Rotate vertical rectangle to horizontal rectangle using Python Kivy - how?

A good way is to use kv, like this:

<PongGame>:
    rotate: False  # property to control rotation
    canvas:
        Rectangle:
            pos:  (0, self.center_y - 5) if self.rotate else (self.center_x - 5, 0)
            size: (self.width, 10) if self.rotate else (10, self.height)

This code defines the property ( rotate) that controls the rotation PongGame. If it rotateis False, Rectangledraw your original , but if it rotateis True, Rectangledraw the rotation . Similar results can be achieved with python code, but you have to write more code (bindings) to handle user changes PongGame. Do all this kvand let kivy handle those bindings.

Once you have this code, you can rotate it PongGameusing :

def rotate(self, dt):
    self.root.rotate = not self.root.rotate

in your PongApp.