[mutter] backend: Freeze frame clock when headless

[Jonas Ådahl <jadahl src gnome org>]

commit 25c53b2fb25d325a40cb12b2e38b2a895983f441
Author: Jonas Ådahl <jadahl gmail com>
Date:   Thu Jul 12 16:21:55 2018 +0200

    backend: Freeze frame clock when headless
    
    Don't schedule redraws when being headless; there is nothing to draw so
    don't attempt to draw. This also makes a flaky test become non-flaky, as
    it previously spuriously got warnings due to windows being "painted"
    when headless but lacking frame timings, as nothing was actually
    painted.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/170

 src/backends/meta-backend.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
---
diff --git a/src/backends/meta-backend.c b/src/backends/meta-backend.c
index 375e9d298..709d4194c 100644
--- a/src/backends/meta-backend.c
+++ b/src/backends/meta-backend.c
@@ -123,6 +123,8 @@ struct _MetaBackendPrivate
   guint sleep_signal_id;
   GCancellable *cancellable;
   GDBusConnection *system_bus;
+
+  gboolean was_headless;
 };
 typedef struct _MetaBackendPrivate MetaBackendPrivate;
 
@@ -223,6 +225,19 @@ meta_backend_monitors_changed (MetaBackend *backend)
     }
 
   meta_cursor_renderer_force_update (priv->cursor_renderer);
+
+  if (meta_monitor_manager_is_headless (priv->monitor_manager) &&
+      !priv->was_headless)
+    {
+      clutter_stage_freeze_updates (CLUTTER_STAGE (priv->stage));
+      priv->was_headless = TRUE;
+    }
+  else if (!meta_monitor_manager_is_headless (priv->monitor_manager) &&
+           priv->was_headless)
+    {
+      clutter_stage_thaw_updates (CLUTTER_STAGE (priv->stage));
+      priv->was_headless = FALSE;
+    }
 }
 
 void