just thrown together by a couple of friends for their own amusement and this usually comes across in the final result.

But one important thing to note from C64CD’s viewpoint is that this demo is relying on music stolen from games; the author bleated petulantly about this when your correspondent covered a C64 release doing so previously, saying that he believed it was “because there are no commands to produce music on Commodore BASIC V2” so it will be interesting to see how he vainly tries to backpedal about the same thing happening a few years later on the Amstrad CPC where said commands are present.

[1] Your correspondent is, as the author has noted, monolingual so obviously isn’t aware that said text would translate as “copy me”.


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2 Responses to Code Notes – HDM Demo 1

  1. ergoGnomik says:

    Better be monolingual than monomaniac. Somebody should offer the author this link: Although he wouldn’t understand why he got it and what to do with it.

    • TMR64 says:

      That’s an interesting read and I recognised a few things that I do in there as well, although they were mostly down to the faux tabloid writing style… I hope!

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