timeline: make log level calculation a lot faster

This is the step where the timeline graph gets colored with the individual log
level colors. It's roughly 4.5 times faster now. Probably can be made even
better, the code also needs a cleanup.

debug-viewer/GstDebugViewer/GUI/models.py

@@ -129,6 +129,13 @@ class LogModelBase (gtk.GenericTreeModel):
 
         return value
 
+    def get_value_range (self, col_id, start, stop):
+
+        if col_id != self.COL_LEVEL:
+            raise NotImplementedError ("XXX FIXME")
+
+        return self.line_levels[start:stop]
+
     def on_iter_next (self, line_index):
 
         last_index = len (self.line_offsets) - 1

debug-viewer/GstDebugViewer/Plugins/Timeline.py

@@ -171,13 +171,26 @@ class LevelDistributionSentinel (object):
         if not partitions:
             return
 
+        level_index = 0
+        level_iter = None
+
         finished = False
         while tree_iter:
             y -= 1
             if y == 0:
                 y = YIELD_LIMIT
                 yield True
-            level = model_get (tree_iter, id_level)
+            if level_iter is None:
+                stop_index = level_index + 512
+                levels = self.model.get_value_range (id_level,
+                                                     level_index, stop_index)
+                level_index = stop_index
+                level_iter = iter (levels)
+            try:
+                level = level_iter.next ()
+            except StopIteration:
+                level_iter = None
+                continue
             while i > partitions[partitions_i]:
                 data.append (tuple (counts))
                 counts = [0] * MAX_LEVELS
@@ -189,7 +202,6 @@ class LevelDistributionSentinel (object):
                 break
             counts[level] += 1
             i += 1
-            tree_iter = model_next (tree_iter)
 
         # Now handle the last one:
         data.append (tuple (counts))