I´m learning c++ and I have found several GUI toolkits. Some of wich I like a lot, but I´m not completely happy with them (for one reason or another).
I am very intersted in GUI development, I would like to know about where to look for info about how to develop GUI´s from scratch.
Books or tutorials, I have been doing some google, but I don´t seem to find anything in this matter.
Another thing, I would like them to be platform independent.
As i said I´m just beggining, but I think that GUI´s is where I would like to get in the future.

Thanks in advance.

What do you mean by “from scratch”?

If you mean that you'd like to start developing new GUIs using existing libraries, then you may want to take a look at the documentation for Qt (www.troll.no). It provides very good tutorials (and I suspect there's something similar on the gtk homepage, although I haven't used gtk myself).

If, on the other hand, you want to learn how the Linux X-windows GUI works from the X server up, then you should look for documentation on a package called Xlib. Good books on Xlib are few, far between, heavy and expensive (in my experience) but it really is the lowest-level API for GUI development in common usage. There are also alternatives, like SVGAlib for drawing in the console rather than on an X server.

I´m interested in writing my own libraries, or new libraries (like new widgets) for already made packages like QT, WideStudio, GTK, WxWidgets and so on, not just using what they already have.

For what I can see I will be talking to the Xlib to draw things in the screen, still, I would like it to be OS independent.

Thanks.

Dive deep into GTk, Qt, or whatever tookit, and try to build your tookit on top of their base-classes, or just try first to make extensions to it.

Could save you a lot of hassle, especially if you want to be OS-independent. Even creating a "Hello World" program using Xlib is a non-trivial task at all. Let alone building a whole new API on top of it. You said you were just beginning...

That´s more less what I´ve been doing (reading their source code).
What I´m looking for is the basics, it is a long term plan.
But I can´t seem to find books or anything that will guide me in this matter.