Wormholes - RISC OS 256 bytes

link (sources in .adf)

A 256 bytes real-time intro for RISC OS / RISC PC+, released at NOVA 2025. A combination of early 2025 experiments with the HAKMEM 149 algorithm.

Base algorithm is a 256 colors (mode 21, 640x512) full-screen "rotozoom" (a rotated / scaled bitmap), HAKMEM 149 algorithm is used all over to generate the texture content and do the rotation / scaling.

The rotozoom is spiced up with a real-time "color palette rotation" (it is a software emulation, the palette doesn't really change) done on the background color (the holes of the texture) to produce a depth effect, an offshoot of Dreamelt.

Initial target platform was the Atari ST (with a variant) but i lose interest half way as i was on tight schedules (probably ran too slow as well) so Isopolis was made instead and i decided to support some RISC OS stuff at NOVA with this intro.

It was fairly fast to do the prototype port to ARM by leveraging previous intros code, the only issue was the software emulation of the "color palette rotation" which was done as a separate pass in the original prototype, i solved this by integrating the effect into the rotozoom draw process.

Tinkering with colors and patterns was the main time consuming process... the front colors were initially bright but i felt they dimmed the background effect so i toned them down, finding an okay combination of colors / patterns was a struggle due to sensitive parameters, it ended up okay, i kinda like the bright red border... i still think it was a bit rushed with some wasted potential in term of patterns / colors.

Briefly tinkered with simple sounds support on this intro but trading escape support for some simple tones was not worth it.

Works ok on A7000, works (slowly) on high end Acorn Archimedes when adapted for mode 13. (320x256)

This effect can target early Archimedes when multi write / read instructions are used.

freshly ported version, kinda liked the bubble borders here especially with certain colors

prototype; RGB colors rotation

RGB prototype with pruned patterns to show more of the background effect

RGB prototype; same idea