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.c

@@ -0,0 +1,104 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+/*
+ * Utilities for use with Cogl
+ *
+ * Copyright 2010 Red Hat, Inc.
+ * Copyright 2010 Intel Corporation
+ *
+ * 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.
+ */
+
+#include "cogl-utils.h"
+
+/**
+ * meta_create_color_texture_4ub:
+ * @red:
+ * @green:
+ * @blue:
+ * @alpha:
+ *
+ * Creates a texture that is a single pixel with the specified
+ * unpremultiplied color components.
+ *
+ * Return value: (transfer full): a newly created Cogl texture
+ */
+CoglHandle
+meta_create_color_texture_4ub (guint8 red,
+                               guint8 green,
+                               guint8 blue,
+                               guint8 alpha)
+{
+  CoglColor color;
+  guint8 pixel[4];
+
+  cogl_color_set_from_4ub (&color, red, green, blue, alpha);
+  cogl_color_premultiply (&color);
+
+  pixel[0] = cogl_color_get_red_byte (&color);
+  pixel[1] = cogl_color_get_green_byte (&color);
+  pixel[2] = cogl_color_get_blue_byte (&color);
+  pixel[3] = cogl_color_get_alpha_byte (&color);
+
+  return cogl_texture_new_from_data (1, 1,
+                                     COGL_TEXTURE_NONE,
+                                     COGL_PIXEL_FORMAT_RGBA_8888_PRE,
+                                     COGL_PIXEL_FORMAT_ANY,
+                                     4, pixel);
+}
+
+
+/* Based on gnome-shell/src/st/st-private.c:_st_create_texture_material.c */
+
+/**
+ * meta_create_texture_material:
+ * @src_texture: (allow-none): texture to use initially for the layer
+ *
+ * Creates a material with a single layer. Using a common template
+ * allows sharing a shader for different uses in Mutter. To share the same
+ * shader with all other materials that are just texture plus opacity
+ * would require Cogl fixes.
+ * (See http://bugzilla.clutter-project.org/show_bug.cgi?id=2425)
+ *
+ * Return value: (transfer full): a newly created Cogl material
+ */
+CoglHandle
+meta_create_texture_material (CoglHandle src_texture)
+{
+  static CoglHandle texture_material_template = COGL_INVALID_HANDLE;
+  CoglHandle material;
+
+  /* We use a material that has a dummy texture as a base for all
+     texture materials. The idea is that only the Cogl texture object
+     would be different in the children so it is likely that Cogl will
+     be able to share GL programs between all the textures. */
+  if (G_UNLIKELY (texture_material_template == COGL_INVALID_HANDLE))
+    {
+      CoglHandle dummy_texture;
+
+      dummy_texture = meta_create_color_texture_4ub (0xff, 0xff, 0xff, 0xff);
+
+      texture_material_template = cogl_material_new ();
+      cogl_material_set_layer (texture_material_template, 0, dummy_texture);
+      cogl_handle_unref (dummy_texture);
+    }
+
+  material = cogl_material_copy (texture_material_template);
+
+  if (src_texture != COGL_INVALID_HANDLE)
+    cogl_material_set_layer (material, 0, src_texture);
+
+  return material;
+}