Skip to content
A silly toy Mandelbrot program for the BBC Micro.
Branch: master
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.


A less stupid mandelbrot program for the BBC Micro. v1.0, 2018-05-26


This started life as a really hacky toy which could draw a sort-of Mandelbrotish image on a BBC Micro in about 12 seconds; it grew into a much less hacky toy which can generate almost real-time (usually 30s per frame) Mandelbrots and Julia sets with 15-bit fixed point arithmetic. It mostly achieves these using a really rather clever Mandelbrot kernel written by reenigne, aka Andrew Jenner, so don't blame me.


To build, you need beebasm. There's a single mandel.asm file in the src directory; assemble this. There's a Makefile with the right command in it.

The resulting problem will only run on an BBC Master 128, as it uses one bank of sideways RAM (#4).


Why not?

This has been a really interesting learning experience in machine code, fixed point arithmetic and cheating the system. There's too much to go into here, but here's the writeup of my 8-bit fixed point version:

...and here's the writeup of the current, much better version:

Why not?

15 bits isn't really enough precision to do much, as you will notice once you hit the zoom limit. (Try looking at Julia sets at maximum zoom. Lots of artifacts there!)


Two-clause BSD; see the COPYING file. Go nuts.


This was written by two people:

Most of the program was by myself, David Given; I have a website at There may or may not be anything interesting there.

The kernel is by reenigne, aka Andrew Jenner; reenigne's musings on very fast Mandelbrots on the 8088 led to this program, so you might like to check out (This was then somewhat hacked by me, so bugs will be my fault.)

You can’t perform that action at this time.