PadController

`GtkPadController` is an event controller for the pads found in drawing tablets.

Pads are the collection of buttons and tactile sensors often found around the stylus-sensitive area.

These buttons and sensors have no implicit meaning, and by default they perform no action. `GtkPadController` is provided to map those to [ iface@Gio.Action] objects, thus letting the application give them a more semantic meaning.

Buttons and sensors are not constrained to triggering a single action, some gdk_source_tablet_pad devices feature multiple "modes". All these input elements have one current mode, which may determine the final action being triggered.

Pad devices often divide buttons and sensors into groups. All elements in a group share the same current mode, but different groups may have different modes. See [method@Gdk.DevicePad.get_n_groups] and [method@Gdk.DevicePad.get_group_n_modes].

Each of the actions that a given button/strip/ring performs for a given mode is defined by a [struct@Gtk.PadActionEntry]. It contains an action name that will be looked up in the given [iface@Gio.ActionGroup] and activated whenever the specified input element and mode are triggered.

A simple example of `GtkPadController` usage: Assigning button 1 in all modes and pad devices to an "invert-selection" action:

```c GtkPadActionEntry *pad_actions[] = { { GTK_PAD_ACTION_BUTTON, 1, -1, "Invert selection", "pad-actions.invert-selection" }, … };

… action_group = g_simple_action_group_new (); action = g_simple_action_new ("pad-actions.invert-selection", NULL); g_signal_connect (action, "activate", on_invert_selection_activated, NULL); g_action_map_add_action (G_ACTION_MAP (action_group), action); … pad_controller = gtk_pad_controller_new (action_group, NULL); ```

The actions belonging to rings/strips will be activated with a parameter of type g_variant_type_double bearing the value of the given axis, it is required that those are made stateful and accepting this `GVariantType`.