main.py

#! /usr/bin/env python


import random

from kivy.app import App
from kivy.clock import Clock
from kivy.properties import (
    NumericProperty,
    ObjectProperty,
    ReferenceListProperty,
)
from kivy.uix.widget import Widget
from kivy.vector import Vector


class PongBall(Widget):

    velocity_x = NumericProperty(0)
    velocity_y = NumericProperty(0)
    velocity = ReferenceListProperty(velocity_x, velocity_y)

    def move(self):
        self.pos = Vector(*self.velocity) + self.pos


class PongPaddle(Widget):

    score = NumericProperty(0)

    def bounce_ball(self, ball):
        if self.collide_widget(ball):
            vx, vy = ball.velocity
            offset = (ball.center_y - self.center_y) / (self.height / 2)
            bounced = Vector(-vx, vy)
            vel = bounced * 1.1
            ball.velocity = vel.x, vel.y + offset


class PongGame(Widget):

    ball = ObjectProperty(None)
    player1 = ObjectProperty(None)
    player2 = ObjectProperty(None)

    def serve_ball(self, reverse=False):
        self.ball.center = self.center
        vel = Vector(4 * (-1 if reverse else 1), 0)
        self.ball.velocity = vel

    def update(self, dt):
        self.ball.move()

        self.player1.bounce_ball(self.ball)
        self.player2.bounce_ball(self.ball)

        if self.ball.y < 0 or self.ball.top > self.height:
            self.ball.velocity_y *= -1

        if self.ball.x < self.x:
            self.player2.score += 1
            self.serve_ball()
        if self.ball.x > self.width:
            self.player1.score += 1
            self.serve_ball(reverse=True)

    def on_touch_move(self, touch):
        left = self.width / 3
        right = self.width - left
        if touch.x < left:
            self.player1.center_y = touch.y
        if touch.x > right:
            self.player2.center_y = touch.y


class PongApp(App):

    def build(self):
        game = PongGame()
        game.serve_ball()
        Clock.schedule_interval(game.update, 1.0 / 60.0)
        return game


if __name__ == "__main__":
    PongApp().run()