It is based on an algorithm published on pouet in 2021. One its implementation uses 16 color mode and another uses 4 color mode and textures to simulate 8 colors. Generated pictures are 128x256 and 256x256 raster images respectively. It is very likely that this algoritm implementation is the fastest known Mandelbrot set computation routine for the 6502.
A zipped dsk-image is here: use
*LOAD M4 or
*LOAD M16 to get 4 (8 because of dithering) or 16 (8 + flashing) color programs respectively. Start any of them with
Sources are available on github.
This program starts from 0xE00 because it needs 11.5 KB RAM for a lookup table, 16 KB RAM for video and 1 KB for its code. So if you want to run it on the BBC Micro where PAGE is above 0xE00 you will need to use some trick.
This program uses video memory directly so it can't be used with the 2nd co-pro.