Re: New Ada binding to OpenGL

[David Holm <david@realityrift.com>]

Joachim Schr�er wrote:

> 4) The subprograms taking system.address parameters are superfluous and
> represent a not very Adalike style. It is very staightforward to call a
> function with access parameter mode or with a general access type. Simply
> declare arrays of aliased variables and pass
> The_Array(The_Array'First)'Unchecked_Access. Take the following example to
> call
> procedure glClipPlane(plane : GLENUM;
> 
>                                   equation: access GLDOUBLE); --
> ./GL/gl.h:791
> 
> 
> 
> package Opengl.Clip_Planes is
> 
> -- Plane coefficients -----------------------------------------------
> 
> 
> A : constant := 1; B : constant := 2; C : constant := 3; D : constant :=
> 4;
> 
> -- Plane-type and simple clip-plane constants -----------------------
> 
> type Plane is array(A .. D) of aliased Gl.Gldouble;
> 
> ...
> 
> 
> and then in the implementation
> 
> procedure Enable(The_Plane : in Plane) is
> 
> begin
> 
>   Counter := Counter + 1;
> 
>   if Counter <= Clip_Plane_Indices'Last then
> 
>     Gl.Glclipplane(Plane     => Clip_Plane_Indices(Counter),
> 
>                           Equation => The_Plane(A)'Unchecked_Access);
> 
>     Gl.Glenable(Clip_Plane_Indices(Counter));
> 
> ...
> 

How can I pass null addresses this way? With System.Address I could use 
GLNULL : System.Address renames System.Null_Address;

//David