vispy/vispy

def _process_mouse_event(self, event, override_picked=False):
        prof = Profiler()  # noqa
        next_picked = None # sync hack
        deliver_types = ['mouse_press', 'mouse_wheel']
        if self._send_hover_events:
            deliver_types += ['mouse_move']

        picked = self._mouse_handler if not override_picked else override_picked
        if picked is None:
            if event.type in deliver_types:
                picked = self.visual_at(event.pos)

        # NOTE: hack to sync other ViewBox, should check a sync dict or parameter of VisualNodes instead
        if type(picked) == ViewBox and not override_picked:
            next_picked = VisualNode._visual_ids[33]

        # No visual to handle this event; bail out now
        if picked is None:
            return

        # Create an event to pass to the picked visual
        scene_event = SceneMouseEvent(event=event, visual=picked)

        # Deliver the event
        if override_picked: # we know ViewBox handles event directly so don't need to search parents and don't want to change _mouse_handler
            getattr(picked.events, event.type)(scene_event)
        elif picked == self._mouse_handler:
            # If we already have a mouse handler, then no other node may
            # receive the event
            if event.type == 'mouse_release':
                self._mouse_handler = None
            getattr(picked.events, event.type)(scene_event)
        else:
            # If we don't have a mouse handler, then pass the event through
            # the chain of parents until a node accepts the event.
            while picked is not None:
                getattr(picked.events, event.type)(scene_event)
                if scene_event.handled:
                    if event.type == 'mouse_press':
                        self._mouse_handler = picked
                    break
                if event.type in deliver_types:
                    # events that are not handled get passed to parent
                    picked = picked.parent
                    scene_event.visual = picked
                else:
                    picked = None

        # If something in the scene handled the scene_event, then we mark
        # the original event accordingly.
        event.handled = scene_event.handled

        if next_picked: # propagate to synced node
            self._process_mouse_event(event, override_picked=next_picked)