Date: Sat, 29 Nov 2003 12:37:54 +0100
To: lablgtk at kaba.or.jp, Jacques Garrigue <garrigue at kurims.kyoto-u.ac.jp>
Cc: 218823 at bugs.debian.org, control at bugs.debian.org
Subject: lablgl and runtime vs compile time GL version detection.
Message-ID: <20031129113754.GA3375 at iliana>
Mime-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
From: Sven Luther <sven.luther at wanadoo.fr>

reassign 218823 lablgl
thanks

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