WPF TranslateTransform performance with many objects

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C#

WPF

performance

I've written some sample code to show a problem I'm experiencing. I need to move many (>>1000) objects around (all together) using the mouse, but it's really laggy and I'm trying to work out why.

This should run in a new WPF project, just need to name the grid "mainGrid" in the XAML:

public partial class MainWindow : Window
{
    readonly TranslateTransform _translator = new TranslateTransform();
    readonly Canvas _canvas = new Canvas();

    public MainWindow()
    {
        InitializeComponent();

        Loaded += new RoutedEventHandler(MainWindow_Loaded);
        WindowState = System.Windows.WindowState.Maximized;
            
        _canvas.RenderTransform = _translator;
        mainGrid.Children.Add(_canvas);
    }

    void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
        Ellipse ellipse;

        for (int x = 0; x < 40; x++)
        {
            for (int y = 0; y < 100; y++)
            {
                ellipse = new Ellipse();
                ellipse.Stroke = Brushes.Black;
                ellipse.StrokeThickness = 1;
                ellipse.Fill = Brushes.Green;
                ellipse.Width = ellipse.Height = 10;

                Canvas.SetLeft(ellipse, y * 15);
                Canvas.SetTop(ellipse, x * 15);
                _canvas.Children.Add(ellipse);
            }
        }
    }

    Point _dragPoint;

    protected override void OnMouseDown(System.Windows.Input.MouseButtonEventArgs e)
    {
        _dragPoint = e.GetPosition(this);
        CaptureMouse();

        base.OnMouseDown(e);
    }

    protected override void OnMouseMove(System.Windows.Input.MouseEventArgs e)
    {
        if (IsMouseCaptured)
        {
            Point newPosition = e.GetPosition(this);
            Vector dragVector = newPosition - _dragPoint;
            _dragPoint = newPosition;

            _translator.X += dragVector.X;
            _translator.Y += dragVector.Y;
        }

        base.OnMouseMove(e);
    }

    protected override void OnMouseUp(System.Windows.Input.MouseButtonEventArgs e)
    {
        ReleaseMouseCapture();

        base.OnMouseUp(e);
    }
}

I noticed that when you drag most of the ellipses of the side of the screen the whole thing speeds up so I'm guessing its related to rendering and there's nothing I can do stop this happening. Also if you comment out the stroke on the ellipses it runs much faster.

Any ideas? Thanks.