demos: Add pad support to "event axes" demo

And rename it to "Touch and Drawing Tablets", since it's no longer about
"axes" really.

As for pad support in the demo, just keep it "simple", make the
controller handle all pad devices, and make all the actions have the
same callback.

https://bugzilla.gnome.org/show_bug.cgi?id=770026

demos/gtk-demo/event_axes.c

@@ -1,11 +1,12 @@
-/* Event Axes
+/* Touch and Drawing Tablets
  *
  * Demonstrates advanced handling of event information from exotic
  * input devices.
  *
- * On one hand, this snippet demonstrates management of input axes,
+ * On one hand, this snippet demonstrates management of drawing tablets,
  * those contain additional information for the pointer other than
- * X/Y coordinates.
+ * X/Y coordinates. Tablet pads events are mapped to actions, which
+ * are both defined and interpreted by the application.
  *
  * Input axes are dependent on hardware devices, on linux/unix you
  * can see the device axes through xinput list <device>. Each time
@@ -20,6 +21,7 @@
  * touchpoints can be tracked.
  */
 
+#include <glib/gi18n.h>
 #include <gtk/gtk.h>
 
 typedef struct {
@@ -51,7 +53,30 @@ const gchar *colors[] = {
   "burlywood"
 };
 
+static GtkPadActionEntry pad_actions[] = {
+  { GTK_PAD_ACTION_BUTTON, 1, -1, N_("Nuclear strike"), "pad.nuke" },
+  { GTK_PAD_ACTION_BUTTON, 2, -1, N_("Release siberian methane reserves"), "pad.heat" },
+  { GTK_PAD_ACTION_BUTTON, 3, -1, N_("Release solar flare"), "pad.fry" },
+  { GTK_PAD_ACTION_BUTTON, 4, -1, N_("De-stabilize Oort cloud"), "pad.fall" },
+  { GTK_PAD_ACTION_BUTTON, 5, -1, N_("Ignite WR-104"), "pad.burst" },
+  { GTK_PAD_ACTION_BUTTON, 6, -1, N_("Lart whoever asks about this button"), "pad.lart" },
+  { GTK_PAD_ACTION_RING, -1, -1, N_("Earth axial tilt"), "pad.tilt" },
+  { GTK_PAD_ACTION_STRIP, -1, -1, N_("Extent of weak nuclear force"), "pad.dissolve" },
+};
+
+static const gchar *pad_action_results[] = {
+  "☢",
+  "♨",
+  "☼",
+  "☄",
+  "⚡",
+  "💫",
+  "◑",
+  "⚛"
+};
+
 static guint cur_color = 0;
+static guint pad_action_timeout_id = 0;
 
 static AxesInfo *
 axes_info_new (void)
@@ -488,12 +513,83 @@ draw_cb (GtkWidget *widget,
   return FALSE;
 }
 
+static void
+update_label_text (GtkWidget   *label,
+                   const gchar *text)
+{
+  gchar *markup = NULL;
+
+  if (text)
+    markup = g_strdup_printf ("<span font='48.0'>%s</span>", text);
+  gtk_label_set_markup (GTK_LABEL (label), markup);
+  g_free (markup);
+}
+
+static gboolean
+reset_label_text_timeout_cb (gpointer user_data)
+{
+  GtkWidget *label = user_data;
+
+  update_label_text (label, NULL);
+  pad_action_timeout_id = 0;
+  return G_SOURCE_REMOVE;
+}
+
+static void
+on_action_activate (GSimpleAction *action,
+                    GVariant      *parameter,
+                    gpointer       user_data)
+{
+  GtkWidget *label = user_data;
+  const gchar *result;
+
+  if (pad_action_timeout_id)
+    g_source_remove (pad_action_timeout_id);
+
+  result = g_object_get_data (G_OBJECT (action), "action-result");
+  update_label_text (label, result);
+  pad_action_timeout_id = g_timeout_add (200, reset_label_text_timeout_cb, label);
+}
+
+static void
+init_pad_controller (GtkWidget *window,
+                     GtkWidget *label)
+{
+  GtkPadController *pad_controller;
+  GSimpleActionGroup *action_group;
+  GSimpleAction *action;
+  gint i;
+
+  action_group = g_simple_action_group_new ();
+  pad_controller = gtk_pad_controller_new (GTK_WINDOW (window),
+                                           G_ACTION_GROUP (action_group),
+                                           NULL);
+
+  for (i = 0; i < G_N_ELEMENTS (pad_actions); i++)
+    {
+      action = g_simple_action_new (pad_actions[i].action_name, NULL);
+      g_signal_connect (action, "activate",
+                        G_CALLBACK (on_action_activate), label);
+      g_object_set_data (G_OBJECT (action), "action-result",
+                         (gpointer) pad_action_results[i]);
+      g_action_map_add_action (G_ACTION_MAP (action_group), G_ACTION (action));
+      g_object_unref (action);
+    }
+
+  gtk_pad_controller_set_action_entries (pad_controller, pad_actions,
+                                         G_N_ELEMENTS (pad_actions));
+  g_object_set_data_full (G_OBJECT (window), "pad-controller",
+                          pad_controller, g_object_unref);
+
+  g_object_unref (action_group);
+}
+
 GtkWidget *
 do_event_axes (GtkWidget *toplevel)
 {
   static GtkWidget *window = NULL;
   EventData *event_data;
-  GtkWidget *box;
+  GtkWidget *box, *label;
 
   if (!window)
     {
@@ -524,6 +620,12 @@ do_event_axes (GtkWidget *toplevel)
                         G_CALLBACK (event_cb), event_data);
       g_signal_connect (box, "draw",
                         G_CALLBACK (draw_cb), event_data);
+
+      label = gtk_label_new ("");
+      gtk_label_set_use_markup (GTK_LABEL (label), TRUE);
+      gtk_container_add (GTK_CONTAINER (box), label);
+
+      init_pad_controller (window, label);
     }
 
   if (!gtk_widget_get_visible (window))