Re: Goocanvas issues

["Paul Davis" <pjdavis engineering uiowa edu>]

On 5/20/07, Paul Davis <pjdavis engineering uiowa edu> wrote:
> On 5/20/07, Paul Davis <pjdavis engineering uiowa edu> wrote:
> > On 5/20/07, Murray Cumming <murrayc murrayc com> wrote:
> > > On Sat, 2007-05-19 at 18:03 -0500, Paul Davis wrote:
> > > > Hey,
> > > >
> > > > I'm running into a some new issues with these wrappings. The biggest
> > > > roadblock right now is the wrapping of GooCanvasTable.  Its got a list
> > > > of child properties and I'm not sure on the best way to wrap them.
> > >
> > > I don't see any list:
> > > http://webcvs.freedesktop.org/cairo/goocanvas/src/goocanvastable.h?view=markup
> > >
> > >
> > > Do you mean the list in the base class?:
> > >
> > > struct _GooCanvasGroup
> > > {
> > >   GooCanvasItemSimple parent_object;
> > >
> > >   /* An array of pointers to GooCanvasItems. The first element is at the
> > >      bottom of the display stack and the last element is at the top. */
> > >   GPtrArray *items;
> > > ...
> > > }
> > >
> > > That's almost certainly a private struct field and I see no API for accessing it.
> > > It should probably be hidden in the C API.
> > >
> > >
> > > If you mean the varargs for this:
> > >
> > > GooCanvasItem*
> > > goo_canvas_table_new (GooCanvasItem  *parent,
> > >                       ...)
> > > {
> > >   GooCanvasItem *item;
> > >   va_list var_args;
> > >   const char *first_property;
> > >
> > >   item = g_object_new (GOO_TYPE_CANVAS_TABLE, NULL);
> > >
> > >   va_start (var_args, parent);
> > >   first_property = va_arg (var_args, char*);
> > >   if (first_property)
> > >     g_object_set_valist (G_OBJECT (item), first_property, var_args);
> > >   va_end (var_args);
> > >
> > >   if (parent)
> > >     {
> > >       goo_canvas_item_add_child (parent, item, -1);
> > >       g_object_unref (item);
> > >     }
> > >
> > >   return item;
> > > }
> > >
> > > you can wrap that as
> > > Canvas();
> > > and
> > > Canvas(Item& parent);
> > >
> > > and just let the application coder use canvas.property_*() = something.
> > >
> > > >  I
> > > > looked at Gtk::Table and its implementation. It uses a
> > > > Table_Helpers::Child class that contains the child-properties
> > >
> > > It provides access to the children, but not to the child properties, I
> > > think. Let's ignore the child properties unless we find they are
> > > necessary.
> > >
> > > It would be nice to have generic child property support for other gtkmm
> > > containers.
> > >
> > > >  and
> > > > allows for STL-Container like access to the children. This Child uses
> > > > a GtkTableChild object thing that I don't think exists for the
> > > > GooCanvasTable equivalent.
> > > >
> > > > Any help or ideas on how to wrap that object would be most welcome.
> > > >
> > > > I've found a bit of a bug when using
> > > > Goocanvas::Canvas::get_root_item().  The Glib::RefPtr< Goocanvas::Item
> > > > > object thats returned contains an GooCanvasItem thats only ref'ed
> > > > once. So when the RefPtr goes out of scope, the root item dies, which
> > > > causes a segfault internally in GooCanvas.
> > >
> > > Yes, you usually need to use the refreturn option on get methods, with
> > > _WRAP_METHOD. I have done that now in the libgoocanvasmm svn.
> > >
> > > > I think  I've verified this, becuase if I store the root item's RefPtr
> > > > as a class member ( so it doesn't get destroyed till the end of the
> > > > program ) the segfault disappears and when the program exits, there's
> > > > an error about g_object_unref fails the G_IS_OBJECT( object ) test (
> > > > Which I'm assuming means it got destroyed by one or the other and the
> > > > second destruction is failing.
> > > >
> > > > So basically, I need to add a ref operation somewhere, but I'm
> > > > uncertain as to where this should happen.
> > > >
> > > > In other news, quite a bit of the GooCanvas API has been wrapped. I'm
> > > > starting to work on getting the examples up and going.
> > >
> > > Thanks for this. Please keep mentioning stuff that you get stuck on,
> > > trying to be precise about what part of the API it is.
> > >
> > > --
> > > Murray Cumming
> > > murrayc murrayc com
> > > www.murrayc.com
> > > www.openismus.com
> > >
> > >
> >
> > Hey,
> >
> > Got fed up with not having the goocanvas api online so i've posted it
> > for now at:
> > http://gooey.ecn.uiowa.edu/goocanvas_api/html/
> >
> > The list of child properties is on the GooCanvasTable page at:
> > http://gooey.ecn.uiowa.edu/goocanvas_api/html/GooCanvasTable.html#id2599395
> >
> > I think there was a bit of misscomunication. Generally when I'm trying
> > to figure out how to wrap something, I try and find an example in
> > Gtkmm. In this case I was using Gtk::Table. This next paragraph is
> > only about Gtk::Table.
> >
> > Gtk::Table uses a Gtk::Table_Helpers::TableChild class. This class is
> > where the child properties can be accessed. This class wraps a Gtk
> > object.
> >
> > ----
> >
> > Now, in GooCanvas. There is no TableChild object for GooCanvasTable.
> > Therefore I don't really have the ability to use the Helper class
> > (AFAIK).
> >
> > For now I'm going to try and wrap as much as I can, although, the
> > child properties seem like the sort of thing that should be used by
> > application coders.
> >
> > In other news, is there a decent way of determining when I need to use
> > refreturn on  a _get() method? Would I just need to check the C docs
> > or source to find if it gets ref'ed before the object is returned?
> >
> > Thanks,
> > Paul Davis
> >
>
> I've run into another issue with getting C->C++ types mapped
> correctly. Specifcally, I can't fill in a property with a
> Cairo::RefPtr<Cairo::Pattern> object.
>
> In itemsimple.hg, I have this:
> _WRAP_PROPERTY("fill-pattern",Cairo::RefPtr<Cairo::Pattern>)
>
> I'm attempting to use it like such:
> Cairo::RefPtr<Cairo::Pattern> create_pattern() { ... }
> item->property_fill_pattern() = create_pattern() ;
>
> But its generating this error:
> (lt-demo:27094): GLib-GObject-WARNING **: unable to set property
> `fill-pattern' of type `GooCairoPattern' from value of type
> `glibmm__CustomBoxed_N5Cairo6RefPtrINS_7PatternEEE'
>
> I've posted a message on the goocanvas list asking about the GooCairo*
> types. I've also been looking through the properties in Gtkmm that use
> RefPtr's and I can't find anywhwere that they do something special to
> account for the refptr being passed in. (Like making a call to
> Glib::unwrap or what not).
>
> Anyone have an idea?
>
> Thanks,
> Paul Davis

Quick follow up, this piece of code actually works:

Cairo::RefPtr<Cairo::Pattern> p = _create_stipple( "mediumseagreen" ) ;
g_object_set( rect->gobj(), "fill-pattern", p->cobj(), NULL ) ;

So the property is fine taking the Cairo pattern which leads me to
believe that there's a problem in how that property is getting
wrapped.

Paul Davis