如何使用C#在画布上用WPF绘制透明的PNG

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Transparent PNG" Height="450" Width="800">
    <Canvas x:Name="canvas"/>
</Window>

using System.Windows;
using System.Windows.Media;
using System.Windows.Media.Imaging;

namespace WpfApp1
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            // 创建一个透明的PNG图像
            RenderTargetBitmap bmp = new RenderTargetBitmap(200, 200, 96, 96, PixelFormats.Pbgra32);
            DrawingVisual drawingVisual = new DrawingVisual();
            using (DrawingContext drawingContext = drawingVisual.RenderOpen())
            {
                // 在画布上绘制图形
                drawingContext.DrawRectangle(Brushes.Red, null, new Rect(50, 50, 100, 100));
            }
            bmp.Render(drawingVisual);

            // 将PNG图像显示在画布上
            Image image = new Image();
            image.Source = bmp;
            canvas.Children.Add(image);
        }
    }
}