Nrrr-ka-rrrk

Nrrr-ka-rrrk screenshot - spinning coloured squares

This reached second place in the 256-byte intro competition at raww.orgy 2006, the UK’s one and only Spectrum demo party. The concept was to take a rotozoomer, a demo effect well known for being smooth and fluid, and add a darker industrial side to it. I didn’t manage to get it to do everything I’d planned, but then that’s 256-byte size limits for you.

Nrrr-ka-rrrk on Pouet | Nrr-ka-rrrk on Demotopia

Source code is included in the download, if reading Z80 assembler is your idea of a good time.

The techy background: normally, to display a pattern rotated at angle θ you would step over a texture, advancing cos θ steps across and sin θ steps down for each pixel you plot. A cosine wave, of course, is a sine wave shifted by a quarter period. If you vary this so that your ‘cosine’ is shifted more or less than a quarter period, it results in the shearing effect you see here.

For the music (if indeed it qualifies as music), I initialised the Spectrum sound chip with 14 carefully-chosen bytes located at the end of the code. However, the rest of the code over-ran slightly, so those bytes were overwritten by some unrelated data. I tried to trim the code down, but soon realised that the random junk actually sounded better than the bytes that were meant to be there, and so I left it at that.

4 Responses to “Nrrr-ka-rrrk”

  1. icabod says:

    It’s interesting to see stuff like this – how a demo/intro came about. In fact it’s one of the good things about getting together with other sceners and watching old demos… “oh, this bit was done by…”.

    I’m also amused to see that the music in this Intro was by accident. I always assumed that was how you did most of your music ;p

  2. Dave says:

    Nice demo, cheers for posting the code as well. I do love having a nose around and seeing how things are done.

    –Dave

  3. icaBlog says:

    Demo Design…

    Over on Gasman’s blog he’s put up an interesting post about his second-place 256b Intro, “Nrrr-ka-rrrk“. If you’ve not seen the Intro I encourage you to download it and at least view it in a ZX emulator – it’s an odd…

  4. icabod says:

    Hmm. So that’s how trackback’s work.

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