XnaControl.cs

public partial class XnaControl : UserControl
{
    private GraphicsDeviceService graphicsService;
    private XnaImageSource imageSource;

    /// <summary>
    /// Gets the GraphicsDevice behind the control.
    /// </summary>
    public GraphicsDevice GraphicsDevice
    {
        get { return graphicsService.GraphicsDevice; }
    }

    /// <summary>
    /// Invoked when the XnaControl needs to be redrawn.
    /// </summary>
    public Action<GraphicsDevice> DrawFunction;

    public XnaControl()
    {
        InitializeComponent();

        // hook up an event to fire when the control has finished loading
        Loaded += new RoutedEventHandler(XnaControl_Loaded);
    }

    ~XnaControl()
    {
        imageSource.Dispose();

        // release on finalizer to clean up the graphics device
        if (graphicsService != null)
            graphicsService.Release();
    }

    void XnaControl_Loaded(object sender, RoutedEventArgs e)
    {
        // if we're not in design mode, initialize the graphics device
        if (DesignerProperties.GetIsInDesignMode(this) == false)
        {
            InitializeGraphicsDevice();
        }
    }

    protected override void OnRenderSizeChanged(SizeChangedInfo sizeInfo)
    {
        // if we're not in design mode, recreate the 
        // image source for the new size
        if (DesignerProperties.GetIsInDesignMode(this) == false && 
            graphicsService != null)
        {
            // recreate the image source
            imageSource.Dispose();
            imageSource = new XnaImageSource(
                GraphicsDevice, (int)ActualWidth, (int)ActualHeight);
            rootImage.Source = imageSource.WriteableBitmap;
        }

        base.OnRenderSizeChanged(sizeInfo);
    }

    private void InitializeGraphicsDevice()
    {
        if (graphicsService == null)
        {
            // add a reference to the graphics device
            graphicsService = GraphicsDeviceService.AddRef(
                (PresentationSource.FromVisual(this) as HwndSource).Handle);

            // create the image source
            imageSource = new XnaImageSource(
                GraphicsDevice, (int)ActualWidth, (int)ActualHeight);
            rootImage.Source = imageSource.WriteableBitmap;

            // hook the rendering event
            CompositionTarget.Rendering += CompositionTarget_Rendering;
        }
    }

    /// <summary>
    /// Draws the control and allows subclasses to override 
    /// the default behavior of delegating the rendering.
    /// </summary>
    protected virtual void Render()
    {
        // invoke the draw delegate so someone will draw something pretty
        if (DrawFunction != null)
            DrawFunction(GraphicsDevice);
    }

    void CompositionTarget_Rendering(object sender, EventArgs e)
    {
        // set the image source render target
        GraphicsDevice.SetRenderTarget(imageSource.RenderTarget);

        // allow the control to draw
        Render();

        // unset the render target
        GraphicsDevice.SetRenderTarget(null);

        // commit the changes to the image source
        imageSource.Commit();
    }
}