[gnome-shell/wip/grab-helper-top-panel: 1/20] st-scroll-view: Add proper smooth scrolling

[Jasper St. Pierre <jstpierre src gnome org>]

commit 165265f4fb9b0bf9b61a6ffcead79442f51f101c
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Sun Nov 4 10:10:50 2012 -0500

    st-scroll-view: Add proper smooth scrolling
    
    The code here before was added as dummy code to satisfy an error
    in the missing switch, and wasn't ever tested due to the lack of XI2
    in mutter. Use the same math as GtkRange does to calculate scroll bar
    positions from raw XI2 deltas to allow for proper smooth scrolling.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=687573

 src/st/st-scroll-view.c |   83 ++++++++++++++++++++++++++--------------------
 1 files changed, 47 insertions(+), 36 deletions(-)
---
diff --git a/src/st/st-scroll-view.c b/src/st/st-scroll-view.c
index c8f89ce..e4b3372 100644
--- a/src/st/st-scroll-view.c
+++ b/src/st/st-scroll-view.c
@@ -666,6 +666,45 @@ st_scroll_view_allocate (ClutterActor          *actor,
 }
 
 static void
+adjust_with_delta (StAdjustment *adj,
+                   gdouble       delta)
+{
+  gdouble new_value, page_size, scroll_unit;
+
+  g_object_get (adj,
+                "page-size", &page_size,
+                NULL);
+  scroll_unit = pow (page_size, 2.0 / 3.0);
+
+  new_value = st_adjustment_get_value (adj) + delta * scroll_unit;
+  st_adjustment_set_value (adj, new_value);
+}
+
+static void
+adjust_with_direction (StAdjustment           *adj,
+                       ClutterScrollDirection  direction)
+{
+  gdouble delta;
+
+  switch (direction)
+    {
+    case CLUTTER_SCROLL_UP:
+    case CLUTTER_SCROLL_LEFT:
+      delta = -1.0;
+      break;
+    case CLUTTER_SCROLL_RIGHT:
+    case CLUTTER_SCROLL_DOWN:
+      delta = 1.0;
+      break;
+    case CLUTTER_SCROLL_SMOOTH:
+      g_assert_not_reached ();
+      break;
+    }
+
+  adjust_with_delta (adj, delta);
+}
+
+static void
 st_scroll_view_style_changed (StWidget *widget)
 {
   StScrollView *self = ST_SCROLL_VIEW (widget);
@@ -687,57 +726,29 @@ st_scroll_view_scroll_event (ClutterActor       *self,
                              ClutterScrollEvent *event)
 {
   StScrollViewPrivate *priv = ST_SCROLL_VIEW (self)->priv;
-  gdouble value, step, hvalue, vvalue, delta_x, delta_y;
 
   /* don't handle scroll events if requested not to */
   if (!priv->mouse_scroll)
     return FALSE;
 
-  switch (event->direction)
-    {
-    case CLUTTER_SCROLL_SMOOTH:
-      clutter_event_get_scroll_delta ((ClutterEvent *)event,
-                                      &delta_x, &delta_y);
-      g_object_get (priv->hadjustment,
-                    "value", &hvalue,
-                    NULL);
-      g_object_get (priv->vadjustment,
-                    "value", &vvalue,
-                    NULL);
-      break;
-    case CLUTTER_SCROLL_UP:
-    case CLUTTER_SCROLL_DOWN:
-      g_object_get (priv->vadjustment,
-                    "step-increment", &step,
-                    "value", &value,
-                    NULL);
-      break;
-    case CLUTTER_SCROLL_LEFT:
-    case CLUTTER_SCROLL_RIGHT:
-      g_object_get (priv->hadjustment,
-                    "step-increment", &step,
-                    "value", &value,
-                    NULL);
-      break;
-    }
 
   switch (event->direction)
     {
     case CLUTTER_SCROLL_SMOOTH:
-      st_adjustment_set_value (priv->hadjustment, hvalue + delta_x);
-      st_adjustment_set_value (priv->vadjustment, vvalue + delta_y);
+      {
+        gdouble delta_x, delta_y;
+        clutter_event_get_scroll_delta ((ClutterEvent *)event, &delta_x, &delta_y);
+        adjust_with_delta (priv->hadjustment, delta_x);
+        adjust_with_delta (priv->vadjustment, delta_y);
+      }
       break;
     case CLUTTER_SCROLL_UP:
-      st_adjustment_set_value (priv->vadjustment, value - step);
-      break;
     case CLUTTER_SCROLL_DOWN:
-      st_adjustment_set_value (priv->vadjustment, value + step);
+      adjust_with_direction (priv->vadjustment, event->direction);
       break;
     case CLUTTER_SCROLL_LEFT:
-      st_adjustment_set_value (priv->hadjustment, value - step);
-      break;
     case CLUTTER_SCROLL_RIGHT:
-      st_adjustment_set_value (priv->hadjustment, value + step);
+      adjust_with_direction (priv->hadjustment, event->direction);
       break;
     }