pouët.net

I should probably explain this prod to everyone. The beam slide said "kieranhj didn't have time to make a new demo this year so instead here's a sneak peak of our upcoming Amiga emulator for the BBC Micro...". This generated lots of 'WTF's in the crowd but what follows, of course, is an 8-bit demake of Patarty which was an Amiga demo at NOVA 2017.

I'll admit this was a shameless vote-grabbing gag targeted specifically at the regular NOVA audience but there were genuine and authentic intentions behind it. NOVA 2017 was my first ever demoparty, so I have many fond memories of the event, not least the original Amiga Patarty demo for both its ridiculously catchy tune and bouncing patarty-potato that has become NOVA's (un)official mascot.

Towards the start of 2019 I decided to see if I could 'party code' a remake for the BBC Micro, giving myself exactly 10 hours, albeit spread over a week. MrsBeanbag kindly agreed to try DefleMask for the first time to give me a version of the tune for the SN76489 chip in the BBC. My motivation was to (a) give some love back to NOVA and (b) try to create something that was a bit more directly sync'd to music compared to my previous prods.

Although the demo is relatively straightforward for an Amiga, there are actually quite a few technical challenges for a BBC Micro. First of all you can't draw a sprite anything like that big so instead the entire screen is shifted up & down to create the bounce. To do this in single line increments (rather than whole characters) requires carefully timed use of Vertical Rupture and the CRTC Vertical Adjust register. In order to stop the raster bars in the background from also bouncing the palette changing code has to be interleaved with the vertical rupture and dynamically cycle counted.

There isn't even time on a 2MHz 6502 to plot the text to screen glyph-by-glyph in a single frame, so instead the text is all pre-rendered into SHADOW RAM and Vertical Rupture used again to make specific lines appear instantly in the correct place. Of course there isn't enough SHADOW RAM to keep all the text required available so new lines are copied down from banked sideways RAM during the vblank whilst the potato is on screen.

I spent a couple of extra hours at the party to tidy up some of the rough edges, add the greets and the front & back end images to complete the gag. I'm certainly pleased with the result for such a short dev time and I learned a ton of stuff, mostly how hard it is to sync to beats & notes without any decent tools. :)

PS. I really didn't have time to make a new demo for the party this year as I've been kinda busy looking for a new job!

not much comment about this lol, STUNNED SILENCE

Quite, LOL. Either 'you had to be there' or 'there's only so much Patarty the scene can take'. :D