WPF 从 DrawingVisual 转 BitmapImage 图片

                DrawingVisual drawingVisual = new DrawingVisual();
                DrawingContext drawingContext = drawingVisual.RenderOpen();

                // 画出界面
                
                drawingContext.Close();

                DrawingVisual drawingVisual = new DrawingVisual();
                DrawingContext drawingContext = drawingVisual.RenderOpen();

                drawingContext.DrawText(new FormattedText("欢迎访问我博客 http://lindexi.gitee.io 里面有大量 UWP WPF 博客",
                    CultureInfo.GetCultureInfo("zh-cn"),
                    FlowDirection.LeftToRight,
                    new Typeface("Verdana"),
                    36, System.Windows.Media.Brushes.Black),
                    new System.Windows.Point(200, 116));
                
                drawingContext.Close();

                  RenderTargetBitmap bmp = new RenderTargetBitmap(宽度, 高度, 96, 96, PixelFormats.Pbgra32);
                bmp.Render(drawingVisual);

                var bitmapImage = new BitmapImage();
                var bitmapEncoder = new PngBitmapEncoder();
                bitmapEncoder.Frames.Add(BitmapFrame.Create(bmp));

                using (var stream = new MemoryStream())
                {
                    bitmapEncoder.Save(stream);
                    stream.Seek(0, SeekOrigin.Begin);

                    bitmapImage.BeginInit();
                    bitmapImage.CacheOption = BitmapCacheOption.OnLoad;
                    bitmapImage.StreamSource = stream;
                    bitmapImage.EndInit();
                }