viewport.py

from kivy.clock import Clock
from kivy.core.window import Window
from kivy.uix.scatter import ScatterPlane


class Viewport(ScatterPlane):
    def __init__(self, **kwargs):
        kwargs.setdefault('size', (1920, 1080))
        kwargs.setdefault('size_hint', (None, None))
        kwargs.setdefault('do_scale', False)
        kwargs.setdefault('do_translation', False)
        kwargs.setdefault('do_rotation', False)
        super(Viewport, self).__init__( **kwargs)
        Clock.schedule_once(self.fit_to_window, -1)

    def fit_to_window(self, *args):
        if self.width < self.height: #portrait
            if Window.width < Window.height: #so is window   
                self.scale = Window.width/float(self.width)
            else: #window is landscape..so rotate vieport
                self.scale = Window.height/float(self.width)
                self.rotation = -90
        else: #landscape
            if Window.width > Window.height: #so is window   
                self.scale = Window.width/float(self.width)
            else: #window is portrait..so rotate vieport
                self.scale = Window.height/float(self.width)
                self.rotation = -90

        self.center = Window.center
        for c in self.children:
            c.size = self.size

    def add_widget(self, w, *args, **kwargs):
        super(Viewport, self).add_widget(w, *args, **kwargs)
        w.size = self.size

    def on_touch_down(self, touch):
        return super(Viewport, self).on_touch_down(touch)

    def on_touch_move(self, touch):
        return super(Viewport, self).on_touch_move(touch)

    def on_touch_up(self, touch):
        return super(Viewport, self).on_touch_up(touch)