From e9b5eb3045d335b6ebbfc7443076754447447065 Mon Sep 17 00:00:00 2001
From: Emmanuele Bassi <ebassi@gnome.org>
Date: Fri, 11 Dec 2015 15:41:35 +0000
Subject: [PATCH] Allow setting the default backend from the configuration file

We should allow a configuration file to set up the initial state of the
global state, which also implies being able to set the backend.

If the allowed backends have already been set programmatically via the
clutter_set_windowing_backend(), though, then the application code takes
precedence, as we assume that the application author knows better than
us what their code supports or requires.
---
 clutter/clutter-backend-private.h |  2 ++
 clutter/clutter-backend.c         |  7 +++++++
 clutter/clutter-main.c            | 11 +++++++++++
 3 files changed, 20 insertions(+)

diff --git a/clutter/clutter-backend-private.h b/clutter/clutter-backend-private.h
index eb44941da..a2b729c2e 100644
--- a/clutter/clutter-backend-private.h
+++ b/clutter/clutter-backend-private.h
@@ -155,6 +155,8 @@ void                    _clutter_backend_reset_cogl_framebuffer         (Clutter
 
 void                    clutter_set_allowed_drivers                     (const char             *drivers);
 
+void                    clutter_try_set_windowing_backend               (const char             *drivers);
+
 G_END_DECLS
 
 #endif /* __CLUTTER_BACKEND_PRIVATE_H__ */
diff --git a/clutter/clutter-backend.c b/clutter/clutter-backend.c
index a29976ac2..bce4e9138 100644
--- a/clutter/clutter-backend.c
+++ b/clutter/clutter-backend.c
@@ -1527,6 +1527,13 @@ clutter_set_windowing_backend (const char *backend_type)
   allowed_backends = g_strdup (backend_type);
 }
 
+void
+clutter_try_set_windowing_backend (const char *backend_type)
+{
+  if (allowed_backends == NULL)
+    clutter_set_windowing_backend (backend_type);
+}
+
 PangoDirection
 _clutter_backend_get_keymap_direction (ClutterBackend *backend)
 {
diff --git a/clutter/clutter-main.c b/clutter/clutter-main.c
index d1cf4f0ca..10fcc2085 100644
--- a/clutter/clutter-main.c
+++ b/clutter/clutter-main.c
@@ -221,6 +221,17 @@ clutter_config_read_from_key_file (GKeyFile *keyfile)
   if (!g_key_file_has_group (keyfile, ENVIRONMENT_GROUP))
     return;
 
+  str_value =
+    g_key_file_get_string (keyfile, ENVIRONMENT_GROUP,
+                           "Backends",
+                           &key_error);
+  if (key_error != NULL)
+    g_clear_error (&key_error);
+  else
+    clutter_try_set_windowing_backend (str_value);
+
+  g_free (str_value);
+
   str_value =
     g_key_file_get_string (keyfile, ENVIRONMENT_GROUP,
                            "Drivers",