Stefan Röttger

void QGLWindow::paintGL()
{
   // clear frame buffer
   glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

   // setup perspective matrix
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   gluPerspective(90.0,(float)width()/height(),0.1,10.0);

   // setup model-view matrix
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();

   // define local rotated coordinate system
   static double angle=0.0; // rotation angle in degrees
   static const double omega=180.0; // rotation speed in degrees/s
   glTranslated(0.0,0.0,-2.0);
   glRotated(angle,0.0,1.0,0.0);

   // render triangles
   glBegin(GL_TRIANGLES);
      glColor3f(0.0f,0.75f,0.0f);
      glVertex3d(-0.5,-0.5,0.0);
      glVertex3d(0.5,-0.5,0.0);
      glVertex3d(0.0,0.5,0.0);
   glEnd();

   // angle delta equals time delta times omega
   double dt=1.0/fps;
   angle+=dt*omega;
}