Many fixes, along with extensive cleanups and refactoring of code to

Fri Jun  6 16:25:44 2003  Owen Taylor  <otaylor@redhat.com>

        * gtk/gtkviewport.c: Many fixes, along with extensive cleanups and
        refactoring of code to reduce duplication; fixes include:

        - gtk_viewport_realize(): Position the window correct from adjustment
        values. (#110737, Michael Natterer)

        - Remove some division-by-zero checks in places where there is no
        longer division. (#110737)

        - gtk_viewport_class_init: Make the hadjustment/vadjustment properties
        G_PARAM_CONSTRUCT, so that there will always be adjustments, even
        if gtk_viewport_new isn't used (#101135, Thomas Leonard).

        - Switch over to encapsulated lazy-creation for hadjustment/
        vadjustment; even with the CONSTRUCT property, we need this after
        destroy.

        - When updating the adjustment, immediate set their values to
        match the the current range of the viewport, and update the
        viewport position to match the value of the new adjustments.
        (Part of #1165

1 files changed, 233 insertions, 227 deletions

diff --git a/gtk/gtkviewport.c b/gtk/gtkviewport.c
index bfe955eab1..e32b2bac60 100644
--- a/gtk/gtkviewport.c
+++ b/gtk/gtkviewport.c
@@ -38,6 +38,7 @@ enum {
 
 static void gtk_viewport_class_init               (GtkViewportClass *klass);
 static void gtk_viewport_init                     (GtkViewport      *viewport);
+static void gtk_viewport_finalize                 (GObject          *object);
 static void gtk_viewport_destroy                  (GtkObject        *object);
 static void gtk_viewport_set_property             (GObject         *object,
 						   guint            prop_id,
@@ -62,8 +63,6 @@ static void gtk_viewport_size_request             (GtkWidget        *widget,
 						   GtkRequisition   *requisition);
 static void gtk_viewport_size_allocate            (GtkWidget        *widget,
 						   GtkAllocation    *allocation);
-static void gtk_viewport_adjustment_changed       (GtkAdjustment    *adjustment,
-						   gpointer          data);
 static void gtk_viewport_adjustment_value_changed (GtkAdjustment    *adjustment,
 						   gpointer          data);
 static void gtk_viewport_style_set                (GtkWidget *widget,
@@ -113,6 +112,7 @@ gtk_viewport_class_init (GtkViewportClass *class)
 
   parent_class = g_type_class_peek_parent (class);
 
+  gobject_class->finalize = gtk_viewport_finalize;
   gobject_class->set_property = gtk_viewport_set_property;
   gobject_class->get_property = gtk_viewport_get_property;
   object_class->destroy = gtk_viewport_destroy;
@@ -134,7 +134,7 @@ gtk_viewport_class_init (GtkViewportClass *class)
 							_("Horizontal adjustment"),
 							_("The GtkAdjustment that determines the values of the horizontal position for this viewport"),
                                                         GTK_TYPE_ADJUSTMENT,
-                                                        G_PARAM_READWRITE));
+                                                        G_PARAM_READWRITE | G_PARAM_CONSTRUCT));
 
   g_object_class_install_property (gobject_class,
                                    PROP_VADJUSTMENT,
@@ -142,7 +142,7 @@ gtk_viewport_class_init (GtkViewportClass *class)
 							_("Vertical adjustment"),
 							_("The GtkAdjustment that determines the values of the vertical position for this viewport"),
                                                         GTK_TYPE_ADJUSTMENT,
-                                                        G_PARAM_READWRITE));
+                                                        G_PARAM_READWRITE | G_PARAM_CONSTRUCT));
 
   g_object_class_install_property (gobject_class,
                                    PROP_SHADOW_TYPE,
@@ -257,33 +257,44 @@ gtk_viewport_new (GtkAdjustment *hadjustment,
   return viewport;
 }
 
