allow to get a gdkrgba from style without boxed copy
@chpe
Submitted by Christian Persch Link to original bug (#650508)
Description
For style properties of type GD_TYPE_COLOR/RGBA installed with gtk_widget_class_install_style_property, there is no way to get these properties from the style without making a boxed copy. (gtk_style_context_lookup_color etc were added specifically for no-copy, but those only works for 'symbolic colours', not for style properties.)
A possibility might be to augment gtk_style_context_get_style with gvariant-style '&' modifier, so that
GdkRGBA color; gtk_style_context_get_style (context, "&my-color-property", &color, NULL)
would expect a GdkRGBA* instead and put the info directly into it, instead of expecting GdkRGBA** and storing a boxed copy.