[Chicken-users] Passing blobs to glGetDoublev in (hacked) OpenGL egg

[Eduardo Cavazos]

Eduardo Cavazos wrote:

> Let's suppose I take this approach, where I use Chicken blobs in place 
> of R6RS bytevectors. There's one problem that exists. Some of the 
> procedures in the OpenGL egg want f64vector objects. For example, this 
> results in an error:
>
> (let ((bv (make-blob (* 16 8))))
>   (glGetDoublev GL_MODELVIEW_MATRIX bv)
>   bv)
>
> Again for comparison, the OpenGL libraries in Larceny, Ypsilon, and 
> Ikarus allow a bytevector to be passed to 'glGetDoublev'.
>
> I'm willing to use a customized gl egg for my purposes. This is from 
> 'gl.scm' in the opengl egg:
>
>     void  glGetDoublev( GLenum pname, GLdouble *params );
>
> What could I change that to such that blobs are allowed as the second 
> argument?

OK, here's what I came up with. The opengl egg uses easyffi. So the line 
for 'glGetDoublev' is:

    void  glGetDoublev( GLenum pname, GLdouble *params );

Again, my goal here is to be able to pass a blob as the second argument. 
By using 'foreign-lambda' directly, I was able to get it to work:

    (define glGetDoublev
      (foreign-lambda void glGetDoublev unsigned-integer blob))

So my question is, how can I express that in easyffi? I.e. I'd like to 
be able to have something like:

    void  glGetDoublev( GLenum pname, blob params );

I'm guessing something involving the ___declare( type , ... ) form.

Ed