Psychedelia was the first ever interactive 'light synthesizer'. It was written for the Commodore 64 by Jeff Minter and published by Llamasoft in 1984.
psychedelia syndrome is a book-length exploration of the assembly code behind the game and an atlas of the pixels and effects it generated. It should appeal to anyone with an interest in computers, old or new, and provide interesting insights into how 40-year old software produced appealing graphical displays. The book consists of many pretty pictures and a complete, academic-style commentary on the code for all editions of Psychedelia on the Commodore 64 plus a bonus section covering Colourspace on the Atari 400/800.
You can download and read the book here
A dual-page view in your PDF reader is recommended to aid viewing code and commentary side-by-side.
If you'd like to read a hard copy instead you can get the current version from Amazon at a very reasonable price.
You can gift what you want.
You can even sponsor future work.
If you like, you can build the book from source.