--- a/python/apps/diagramitems.py	Sat Dec 15 23:56:26 2012 +0100
+++ b/python/apps/diagramitems.py	Mon Dec 24 12:52:13 2012 +0100
@@ -176,7 +176,7 @@
 
 class ResizeSelectionHandle(Handle):
    def __init__(self, position, block):
-      super(ResizeSelectionHandle, self).__init__(dx=6, parent=block)
+      super(ResizeSelectionHandle, self).__init__(dx=12, parent=block)
       self.position = position
       self.block = block
       if position in [Position.TOP_LEFT, Position.BOTTOM_RIGHT]:
@@ -221,13 +221,6 @@
    def editParameters(self):
       pd = ParameterDialog(self, self.window())
       pd.exec_()
-   def mouseDoubleClickEvent(self, event):
-      #self.editParameters()
-      scene = self.scene()
-      if scene:
-         for view in scene.views():
-            view.diagram = self.subModel
-            view.zoomAll()
    def newInputPort(self):
       names = [i.name for i in self.inputs + self.outputs]
       self.addInput(InputPort(uniqify('in', names), self))
@@ -360,15 +353,33 @@
       self.subModel.containingBlock = self
    def setDict(self, d):
       self.subModel.Dict = d['submodel']
+   def mouseDoubleClickEvent(self, event):
+      # descent into child diagram
+      #self.editParameters()
+      print('descent')
+      scene = self.scene()
+      if scene:
+         for view in scene.views():
+            view.diagram = self.subModel
+            view.zoomAll()
 
 class DiagramScene(QGraphicsScene):
    """ A diagram scene consisting of blocks and connections """
+   structureChanged = pyqtSignal()
    def __init__(self):
       super(DiagramScene, self).__init__()
       self.startedConnection = None
 
    blocks = property(lambda sel: [i for i in sel.items() if isinstance(i, Block)])
    connections = property(lambda sel: [i for i in sel.items() if type(i) is Connection])
+   def addItem(self, item):
+      super(DiagramScene, self).addItem(item)
+      if isinstance(item, Block):
+         self.structureChanged.emit()
+   def removeItem(self, item):
+      super(DiagramScene, self).removeItem(item)
+      if isinstance(item, Block):
+         self.structureChanged.emit()
    def setDict(self, d):
       for block in d['blocks']:
          b = Block()