+#define ADJUSTMENT_POINTER(viewport, orientation)         \
+  (((orientation) == GTK_ORIENTATION_HORIZONTAL) ?        \
+     &(viewport)->hadjustment : &(viewport)->vadjustment)
+
 static void
-gtk_viewport_destroy (GtkObject *object)
+viewport_disconnect_adjustment (GtkViewport    *viewport,
+				GtkOrientation  orientation)
 {
-  GtkViewport *viewport = GTK_VIEWPORT (object);
+  GtkAdjustment **adjustmentp = ADJUSTMENT_POINTER (viewport, orientation);
 
-  if (viewport->hadjustment)
-    {
-      g_signal_handlers_disconnect_by_func (viewport->hadjustment,
-					    gtk_viewport_adjustment_changed,
-					    viewport);
-      g_signal_handlers_disconnect_by_func (viewport->hadjustment,
-					    gtk_viewport_adjustment_value_changed,
-					    viewport);
-      g_object_unref (viewport->hadjustment);
-      viewport->hadjustment = NULL;
-    }
-  if (viewport->vadjustment)
+  if (*adjustmentp)
     {
-      g_signal_handlers_disconnect_by_func (viewport->vadjustment,
-					    gtk_viewport_adjustment_changed,
-					    viewport);
-      g_signal_handlers_disconnect_by_func (viewport->vadjustment,
+      g_signal_handlers_disconnect_by_func (*adjustmentp,
 					    gtk_viewport_adjustment_value_changed,
 					    viewport);
-      g_object_unref (viewport->vadjustment);
-      viewport->vadjustment = NULL;
+      g_object_unref (*adjustmentp);
+      *adjustmentp = NULL;
     }
+}
+
+static void
+gtk_viewport_finalize (GObject *object)
+{
+  GtkViewport *viewport = GTK_VIEWPORT (object);
+
+  viewport_disconnect_adjustment (viewport, GTK_ORIENTATION_HORIZONTAL);
+  viewport_disconnect_adjustment (viewport, GTK_ORIENTATION_VERTICAL);
+
+  G_OBJECT_CLASS (parent_class)->finalize (object);
+}
+
+static void
+gtk_viewport_destroy (GtkObject *object)
+{
+  GtkViewport *viewport = GTK_VIEWPORT (object);
+
+  viewport_disconnect_adjustment (viewport, GTK_ORIENTATION_HORIZONTAL);
+  viewport_disconnect_adjustment (viewport, GTK_ORIENTATION_VERTICAL);
 
   GTK_OBJECT_CLASS (parent_class)->destroy (object);
 }
@@ -326,6 +337,138 @@ gtk_viewport_get_vadjustment (GtkViewport *viewport)
   return viewport->vadjustment;
 }
 
