Environments like threejs, unity3D and unreal engine include many materials and effects to control how things look like. I feel there is no simple way to go from the barebones look of OF and Processing to something that includes shadows, reflection, etc. Using addons helps, but they are not always up to date, performing, or it may be hard to mix several of those addons in one program.
I just came across this post from the free open source Godot game engine: https://godotengine.org/article/godot-3-renderer-design-explained It includes interesting thoughts about designing rendering engines, and maybe the code, which is MIT licensed, could be useful for OF in some way. I think here is the relevant code and shaders: https://github.com/godotengine/godot/tree/master/drivers/gles3
I don’t have enough experience to make much use of it, but maybe someone else is