material: Adds a simple material age getter

When we add support for weak materials it's expected that Clutter will
want to attach them as private data to other materials and it needs a
mechanism to determine when a weak material should be re-created because
its parent has changed somehow.

This adds the concept of a material age (internal only currently) which
increments whenever a material is modified. Clutter can then save the
age of the material which its weak materials are derived from and later
determine when the weak material may be invalid.

clutter/cogl/cogl/cogl-material-private.h

@@ -472,6 +472,13 @@ struct _CoglMaterial
    * bitfield can associate private data with a material. */
   void		  *backend_priv;
 
+  /* Whenever a material is modified we increment the age. There's no
+   * guarantee that it won't wrap but it can nevertheless be a
+   * convenient mechanism to determine when a material has been
+   * changed to you can invalidate some some associated cache that
+   * depends on the old state. */
+  unsigned long    age;
+
   /* This is the primary color of the material.
    *
    * This is a sparse property, ref COGL_MATERIAL_STATE_COLOR */
@@ -761,5 +768,8 @@ void
 _cogl_material_set_static_breadcrumb (CoglHandle handle,
                                       const char *breadcrumb);
 
+unsigned long
+_cogl_material_get_age (CoglHandle handle);
+
 #endif /* __COGL_MATERIAL_PRIVATE_H */
 

clutter/cogl/cogl/cogl-material.c

@@ -368,6 +368,8 @@ _cogl_material_init_default_material (void)
   material->static_breadcrumb = "default material";
   material->has_static_breadcrumb = TRUE;
 
+  material->age = 0;
+
   /* Use the same defaults as the GL spec... */
   cogl_color_init_from_4ub (&material->color, 0xff, 0xff, 0xff, 0xff);
 
@@ -469,6 +471,8 @@ cogl_material_copy (CoglHandle handle)
 
   material->has_static_breadcrumb = FALSE;
 
+  material->age = 0;
+
   return _cogl_material_handle_new (material);
 }
 
@@ -1184,6 +1188,8 @@ _cogl_material_pre_change_notify (CoglMaterial     *material,
    * are now free to modify the material. */
   g_assert (!material->has_children);
 
+  material->age++;
+
   /* If the material isn't already an authority for the state group
    * being modified then we need to initialize the corresponding
    * state. */
@@ -1561,6 +1567,9 @@ _cogl_material_layer_pre_change_notify (CoglMaterial *required_owner,
 
 init_layer_state:
 
+  if (required_owner)
+    required_owner->age++;
+
   /* If the material isn't already an authority for the state group
    * being modified then we need to initialize the corresponding
    * state. */
@@ -4109,6 +4118,16 @@ cogl_material_get_depth_range (CoglHandle handle,
   *far = authority->big_state->depth_state.depth_range_far;
 }
 
+unsigned long
+_cogl_material_get_age (CoglHandle handle)
+{
+  CoglMaterial *material = COGL_MATERIAL (handle);
+
+  g_return_val_if_fail (cogl_is_material (handle), 0);
+
+  return material->age;
+}
+
 static CoglMaterialLayer *
 _cogl_material_layer_copy (CoglMaterialLayer *src)
 {