+static void
+viewport_get_view_allocation (GtkViewport   *viewport,
+			      GtkAllocation *view_allocation)
+{
+  GtkWidget *widget = GTK_WIDGET (viewport);
+  GtkAllocation *allocation = &widget->allocation;
+  gint border_width = GTK_CONTAINER (viewport)->border_width;
+  
+  view_allocation->x = 0;
+  view_allocation->y = 0;
+
+  if (viewport->shadow_type != GTK_SHADOW_NONE)
+    {
+      view_allocation->x = widget->style->xthickness;
+      view_allocation->y = widget->style->ythickness;
+    }
+
+  view_allocation->width = MAX (1, allocation->width - view_allocation->x * 2 - border_width * 2);
+  view_allocation->height = MAX (1, allocation->height - view_allocation->y * 2 - border_width * 2);
+}
+
+static void
+viewport_reclamp_adjustment (GtkAdjustment *adjustment,
+			     gboolean      *value_changed)
+{
+  gdouble value = adjustment->value;
+  
+  value = CLAMP (value, 0, adjustment->upper - adjustment->page_size);
+  if (value != adjustment->value)
+    {
+      adjustment->value = value;
+      if (value_changed)
+	*value_changed = TRUE;
+    }
+  else if (value_changed)
+    *value_changed = FALSE;
+}
+
+static void
+viewport_set_hadjustment_values (GtkViewport *viewport,
+				 gboolean    *value_changed)
+{
+  GtkBin *bin = GTK_BIN (viewport);
+  GtkAllocation view_allocation;
+  GtkAdjustment *hadjustment = gtk_viewport_get_hadjustment (viewport);
+
+  viewport_get_view_allocation (viewport, &view_allocation);  
+
+  hadjustment->page_size = view_allocation.width;
+  hadjustment->step_increment = view_allocation.width * 0.1;
+  hadjustment->page_increment = view_allocation.width * 0.9;
+  
+  hadjustment->lower = 0;
+
+  if (bin->child && GTK_WIDGET_VISIBLE (bin->child))
+    {
+      GtkRequisition child_requisition;
+      
+      gtk_widget_get_child_requisition (bin->child, &child_requisition);
+      hadjustment->upper = MAX (child_requisition.width, view_allocation.width);
+    }
+  else
+    hadjustment->upper = view_allocation.width;
+
+  viewport_reclamp_adjustment (hadjustment, value_changed);
+}
+
+static void
+viewport_set_vadjustment_values (GtkViewport *viewport,
+				 gboolean    *value_changed)
+{
+  GtkBin *bin = GTK_BIN (viewport);
+  GtkAllocation view_allocation;
+  GtkAdjustment *vadjustment = gtk_viewport_get_vadjustment (viewport);
+
+  viewport_get_view_allocation (viewport, &view_allocation);  
+
+  vadjustment->page_size = view_allocation.height;
+  vadjustment->step_increment = view_allocation.height * 0.1;
+  vadjustment->page_increment = view_allocation.height * 0.9;
+  
+  vadjustment->lower = 0;
+
+  if (bin->child && GTK_WIDGET_VISIBLE (bin->child))
+    {
+      GtkRequisition child_requisition;
+      
+      gtk_widget_get_child_requisition (bin->child, &child_requisition);
+      vadjustment->upper = MAX (child_requisition.height, view_allocation.height);
+    }
+  else
+    vadjustment->upper = view_allocation.height;
+
+  viewport_reclamp_adjustment (vadjustment, value_changed);
+}
+
+static void
+viewport_set_adjustment (GtkViewport    *viewport,
+			 GtkOrientation  orientation,
+			 GtkAdjustment  *adjustment)
+{
+  GtkAdjustment **adjustmentp = ADJUSTMENT_POINTER (viewport, orientation);
+  gboolean value_changed;
+
+  if (adjustment == *adjustmentp)
+    return;
+
+  if (!adjustment)
+    adjustment = GTK_ADJUSTMENT (gtk_adjustment_new (0.0, 0.0, 0.0,
+						     0.0, 0.0, 0.0));
+
+  *adjustmentp = adjustment;
+  g_object_ref (adjustment);
+  gtk_object_sink (GTK_OBJECT (adjustment));
+
+  if (orientation == GTK_ORIENTATION_HORIZONTAL)
+    viewport_set_hadjustment_values (viewport, &value_changed);
+  else
+    viewport_set_vadjustment_values (viewport, &value_changed);
+
+  g_signal_connect (adjustment, "value_changed",
+		    G_CALLBACK (gtk_viewport_adjustment_value_changed),
+		    viewport);
+
+  gtk_adjustment_changed (adjustment);
+  
+  if (value_changed)
+    gtk_adjustment_value_changed (adjustment);
+  else
+    gtk_viewport_adjustment_value_changed (adjustment, viewport);
+}
+
 /**
  * gtk_viewport_set_hadjustment:
  * @viewport: a #GtkViewport.
@@ -341,37 +484,7 @@ gtk_viewport_set_hadjustment (GtkViewport   *viewport,
   if (adjustment)
     g_return_if_fail (GTK_IS_ADJUSTMENT (adjustment));
 
