[C++] SDL OPENGL - problème de frame rate

#include <cstdlib>
#include <iostream>
#include "windows.h"
#include "GL/GL.h"
#include "SDL/SDL.h"
using namespace std;
#pragma comment(lib,"SDL.lib")
#pragma comment(lib,"SDLmain.lib")
#pragma comment(lib,"OpenGL32.Lib")

void affiche()
{
   //Mettre a zero le tampon de couleurs
   glClear(GL_COLOR_BUFFER_BIT);
   glLoadIdentity();

   SDL_GL_SwapBuffers();
}

int main(int argc,char **argv)
{
	const int WIDTH=800;
	const int HEIGHT=600;
	SDL_Event event;
    SDL_Surface *screen;
    int done = 0;
    int fps, last,now;


    //Initialisation
    if(SDL_Init(SDL_INIT_VIDEO)!=0) {
	   cerr << "Probleme pour initialiser SDL: " << SDL_GetError() << endl;
	   return EXIT_FAILURE;
    }

    //Mettre un titre à la fenetre
    SDL_WM_SetCaption("Pong Version 1.0", NULL);

    //Double tampon
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER,1);

    //Ouvrir une fenetre
    screen = SDL_SetVideoMode(WIDTH, HEIGHT, 32, SDL_OPENGL);
    if(screen==NULL)
      	done = 1;
    //Remettre a zero la matrice de projection
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    // Mettre les matrices en place pour une vue orthogonale
    glOrtho(0,WIDTH,HEIGHT,0,-1,1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    last = SDL_GetTicks()/1000;
    fps = 0;

	//Boucle generale
    while(!done)
    {
        //Traiter les evenements
		while(SDL_PollEvent(&event))
		{
			switch(event.type)
			{
				case SDL_QUIT:
					done=1;
					break;
  				case SDL_KEYUP:
					if(event.key.keysym.sym==SDLK_q)
						done=1;
					break;
				default:
					break;
			}
		}
    fps++;

    now = SDL_GetTicks()/1000;
    if(now!=last)
	    {
	    cout << "FPS: " << fps/(now-last) << endl;
	    last = now;
	    fps = 0;
	    }

    affiche();
    }

    SDL_Quit();
	return 0;
}

typedef BOOL (APIENTRY *PFNWGLSWAPINTERVALFARPROC)( int );
PFNWGLSWAPINTERVALFARPROC wglSwapIntervalEXT = 0;

void setVSync(int interval=1)
{
  const char *extensions = glGetString( GL_EXTENSIONS );

  if( strstr( extensions, "WGL_EXT_swap_control" ) == 0 )
    return; // Error: WGL_EXT_swap_control extension not supported on your computer.\\n");
  else
  {
    wglSwapIntervalEXT = (PFNWGLSWAPINTERVALFARPROC)wglGetProcAddress( "wglSwapIntervalEXT" );

    if( wglSwapIntervalEXT )
      wglSwapIntervalEXT(interval);
  }
}