overgrowth VS lugaru

No but they released the source code, so many one day? Lol https://github.com/WolfireGames/overgrowth

Overgrowth does this as well

Looks like Lugaru is fully open sourced (All Wolfire assets are now licensed under CC-BY-SA 3.0). You can get it here: https://github.com/osslugaru/lugaru/releases If you want something newer, then there is engine for Overgrowth: https://github.com/WolfireGames/overgrowth But game data Overgrowth is still proprietary.

Here's the FOSS source code, the buy page, the Steam page, and the blog announcement.

Overgrowth is the only one that I know of that uses OpenGL exclusively. Just checked it again and they actually released source code just two weeks ago!

Wolfire Games is a tiny studio. Wikipedia says 4 employees. Development of Overgrowth is mostly one person, who documented the whole process in fascinating weekly videos:

https://m.youtube.com/c/WolfireGames/videos

The title says "game engine" because the artwork remains proprietary (similar to old id games, buy the game to get it).

However, just to clarify, all the game code (including gameplay logic, which is sometimes not considered part of the "game engine") is Apache 2.0.

GitHub page: https://github.com/WolfireGames/overgrowth

The (not linked?) GitHub repository WolfireGames/overgrowth

If you're referring to riggedobject.cpp, that apparently includes most of their procedural/physics based animation code. 5k lines sounds reasonable for that.

Looks like Lugaru is fully open sourced (All Wolfire assets are now licensed under CC-BY-SA 3.0). You can get it here: https://github.com/osslugaru/lugaru/releases If you want something newer, then there is engine for Overgrowth: https://github.com/WolfireGames/overgrowth But game data Overgrowth is still proprietary.