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From: "Luke A. Guest" <laguest@n_o_p_o_r_k_a_n_d_h_a_m.abyss2.demon.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: Access type conversions, how?
Date: Tue, 13 Apr 2004 20:31:43 +0100
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On Tue, 13 Apr 2004 18:54:20 +0100, chris wrote:

>  From the code you posted it looks like a convoluted solution.  Maybe 
> it's the lack of context.

No, it's really really simple...the code I posted was all you needed.
 
> I would do one of two things.  Either just stick with the native GL 
> types or make Ada ones corresponding to them and convert like this...

Yes, and like I said before, when writing portable games, i.e. games that
will not always have OpenGL available, I need to to not do this. I need to
abstract it away, hide the rendering code, etc. I cannot say this any
other way.
 
> type GLMatrix is array (1..15) of GLFloat; pragma Convention (C,
> GLMatrix);
> 
> type OpenGLMatrix is array (1..15) of GLFloat;
> 
> 
> A : OpenGLMatrix;
> 
> A (1..15) := OpenGLMatrix (SomeMatrix (1..15));
> 
> or A := OpenGLMatrix(SomeMatrix);

No, unacceptable. I don't want to be creating/destroying temporary arrays
like that, especially for a 3D game.

>> But as GL bindings use the GL types, I cannot get a pointer to convert
>> to another pointer with the same base types.
> 
> Why do that?

Take the glMultMatrixf procedure I posted before, *you want to have your
own types* but *you also want to be able to pass them to the GL functions*
but it's tricky because the strong typing is getting in the way. I need a
way to convert my aliased matrix type to another. That function expects a
GL.GLfloatPtr, I want to use something else, do you understand?

Luke.