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

[Murray Cumming <murrayc usa net>]

On Wed, 2002-07-17 at 19:54, Michael Babcock wrote:
> 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 ;)

They aren't meant to, though they would to a GTK+ coder. Just trust me
on this one. If it works then we'll make it easier.
 
> 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?

The most-derived wrapped type - Canvas::Item if you inherit from that.

> Do I have to create a new C 
> type?

Hopefully not. Try it and see. If you do need to then we already have a
system for that too.
 
> 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.

Like I said, I don't know how this is done in C, or whether it's
something that makes sense. If you just try it then we will know
something from your results.

> 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?

Possibly. I don't know much about CanvasItems. Maybe they use properties
in the same way as Gtk::CellRenderers. I've never investigated them.

> Am I suppose to use 
> the ConstructParams constructor for this?

Almost certainly not.

-- 
Murray Cumming
murrayc usa net
www.murrayc.com