def dropEvent(self, event):
     data = event.mimeData()
     if (hasattr(data, 'versionId') and hasattr(data, 'controller') and
         data.controller==self.scene().controller):
         event.accept()
         visDiff = QVisualDiff(self.scene().controller.vistrail,
                               data.versionId,
                               self.id,
                               self.scene().controller,
                               self.scene().views()[0])
         visDiff.show()
     else:
         event.ignore()  
    def showDiff(self):
        """showDiff() -> None
        Show the visual difference interface

        """
        currentView = self.viewManager.currentWidget()
        if (currentView and currentView.execDiffId1 > 0 and
            currentView.execDiffId2 > 0):
            visDiff = QVisualDiff(currentView.controller.vistrail,
                                  currentView.execDiffId1,
                                  currentView.execDiffId2,
                                  currentView.controller,
                                  self)
            visDiff.show()