From 165265f4fb9b0bf9b61a6ffcead79442f51f101c Mon Sep 17 00:00:00 2001
From: "Jasper St. Pierre" <jstpierre@mecheye.net>
Date: Sun, 4 Nov 2012 10:10:50 -0500
Subject: [PATCH] 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 file changed, 47 insertions(+), 36 deletions(-)

diff --git a/src/st/st-scroll-view.c b/src/st/st-scroll-view.c
index c8f89ceee..e4b3372b2 100644
--- a/src/st/st-scroll-view.c
+++ b/src/st/st-scroll-view.c
@@ -665,6 +665,45 @@ 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)
 {
@@ -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;
     }