Date: Thu, 8 Jan 2004 17:19:50 +0100
To: Sven Luther <sven.luther at wanadoo.fr>
Cc: lablgtk at kaba.or.jp, Jacques Garrigue <garrigue at kurims.kyoto-u.ac.jp>,
        218823@bugs.debian.org, control@bugs.debian.org
Subject: Re: lablgl and runtime vs compile time GL version detection.
Message-ID: <20040108161950.GA18528 at iliana>
References: <20031129113754.GA3375 at iliana>
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In-Reply-To: <20031129113754.GA3375 at iliana>
From: Sven Luther <sven.luther at wanadoo.fr>

hello,

I want to fix this before the debian/sarge release, but have got 0
feedback on this. I may find time to do the work needed, but would like
to get feedback on the idea before i commit time to it, that may then
later be rejected.

Friendly,

Sven Luther

On Sat, Nov 29, 2003 at 12:37:54PM +0100, Sven Luther wrote:
> Hello,
> 
> I have got a bug report against lablgl (well, against lablgtk2, but the
> problem is pulled in by lablgl).
> 
> Advice from Michael Daenzer, from the DRI project, was :
> 
> |> I suppose that glMultTransposeMatrixd is a new symbol of GL 1.3 it
> |> seems (formely known as glMultTransposeMatrixdARB i hear). Anyway,
> |> i have code of the kind :
> |> 
> |> #ifdef GL_VERSION_1_3
> |> ML_1 (glMultTransposeMatrixd, Double_raw)
> |> #else
> |> CAMLprim void ml_glMultTransposeMatrixd (value raw)
> |> {
> |>   ml_raise_gl ("Function: glMultTransposeMatrixd not available");
> |> }
> |> #endif 
> |> 
> |> Where naturally GL_VERSION_1_3 and GL_VERSION_1_4 and so on come from
> |> the OpenGL headers, i think.
> |
> |You should probably post about this to an OpenGL related mailing list,
> |but AFAIK compile-time checks aren't adequate for something like this.
> |
> |> Naturally, these are present on my system (and when using the non
> |> XFree86 mesa packages too, but then you loose acceleration, no ?) 
> |
> |The only thing that limits the available OpenGL functionality is the
> |library used at runtime, so long as everything conforms to the ABI.
> 
> So, if i understood this right, the checking for OpenGL versions should
> be done at runtime and not at compile time. I am not sure about the
> exact syntax of that, but i guess there is an OpenGL function which
> enables you to check for either the presence of an extension and/or the
> version of GL used. Ideally, the above code (and all the one like it)
> should be changed to something like :
> 
> CAMLprim void ml_glMultTransposeMatrixd (value raw)
> {
>   if (<code to check for GL_VERSION_1_3>)
>     glMultTransposeMatrixd(<ml_to_c raw>);
>   else if (<code to check for glMultTransposeMatrixdARB>)
>     glMultTransposeMatrixdARB(<ml_to_c raw>);
>   else
>     ml_raise_gl ("Function: glMultTransposeMatrixd not available");
> }
> 
> Sure, it does uglify the code a lot, but it is, i think, the only way to
> solve this problem in a sane way, without needing to build one version
> of the lablgl package for every opengl library out there the user will
> want to use, especially when linking in -custom mode, and thus including
> the stublibs statically.
> 
> Friendly,
> 
> Sven Luther
>