PadController is an event controller for the pads found in drawing tablets (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, this event controller is provided to map those to Action objects, thus letting the application give those 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 get_n_groups and get_group_n_modes.
Each of the actions that a given button/strip/ring performs for a given mode is defined by PadActionEntry, it contains an action name that will be looked up in the given ActionGroup and activated whenever the specified input element and mode are triggered.
A simple example of PadController usage, assigning button 1 in all modes and pad devices to an "invert-selection" action:
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 (window, action_group, NULL);