From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,39c061fa6e3ec349
X-Google-NewGroupId: yes
X-Google-Attributes: gida07f3367d7,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news3.google.com!proxad.net!feeder1-2.proxad.net!feeder.erje.net!eternal-september.org!feeder.eternal-september.org!.POSTED!not-for-mail
From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: acceess problem
Date: Sun, 24 Jul 2011 18:27:33 +0100
Organization: A noiseless patient Spider
Message-ID: <m2fwlvzj0a.fsf@pushface.org>
References: <4e2c416b$0$2574$703f8584@news.kpn.nl>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Injection-Info: mx04.eternal-september.org;
 posting-host="dFCm8HWntFqmDIilBLqEJQ";
	logging-data="2452"; mail-complaints-to="abuse@eternal-september.org";
	posting-account="U2FsdGVkX1/dr2/5yZ5qmql0Ym2tEjMIkU7heV6+hU0="
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (darwin)
Cancel-Lock: sha1:AwH2DLh++njlQRhIA0ba4nNGyfE=
	sha1:PiTfLoNhfF+EEirB4oJENqzZdhk=
Xref: g2news2.google.com comp.lang.ada:21306
Date: 2011-07-24T18:27:33+01:00
List-Id: <comp.lang.ada>

"ldries46" <bertus.dries@planet.nl> writes:

> I am converting a C/C++ program with openGL to Ada and found the
> following problem:
>
> C/C++ code: float pAxis1Amb[] = { AxL, 0, 0, 1};
>                     glMaterialfv(vSide, GL_AMBIENT, pAxis1Amb);
> where         : GLAPI void APIENTRY glMaterialfv( GLenum face, GLenum
> pname, const GLfloat *params );
>
> In the Ada bindings the routine is declared as:
>                     procedure glMaterialfv (face   : GLenum; pname  :
> GLenum; params : GLfloatPtr);
> where :         type GLfloatPtr is access all GLfloat;
> and     :         subtype GLfloat is Float;
> I have created the following declarations : Axis1Amb   : array(0..3)
> of GLfloat := ( AxL, 0.0, 0.0, 1.0);
>                                                                                        pAxis1Amb
> : GLfloatPtr := Axis1Amb'Access;
> Now I get the following error message : prefix of "Access" attribute
> must be aliased
> I have to follow the C/C++ code as close as possible.
> What do I do wrong?

That managed to get formatted _really_ strangely!

You could write

   Axis1Amb : array (0 .. 3) of aliased GLfloat := (AxL, 0.0, 0.0, 1.0);

and then

   pAxis1Amb : GLfloatPtr := Axis1Amb (0)'Access;

I guess you're going to pass pAxisAmb to glMaterialfv()? you will
probably get away with this, since a pointer to the first element is
very likely to be a pointer to the array. It might help to tie things
down to add

  pragma Convention (C, Axis1Amb);

I must say, this is a pretty low-quality binding! There appear to be 5
cases of 'pname' where 'params' is a 4-element array, one case where
it's a 3-element array, and one where a single value is required.

Actually IMO it's a low-quality C spec, too; a case of control coupling.