[clutter] Add a configuration option for deciding the Cogl drivers to use

[Emmanuele Bassi <ebassi src gnome org>]

commit bb23335b5fd29fb1d63e99b8f9eb32c5f11b4405
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Wed Dec 9 14:26:28 2015 +0000

    Add a configuration option for deciding the Cogl drivers to use
    
    Using environment variables only is not convenient for all platforms,
    and in some cases it's beneficial to decide the default driver when
    building Clutter. Cogl already has a similar configuration switch, and
    since Clutter is overriding the default Cogl behaviour, it should offer
    the same mechanism.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=742678

 clutter/clutter-backend.c |    2 +-
 configure.ac              |    9 +++++++++
 2 files changed, 10 insertions(+), 1 deletions(-)
---
diff --git a/clutter/clutter-backend.c b/clutter/clutter-backend.c
index 62f33ec..71710e3 100644
--- a/clutter/clutter-backend.c
+++ b/clutter/clutter-backend.c
@@ -386,7 +386,7 @@ clutter_backend_real_create_context (ClutterBackend  *backend,
   int i;
 
   if (allowed_drivers == NULL)
-    allowed_drivers = "*";
+    allowed_drivers = CLUTTER_DRIVERS;
 
   allow_any = strstr (allowed_drivers, "*") != NULL;
 
diff --git a/configure.ac b/configure.ac
index 985dc1b..e32f5dd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -585,6 +585,13 @@ dnl other tools such as glib-mkenums and gir-scanner don't end up
 dnl using the define also.
 AC_DEFINE([COGL_ENABLE_EXPERIMENTAL_2_0_API], [1], [Can use Cogl 2.0 API internally])
 
+AC_ARG_WITH([default-drivers],
+            [AS_HELP_STRING([--with-default-drivers=DRIVER], [Comma-separated list of Cogl drivers to use])],
+            [clutter_drivers=$withval],
+            [clutter_drivers="*"])
+
+AC_DEFINE_UNQUOTED([CLUTTER_DRIVERS], ["$clutter_drivers"], [List of Cogl drivers])
+
 dnl strip leading spaces
 CLUTTER_BACKENDS=${CLUTTER_BACKENDS#* }
 AC_SUBST(CLUTTER_BACKENDS)
@@ -1285,6 +1292,8 @@ else
 echo "        Input backends: ${CLUTTER_INPUT_BACKENDS} (WARNING: Experimental backends enabled)"
 fi
 
+echo "        Cogl drivers: $clutter_drivers"
+
 if test "x$SUPPORT_X11" = "x1"; then
 echo ""
 echo "     - X11 backend options:"