cssvalue: Add _gtk_css_value_transition()

Returns a value that transitions between start and end or %NULL if the
values cannot be transitioned.

So far, all implementations but numbers and rgba return NULL.

1 files changed, 9 insertions, 0 deletions

diff --git a/gtk/gtkcssshadowvalue.c b/gtk/gtkcssshadowvalue.c
index 370e1dba97..2898a78477 100644
--- a/gtk/gtkcssshadowvalue.c
+++ b/gtk/gtkcssshadowvalue.c
@@ -129,6 +129,14 @@ gtk_css_value_shadow_equal (const GtkCssValue *shadow1,
   return shadow1 == shadow2;
 }
 
+static GtkCssValue *
+gtk_css_value_shadow_transition (GtkCssValue *start,
+                                 GtkCssValue *end,
+                                 double       progress)
+{
+  return NULL;
+}
+
 static void
 gtk_css_value_shadow_print (const GtkCssValue *shadow,
                             GString           *string)
@@ -159,6 +167,7 @@ gtk_css_value_shadow_print (const GtkCssValue *shadow,
 static const GtkCssValueClass GTK_CSS_VALUE_SHADOW = {
   gtk_css_value_shadow_free,
   gtk_css_value_shadow_equal,
+  gtk_css_value_shadow_transition,
   gtk_css_value_shadow_print
 };