sx:make-draw-area (was Re: [Chicken-users] what are pointers (in scheme))

[Stephan Lukits]

felix winkelmann schrieb:
> On Nov 29, 2007 6:01 AM, Stephan Lukits <address@hidden> wrote:
> > Hi,
> >
> > could anyone please direct my to the right documentation
> > for using eggs which implement c-libraries?
> >
> > I have no idear how I should call function like
> >
> > (sx:open-display INT (POINTER (POINTER CHAR)))
> >
> > and how I get the data which will be bound to
> > the (two-dimensional I guess) "pointer"?
>
> Hi!
>
> Some APIs are generated semi-automatically, for example using
> easyffi. The C function behind sx:open-display expects an argc/argv
> argument pair, which is not directly representable in Scheme, but
> (and this is exclusively for this particular case) "(argc+argv)" will return
> two values that can be passed to the mentioned function.
>
> In case of the sx egg: you don't need to call sx:open-display, this is
> done automatically.

Yes, thats what I red in the libsx docs, but modifying your
libsx example slightly through replacing the selection-list
by a draw-area leads to an error if the line which defines
the draw-area comes before the definition of the button.

e.g.:


(require-extension sx posix (srfi 1))

(define (button)
  (sx:close-window))

(define (redraw width height)
  (print "da-size: " width "x" height) )

(define b (sx:make-button "Update" button))
(define da (sx:make-draw-area 300 200 redraw))

(sx:set-widget-pos da sx:place-under b)

(sx:main-loop)


works fine, but


(require-extension sx posix (srfi 1))

(define (button)
  (sx:close-window))

(define (redraw width height)
  (print "da-size: " width "x" height) )

(define da (sx:make-draw-area 300 200 redraw))
(define b (sx:make-button "Update" button))

(sx:set-widget-pos da sx:place-under b)

(sx:main-loop)


leads to a "Speicherzugriffsfehler", thus I thought
I call "sx:open-display" first maybe it's working then
but using (sx:open-display 0 (argc+argv)) still
raises "Error: bad argument type - not a pointer: 1"


llap
Stephan