Little help setting up OpenGL

[manasij7479]

How do I change the following lines during the initialization, so that
the origin is at the center and not at the bottom left ?

    glMatrixMode ( GL_PROJECTION );
     glLoadIdentity(); 
    gluOrtho2D ( 0.0, (GLdouble)320, 0.0, (GLdouble)240 );

[bernt]

For a clipping rectangle with width xSize and height ySize:

gluOrtho2D(-xSize/2.0, xSize/2.0, -ySize/2.0, ySize/2.0);

[manasij7479]

Excellent.
Thank you very much...