How OpenFramework changed the position of the origin?

I’ve just learned a little knowledge about OpenGL. And I would init an application just like this

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    gluPerspective(90.0, 960.0 / 640.0, 0.1, 50000);


    glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();

    gluLookAt(0.0, 0.0, 320.0 / tanf(PI * 90.0 / 360.0),
              0.0, 0.0, 0.0,
              0.0, 1.0, 0.0);

So my origin was always in the center of the window

MyApp

Different from OpenFrameworks

After long time reading of the OF’s src code, I guess maybe this is the key to change the position of the origin.

But till now I still can not find the true key to solve my problem.

the easiest way to have traditional GL coordinates with the origin at the center and y growing upwards is to use an ofCamera