Re: WIA

[Stephen Leake <stephen_leake@acm.org>]

"david" <bsvj2421y19cbiun@jetable.org> writes:

> I'm trying to use wia in an ADA software.

"Ada" is a woman's name, so it is not all caps.

> My problem is to use  (Wia_Property_Storage_Interface.Lpvtbl.)
> Writemultiple : i'm not sure about interfacing the two types propspec
> and propvariant and the writemultiple call.
> In C, writemultiple is :
>
> HRESULT WriteMultiple(
>   ULONG cpspec,
>   const PROPSPEC rgpspec[],
>   const PROPVARIANT rgpropvar[],
>   PROPID propidNameFirst
> );

I found this at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/stg/stg/ipropertystorage_writemultiple.asp

> I'm not sure about the ada corresponding specifications for the "const
> type var[]".
> I wrote :
>
>    type Propspec (Kind : Win32.Ulong) is
>       record
>          case Kind is
>             when Prspec_Propid =>
>                Propid : Win32.Oleauto.Propid;
>             when Prspec_Lpwstr =>
>                Lpwstr : Win32.Objbase.Lpolestr;
>             when others =>
>                null;
>          end case;
>       end record;
>    pragma Convention (C, Propspec);
>    type Ppropspec is access all Propspec;
>    function To_Ppropspec is new Ada.Unchecked_Conversion
> (System.Address, Ppropspec);

This looks good; it matches http://msdn.microsoft.com/library/default.asp?url=/library/en-us/stg/stg/propspec.asp

>    type Tab_Propspec_Propid is array (Positive range <>) of Propspec
> (Prspec_Propid);

This doesn't match any C type; an Ada unconstrained array has the
array bounds in the first few bytes.

>    type Propvariant (Vt : Win32.Oleauto.Varenum) is
>       record
>          Wreserved1 : Win32.Word;
>          Wreserved2 : Win32.Word;
>          Wreserved3 : Win32.Word;
>          case Vt is
>             when Win32.Oleauto.Vt_I4 =>
>                Ival : Win32.Long;
>             when Win32.Oleauto.Vt_Bstr =>
>                Bstrval : Win32.Oleauto.Bstr;
>             when others =>
>                null;
>          end case;
>       end record;
>    pragma Convention (C, Propvariant);
>    type Ppropvariant is access all Propvariant;
>    function To_Ppropvar is new Ada.Unchecked_Conversion
> (System.Address, Ppropvariant);

I'll assume this is right.

>    type Tab_Propvariant_Vt_I4 is array (Positive range <>) of
> Propvariant (Win32.Oleauto.Vt_I4);
>
>    type Af_I_Wia_Property_Storage_Writemultiple is access
>      function (This      : access I_Wia_Property_Storage;
>                Cpspec    : Win32.Ulong; -- in
>                Rgpspec   : Ppropspec;-- in const propspec []
>                Rgpropvar : Ppropvariant;-- in const propvariant []
>                Propidnamefirst : Win32.Oleauto.Propid) -- in essayer
> avec 2
>        return Win32.Objbase.HRESULT;
>    pragma Convention (Stdcall,
> Af_I_Wia_Property_Storage_Writemultiple);
>
> When calling this method, I write :
>
> Propspec_Flash_Mode   : Tab_Propspec_Propid (1 .. 1) := (1 => (Kind =>
> Prspec_Propid,
>
> Propid => Win32.Oleauto.Propid (Wia_Dpc_Flash_Mode)));
> Propvar_Flash_Fill   : Tab_Propvariant_Vt_I4 (1 .. 1) := (1 =>
> (Win32.Oleauto.Vt_I4,
>
> Win32.Word (0),
>
> Win32.Word (0),
>
> Win32.Word (0),
>
> Win32.Long (Wia_Flash_Mode_Fill)));
>
>
> My_Hresult := Wia_Property_Storage_Interface.Lpvtbl.Writemultiple
> (Wia_Property_Storage_Interface,
>
>     1,
>
>     To_Ppropspec (Propspec_Flash_Mode (1)'Address),
>
>     To_Ppropvar (Propvar_Flash_Fill (1)'Address),
>
>     2);

Actually, this looks good. 

Although I would just declare the arguments to Writemultiple as
System.Address, and avoid the calls to Unchecked_Conversion. That
makes it clearer that you do _not_ have strong typing here.

> I tried to work without tab_prospec_propid and tab_propvariant_vt_i4
> but this doesn't work.
> When executing, my_hresult is s_false.

The hardest part about using Win32 is finding the bugs in the manual.
I suspect you are using the data structures in a way that the function
can't handle.

If you can find a working example of this in C or C++, and translate
that as closely as possible into Ada, you might get somewhere.

> I tried to use gnatcom to verify my interfacing but createcom seems to
> not work on wiaservc.dll (whereas it works on wiaaut.dll for example.

You should ask about that on the gnavi mailing list; see
http://sourceforge.net/projects/gnavi/ 

-- 
-- Stephe