[pitivi] ui/timeline: fix scrollToPlayhead() so it doesn't scroll too far. Fixes #573886.

[Edward Hervey <edwardrv src gnome org>]

commit a4abbcbebb8c2e0cf496efe7e54646709ecb5e30
Author: Volker Sobek <reklov live com>
Date:   Thu Jul 29 19:08:40 2010 +0200

    ui/timeline: fix scrollToPlayhead() so it doesn't scroll too far. Fixes #573886.

 pitivi/ui/timeline.py |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)
---
diff --git a/pitivi/ui/timeline.py b/pitivi/ui/timeline.py
index 5c15954..97d3983 100644
--- a/pitivi/ui/timeline.py
+++ b/pitivi/ui/timeline.py
@@ -464,11 +464,16 @@ class Timeline(gtk.Table, Loggable, Zoomable):
         self._state = state
 
     def scrollToPlayhead(self):
-        width = self.get_allocation().width
+        """
+        Scroll the current position as close to the center of the view
+        as possible (as close as the timeline canvas allows).
+        """
+        page_size = self.hadj.get_page_size()
+
         new_pos = Zoomable.nsToPixel(self._position)
         scroll_pos = self.hadj.get_value()
-        if (new_pos < scroll_pos) or (new_pos > scroll_pos + width):
-            self.scrollToPosition(new_pos - width / 2)
+        if (new_pos > scroll_pos + page_size) or (new_pos < scroll_pos):
+            self.scrollToPosition(min(new_pos - page_size / 2, self.hadj.upper - page_size - 1))
         return False
 
     def scrollToPosition(self, position):