wayland: implement support for plugin modality

Calling XIGrabDevice has no effect under wayland, because the
xserver is getting events from us. Instead, we need to use our
own interfaces for grabs.
At the same time, we can simplify the public API, as plugins
should always listen for events using clutter.

https://bugzilla.gnome.org/show_bug.cgi?id=705917

src/wayland/meta-wayland-pointer.c

@@ -262,3 +262,65 @@ meta_wayland_pointer_set_current (MetaWaylandPointer *pointer,
                                     &pointer->current_listener);
   pointer->current_listener.notify = current_surface_destroy;
 }
+
+static void
+modal_focus (MetaWaylandPointerGrab *grab,
+	     MetaWaylandSurface     *surface,
+	     wl_fixed_t              x,
+	     wl_fixed_t              y)
+{
+}
+
+static void
+modal_motion (MetaWaylandPointerGrab *grab,
+	      uint32_t                time,
+	      wl_fixed_t              x,
+	      wl_fixed_t              y)
+{
+}
+
+static void
+modal_button (MetaWaylandPointerGrab *grab,
+	      uint32_t                time,
+	      uint32_t                button,
+	      uint32_t                state)
+{
+}
+
+static MetaWaylandPointerGrabInterface modal_grab = {
+  modal_focus,
+  modal_motion,
+  modal_button
+};
+
+gboolean
+meta_wayland_pointer_begin_modal (MetaWaylandPointer *pointer)
+{
+  MetaWaylandPointerGrab *grab;
+
+  if (pointer->grab != &pointer->default_grab)
+    return FALSE;
+
+  meta_wayland_pointer_set_focus (pointer, NULL,
+				  wl_fixed_from_int (0),
+				  wl_fixed_from_int (0));
+
+  grab = g_slice_new0 (MetaWaylandPointerGrab);
+  grab->interface = &modal_grab;
+  meta_wayland_pointer_start_grab (pointer, grab);
+
+  return TRUE;
+}
+
+void
+meta_wayland_pointer_end_modal (MetaWaylandPointer *pointer)
+{
+  MetaWaylandPointerGrab *grab;
+
+  grab = pointer->grab;
+
+  g_assert (grab->interface == &modal_grab);
+
+  meta_wayland_pointer_end_grab (pointer);
+  g_slice_free (MetaWaylandPointerGrab, grab);
+}