Re: Ada OpenGL question

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Olivier Scalbert wrote:
> Ludovic Brenta wrote:
>> In your example, Expose'Access presumably designates a procedure.
>> This is wrong.  Expose should be a function returning Boolean.  The
>> return value means:
>>
>> False: pass the signal to any other signal handlers attached to it
>> True: abort processing of the signal.
>>
>> The same holds for delete_event and a few other signals as documented
>> in the GTK+ reference athttp://www.gtk.org.
>>
>> The GtkAda signal handler infrastructure makes it impossible to detect
>> the type mismatch at compile time, so it has run-time checks instead.
>> This is the source of the error message.
>>
>> HTH
>
> Thanks for your help Ludovic!
>
> I do not know how to solve it.
> I have tried to change the Expose procedure into a function returning a
> Boolean, but then it does not compile anymore:
>
> gtkgl.adb:89:66: no candidate interpretations match the actuals:
> gtkgl.adb:89:87: expected type "Handler" defined at
> gtk-marshallers.ads:355, instance at gtk-handlers.ads:915, instance at
> line 68
> gtkgl.adb:89:87: found type access to function "Expose" defined at line 89
> gtkgl.adb:89:87:   ==> in call to "To_Marshaller" at
> gtk-handlers.ads:939, instance at line 68
> gtkgl.adb:89:87:   ==> in call to "To_Marshaller" at
> gtk-handlers.ads:934, instance at line 68
> gtkgl.adb:89:87:   ==> in call to "To_Marshaller" at
> gtk-handlers.ads:930, instance at line 68
> gtkgl.adb:89:87:   ==> in call to "To_Marshaller" at
> gtk-handlers.ads:926, instance at line 68
> gtkgl.adb:89:87:   ==> in call to "To_Marshaller" at
> gtk-handlers.ads:922, instance at line 68
> gtkgl.adb:89:87:   ==> in call to "To_Marshaller" at
> gtk-handlers.ads:918, instance at line 68

You must call GtkAda.Handlers.Return_Callback.Connect as opposed to
GtkAda.Handlers.Widget_Callback.Connect. (If you use some other
instances of Gtk.Handlers, the same holds: Return_Callback instead of
Callback).

--
Ludovic Brenta.