Using Qt, you mean that I no longer need to use the other as GLEW?
Qt gives you access to the OpenGL context, as well as many other user input/output resources. So with Qt you don't need GLUT or glfw.
GLEW makes it possible for you to get an access to the OpenGL specific API that is portable. I haven't used Qt myself, but a quick look shows there is the class QGLFunctions that seems to do the same thing. Someone else will have to comment on it. This link and linkwould seem to me that glew is preferable.
I would like someone to answer this question for both of us
glClearColor states what color to use when you clear, so you should call it before glClear.
I would recommend having a look at Learning Modern 3D Graphics Programming. You can browse quickly through the parts you already understand, and quickly get to know how it is done the OpenGL way.
One problem is that Windows only support a very old API to OpenGL (1.1 or something like that), but the device drivers provides full support. To get access to the full functionality, you either have to use a special function to get the address of the extended functions, or you use a library that has it all prepared. I would recommend GLEW for this. I have heard gl3w is also good, but haven't used it myself.
If you want to write code that is compatible with Linux and other platforms, I would recommend glfw for a minimal library that provides an interface to windows management and other input and output devices. Stay away from GLUT.
thank you very much
I'm using Qt 4 (QtOpenGL4.dll) what do you think? That has nothing to do? I program for windows and mac osx