wayland: add support for connecting to a foreign display

This allows the reuse of the display connection and hence objects with
existing code that is using Wayland.

https://bugzilla.gnome.org/show_bug.cgi?id=703566

clutter/clutter.symbols

@@ -1597,6 +1597,7 @@ clutter_vertex_new
 clutter_wayland_input_device_get_wl_seat
 clutter_wayland_stage_get_wl_shell_surface
 clutter_wayland_stage_get_wl_surface
+clutter_wayland_set_display
 #endif
 #ifdef CLUTTER_WINDOWING_WIN32
 clutter_win32_disable_event_retrieval

clutter/wayland/clutter-backend-wayland.c

@@ -46,6 +46,7 @@
 #include "wayland/clutter-device-manager-wayland.h"
 #include "wayland/clutter-event-wayland.h"
 #include "wayland/clutter-stage-wayland.h"
+#include "wayland/clutter-wayland.h"
 #include "cogl/clutter-stage-cogl.h"
 
 #include <wayland-client.h>
@@ -59,6 +60,8 @@
 
 G_DEFINE_TYPE (ClutterBackendWayland, clutter_backend_wayland, CLUTTER_TYPE_BACKEND);
 
+static struct wl_display *_foreign_display = NULL;
+
 static void clutter_backend_wayland_load_cursor (ClutterBackendWayland *backend_wayland);
 
 static void
@@ -175,7 +178,10 @@ clutter_backend_wayland_post_parse (ClutterBackend  *backend,
   ClutterBackendWayland *backend_wayland = CLUTTER_BACKEND_WAYLAND (backend);
 
   /* TODO: expose environment variable/commandline option for this... */
-  backend_wayland->wayland_display = wl_display_connect (NULL);
+  backend_wayland->wayland_display = _foreign_display;
+  if (backend_wayland->wayland_display == NULL)
+    backend_wayland->wayland_display = wl_display_connect (NULL);
+
   if (!backend_wayland->wayland_display)
     {
       g_set_error (error, CLUTTER_INIT_ERROR,
@@ -322,3 +328,31 @@ static void
 clutter_backend_wayland_init (ClutterBackendWayland *backend_wayland)
 {
 }
+
+/**
+ * clutter_wayland_set_display
+ * @display: pointer to a wayland display
+ *
+ * Sets the display connection Clutter should use; must be called
+ * before clutter_init(), clutter_init_with_args() or other functions
+ * pertaining Clutter's initialization process.
+ *
+ * If you are parsing the command line arguments by retrieving Clutter's
+ * #GOptionGroup with clutter_get_option_group() and calling
+ * g_option_context_parse() yourself, you should also call
+ * clutter_wayland_set_display() before g_option_context_parse().
+ *
+ * Since: 1.16
+ */
+void
+clutter_wayland_set_display (struct wl_display *display)
+{
+  if (_clutter_context_is_initialized ())
+    {
+      g_warning ("%s() can only be used before calling clutter_init()",
+                 G_STRFUNC);
+      return;
+    }
+
+  _foreign_display = display;
+}

clutter/wayland/clutter-wayland.h

@@ -48,6 +48,9 @@ struct wl_shell_surface *clutter_wayland_stage_get_wl_shell_surface (ClutterStag
 
 CLUTTER_AVAILABLE_IN_1_10
 struct wl_surface *clutter_wayland_stage_get_wl_surface (ClutterStage *stage);
-G_END_DECLS
 
+CLUTTER_AVAILABLE_IN_1_16
+void clutter_wayland_set_display (struct wl_display *display);
+
+G_END_DECLS
 #endif /* __CLUTTER_WAYLAND_H__ */

doc/reference/clutter/clutter-sections.txt

@@ -1429,6 +1429,7 @@ clutter_glx_texture_pixmap_get_type
 clutter_wayland_input_device_get_wl_seat
 clutter_wayland_stage_get_wl_shell_surface
 clutter_wayland_stage_get_wl_surface
+clutter_wayland_set_display
 </SECTION>
 
 <SECTION>