void display() 
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();
    gluLookAt( 0,0,30, 0,0,0, 0,1,0);
    glPushMatrix();
    glRotatef(g_rotation,0,1,0);
    g_rotation += 0.5f;
    obj.draw();
    glPopMatrix();
    glutSwapBuffers();
}