Right now I don't change the logics of any of the tools, except that the
GimpTool class now stores a list of drawables instead of a single
drawable. This can be later used on a case-by-case basis to make various
tools actually work on multiple drawables.
gimp_int_radio_group_new() was still complaining about the scope of
radio_button_callback(). Make it (scope notified) because it needs to
stay alive after the function returns and may be called multiple times.
Also adding a GDestroyNotify to free the callback data once the widget
is destroyed (additionally it will also serve as a notifier for bindings
to properly free the callback closure itself, not only it's data).
With this last one done, GObject Introspection generation now happens
without any warning output.
Add a new GimpFilterTool::region_changed() virtual function, which
gets called whenever the filter region changes, either due to a
change to the tool's "region" option, or a change to the image
mask.
Override GimpFilterTool::region_changed() in GimpOperationTool and
GimpOffsetTool, instead of listening to a change to the "region"
option in GimpTool::options_notify(), so that the tools are
properly updated when the image mask changes.
Add a new Offset filter tool, as a front-end to gimp:offset. The
tool replaces, and provides the same interface as, the drawable-
offset dialog, while also providing live preview and on-canvas
interaction.
Note that we don't simply use a custom propgui constructor for
gimp:offset, since we need a little more control.