-  if (viewport->hadjustment && viewport->hadjustment != adjustment)
-    {
-      g_signal_handlers_disconnect_by_func (viewport->hadjustment,
-					    gtk_viewport_adjustment_changed,
-					    viewport);
-      g_signal_handlers_disconnect_by_func (viewport->hadjustment,
-					    gtk_viewport_adjustment_value_changed,
-					    viewport);
-      g_object_unref (viewport->hadjustment);
-      viewport->hadjustment = NULL;
-    }
-
-  if (!adjustment)
-    adjustment = GTK_ADJUSTMENT (gtk_adjustment_new (0.0, 0.0, 0.0,
-						     0.0, 0.0, 0.0));
-
-  if (viewport->hadjustment != adjustment)
-    {
-      viewport->hadjustment = adjustment;
-      g_object_ref (viewport->hadjustment);
-      gtk_object_sink (GTK_OBJECT (viewport->hadjustment));
-      
-      g_signal_connect (adjustment, "changed",
-			G_CALLBACK (gtk_viewport_adjustment_changed),
-			viewport);
-      g_signal_connect (adjustment, "value_changed",
-			G_CALLBACK (gtk_viewport_adjustment_value_changed),
-			viewport);
-
-      gtk_viewport_adjustment_changed (adjustment, viewport);
-    }
+  viewport_set_adjustment (viewport, GTK_ORIENTATION_HORIZONTAL, adjustment);
 
   g_object_notify (G_OBJECT (viewport), "hadjustment");
 }
@@ -391,39 +504,9 @@ gtk_viewport_set_vadjustment (GtkViewport   *viewport,
   if (adjustment)
     g_return_if_fail (GTK_IS_ADJUSTMENT (adjustment));
 
-  if (viewport->vadjustment && viewport->vadjustment != adjustment)
-    {
-      g_signal_handlers_disconnect_by_func (viewport->vadjustment,
-					    gtk_viewport_adjustment_changed,
-					    viewport);
-      g_signal_handlers_disconnect_by_func (viewport->vadjustment,
-					    gtk_viewport_adjustment_value_changed,
-					    viewport);
-      g_object_unref (viewport->vadjustment);
-      viewport->vadjustment = NULL;
-    }
-
-  if (!adjustment)
-    adjustment = GTK_ADJUSTMENT (gtk_adjustment_new (0.0, 0.0, 0.0,
-						     0.0, 0.0, 0.0));
-
-  if (viewport->vadjustment != adjustment)
-    {
-      viewport->vadjustment = adjustment;
-      g_object_ref (viewport->vadjustment);
-      gtk_object_sink (GTK_OBJECT (viewport->vadjustment));
-      
-      g_signal_connect (adjustment, "changed",
-			G_CALLBACK (gtk_viewport_adjustment_changed),
-			viewport);
-      g_signal_connect (adjustment, "value_changed",
-			G_CALLBACK (gtk_viewport_adjustment_value_changed),
-			viewport);
-
-      gtk_viewport_adjustment_changed (adjustment, viewport);
-    }
+  viewport_set_adjustment (viewport, GTK_ORIENTATION_VERTICAL, adjustment);
 
-    g_object_notify (G_OBJECT (viewport), "vadjustment");
+  g_object_notify (G_OBJECT (viewport), "vadjustment");
 }
 
 static void
@@ -431,10 +514,8 @@ gtk_viewport_set_scroll_adjustments (GtkViewport      *viewport,
 				     GtkAdjustment    *hadjustment,
 				     GtkAdjustment    *vadjustment)
 {
-  if (viewport->hadjustment != hadjustment)
-    gtk_viewport_set_hadjustment (viewport, hadjustment);
-  if (viewport->vadjustment != vadjustment)
-    gtk_viewport_set_vadjustment (viewport, vadjustment);
+  gtk_viewport_set_hadjustment (viewport, hadjustment);
+  gtk_viewport_set_vadjustment (viewport, vadjustment);
 }
 
