GTK theme engine: where to start?

I would like to start coding a gtk theme engine, but i'm wondering where i can find some documentation, if any exists. I know how to have look at someone else engine's code, examples, or torture tests and widget factories etc.., what i want instead is any documentation type, design, references, examples or tutorials possibly from reliable sources such as the Gnome foundation or the like. You know, when coding for the Win32 platform one can pinpoint reliable references on the subject by following the MSDN and then read a variety of other sources to see how the problem has been tackled, if any.

So, where to find an authoritative, reliable and possibly complete source of documentation about GTK theme engine development? Is there any for real?

Later added:

Also, how to debug such an engine? What's the most sane and pain开发者_如何学Pythonless way to perform testing and debugging on such a delicate os' ui component?

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Well, you can look for instance at the source for the gtk smooth engine in Ubuntu most of which is in one fairly enormous C file smooth_gtk2_drawing.c. I don't know if that's an especially good example, but probably finding whichever looks simplest or most actively maintained would be a good idea.

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A theme engine is typically used to change the shape of widgets among other things. If you're just trying to change the color scheme and so on, you just need to create a theme.

Just like the theme engines, theres not a whole lot of documentation when it comes to creating a theme either. However, there are a ton of examples at http://www.gnome-look.org