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.

Building Inkscape against GTK+ 3

First, configure Inkscape to build against GTK+ 3 using configure --enable-gtk3-experimental. I prefer to use a separate subfolder for these (broken) builds.

# Create a subfolder in the source directory for the experimental builds
mkdir build-gtk3
cd build-gtk3

# Configure to use GTK+ 3
../configure --enable-gtk3-experimental

After this, you can build as usual. However, as there are a huge number of errors, it is useful to instruct the build to continue even if errors are encountered. This is achieved by using the "-k" flag with Make. It is also helpful to dump a log of the errors (>5000 lines at the time of writing!). In summary, I use something like:

make -k 2> gtk3-experimental.txt

Guidance from upstream

The GTK+ 3 reference manual offers some 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The GtkType and GtkObject API has been replaced by the gobject library.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 gtk_widget_has_focus() should be used instead of deprecated macros such as GTK_WIDGET_HAS_FOCUS()

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. gtk_widget_set_visual(), gtk_widget_set_default_visual(), gtk_widget_push_visual() and gtk_widget_pop_visual() 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 Valavanisalex 09:55, 23 June 2011 (UTC)

Don't use GtkNotebookPage

The GtkNotebookPage 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 [1]

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. 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.

Build against external GDL

We currently use our own fork of the GDL library (based on GDL 2.30.0). This version of GDL contains a few deprecated GTK symbols. Eventually, we need to get rid of our own fork, and build against the external library. Progress is being tracked at https://bugs.launchpad.net/inkscape/+bug/792115