在kivy中旋转后矩形变大

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.graphics import Rotate, Rectangle

class MyLayout(BoxLayout):
    def __init__(self, **kwargs):
        super(MyLayout, self).__init__(**kwargs)
        
        # 创建一个矩形对象
        with self.canvas.before:
            self.rect = Rectangle(pos=(100, 100), size=(200, 200))
        
        # 创建一个旋转按钮
        self.rotate_btn = Button(text='Rotate', on_press=self.rotate)
        self.add_widget(self.rotate_btn)

    def rotate(self, instance):
        # 通过旋转角度和中心点信息创建一个旋转对象
        rotation = Rotate(origin=self.rect.pos, angle=45)
        
        # 更新矩形对象的大小
        self.rect.size = (300, 300)
        
        # 应用旋转对象到矩形
        self.rect.canvas.before.add(rotation)

class MyApp(App):
    def build(self):
        return MyLayout()

if __name__ == '__main__':
    MyApp().run()