[gtk+] cssstyleproperty: Make it possible to query CSS opacity with gtk_style_context_get()

[Carlos Garcia Campos <carlosgc src gnome org>]

commit 0f7b4dad0f6cef80172638efb019ce094d7eadee
Author: Carlos Garcia Campos <cgarcia igalia com>
Date:   Thu Jan 21 14:36:42 2016 +0100

    cssstyleproperty: Make it possible to query CSS opacity with gtk_style_context_get()
    
    Add a query implementation to opacity property. Also fix the assert in
    gtk_css_style_property_register() to allow registering properties with
    query but without assign function.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=760933

 gtk/gtkcssstylepropertyimpl.c |   15 ++++++++++++---
 1 files changed, 12 insertions(+), 3 deletions(-)
---
diff --git a/gtk/gtkcssstylepropertyimpl.c b/gtk/gtkcssstylepropertyimpl.c
index b817f16..1b99a78 100644
--- a/gtk/gtkcssstylepropertyimpl.c
+++ b/gtk/gtkcssstylepropertyimpl.c
@@ -88,7 +88,7 @@ gtk_css_style_property_register (const char *                   name,
   g_assert (initial_value != NULL);
   g_assert (parse_value != NULL);
   g_assert (value_type == G_TYPE_NONE || query_value != NULL);
-  g_assert (value_type == G_TYPE_NONE || assign_value != NULL);
+  g_assert (assign_value == NULL || query_value != NULL);
 
   node = g_object_new (GTK_TYPE_CSS_STYLE_PROPERTY,
                        "value-type", value_type,
@@ -457,6 +457,15 @@ opacity_parse (GtkCssStyleProperty *property,
   return _gtk_css_number_value_parse (parser, GTK_CSS_PARSE_NUMBER);
 }
 
+static void
+opacity_query (GtkCssStyleProperty *property,
+               const GtkCssValue   *css_value,
+               GValue              *value)
+{
+  g_value_init (value, G_TYPE_DOUBLE);
+  g_value_set_double (value, _gtk_css_number_value_get (css_value, 100));
+}
+
 
 static GtkCssValue *
 parse_one_css_play_state (GtkCssParser *parser)
@@ -1761,11 +1770,11 @@ _gtk_css_style_property_init_properties (void)
 
   gtk_css_style_property_register        ("opacity",
                                           GTK_CSS_PROPERTY_OPACITY,
-                                          G_TYPE_NONE,
+                                          G_TYPE_DOUBLE,
                                           GTK_STYLE_PROPERTY_ANIMATED,
                                           0,
                                           opacity_parse,
-                                          NULL,
+                                          opacity_query,
                                           NULL,
                                           _gtk_css_number_value_new (1, GTK_CSS_NUMBER));
   gtk_css_style_property_register        ("-gtk-icon-effect",