Reddit mentions of Generative Art: A Practical Guide Using Processing

This is one of my favorites https://natureofcode.com/

This is also well regarded https://www.amazon.com/Generative-Art-Practical-Guide-Processing/dp/1935182625

They're also a ton of processing specific articles and many people here will describe their algorithms and share their code if you ask (and often even if you don't)

If "Generative Design" is a bit too pricey, you'd might want to consider
"Generative Art" by Matt Pearson.

Lots of fun generative projects to fool around with!

I'd definitely recommend Learning Processing which is also by Dan Shiffman. It's probably more basic than Nature of Code but if you're only just starting Processing it's a better place to start, I think. I'm making my way through it at the moment and THEN i intend to go on to Nature of Code.

If you particularly want to create stuff like the sketches you linked, then this book seems like a good bet and is on my list to read after Nature of Code. I can't personally recommend it though as obviously I haven't got to it yet.

Unless you are well versed in other programming languages though, I think it is really important to get the basics down first so I'd suggest starting with Learning Processing.

Thanks! I think the best way to start is this book: https://www.amazon.com/Generative-Art-Matt-Pearson/dp/1935182625

Afterwards, less of an introduction and more a collection of generative art recipes, this book is worth every cent: https://www.amazon.com/Generative-Design-Visualize-Program-Processing/dp/1616890770

A great, free and often mentioned introduction to Processing and a lot of interesting concepts is http://natureofcode.com/book, but there is less of a focus on interesting visuals.

If you like books, you could check out this: https://www.amazon.de/Generative-Art-Practical-Guide-Processing/dp/1935182625