Re: [gnomemm] Creating a custom Gnome::Canvas::Item

[Michael Babcock <mbabcock la creatureshop henson com>]

Murray Cumming wrote:
> On Wed, 2002-07-17 at 01:59, Michael Babcock wrote:
>
> > Does anybody have an example that creates a new Canvas::Item class by 
> > derivation in C++?
> >
> > There is no default constructor,
>
>
> A default constructor would probably just call g_object_new() without
> property values, but I'm not sure whether that would create anything
> useful. You could try to simulate it by calling the base cast
> constructor, like so:
>
> Thing::Thing(Group& parentx, int something)
> : Gnome::Canvas;:Item(GNOME_CANVAS_ITEM(g_object_new(get_type(), 0)))
> {
>   item_construct(parentx);
> }
>
> That's just some code that I copied from line.ccg and modified.
>
> If that is useful then we could add a real default constructor to make
> it easier.
>  

Hmmm. I'm not familiar with the internals of how gtkmm wraps gtk (or I 
try not to be), so tokens like GNOME_CANVAS_ITEM, g_object_new, and 
get_type don't mean much to me ;)

I looked at line.{h,cc}g but it is also wrapping an existing C type. In 
the above what does get_type() return, the C equivalent of a 
Canvas::Item type or of a Canvas::Line type? Do I have to create a new C 
type?

I was hoping to be able to derive a new C++ Canvas::Item type and have 
the library handle the conversion issues between the C++ and the Glib 
object systems, like gtkmm does so that we can derive a new Gtk::Widget.

I guess I have to use the property system in order to get the canvas to 
properly update my new item when I change it, right? Am I suppose to use 
the ConstructParams constructor for this? How do I do it?

Thanks again.

--
Michael Babcock
Jim Henson's Creature Shop