Re: Gnome2::Canvas

[muppet <scott asofyet org>]

On Sunday, March 14, 2004, at 05:08 AM, john knops wrote:

> 1. Why  is it called Gnome2::Canvas. Isn't Gnome built with Gtk so 
> wouldn't Gtk2::Canvas be a better name?

these are not the definitive answers (i couldn't find what i wanted in 
thirty seconds of googling) but here goes:

a) it was written for gnome
b) it has dependencies that gtk+ does not (libart, namely)
c) because it's not actually part of the gtk+ project, so putting their 
widget into the Gtk namespace would be rude and would make it difficult 
for gtk+ to add a canvas widget in the future.  (GtkSpell, GtkHTML, and 
GtkDatabox are all offenders here.)


> 2. Where does it fit in the Gtk hierarchy tree?

the manpage for the previously released versions which don't require 
the bleeding edge Glib don't show this, but the current and 
about-to-be-released stable versions do:

  HIERARCHY
         Glib::Object
         +----Gtk2::Object
               +----Gtk2::Widget
                     +----Gtk2::Container
                           +----Gtk2::Layout
                                 +----Gnome2::Canvas



> 3. When creating a canvas item why the call to $root? eg.
> my $root =$canvas->root;
> my $item = Gnome2::Canvas::Item->new ($root,
>                                       'Gnome2::Canvas::Ellipse');
> Am I correct in thinking that no other widget makes this sort of call 
> so why does this one need it?

for better or worse, this is an artifact of the way the interaction 
between GnomeCanvas and GnomeCanvasItem was designed.  a 
GnomeCanvasItem knows the canvas to which it belongs, and it also knows 
its parent.  it is not valid to have a GnomeCanvasItem which is not 
associated with a GnomeCanvas; so, you tell the item factory what 
parent to use for the new item, which implies the canvas.

the fragment you posted is a direct port from the corresponding C code:

  root = gnome_canvas_root (canvas);
  item = gnome_canvas_item_new (root, GNOME_TYPE_CANVAS_ELLIPSE, NULL);

note that it doesn't have to be "root" --- you could instead do:

  $group1 = Gnome2::Canvas::Item->new ($canvas->root, 
'Gnome2::Canvas::Group');
  Gnome2::Canvas::Item->new ($group1, 'Gnome2::Canvas::Rect');
  Gnome2::Canvas::Item->new ($group1, 'Gnome2::Canvas::Ellipse');
  $group2 = Gnome2::Canvas::Item->new ($canvas->root, 
'Gnome2::Canvas::Group');
  Gnome2::Canvas::Item->new ($group2, 'Gnome2::Canvas::Rect');
  Gnome2::Canvas::Item->new ($group2, 'Gnome2::Canvas::Ellipse');

more info:

http://developer.gnome.org/doc/whitepapers/canvas/canvas.html

--
"that's it! you're a genius!"  "yes.  that's what i think.  do you 
think i deserve a raise?"
        - dialogue from 'Godzilla versus Mothra', 1964