Refactor "texture material" creation from MetaShadowFactory

Create new cogl-utils.[ch] and move a helper function from
MetaShadowFactory there as meta_create_texture_material(); this
allows us to create single-layer materials from different parts of
Mutter and have them share the same template material.

Also expose a function for creating a 1x1 texture of a given
color meta_create_color_texture_4ub().

https://bugzilla.gnome.org/show_bug.cgi?id=634833

src/compositor/cogl-utils.h

@@ -0,0 +1,34 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+/*
+ * Utilities for use with Cogl
+ *
+ * Copyright 2010 Red Hat, Inc.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ */
+
+#ifndef __META_COGL_UTILS_H__
+#define __META_COGL_UTILS_H__
+
+#include <cogl/cogl.h>
+
+CoglHandle meta_create_color_texture_4ub (guint8     red,
+                                          guint8     green,
+                                          guint8     blue,
+                                          guint8     alpha);
+CoglHandle meta_create_texture_material  (CoglHandle src_texture);
+
+#endif /* __META_COGL_UTILS_H__ */