[gdm] Compute needs-scrollbar logic differently

[Ray Strode <halfline src gnome org>]

commit f685f9fe038d891026fce69a47a7ab7c3e438d37
Author: Ray Strode <rstrode redhat com>
Date:   Fri Oct 30 16:44:29 2009 -0400

    Compute needs-scrollbar logic differently
    
    This way is a little clearer to read and seems to work
    around a bug where the scrollbar gets shown briefly at
    the end of an animation.

 gui/simple-greeter/gdm-scrollable-widget.c |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)
---
diff --git a/gui/simple-greeter/gdm-scrollable-widget.c b/gui/simple-greeter/gdm-scrollable-widget.c
index 6d9dc83..d55013d 100644
--- a/gui/simple-greeter/gdm-scrollable-widget.c
+++ b/gui/simple-greeter/gdm-scrollable-widget.c
@@ -252,7 +252,7 @@ gdm_scrollable_widget_animation_stop (GdmScrollableWidgetAnimation *animation)
 static gboolean
 gdm_scrollable_widget_needs_scrollbar (GdmScrollableWidget *widget)
 {
-        GtkAdjustment *adjustment;
+        gboolean needs_scrollbar;
 
         if (widget->priv->scrollbar == NULL) {
                 return FALSE;
@@ -266,9 +266,19 @@ gdm_scrollable_widget_needs_scrollbar (GdmScrollableWidget *widget)
                 return FALSE;
         }
 
-        adjustment = gtk_range_get_adjustment (GTK_RANGE (widget->priv->scrollbar));
+        if (GTK_BIN (widget)->child != NULL) {
+                GtkRequisition child_requisition;
+                int available_height;
+
+                gtk_widget_get_child_requisition (GTK_BIN (widget)->child,
+                                                  &child_requisition);
+                available_height = GTK_WIDGET (widget)->allocation.height;
+                needs_scrollbar = child_requisition.height > available_height;
+        } else {
+                needs_scrollbar = FALSE;
+        }
 
-        return adjustment->upper - adjustment->lower > adjustment->page_size;
+        return needs_scrollbar;
 }
 
 static void