Re: OpenGL orthographic projection

[Gregor Mückl <GregorMueckl@gmx.de>]

On Sunday 25 July 2004 18:45, Steve Baker wrote:
> Gregor Mückl wrote:
>  >     glMatrixMode(GL_MODELVIEW);
>  >     glLoadIdentity();
>  >     glPushMatrix();
>  >     glOrtho(-3,3,3,-3,-20,20);
>
> You havn't set the projection matrix - so probably there is still a
> perspective matrix there.
>

Yes, that was the error.

> I would do this:
>
>       glMatrixMode(GL_PROJECTION);
>       glLoadIdentity();
>       glOrtho(-3,3,3,-3,-20,20);
>       glMatrixMode(GL_MODELVIEW);
>       glLoadIdentity();
>
> Also, you'll probably want to do a glDisable(GL_DEPTH_TEST) because
> you probably still have it turned on from the 3D rendering part of your
> code.
>

Yes, GL_DEPTH_TEST is still turned on. Thanks for pointing that one out. 
However, I have only a limited set of fixed geometry with a distance from the 
camera which is larger than that of the mouse cursor. Unless the contents of 
the z buffer could change its meaning radically when switiching projection 
matrix this should not be a problem. I understand that the z buffer layout 
depends on the near and far clilpping plane distance in projection mode, so I 
don't know how the graphics card will actually behave with respect to the z 
buffer.

Regards,
Gregor