用画布撤消和重做按钮

Question

昨天我完成了一个简单的油漆应用程序的Kivy项目，然后将其交给我的一个朋友，他告诉我，如果您添加两个撤消和重做按钮，那么您的应用程序看起来会很好，并且会更有用。但是当我尝试这样做时，我无法做很多事情，我搜索很多，但我无法得到任何令人满意的答案

带有撤消按钮的主python文件，但没有功能

from random import random
from kivy.app import App
from kivy.clock import Clock
from kivy.core.window import Window
from kivy.graphics import Color, Ellipse, Line
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.uix.spinner import Spinner
from kivy.uix.widget import Widget


class MyPaintWidget(Widget):
    def on_touch_down(self, touch):
        self.d = MyPaintApp.sizeSpinner.text
        if MyPaintApp.colorSpinner.text == "Random Changing":
            color = (random(), random(), random())
        if MyPaintApp.colorSpinner.text == "Black":
            color = (0, 0, 0)
        if MyPaintApp.colorSpinner.text == "Red":
            color = (1, 0, 0)
        if MyPaintApp.colorSpinner.text == "Green":
            color = (0, 1, 0)
        if MyPaintApp.colorSpinner.text == "Blue":
            color = (0, 0, 1)
        if MyPaintApp.colorSpinner.text == "Pink":
            color = (1, 0, 1)
        if MyPaintApp.colorSpinner.text == "Sky Blue":
            color = (50/255.0, 150/255.0, 209/255.0)
        if MyPaintApp.colorSpinner.text == "Gray":
            color = (75/255.0, 82/255.0, 92/255.0)
        if MyPaintApp.colorSpinner.text == "White":
            color = (1, 1, 1)

        with self.canvas:
            Color(*color)
            Ellipse(pos=(touch.x - int(self.d) / 2, touch.y -int(self.d) / 2), size=(int(self.d), int(self.d)))
            if int(self.d)<=25:
                self.line = Line(points=(touch.x, touch.y), width=int(self.d)/3)
            else:
                self.line = Line(points=(touch.x, touch.y), width=int(self.d)/2.5)

    def on_touch_move(self, touch):
        self.line.points += [touch.x, touch.y]



class MyPaintApp(App):
    colorSpinner = Spinner(
        text="Black",
        values=["Random Changing", "Red", "Green", "Blue", "Black", "White", "Pink", "Gray", "Sky Blue"],
        font_size=20,
        background_normal="",
        background_color=(0, 0, 1, .75),
        bold=True,
        italic=True
    )
    sizeSpinner = Spinner(
        text="10",
        values=["5", "10", "15", "20", "25", "30", "35", "40", "45", "50"],
        font_size=20,
        background_normal="",
        background_color=(0, 1, 0, .75),
        bold=True,
        italic=True,
    )
    bgColor = Spinner(
        text="White",
        values=["White", "Red", "Green", "Blue", "Black", "Pink", "Gray", "Sky Blue"],
        font_size=20,
        background_normal="",
        background_color=(0, 0, 1, .75),
        bold=True,
        italic=True
    ) 

    undoBtn = Button(
        text="Undo",
        background_normal="",
        background_color=(1, 0, 1, .75),
        bold=True,
        italic=True,
        font_size=20
    )

    def __init__(self, **kw):
        super(MyPaintApp, self).__init__(**kw)
        Clock.schedule_interval(self.update, 1/60)


    def build(self):
        parent = BoxLayout(
            orientation="vertical"
        )
        self.painter = MyPaintWidget()
        bottom_bar=BoxLayout(size_hint=(1, .1))
        clearbtn = Button(
            text='Clear',
            bold=True,
            italic=True,
            font_size=24,
            background_normal="",
            background_color=(1, 0, 0, .75),
        )
        clearbtn.bind(
            on_release=self.clear_canvas
        )

        bottom_bar.add_widget(clearbtn)
        bottom_bar.add_widget(self.colorSpinner)
        bottom_bar.add_widget(self.sizeSpinner)
        bottom_bar.add_widget(self.bgColor)
        bottom_bar.add_widget(self.undoBtn)



        parent.add_widget(self.painter)
        parent.add_widget(bottom_bar)
        return parent

   def clear_canvas(self, obj):
       self.painter.canvas.clear()

   def update(self, dt):
        if self.bgColor.text == "Random Changing":
            Window.clearcolor = (random(), random(), random(), 1)
        if self.bgColor.text == "Black":
            Window.clearcolor = (0, 0, 0, 1)
        if self.bgColor.text == "Red":
            Window.clearcolor = (1, 0, 0, 1)
        if self.bgColor.text == "Green":
           Window.clearcolor = (0, 1, 0, 1)
        if self.bgColor.text == "Blue":
            Window.clearcolor = (0, 0, 1, 1)
        if self.bgColor.text == "Pink":
           Window.clearcolor = (1, 0, 1, 1)
        if self.bgColor.text == "Sky Blue":
            Window.clearcolor = (50/255.0, 150/255.0, 209/255.0, 1)
        if self.bgColor.text == "Gray":
            Window.clearcolor = (75/255.0, 82/255.0, 92/255.0, 1)
        if self.bgColor.text == "White":
            Window.clearcolor = (1, 1, 1, 1)


if __name__ == "__main__":
    app = MyPaintApp(title="PaintVerse: A Simple And Easy To Use Paint App")
    app.run()