st/scroll-view: Only update fade effect on CSS changes if CSS sets it

The fade effect can also be added to the scroll view programatically
instead of using CSS via the st_scroll_view_update_fade_effect() API.

We make use of this API in the appDisplay, but since commit ba547ec1d
the fade margins get overridden to 0.0 from the ::style-changed handler.
Fix this by only setting the fade margins when CSS actually defines a
custom vfade/hfade offset.

Related: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5079
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2189>

diff --git a/src/st/st-scroll-view.c b/src/st/st-scroll-view.c
index 949d7994c667a8a22b656b27cd1ea6e507e7832d..7dedc45b4579e358f0d11ee13ab07a4ee2a251f8 100644 (file)
--- a/src/st/st-scroll-view.c
+++ b/src/st/st-scroll-view.c
@@ -770,17 +770,24 @@ static void
 st_scroll_view_style_changed (StWidget *widget)
 {
   StScrollView *self = ST_SCROLL_VIEW (widget);
+  gboolean has_vfade, has_hfade;
+  double vfade_offset = 0.0;
+  double hfade_offset = 0.0;
 
   StThemeNode *theme_node = st_widget_get_theme_node (widget);
-  gdouble vfade_offset = st_theme_node_get_length (theme_node, "-st-vfade-offset");
-  gdouble hfade_offset = st_theme_node_get_length (theme_node, "-st-hfade-offset");
-  st_scroll_view_update_fade_effect (self,
-                                     &(ClutterMargin) {
-                                       .top = vfade_offset,
-                                       .bottom = vfade_offset,
-                                       .left = hfade_offset,
-                                       .right = hfade_offset,
-                                     });
+
+  has_vfade = st_theme_node_lookup_length (theme_node, "-st-vfade-offset", FALSE, &vfade_offset);
+  has_hfade = st_theme_node_lookup_length (theme_node, "-st-hfade-offset", FALSE, &hfade_offset);
+  if (has_vfade || has_hfade)
+    {
+      st_scroll_view_update_fade_effect (self,
+                                         &(ClutterMargin) {
+                                           .top = vfade_offset,
+                                           .bottom = vfade_offset,
+                                           .left = hfade_offset,
+                                           .right = hfade_offset,
+                                         });
+    }
 
   ST_WIDGET_CLASS (st_scroll_view_parent_class)->style_changed (widget);
 }