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[TheRLG]

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[ThereIsNoSpoon]

You start out by reading the new manual and source code for the game.

[XargoL]

I haven't tried this myself, but I think it's like this:

1. Make your skin class and derive it from IGUISkin (http://irrlicht.sourceforge.net/docu/cl ... _skin.html).
2. Implement all the methods from IGUISkin.
3. Set this class as the current GUI skin with IGUIEnvironment::setSkin().

Have a look at the files CGUISkin.cpp and CGUISkin.h in the source code, which are the implementation of the default skin.