'MouseWheel event processor'

def scroll_event_windows(self, event):

    w = event.widget.winfo_containing(event.x_root, event.y_root)
    if (w == self._tkcanvas):
        x = (event.x_root - w.winfo_rootx())
        y = (event.y_root - w.winfo_rooty())
        y = (self.figure.bbox.height - y)
        step = (event.delta / 120.0)
        FigureCanvasBase.scroll_event(self, x, y, step, guiEvent=event)
