[gnome-shell] [StyleTransition] Improve style changes during transitions

[Florian Müllner <fmuellner src gnome org>]

commit 49919acb7cab14353a78cecdf652cb1dce9cba34
Author: Florian Müllner <fmuellner gnome org>
Date:   Wed Jun 9 10:56:19 2010 +0200

    [StyleTransition] Improve style changes during transitions
    
    Our behavior of reversing the animation when the widget's style
    changes back to the previous one is sound. On the other hand, when
    there's a change to a new style while a transition is active, we
    simply cancel the ongoing transition. Updating the transition
    correctly so that the new one starts from an intermediate state
    is hard.
    Nevertheless, if the style changes before any time of the transition
    has elapsed, we should do better than the current behavior.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=621140

 src/st/st-theme-node-transition.c |   42 +++++++++++++++++++++++++++---------
 1 files changed, 31 insertions(+), 11 deletions(-)
---
diff --git a/src/st/st-theme-node-transition.c b/src/st/st-theme-node-transition.c
index 37fbdf5..02b77e4 100644
--- a/src/st/st-theme-node-transition.c
+++ b/src/st/st-theme-node-transition.c
@@ -129,27 +129,47 @@ st_theme_node_transition_update (StThemeNodeTransition *transition,
   /* If the update is the reversal of the current transition,
    * we reverse the timeline.
    * Otherwise, we should initiate a new transition from the
-   * current state to the new one; this is hard to do, so we
-   * just cancel the ongoing transition in that case.
+   * current state to the new one; this is hard to do if the
+   * transition is in an intermediate state, so we just cancel
+   * the ongoing transition in that case.
    * Note that reversing a timeline before any time elapsed
    * results in the timeline's time position being set to the
    * full duration - this is not what we want, so we cancel the
    * transition as well in that case.
    */
-  if (st_theme_node_equal (new_node, old_node)
-      && clutter_timeline_get_elapsed_time (priv->timeline) > 0)
+  if (st_theme_node_equal (new_node, old_node))
     {
-      if (direction == CLUTTER_TIMELINE_FORWARD)
-        clutter_timeline_set_direction (priv->timeline,
-                                        CLUTTER_TIMELINE_BACKWARD);
+      if (clutter_timeline_get_elapsed_time (priv->timeline) > 0)
+        {
+          if (direction == CLUTTER_TIMELINE_FORWARD)
+            clutter_timeline_set_direction (priv->timeline,
+                                            CLUTTER_TIMELINE_BACKWARD);
+          else
+            clutter_timeline_set_direction (priv->timeline,
+                                            CLUTTER_TIMELINE_FORWARD);
+        }
       else
-        clutter_timeline_set_direction (priv->timeline,
-                                        CLUTTER_TIMELINE_FORWARD);
+        {
+          clutter_timeline_stop (priv->timeline);
+          g_signal_emit (transition, signals[COMPLETED], 0);
+        }
     }
   else
     {
-      clutter_timeline_stop (priv->timeline);
-      g_signal_emit (transition, signals[COMPLETED], 0);
+      if (clutter_timeline_get_elapsed_time (priv->timeline) > 0)
+        {
+          clutter_timeline_stop (priv->timeline);
+          g_signal_emit (transition, signals[COMPLETED], 0);
+        }
+      else
+        {
+          guint new_duration = st_theme_node_get_transition_duration (new_node);
+
+          clutter_timeline_set_duration (priv->timeline, new_duration);
+          g_object_unref (priv->new_theme_node);
+          priv->new_theme_node = g_object_ref (new_node);
+          priv->needs_setup = TRUE;
+        }
     }
 }