kv 39 moving ball

#widget3.py

from kivy.app import App

from kivy.graphics import Ellipse

from kivy.metrics import dp

from kivy.properties import Clock

from kivy.uix.widget import Widget

class Widget3(Widget):

    def __init__(self, **kwargs):

        super().__init__(**kwargs)

        self.ball_size = dp(50)

        self.vx = 3

        self.vy = 3

        with self.canvas:

            self.ball = Ellipse(pos=self.center, size=(self.ball_size, self.ball_size))

        Clock.schedule_interval(self.update, 0.01)

    def on_size(self, *args):

        self.ball.pos = (self.center_x-self.ball_size/2, self.center_y-self.ball_size/2)

    def update(self, dt):

        x, y = self.ball.pos

        x += self.vx

        y += self.vy

        if y + self.ball_size > self.height:

            y = self.height  - self.ball_size

            self.vy = -self.vy

        if x + self.ball_size > self.width:

            x = self.width - self.ball_size

            self.vx = -self.vx

        if y < 0:

            y = 0

            self.vy = -self.vy

        if x < 0:

            x = 0

            self.vx = -self.vx

        self.ball.pos = (x,y)

class Widget3App(App):

    def build(self):

        return Widget3()

Widget3App().run()

reference:

https://www.youtube.com/watch?v=l8Imtec4ReQ&t=529s