如何在开罗/ Gtk中绘制带圆角的图像？

import cairo
import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk

def draw_rounded_image(widget, cr):
    # 设置绘制区域大小
    width, height = widget.get_allocated_width(), widget.get_allocated_height()
    cr.set_source_rgb(1, 1, 1)  # 设置绘制颜色为白色
    cr.rectangle(0, 0, width, height)  # 绘制一个矩形
    cr.fill()  # 填充矩形

    # 绘制圆角矩形
    radius = 20  # 圆角半径
    cr.set_source_rgb(0, 0, 0)  # 设置绘制颜色为黑色
    cr.move_to(radius, 0)  # 移动到起始点
    cr.arc(radius, radius, radius, 1.5 * math.pi, math.pi)  # 绘制左上角圆弧
    cr.arc(width - radius, radius, radius, 0, 0.5 * math.pi)  # 绘制右上角圆弧
    cr.arc(width - radius, height - radius, radius, 0.5 * math.pi, 0)  # 绘制右下角圆弧
    cr.arc(radius, height - radius, radius, math.pi, 1.5 * math.pi)  # 绘制左下角圆弧
    cr.close_path()  # 闭合路径
    cr.fill()  # 填充路径

def main():
    # 创建窗口
    window = Gtk.Window()
    window.connect("destroy", Gtk.main_quit)
    window.set_default_size(400, 300)

    # 创建绘图区域
    drawing_area = Gtk.DrawingArea()
    drawing_area.connect("draw", draw_rounded_image)
    window.add(drawing_area)

    window.show_all()
    Gtk.main()

if __name__ == "__main__":
    main()