def __init__(self):
"""
FlowGraph constructor.
Create a list for signal blocks and connections. Connect mouse handlers.
"""
Element.__init__(self)
#when is the flow graph selected? (used by keyboard event handler)
self.is_selected = lambda: bool(self.get_selected_elements())
#important vars dealing with mouse event tracking
self.element_moved = False
self.mouse_pressed = False
self.unselect()
self.press_coor = (0, 0)
#selected ports
self._old_selected_port = None
self._new_selected_port = None
# current mouse hover element
self.element_under_mouse = None
#context menu
self._context_menu = Bars.ContextMenu()
self.get_context_menu = lambda: self._context_menu
