keyboard: Add a way to use the OSK on shell chrome in wayland sessions

libcaribou was designed to generate X events which works under wayland
sessions for X clients but obviously doesn't work for wayland clients
and for shell chrome.

This patch adds a simple caribou display adapter which inherits from
its X display adapter and allows us to continue to work for X clients
and at the same time makes the OSK work on shell text entries by
sending key events directly to the focused text actor.

Making the OSK work for wayland clients requires much bigger changes
at various levels in the stack and either not using libcaribou or
re-working it substantially so that's left for future work.

https://bugzilla.gnome.org/show_bug.cgi?id=747274

js/ui/keyboard.js

@@ -184,6 +184,10 @@ const Keyboard = new Lang.Class({
         this._daemonProxy = null;
         this._lastDeviceId = null;
 
+        if (Meta.is_wayland_compositor() &&
+            Caribou.DisplayAdapter.set_default)
+            Caribou.DisplayAdapter.set_default(new ShellWaylandAdapter());
+
         Meta.get_backend().connect('last-device-changed', Lang.bind(this,
             function (backend, deviceId) {
                 let manager = Clutter.DeviceManager.get_default();
@@ -725,3 +729,24 @@ const KeyboardSource = new Lang.Class({
         this._keyboard.show(Main.layoutManager.bottomIndex);
     }
 });
+
+const ShellWaylandAdapter = new Lang.Class({
+    Name: 'ShellWaylandAdapter',
+    Extends: Caribou.XAdapter,
+
+    vfunc_keyval_press: function(keyval) {
+        let focus = global.stage.get_key_focus();
+        if (focus instanceof Clutter.Text)
+            Shell.util_text_insert_keyval(focus, keyval);
+        else
+            this.parent(keyval);
+    },
+
+    vfunc_keyval_release: function(keyval) {
+        let focus = global.stage.get_key_focus();
+        if (focus instanceof Clutter.Text)
+            return;             // do nothing
+        else
+            this.parent(keyval);
+    },
+});

src/shell-util.c

@@ -391,3 +391,15 @@ shell_util_need_background_refresh (void)
 
   return FALSE;
 }
+
+void
+shell_util_text_insert_keyval (ClutterActor *actor,
+                               guint         keyval)
+{
+  ClutterEvent event = { 0 };
+
+  event.type = CLUTTER_KEY_PRESS;
+  event.key.keyval = keyval;
+
+  clutter_actor_event (actor, &event, FALSE);
+}

src/shell-util.h

@@ -47,6 +47,9 @@ void    shell_util_cursor_tracker_to_clutter (MetaCursorTracker *tracker,
 
 gboolean shell_util_need_background_refresh (void);
 
+void shell_util_text_insert_keyval (ClutterActor *actor,
+                                    guint         keyval);
+
 G_END_DECLS
 
 #endif /* __SHELL_UTIL_H__ */