I have tried to find cpp source code on github.
I meant that, I can't find the exact file that make control node for inspector property for Vector2 or Layer bitmap.
if you are going to use their code you should contribute to their project.
I'm going to use code because the property I'm making is close or the exact same property type with the engine but with some addon.
I don't think I should be contributing the code of this project because it's seems to be an obscure feature if implement onto the core. This project will be publish at the asset library anyways.