From 9a510c011746ba7e0d258c76302e83e16e371ec7 Mon Sep 17 00:00:00 2001
From: Adel Gadllah <adel.gadllah@gmail.com>
Date: Sun, 26 Jul 2015 11:29:10 +0200
Subject: [PATCH] backend: Check for a known set of drivers

We want to use the Cogl GL3 driver, if possible, and then go through a
known list of Cogl drivers, before giving up and using COGL_DRIVER_ANY.

Based on original patch from Emmanuele Bassi.

We have to create and tear down the whole context when trying
out the drivers though because the extension checks do not happen
until cogl_context_init.

https://bugzilla.gnome.org/show_bug.cgi?id=742678
---
 clutter/clutter-backend.c | 69 +++++++++++++++++++++++++++++++--------
 1 file changed, 56 insertions(+), 13 deletions(-)

diff --git a/clutter/clutter-backend.c b/clutter/clutter-backend.c
index 04079518a..e1d2336c2 100644
--- a/clutter/clutter-backend.c
+++ b/clutter/clutter-backend.c
@@ -243,8 +243,9 @@ clutter_backend_real_font_changed (ClutterBackend *backend)
 }
 
 static gboolean
-clutter_backend_real_create_context (ClutterBackend  *backend,
-                                     GError         **error)
+clutter_backend_do_real_create_context (ClutterBackend  *backend,
+                                        CoglDriver       driver_id,
+                                        GError         **error)
 {
   ClutterBackendClass *klass;
   CoglSwapChain *swap_chain;
@@ -276,6 +277,7 @@ clutter_backend_real_create_context (ClutterBackend  *backend,
 #endif
 
   CLUTTER_NOTE (BACKEND, "Connecting the renderer");
+  cogl_renderer_set_driver (backend->cogl_renderer, driver_id);
   if (!cogl_renderer_connect (backend->cogl_renderer, &internal_error))
     goto error;
 
@@ -332,10 +334,6 @@ clutter_backend_real_create_context (ClutterBackend  *backend,
   if (backend->cogl_context == NULL)
     goto error;
 
-  backend->cogl_source = cogl_glib_source_new (backend->cogl_context,
-                                               G_PRIORITY_DEFAULT);
-  g_source_attach (backend->cogl_source, NULL);
-
   /* the display owns the renderer and the swap chain */
   cogl_object_unref (backend->cogl_renderer);
   cogl_object_unref (swap_chain);
@@ -358,16 +356,61 @@ error:
   if (swap_chain != NULL)
     cogl_object_unref (swap_chain);
 
-  if (internal_error != NULL)
-    g_propagate_error (error, internal_error);
-  else
-    g_set_error_literal (error, CLUTTER_INIT_ERROR,
-                         CLUTTER_INIT_ERROR_BACKEND,
-                         _("Unable to initialize the Clutter backend"));
-
   return FALSE;
 }
 
+static gboolean
+clutter_backend_real_create_context (ClutterBackend  *backend,
+                                     GError         **error)
+{
+  static const struct {
+    const char *driver_name;
+    CoglDriver driver_id;
+  } known_drivers[] = {
+    { "GL3", COGL_DRIVER_GL3 },
+    { "GL (Legacy)", COGL_DRIVER_GL },
+    { "GLES 2.0", COGL_DRIVER_GLES2 },
+    { "ANY", COGL_DRIVER_ANY },
+  };
+
+  GError *internal_error = NULL;
+  int i;
+
+  for (i = 0; i < G_N_ELEMENTS (known_drivers); i++)
+    {
+      CLUTTER_NOTE (BACKEND, "Checking for the %s driver", known_drivers[i].driver_name);
+
+      if (clutter_backend_do_real_create_context (backend, known_drivers[i].driver_id, &internal_error))
+        break;
+
+      if (internal_error)
+        {
+          CLUTTER_NOTE (BACKEND, "Unable to use the %s driver: %s",
+                        known_drivers[i].driver_name,
+                        internal_error->message);
+          g_clear_error (&internal_error);
+        }
+    }
+
+  if (backend->cogl_context == NULL)
+    {
+      if (internal_error != NULL)
+        g_propagate_error (error, internal_error);
+      else
+        g_set_error_literal (error, CLUTTER_INIT_ERROR,
+                             CLUTTER_INIT_ERROR_BACKEND,
+                            _("Unable to initialize the Clutter backend"));
+
+      return FALSE;
+    }
+
+  backend->cogl_source = cogl_glib_source_new (backend->cogl_context,
+                                               G_PRIORITY_DEFAULT);
+  g_source_attach (backend->cogl_source, NULL);
+
+  return TRUE;
+}
+
 static void
 clutter_backend_real_ensure_context (ClutterBackend *backend,
                                      ClutterStage   *stage)