Sunday, 30 June 2013

Chromatrons Attack

Genre: Arcade: Smart arse action

By Guesser, music by Gasman

Any CSS or WoS regular will know this entry has been a long time coming, with work on the engine predating this years competition.  Guesser started cranking up his hype machine earlier this year by announcing…”THEY’RE COMING”, well now finally they’re here – and what a formidable foe the Chromatrons prove to be.
Guesser points out that the purpose of the game is not necessarily to be fun (glad to hear it!) but to “wind up emulator authors”.  Load Chromatrons up in any emulator and you’ll see what he means, you can hear Gasman’s nifty AY music but this is what you’ll see:

 You can just about make out the drawing through the shimmering moire pattern, and when you press caps shift to start the game it’s possible to make out a few sprites (which can naturally be controlled with the keys WASD) but that’s about it.  Clearly there is some trickery going on here, this game is specially formulated to only be playable on a real spectrum connected to a TV.  For those blessed with this set up I recommend giving it a go (128k only, paging must be enabled), and you will see this:

I didn’t expect that.  I thought it would still be a grey mess, just a clearer grey mess.  I’ll leave it to the hardware people to explain the technical aspects of it, but I can confirm that the attributes are set to black on white, not magenta on cyan.  Which finally brings us onto the game itself, while you can just see the sprites on an emulator what you can’t see is the scrolling landscape.
2 pics provided by p13z

You must pilot your spacecraft (forever it seems, there is no endgame here) while being pursued by the deadly Chromatrons.  Basically avoid the ever increasing numbers of aliens and the walls.  The sprites move in character steps and the scrolling landscape is (I think) attribute based.  The further you go the higher the score, a formula many of us love and will find quite addictive.  It’s also a great feature that your shields build up after a loss, so all is not lost if you screw up.  Guesser (or his beta tester) start the Hi Score challenge at 1923.
So this game displays a great knowledge of the hardware and coding skill (done in assembly), but is it crap?  Well the fact I’ve just loaded it up again on tape to try and beat my own hi score of 1313 suggests not, but the WASD keys might just be enough to save it…
Thankyou Guesser!


  1. Guesser added this explanation of how the game works over at the CSS site:

    The short and techy answer is that the TV is unable to completely
    separate the high frequency transitions in the luminance signal from the
    modulated chrominance, so some of the black and white signal leaks into
    the colour.

    By generating a specific pattern on screen that high frequency cross
    colour interference can be manipulated to make the TV generate stable
    blocks of colour.

    The effect is being caused by the limitations of the analogue video
    circuitry and the way a PAL video signal works. Emulators of course
    represent an ideal video signal with unlimited bandwidth etc and make no
    attempt to accurately model a PAL signal.

    (Errr easy! DH)

  2. i think that games from Apple-II and CoCo2 uses a lot these artifact effects

  3. "Load Chromatrons up in any emulator and you’ll see what he means"?
    Not if that emulator is Spiffy...

    Actually I had working PAL chroma bleed months ago, but I've only just implemented 128k support. (Previously, Spiffy could only run some of Guesser's earlier experimental demos of the effect.)

    So, if you don't have a real 128 lying around, but you _do_ have a Linux box lying around, you can now play Chromatrons in an emulator!