Kivy image transition

main.py

from kivy.app import App
from kivy.lang import Builder

KV = """
FloatLayout
    MyWidget
        source1:'1.jpg'
        source2:'cosmos.webp'

<MyWidget>
    left:False

    source1:None
    source2:None
    split_x: 0

    on_touch_down: self.test()

    canvas.before:
        Rectangle:
            size: self.size
            pos: self.pos
            source:root.source2

        StencilPush
        PushMatrix


        Rectangle:
            size: root.split_x, self.height
            pos: self.pos


        PopMatrix
        StencilUse

    canvas:

        Rectangle:
            pos: self.pos
            size: self.size
            source: root.source1


    canvas.after:
        StencilUnUse
        StencilPop


"""
from kivy.animation import Animation as A
from kivy.uix.widget import Widget

def custom_anim(x):
    return x**((1 - x)*2)

class MyWidget(Widget):
    def test(self, *_):
        new_split_x= 0 if self.left else self.width
        a = A(split_x = new_split_x, t=custom_anim, d= 0.5)
        #a = A(split_x = new_split_x, t='in_out_sine', d= 0.5)
        self.left = not self.left
        a.start(self)

class MyApp(App):
    def build(self):
        return Builder.load_string(KV)


MyApp().run()

to make it work, pls specify your images (source1, source2) names.

demo https://imgur.com/a/lZI3CsR