Here's an old repo last modified 11 years ago, Pie Menus for Gtk+ 1.2.x:

https://github.com/Osndok/gtk-pie-menu

You might look at Simon Schneegans's repos and old web pages about gnome-pie:

https://github.com/Schneegans?tab=repositories

https://schneegans.github.io/gnome-pie

https://github.com/Schneegans/Fly-Pie

But he has moved on to cross platform pie menus with Kando based on Electron:

https://kando.menu/

Show HN: Kando – A cross-platform pie menu for your desktop (kando.menu):

https://news.ycombinator.com/item?id=42525290