kivy-gamecamp-pong-tutorial/main.py

import random

from kivy import app, clock, properties, vector
from kivy.uix import widget


class PongGame(widget.Widget):
    # ADD note: why the None needed... the API allows for *args, **kwargs
    ball = properties.ObjectProperty(None)
    player_one = properties.ObjectProperty(None)
    player_two = properties.ObjectProperty(None)

    def serve_ball(self, vel=(4, 0)):
        self.ball.center = self.center
        self.ball.velocity = vel

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

        # bounce ball off bottom or top
        if (self.ball.y < self.y) or (self.ball.top > self.top):
            self.ball.velocity_y *= -1

        # went of to a side to score point?
        if self.ball.x < self.x:
            self.player_two.score += 1
            self.serve_ball(vel=(4, 0))
        if self.ball.x > self.width:
            self.player_one.score += 1
            self.serve_ball(vel=(-4, 0))

    def on_touch_move(self, touch):
        if touch.x < self.width / 3:
            self.player_one.center_y = touch.y

        if touch.x > self.width - self.width / 3:
            self.player_two.center_y = touch.y


class PongBall(widget.Widget):
    velocity_x = properties.NumericProperty(0)
    velocity_y = properties.NumericProperty(0)

    velocity = properties.ReferenceListProperty(velocity_x, velocity_y)

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


class PongPaddle(widget.Widget):
    score = properties.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.Vector(-1 * vx, vy)
            vel = bounced * 1.1
            ball.velocity = vel.x, vel.y + offset


class PongApp(app.App):

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


def run_pong_game():
    PongApp().run()


if __name__ == '__main__':
    run_pong_game()