I want to add another one of these things (see picure) to the 3d editor window via a plug-in but I dont know theire name. I dont know to where to add them.
I'm not sure there is a way to add them from an editor script or plugin. I think it is part of the C++ code. I have not really looked at it myself, but I think camera_editor_plugin.cpp probably is a good starting point for figuring out how those buttons are implemented in the Godot editor.
