[backend] Constify font options

The font options accessors in ClutterBackend only deal with const
cairo_font_options_t values, since:

  - set_font_options() will copy the font options
  - get_font_options() will return a pointer to the internal
    font options

Not using const in these cases makes the API confusing and might lead
to erroneous calls to cairo_font_options_destroy().

clutter/clutter-backend.c

@@ -533,9 +533,12 @@ clutter_backend_get_resolution (ClutterBackend *backend)
  * @backend: a #ClutterBackend
  * @options: Cairo font options for the backend, or %NULL
  *
- * Sets the new font options for @backend. If @options is %NULL,
+ * Sets the new font options for @backend. The #ClutterBackend will
- * the first following call to clutter_backend_get_font_options()
+ * copy the #cairo_font_options_t.
- * will return the default font options for @backend.
+ *
+ * If @options is %NULL, the first following call to
+ * clutter_backend_get_font_options() will return the default font
+ * options for @backend.
  *
  * This function is intended for actors creating a Pango layout
  * using the PangoCairo API.
@@ -544,7 +547,7 @@ clutter_backend_get_resolution (ClutterBackend *backend)
  */
 void
 clutter_backend_set_font_options (ClutterBackend       *backend,
-                                  cairo_font_options_t *options)
+                                  const cairo_font_options_t *options)
 {
   ClutterBackendPrivate *priv;
 
@@ -572,11 +575,13 @@ clutter_backend_set_font_options (ClutterBackend       *backend,
  *
  * Retrieves the font options for @backend.
  *
- * Return value: (transfer none): the font options of the #ClutterBackend
+ * Return value: (transfer none): the font options of the #ClutterBackend.
+ *   The returned #cairo_font_options_t is owned by the backend and should
+ *   not be modified or freed
  *
  * Since: 0.8
  */
-cairo_font_options_t *
+const cairo_font_options_t *
 clutter_backend_get_font_options (ClutterBackend *backend)
 {
   ClutterBackendPrivate *priv;

clutter/clutter-backend.h

@@ -99,11 +99,11 @@ void                  clutter_backend_set_double_click_distance (ClutterBackend
                                                                        guint                       distance);
 guint                       clutter_backend_get_double_click_distance (ClutterBackend             *backend);
 void                        clutter_backend_set_font_options          (ClutterBackend             *backend,
-                                                                 cairo_font_options_t *options);
+                                                                       const cairo_font_options_t *options);
-cairo_font_options_t *clutter_backend_get_font_options          (ClutterBackend       *backend);
+const cairo_font_options_t *clutter_backend_get_font_options          (ClutterBackend             *backend);
 void                        clutter_backend_set_font_name             (ClutterBackend             *backend,
                                                                        const gchar                *font_name);
-G_CONST_RETURN gchar *clutter_backend_get_font_name             (ClutterBackend       *backend);
+G_CONST_RETURN gchar *      clutter_backend_get_font_name             (ClutterBackend             *backend);
 
 G_END_DECLS
 

clutter/clutter-main.c

@@ -447,7 +447,7 @@ update_pango_context (ClutterBackend *backend,
                       PangoContext   *context)
 {
   PangoFontDescription *font_desc;
-  cairo_font_options_t *font_options;
+  const cairo_font_options_t *font_options;
   const gchar *font_name;
   gdouble resolution;
 
@@ -2671,7 +2671,11 @@ void
 clutter_set_font_flags (ClutterFontFlags flags)
 {
   ClutterFontFlags old_flags, changed_flags;
-  cairo_font_options_t *font_options;
+  const cairo_font_options_t *font_options;
+  cairo_font_options_t *new_font_options;
+  ClutterBackend *backend;
+
+  backend = clutter_get_default_backend ();
 
   if (CLUTTER_CONTEXT ()->font_map)
     cogl_pango_font_map_set_use_mipmapping (CLUTTER_CONTEXT ()->font_map,
@@ -2680,26 +2684,25 @@ clutter_set_font_flags (ClutterFontFlags flags)
 
   old_flags = clutter_get_font_flags ();
 
-  font_options = clutter_backend_get_font_options (CLUTTER_CONTEXT ()->backend);
+  font_options = clutter_backend_get_font_options (backend);
-  font_options = cairo_font_options_copy (font_options);
+  new_font_options = cairo_font_options_copy (font_options);
 
   /* Only set the font options that have actually changed so we don't
      override a detailed setting from the backend */
   changed_flags = old_flags ^ flags;
 
   if ((changed_flags & CLUTTER_FONT_HINTING))
-    cairo_font_options_set_hint_style (font_options,
+    cairo_font_options_set_hint_style (new_font_options,
                                        (flags & CLUTTER_FONT_HINTING)
                                        ? CAIRO_HINT_STYLE_FULL
                                        : CAIRO_HINT_STYLE_NONE);
 
-  clutter_backend_set_font_options (CLUTTER_CONTEXT ()->backend, font_options);
+  clutter_backend_set_font_options (backend, new_font_options);
 
-  cairo_font_options_destroy (font_options);
+  cairo_font_options_destroy (new_font_options);
 
   if (CLUTTER_CONTEXT ()->pango_context)
-    update_pango_context (CLUTTER_CONTEXT ()->backend,
+    update_pango_context (backend, CLUTTER_CONTEXT ()->pango_context);
-                          CLUTTER_CONTEXT ()->pango_context);
 }
 
 /**
@@ -2717,7 +2720,7 @@ clutter_get_font_flags (void)
 {
   ClutterMainContext *ctxt = CLUTTER_CONTEXT ();
   CoglPangoFontMap *font_map = NULL;
-  cairo_font_options_t *font_options;
+  const cairo_font_options_t *font_options;
   ClutterFontFlags flags = 0;
 
   font_map = CLUTTER_CONTEXT ()->font_map;