SDL_GL_SwapBuffers() in a loop = Freeze?

I read a few tutorials about OpenGL and now I'm trying to use it with SDL. The thing is that when I use SDL_GL_SwapBuffers() in a while loop the window just freezes. Here's some code:

#include "SDL.h"
#include "system.h"
#include "SD开发者_如何学PythonL_opengl.h"
System Sys(800, 600, 32);
SDL_Event kpress;
int main( int argc, char* args[] )
{
    Sys.init();
    bool quit = false;
    while (!quit)
    {
         while (SDL_PollEvent(&kpress)) if(kpress.type == SDL_QUIT) quit = true;
         glClear(GL_COLOR_BUFFER_BIT);
         SDL_GL_SwapBuffers();
    }
    SDL_Quit();
    return 0;
}

------------------------------These are in system.h, class System----------------
    bool System::init()
    {
        if (SDL_Init(SDL_INIT_EVERYTHING) < 0) 
        {
            errorCode = 1;
            return false;
        }
        if (SDL_SetVideoMode(screen_h, screen_w, bpp, SDL_OPENGL) == 0)
        {
            errorCode = 2;
            return false;
        }
        SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
        if (!init_GL())
        {
            errorCode = 3;
            return false;
        }
        SDL_WM_SetCaption("Engine", 0);
        return true;
    }
    bool System::init_GL()
    {
        glClearColor(1, 0, 0, 0);
        glClear(GL_COLOR_BUFFER_BIT);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(0, screen_h, screen_w, 0, -1, 1);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        if (glGetError() != GL_NO_ERROR) return false;
        return true;
    }

If I draw some shapes or use a timer for limiting FPS - nothing changes. Do you have any ideas?

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My first advice: Get rid of that bogus System class: So far all the tasks it does are purely sequential/procedural and that should be reflected in the programs outline. People tend to put everything into classes just becase they're taught see everything in terms of object models. But this System class would have to follow the singleton pattern, which, in my opinion, is an anti-pattern.

All the stuff you placed in init_GL belong into the rendering loop. OpenGL initialization ends after creating a render context. OpenGL state is not initialized it is set on demand. OpenGL objects are initialized, but also on demand.

Also you're using glGetError not correctly. It needs to be called in a loop until no more errors are reported. It thus also makes little sense to bail out if a GL error is reported. OpenGL errors should be considered diagnostic.

SDL_GL_SetAttribute must be set before calling SDL_SetVideoMode so you're probably not double buffering.

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Hey, you aren't calling the function which initializes OpenGL: init_GL()

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youre not checking the result from system::init - it might be failing somewhere in that function and not setting up your initial state correctly

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SDL #defines main() to be SDL_main() to allow it to do some extra initialization before program start. Which you seem to be bypassing via the statically initialized class.

Try constructing your System object in main().