Tutorial / references / resources for augmenting ggplot2

Hi

There is a sea of blog posts / user manuals / gitbooks (starting with Hadley Hickman's book) on the topic of customizing ggplot2 calls. However, I am struggling to find resources explaining how to create new functions to augment and works within the ggplot2 framework.

Any advise on the matter would be appreciated.

Sebastien

Here are two links:
Extending ggplot2 • ggplot2 (tidyverse.org)

21 Writing ggplot2 extensions | ggplot2 (ggplot2-book.org)

P.S. It's Hadley Wickham by the way.

Awesome... bedtime reading!