[clutter] cogl: fallback to non-transparent stages if unsupported

[Robert Bragg <rbragg src gnome org>]

commit db53ca382c5db10fa19f93761b8f898b20a4534f
Author: Robert Bragg <robert linux intel com>
Date:   Tue Nov 1 13:42:40 2011 +0000

    cogl: fallback to non-transparent stages if unsupported
    
    If our check of the CoglOnscreenTemplate during initialization fails
    then we disable the request for an alpha component in the swap chain and
    try the check again.
    
    Reviewed-by: Neil Roberts <neil linux intel com>
    Reviewed-by: Emmanuele Bassi <ebassi linux intel com>

 clutter/cogl/clutter-backend-cogl.c |   26 +++++++++++++++++++++++---
 1 files changed, 23 insertions(+), 3 deletions(-)
---
diff --git a/clutter/cogl/clutter-backend-cogl.c b/clutter/cogl/clutter-backend-cogl.c
index f54776e..f37ca19 100644
--- a/clutter/cogl/clutter-backend-cogl.c
+++ b/clutter/cogl/clutter-backend-cogl.c
@@ -289,6 +289,7 @@ clutter_backend_cogl_create_context (ClutterBackend  *backend,
 #endif
   CoglSwapChain *swap_chain = NULL;
   CoglOnscreenTemplate *onscreen_template = NULL;
+  gboolean status;
 
   if (backend->cogl_context)
     return TRUE;
@@ -318,9 +319,28 @@ clutter_backend_cogl_create_context (ClutterBackend  *backend,
    * Conceptually should we be able to check an onscreen_template
    * without more details about the CoglDisplay configuration?
    */
-  if (!cogl_renderer_check_onscreen_template (backend->cogl_renderer,
-                                              onscreen_template,
-                                              error))
+  status = cogl_renderer_check_onscreen_template (backend->cogl_renderer,
+                                                  onscreen_template,
+                                                  error);
+#ifdef COGL_HAS_XLIB_SUPPORT
+  if (!status && clutter_x11_get_use_argb_visual ())
+    {
+      g_clear_error (error);
+      /* It's possible that the current renderer doesn't support transparency
+       * in a swap_chain so lets see if we can fallback to not having any
+       * transparency...
+       *
+       * XXX: It might be nice to have a CoglRenderer feature we could
+       * explicitly check for ahead of time.
+       */
+      cogl_swap_chain_set_has_alpha (swap_chain, FALSE);
+      status = cogl_renderer_check_onscreen_template (backend->cogl_renderer,
+                                                      onscreen_template,
+                                                      error);
+    }
+#endif
+
+  if (!status)
     goto error;
 
   backend->cogl_display = cogl_display_new (backend->cogl_renderer,