def _mouseVector(self):
        """
            returns a vector reflecting a ray cast from the camera
        position to the mouse position on the near plane
        """
        x, y = mouse.get_pos()
        # if (x, y) not in self.rect:
        # return (0, 0, 0);  # xxx

        y = self.root.height - y
        point1 = unproject(x, y, 0.0)
        point2 = unproject(x, y, 1.0)
        v = numpy.array(point2) - point1
        v = mceutils.normalize(v)
        return v

            returns a vector reflecting a ray cast from the camera
        position to the mouse position on the near plane
        
viewports/camera.py