kivy pongball class
class PongBall(Widget):
# velocity of the ball on x and y axis
velocity_x = NumericProperty(0)
velocity_y = NumericProperty(0)
# referencelist property so we can use ball.velocity as
# a shorthand, just like e.g. w.pos for w.x and w.y
velocity = ReferenceListProperty(velocity_x, velocity_y)
# ``move`` function will move the ball one step. This
# will be called in equal intervals to animate the ball
def move(self):
self.pos = Vector(*self.velocity) + self.pos