 /** 
@@ -484,17 +565,17 @@ gtk_viewport_get_shadow_type (GtkViewport *viewport)
 static void
 gtk_viewport_realize (GtkWidget *widget)
 {
-  GtkBin *bin;
-  GtkViewport *viewport;
+  GtkViewport *viewport = GTK_VIEWPORT (widget);
+  GtkBin *bin = GTK_BIN (widget);
+  GtkAdjustment *hadjustment = gtk_viewport_get_hadjustment (viewport);
+  GtkAdjustment *vadjustment = gtk_viewport_get_vadjustment (viewport);
+  gint border_width = GTK_CONTAINER (widget)->border_width;
+  
+  GtkAllocation view_allocation;
   GdkWindowAttr attributes;
   gint attributes_mask;
   gint event_mask;
-  gint border_width;
 
-  border_width = GTK_CONTAINER (widget)->border_width;
-
-  bin = GTK_BIN (widget);
-  viewport = GTK_VIEWPORT (widget);
   GTK_WIDGET_SET_FLAGS (widget, GTK_REALIZED);
 
   attributes.x = widget->allocation.x + border_width;
@@ -517,32 +598,21 @@ gtk_viewport_realize (GtkWidget *widget)
 				   &attributes, attributes_mask);
   gdk_window_set_user_data (widget->window, viewport);
 
-  if (viewport->shadow_type != GTK_SHADOW_NONE)
-    {
-      attributes.x = widget->style->xthickness;
-      attributes.y = widget->style->ythickness;
-    }
-  else
-    {
-      attributes.x = 0;
-      attributes.y = 0;
-    }
-
-  attributes.width = MAX (1, (gint)widget->allocation.width - attributes.x * 2 - border_width * 2);
-  attributes.height = MAX (1, (gint)widget->allocation.height - attributes.y * 2 - border_width * 2);
+  viewport_get_view_allocation (viewport, &view_allocation);
+  
+  attributes.x = view_allocation.x;
+  attributes.y = view_allocation.y;
+  attributes.width = view_allocation.width;
+  attributes.height = view_allocation.height;
   attributes.event_mask = 0;
 
   viewport->view_window = gdk_window_new (widget->window, &attributes, attributes_mask);
   gdk_window_set_user_data (viewport->view_window, viewport);
 
-  attributes.x = 0;
-  attributes.y = 0;
-
-  if (bin->child)
-    {
-      attributes.width = viewport->hadjustment->upper;
-      attributes.height = viewport->vadjustment->upper;
-    }
+  attributes.x = - hadjustment->value;
+  attributes.y = - vadjustment->value;
+  attributes.width = hadjustment->upper;
+  attributes.height = vadjustment->upper;
   
   attributes.event_mask = event_mask;
 
@@ -556,10 +626,12 @@ gtk_viewport_realize (GtkWidget *widget)
   gtk_style_set_background (widget->style, widget->window, GTK_STATE_NORMAL);
   gtk_style_set_background (widget->style, viewport->bin_window, GTK_STATE_NORMAL);
 
-   gtk_paint_flat_box(widget->style, viewport->bin_window, GTK_STATE_NORMAL,
-		      GTK_SHADOW_NONE,
-		      NULL, widget, "viewportbin",
-		      0, 0, -1, -1);
+  /* Call paint here to allow a theme to set the background without flashing
+   */
+  gtk_paint_flat_box(widget->style, viewport->bin_window, GTK_STATE_NORMAL,
+		     GTK_SHADOW_NONE,
+		     NULL, widget, "viewportbin",
+		     0, 0, -1, -1);
    
   gdk_window_show (viewport->bin_window);
   gdk_window_show (viewport->view_window);
@@ -625,8 +697,6 @@ gtk_viewport_expose (GtkWidget      *widget,
 	  
 	  (* GTK_WIDGET_CLASS (parent_class)->expose_event) (widget, event);
 	}
-	
-
     }
 
   return FALSE;
@@ -679,15 +749,11 @@ gtk_viewport_size_allocate (GtkWidget     *widget,
 {
   GtkViewport *viewport = GTK_VIEWPORT (widget);
   GtkBin *bin = GTK_BIN (widget);
-  GtkAllocation child_allocation;
-  gint hval, vval;
   gint border_width = GTK_CONTAINER (widget)->border_width;
+  gboolean hadjustment_value_changed, vadjustment_value_changed;
 
