View source for GTK+ 3 migration

Inkscape currently makes use of the GTK+ 2.20 library API.  Ultimately, we will need to switch to the new GTK+ 3 API.  This version of the library introduces a number of major changes that are incompatible with GTK, so we need to make some changes to Inkscape.

== Guidance from upstream ==
The GTK+ 3 reference manual offers some [http://developer.gnome.org/gtk3/stable/gtk-migrating-2-to-3.html#id1391340 guidance] for the upgrade process.

== Deprecated symbols ==
Inkscape currently makes use of a number of deprecated GTK+ symbols.  We need to get rid of all of these before we can upgrade.  Some are very easy to replace.  Some are a little more challenging.  We need to ensure that Inkscape still builds correctly when the "-DGTK_DISABLE_DEPRECATED" compiler flag is applied.  An incomplete "to do" list follows:

=== Switch to gobject ===
<https://bugs.launchpad.net/inkscape/+bug/813212>

The GtkType and GtkObject API has been replaced by the gobject library.  One of the few remaining issues here is that SPCanvasItem is a subclass of GtkObject.  However, this part of the class hierarchy is currently being rewritten, and will be based on a different parent class.

=== Use accessor functions to GtkWidget ===
Accessor functions such as <code>gtk_widget_has_focus()</code> should be used instead of deprecated macros such as <code>GTK_WIDGET_HAS_FOCUS()</code>

=== Get rid of "visual" functions for GtkWidgets ===
The visual for a widget, and also the default visual is now derived from the colormap for the widget and the default colormap. <code>gtk_widget_set_visual()</code>, <code>gtk_widget_set_default_visual()</code>, <code>gtk_widget_push_visual()</code> and <code>gtk_widget_pop_visual()</code> now do nothing. Since the visual always had to match that of the colormap, it is safe to simply delete all references to these functions.
:Done [[User:Valavanisalex|Valavanisalex]] 09:55, 23 June 2011 (UTC)

=== Don't use GtkNotebookPage ===
The <code>GtkNotebookPage</code> structure has been removed from the public header files; this was never meant to be a public structure, and all functionality that could be done by accessing the struct fields of this structure should be accessible otherwise.

=== Switch from GtkCombo to GtkComboBoxEntry ===
See [http://developer.gnome.org/gtk/2.24/migrating-GtkCombo.html]
:Done.  A few symbols are left in #if/#else blocks in src/dialogs/text-edit.cpp to allow build compatibility with GTK+ 2.20.  These can be removed once Inkscape has bumped its dependency level to GTK+ >= 2.24. [[User:Valavanisalex|Valavanisalex]] 09:46, 23 June 2011 (UTC)

=== Get rid of GtkAction proxy functions ===
gtk_action_connect_proxy has been deprecated since version 2.16 and should not be used in newly-written code. Use gtk_activatable_set_related_action() instead.

=== Merge GtkRuler into Inkscape ===
The GtkRuler class has been completely removed from GTK+ 3, and will not be replaced.  GIMP got around the problem by merging the GtkRuler code into their own project.