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From: "Joachim Schr�er" <joachim.schroeer@web.de>
Newsgroups: comp.lang.ada
Subject: Re: New Ada binding to OpenGL
Date: Fri, 3 Jan 2003 19:38:41 +0100
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Xref: archiver1.google.com comp.lang.ada:32499
Date: 2003-01-03T19:38:41+01:00
List-Id: <comp.lang.ada>

Hello,

to pass null simply write something like
Gl.Glclipplane(Plane => 1, Equation => null);

But why do you want to pass null access values.

I expect some kind of error in the C code then.

I will have a look for books were Ada/C coding is documented.

I thing, the Ada95 rationale is a good reference. I will give you links
later.

    J. Schr�er

"David Holm" <david@realityrift.com> schrieb im Newsbeitrag
news:V54Q9.3365$FF4.203703@newsb.telia.net...
> Joachim Schr�er wrote:
>
> > 4) The subprograms taking system.address parameters are superfluous and
> > represent a not very Adalike style. It is very staightforward to call a
> > function with access parameter mode or with a general access type.
Simply
> > declare arrays of aliased variables and pass
> > The_Array(The_Array'First)'Unchecked_Access. Take the following example
to
> > call
> > procedure glClipPlane(plane : GLENUM;
> >
> >                                   equation: access GLDOUBLE); --
> > ./GL/gl.h:791
> >
> >
> >
> > package Opengl.Clip_Planes is
> >
> > -- Plane coefficients -----------------------------------------------
> >
> >
> > A : constant := 1; B : constant := 2; C : constant := 3; D : constant :=
> > 4;
> >
> > -- Plane-type and simple clip-plane constants -----------------------
> >
> > type Plane is array(A .. D) of aliased Gl.Gldouble;
> >
> > ...
> >
> >
> > and then in the implementation
> >
> > procedure Enable(The_Plane : in Plane) is
> >
> > begin
> >
> >   Counter := Counter + 1;
> >
> >   if Counter <= Clip_Plane_Indices'Last then
> >
> >     Gl.Glclipplane(Plane     => Clip_Plane_Indices(Counter),
> >
> >                           Equation => The_Plane(A)'Unchecked_Access);
> >
> >     Gl.Glenable(Clip_Plane_Indices(Counter));
> >
> > ...
> >
>
> How can I pass null addresses this way? With System.Address I could use
> GLNULL : System.Address renames System.Null_Address;
>
> //David