[gtk+] build: Add an enable flag to allow enabling Cairo GL backend

[Rob Bradford <rbradford src gnome org>]

commit ba81a3a14c6f6d58d08632c4a10c3f21fd3d1b73
Author: Rob Bradford <rob linux intel com>
Date:   Mon Apr 16 15:29:44 2012 +0100

    build: Add an enable flag to allow enabling Cairo GL backend
    
    This change adds --enable-wayland-cairo-gl which turns on the define used in
    the Wayland backend to determine whether to use EGL surfaces with Cairo GL or
    whether to use the Cairo image backend with an SHM surface (the default).
    
    Part of the fix for: https://bugzilla.gnome.org/show_bug.cgi?id=672361

 configure.ac |   16 ++++++++++++++--
 1 files changed, 14 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 8e1d691..3cbfa03 100644
--- a/configure.ac
+++ b/configure.ac
@@ -316,6 +316,12 @@ AC_ARG_ENABLE(quartz-relocation,
                               [enable bundle-based relocation functions])],
                               [quartz_relocation=yes])
 
+AC_ARG_ENABLE(wayland-cairo-gl,
+              AS_HELP_STRING([--enable-wayland-cairo-gl],
+                             [enable the use of Cairo GL in the Wayland backend]),
+              [enable_wayland_cairo_gl=yes])
+
+
 cairo_backends=
 backend_immodules=
 have_gio_unix=no
@@ -379,8 +385,14 @@ else
 fi
 
 if test "x$enable_wayland_backend" == "xyes"; then
-  # For the cairo image backend
-  cairo_backends="$cairo_backends cairo"
+  if test "x$enable_wayland_cairo_gl" == "xyes"; then
+    # Wayland can use cairo-gl
+    cairo_backends="$cairo_backends cairo-gl"
+    AC_DEFINE(GDK_WAYLAND_USE_EGL, [1], [Whether to use EGL in Wayland backend])
+  else
+    # For the cairo image backend
+    cairo_backends="$cairo_backends cairo"
+  fi
   GDK_BACKENDS="$GDK_BACKENDS wayland"
   have_gio_unix=yes
   GDK_WINDOWING="$GDK_WINDOWING