OpenGL: save screenshot

Bonjour,

Je programme en C++ et j'utilise OpenGL pour faire une animation. Je n'arrive pas cependant à sauvegarder les images créées par opengl. J'utilise glreadbuffer et glreadpixels mais l'image créée ne contient que la moitié du buffer.

Voici ma fonction display

void display(void)
{
 
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glMatrixMode(GL_MODELVIEW);
  glClearColor(0.8f, 0.8f, 0.8f, 0.0f);			
 
 
  glPushMatrix();
	glTranslatef(0.0, 0.0, -5.0);
	displayObject();
  glPopMatrix();
 
  glPushAttrib(GL_ENABLE_BIT);
  glDisable(GL_DEPTH_TEST); glDisable(GL_LIGHTING);
  glMatrixMode(GL_PROJECTION);
 
  glPushMatrix();
	  glLoadIdentity();
	  gluOrtho2D(0, 3000, 0, 3000);
	  glMatrixMode(GL_MODELVIEW);
	  glPushMatrix();
		  glLoadIdentity();
	  glPopMatrix();
	  glMatrixMode(GL_PROJECTION);
  glPopMatrix();
 
  glPopAttrib();
 
  OGL_SaveScreenshot(counter++);
 
  glutSwapBuffers();
}

et la fonction pour sauvegarder le contenu du buffer:

void OGL_SaveScreenshot(int i)
{
 
    char filename[2048];
 
    std::ostringstream buff;  buff<<"SavedImage"<<i<<".png";
    strcpy(filename, buff.str().c_str());
 
    png_structp png_write = png_create_write_struct(PNG_LIBPNG_VER_STRING,NULL, OGL_png_error, OGL_png_warn);
 
    if (!png_write)
    {
        printf("Error creating PNG write struct.\n");
        return;
    }
 
    png_infop png_info = png_create_info_struct(png_write);
    if (!png_info)
    {
        png_destroy_write_struct(&png_write, (png_infopp)NULL);
        printf("Error creating PNG info struct.\n");
        return;
    }
 
    if (setjmp(png_jmpbuf(png_write)))
    {
        png_destroy_write_struct(&png_write, &png_info);
        printf("Error calling setjmp()\n");
        return;
    }
 
    // open the file to write
    FILE *savefile = fopen(filename, "wb");
    if (savefile == NULL)
    {
        printf("Error opening '%s' to save screenshot.\n", filename);
        return;
    }
 
    png_init_io(png_write, savefile);
 
   unsigned char *pixels = (unsigned char*)malloc( glWindowWidth * glWindowHeight*3  );
   glReadBuffer(GL_BACK);
   glReadPixels(0,0,glWindowWidth,glWindowHeight,GL_RGB,GL_UNSIGNED_BYTE,pixels);
 
   if(NULL==pixels)
	   printf("Error NO PIXELS \n");
 
   // set the info
    png_set_IHDR(png_write, png_info, glWindowWidth, glWindowHeight, 8, PNG_COLOR_TYPE_RGB,
                 PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,PNG_FILTER_TYPE_DEFAULT);
    // lock the screen, get a pointer and row pitch
    long pitch = glWindowWidth * 3;
 
    png_byte **row_pointers;
    row_pointers = (png_byte **) malloc(glWindowHeight * sizeof(png_bytep));
    for (int i = 0; i < glWindowHeight; i++)
    {
        row_pointers[i] = (png_byte *) (pixels + i * pitch);
    }
 
    png_set_rows(png_write, png_info, row_pointers);
    png_write_png(png_write, png_info, 0, NULL);
 
    // free memory
    free(row_pointers);
    png_destroy_write_struct(&png_write, &png_info);
    free(pixels);
}

Est-ce que quelqu'un aurait une idée ?

Merci