WPF save canvas as pictures via rendetargetbitmap DrawingVisual DrawingContext VisualBrush

//xaml
<Window x:Class="WpfApp27.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp27"
        WindowState="Maximized"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Canvas x:Name="cvs" Background="White">
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition/> 
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition/>
                    <ColumnDefinition/>
                    <ColumnDefinition/>
                </Grid.ColumnDefinitions>
                <Ellipse x:Name="elp"
                         Grid.Row="0"
                         Grid.Column="0"
                         Stroke="Red"
                         StrokeThickness="20"
                         Width="500"
                         Height="500"
                         Fill="Cyan"/>
                
                <Rectangle x:Name="rect"
                            Grid.Row="0"
                            Grid.Column="1"
                            Width="500"
                            Height="500"
                            Stroke="Red"
                            StrokeThickness="30"
                            HorizontalAlignment="Stretch"/>


                <Rectangle x:Name="rect2"
                           Grid.Row="0"
                           Grid.Column="2"
                           Width="500"
                           Height="500"
                           Stroke="Blue"
                           StrokeThickness="30"
                           HorizontalAlignment="Stretch"/>
            </Grid>
            <Canvas.ContextMenu>
                <ContextMenu>
                    <MenuItem Header="Save As Picture"
                              Command="{Binding SaveAsPictureCommand}"
                              CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor,
                        AncestorType={x:Type ContextMenu}},Path=PlacementTarget}"/>
                    <MenuItem Header="Save Canvas As Image"
                              Command="{Binding SaveCanvasAsImageCommand}"
                              CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor,
                        AncestorType={x:Type ContextMenu}},Path=PlacementTarget}"/>
                </ContextMenu>
            </Canvas.ContextMenu>
        </Canvas>
    </Grid>
</Window>



//cs
using Microsoft.Win32;
using System.ComponentModel;
using System.Diagnostics;
using System.IO;
using System.Runtime.CompilerServices;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp27
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            var vm = new MainVM(this, cvs);
            this.DataContext=vm;
        }
    }

    public class MainVM : INotifyPropertyChanged
    {
        private Window win;
        private Canvas cvs;
        private int dpiFactor = 2;
        public MainVM(Window winValue, Canvas cvsValue)
        {
            this.win=winValue;
            this.cvs=cvsValue;
        }

        public event PropertyChangedEventHandler? PropertyChanged;
        public void OnPropertyChanged([CallerMemberName] string propName = "")
        {
            var handler = PropertyChanged;
            if (handler!=null)
            {
                handler?.Invoke(this, new PropertyChangedEventArgs(propName));
            }
        }

        private DelCommand saveAsPictureCommand;
        public DelCommand SaveAsPictureCommand
        {
            get
            {
                if (saveAsPictureCommand==null)
                {
                    saveAsPictureCommand=new DelCommand(SaveAsPictureCommandExecuted);
                }
                return saveAsPictureCommand;
            }
        }

        private void SaveAsPictureCommandExecuted(object? obj)
        {
            SaveFileDialog dialog = new SaveFileDialog();
            dialog.Filter="Jpg Files|*.jpg|All Files|*.*";
            dialog.FileName=$"Canvas_{DateTime.Now.ToString("yyyyMMddHHmmssffff")}";
            if (dialog.ShowDialog()==true && cvs!=null)
            {
                SaveCanvasAsPicture(cvs, dialog.FileName);
                MessageBox.Show($"Saved in {dialog.FileName}", "Save Canvas As Picture");
                OpenPicture(dialog.FileName);
            }
        }

        private void SaveCanvasAsPicture(Canvas cvs, string fileName)
        {
            Size size = new Size(cvs.ActualWidth, cvs.ActualHeight);
            cvs.Measure(size);
            cvs.Arrange(new Rect(size));

            RenderTargetBitmap renderBmp = new RenderTargetBitmap((int)size.Width*dpiFactor,
                (int)size.Height*dpiFactor, 96*dpiFactor, 96*dpiFactor, PixelFormats.Pbgra32);
            renderBmp.Render(cvs);
            using (FileStream fs = new FileStream(fileName, FileMode.Create))
            {
                JpegBitmapEncoder encoder = new JpegBitmapEncoder();
                encoder.Frames.Add(BitmapFrame.Create(renderBmp));
                encoder.Save(fs);
            }
        }

        private void OpenPicture(string fileName)
        {
            try
            {
                Process.Start(new ProcessStartInfo
                {
                    FileName = fileName,
                    UseShellExecute=true
                });
            }
            catch (Exception ex)
            {
                MessageBox.Show($"Error opening image:{ex.Message}");
            }
        }

        private DelCommand saveCanvasAsImageCommand;
        public DelCommand SaveCanvasAsImageCommand
        {
            get
            {
                if (saveCanvasAsImageCommand==null)
                {
                    saveCanvasAsImageCommand=new DelCommand(SaveCanvasAsImageCommandExecuted);
                }
                return saveCanvasAsImageCommand;
            }
        }

        private void SaveCanvasAsImageCommandExecuted(object? obj)
        {
            SaveFileDialog dialog = new SaveFileDialog()
            {
                Filter="PNG Image|*.png|JPEG Image|*.jpg|Bitmap Image|*.bmp",
                Title="Save Canvas As Image",
                FileName = $"Image_{DateTime.Now.ToString("yyyyMMddHHmmssffff")}"
            };
            if (dialog.ShowDialog()==true)
            {
                SaveCanvasToImage(cvs, dialog.FileName);
                MessageBox.Show($"Save canvas in {dialog.FileName}");
                OpenPicture(dialog.FileName);
            }
        }

        private void SaveCanvasToImage(Canvas cvs, string fileName)
        {
            string ext = System.IO.Path.GetExtension(fileName).ToLower();
            Rect bounds = VisualTreeHelper.GetDescendantBounds(cvs);
            RenderTargetBitmap rtb = new RenderTargetBitmap(
                (int)bounds.Width*dpiFactor, (int)bounds.Height*dpiFactor,
                96*dpiFactor, 96*dpiFactor, PixelFormats.Pbgra32);

            DrawingVisual dv = new DrawingVisual();
            using (DrawingContext dc = dv.RenderOpen())
            {
                VisualBrush vb = new VisualBrush(cvs);
                dc.DrawRectangle(vb, null, new Rect(new Point(), bounds.Size));
            }
            rtb.Render(dv);
            BitmapEncoder encoder = null;
            switch (ext)
            {
                case ".jpg":
                    encoder = new JpegBitmapEncoder();
                    break;
                case ".bmp":
                    encoder=new BmpBitmapEncoder();
                    break;
                case ".png":
                    encoder=new PngBitmapEncoder();
                    break;
            }

            encoder.Frames.Add(BitmapFrame.Create(rtb));
            using (FileStream fs = File.Open(fileName, FileMode.Create))
            {
                encoder.Save(fs);
            }
        }
    }

    public class DelCommand : ICommand
    {
        private Action<object?> execute;
        private Predicate<object?> canExecute;
        public DelCommand(Action<object?> executeValue, Predicate<object?> canExecuteValue = null)
        {
            execute=executeValue;
            canExecute=canExecuteValue;
        }

        public event EventHandler? CanExecuteChanged
        {
            add
            {
                CommandManager.RequerySuggested += value;
            }
            remove
            {
                CommandManager.RequerySuggested -= value;
            }
        }

        public bool CanExecute(object? parameter)
        {
            return canExecute==null ? true : canExecute(parameter);
        }

        public void Execute(object? parameter)
        {
            execute(parameter);
        }
    }
}