-  /* demand creation */
-  if (!viewport->hadjustment)
-    gtk_viewport_set_hadjustment (viewport, NULL);
-  if (!viewport->vadjustment)
-    gtk_viewport_set_vadjustment (viewport, NULL);
+  GtkAdjustment *hadjustment = gtk_viewport_get_hadjustment (viewport);
+  GtkAdjustment *vadjustment = gtk_viewport_get_vadjustment (viewport);
 
   /* If our size changed, and we have a shadow, queue a redraw on widget->window to
    * redraw the shadow correctly.
@@ -700,20 +766,15 @@ gtk_viewport_size_allocate (GtkWidget     *widget,
   
   widget->allocation = *allocation;
 
-  child_allocation.x = 0;
-  child_allocation.y = 0;
-
-  if (viewport->shadow_type != GTK_SHADOW_NONE)
-    {
-      child_allocation.x = widget->style->xthickness;
-      child_allocation.y = widget->style->ythickness;
-    }
-
-  child_allocation.width = MAX (1, allocation->width - child_allocation.x * 2 - border_width * 2);
-  child_allocation.height = MAX (1, allocation->height - child_allocation.y * 2 - border_width * 2);
+  viewport_set_hadjustment_values (viewport, &hadjustment_value_changed);
+  viewport_set_vadjustment_values (viewport, &vadjustment_value_changed);
 
   if (GTK_WIDGET_REALIZED (widget))
     {
+      GtkAllocation view_allocation;
+      
+      viewport_get_view_allocation (viewport, &view_allocation);
+  
       gdk_window_move_resize (widget->window,
 			      allocation->x + border_width,
 			      allocation->y + border_width,
@@ -721,87 +782,37 @@ gtk_viewport_size_allocate (GtkWidget     *widget,
 			      allocation->height - border_width * 2);
 
       gdk_window_move_resize (viewport->view_window,
-			      child_allocation.x,
-			      child_allocation.y,
-			      child_allocation.width,
-			      child_allocation.height);
+			      view_allocation.x,
+			      view_allocation.y,
+			      view_allocation.width,
+			      view_allocation.height);
     }
 
-  viewport->hadjustment->page_size = child_allocation.width;
-  viewport->hadjustment->step_increment = child_allocation.width * 0.1;
-  viewport->hadjustment->page_increment = child_allocation.width * 0.9;
-
-  viewport->vadjustment->page_size = child_allocation.height;
-  viewport->vadjustment->step_increment = child_allocation.height * 0.1;
-  viewport->vadjustment->page_increment = child_allocation.height * 0.9;
-
-  hval = viewport->hadjustment->value;
-  vval = viewport->vadjustment->value;
-
   if (bin->child && GTK_WIDGET_VISIBLE (bin->child))
     {
-      GtkRequisition child_requisition;
-      gtk_widget_get_child_requisition (bin->child, &child_requisition);
+      GtkAllocation child_allocation;
       
-      viewport->hadjustment->lower = 0;
-      viewport->hadjustment->upper = MAX (child_requisition.width,
-					  child_allocation.width);
-
-      hval = CLAMP (hval, 0,
-		    viewport->hadjustment->upper -
-		    viewport->hadjustment->page_size);
-
-      viewport->vadjustment->lower = 0;
-      viewport->vadjustment->upper = MAX (child_requisition.height,
-					  child_allocation.height);
-
-      vval = CLAMP (vval, 0,
-		    viewport->vadjustment->upper -
-		    viewport->vadjustment->page_size);
-    }
-
-  if (bin->child && GTK_WIDGET_VISIBLE (bin->child))
-    {
       child_allocation.x = 0;
       child_allocation.y = 0;
-
-      child_allocation.width = viewport->hadjustment->upper;
-      child_allocation.height = viewport->vadjustment->upper;
+      child_allocation.width = hadjustment->upper;
+      child_allocation.height = vadjustment->upper;
 
       if (GTK_WIDGET_REALIZED (widget))
-	gdk_window_resize (viewport->bin_window,
-			   child_allocation.width,
-			   child_allocation.height);
+	gdk_window_move_resize (viewport->bin_window,
+				- hadjustment->value,
+				- vadjustment->value,
+				child_allocation.width,
+				child_allocation.height);
 
