menzel, what do you mean by "fragment varying out variable"? 'Varying' was used for the interpolators that link vertex/geometry with fragment shaders, but now the term is dropped altogether.
If you mean just the fragment shader outputs, then i'm for it. If vertex attribs and uniforms can be queried then fragment outputs should too, at least for consistency.
There are APIs (BindFragDataLocation, GetFragDataLocation) that accept those names as arguments but there is no way to find what the names are (except by parsing the shader text by hand).
I think this inconsistency should be addressed.
I_belev : Yes, I mean the fragment shader outputs.
As for it's usefulness, it sure is useful. For example you can think of some wrapper library that stays between the application and the OpenGL. That wrapper does not know the names of the fragment output variables in the shaders that the application gives (its a separate piece of software) but it still may want to do something with them (depending on what is the purpose of the wrapper).
Welcome to three months ago; glad you could make it. I even made a convenient OpenGL Wiki article on the topic.I'm disappointed that my words were misinterpreted and ignored.
Thanks ScottManDepth and Alfonse!
My knowledge of cutting-edge GL is not up to date, and looking for fragment output queries got me only to this thread.
That's nice to finally have this functionality in GL4.3! I'm still a bit sad that it's not possible to query fragment outputs on my R700.
Blame AMD's slow implosion for that, not OpenGL.