-      child_allocation.x = 0;
-      child_allocation.y = 0;
       gtk_widget_size_allocate (bin->child, &child_allocation);
     }
 
-  gtk_adjustment_changed (viewport->hadjustment);
-  gtk_adjustment_changed (viewport->vadjustment);
-  if (viewport->hadjustment->value != hval)
-    {
-      viewport->hadjustment->value = hval;
-      gtk_adjustment_value_changed (viewport->hadjustment);
-    }
-  if (viewport->vadjustment->value != vval)
-    {
-      viewport->vadjustment->value = vval;
-      gtk_adjustment_value_changed (viewport->vadjustment);
-    }
-}
-
-static void
-gtk_viewport_adjustment_changed (GtkAdjustment *adjustment,
-				 gpointer       data)
-{
-  GtkViewport *viewport;
-
-  g_return_if_fail (GTK_IS_ADJUSTMENT (adjustment));
-  g_return_if_fail (GTK_IS_VIEWPORT (data));
-
-  viewport = GTK_VIEWPORT (data);
+  gtk_adjustment_changed (hadjustment);
+  gtk_adjustment_changed (vadjustment);
+  if (hadjustment_value_changed)
+    gtk_adjustment_value_changed (hadjustment);
+  if (vadjustment_value_changed)
+    gtk_adjustment_value_changed (vadjustment);
 }
 
 static void
@@ -810,7 +821,6 @@ gtk_viewport_adjustment_value_changed (GtkAdjustment *adjustment,
 {
   GtkViewport *viewport;
   GtkBin *bin;
-  GtkAllocation child_allocation;
 
   g_return_if_fail (GTK_IS_ADJUSTMENT (adjustment));
   g_return_if_fail (GTK_IS_VIEWPORT (data));
@@ -818,25 +828,21 @@ gtk_viewport_adjustment_value_changed (GtkAdjustment *adjustment,
   viewport = GTK_VIEWPORT (data);
   bin = GTK_BIN (data);
 
-  if (bin->child && GTK_WIDGET_VISIBLE (bin->child))
+  if (bin->child && GTK_WIDGET_VISIBLE (bin->child)  &&
+      GTK_WIDGET_REALIZED (viewport))
     {
-      child_allocation.x = 0;
-      child_allocation.y = 0;
+      GtkAdjustment *hadjustment = gtk_viewport_get_hadjustment (viewport);
+      GtkAdjustment *vadjustment = gtk_viewport_get_vadjustment (viewport);
+      gint old_x, old_y;
+      gint new_x, new_y;
 
-      if (viewport->hadjustment->lower != (viewport->hadjustment->upper -
-					   viewport->hadjustment->page_size))
-	child_allocation.x =  viewport->hadjustment->lower - viewport->hadjustment->value;
+      gdk_window_get_position (viewport->bin_window, &old_x, &old_y);
+      new_x = - hadjustment->value;
+      new_y = - vadjustment->value;
 
-      if (viewport->vadjustment->lower != (viewport->vadjustment->upper -
-					   viewport->vadjustment->page_size))
-	child_allocation.y = viewport->vadjustment->lower - viewport->vadjustment->value;
-
-      if (GTK_WIDGET_REALIZED (viewport))
+      if (new_x != old_x || new_y != old_y)
 	{
-	  gdk_window_move (viewport->bin_window,
-			   child_allocation.x,
-			   child_allocation.y);
-      
+	  gdk_window_move (viewport->bin_window, new_x, new_y);
 	  gdk_window_process_updates (viewport->bin_window, TRUE);
 	}
     }