Creating a Viewport snapshot in RadPdfViewer

Updated on Sep 15, 2025

Environment

Product Version	2021.1.319
Product	RadPDFViewer for WPF

Description

How to create a snapshot of the visible part (viewport) of a PDF document loaded in the RadPdfViewer.

Solution

The first step is to create a custom IUILayer, which will help us to obtain the Viewport and store it in the VisiblePagesToViewport dictionary.

Example 1: Creating the custom IUILayer

C#

    public class ViewportUILayer : IUILayer
    {
        private RadFixedPage page;
        private readonly Canvas canvas;

        public ViewportUILayer()
        {
            this.canvas = new Canvas();
            this.canvas.Background = Brushes.Transparent;
        }

        public Canvas UIElement => this.canvas;

        public string Name => "ViewportUILayer";

        public void Clear()
        {
            MainWindow.VisiblePagesToViewport.Remove(this.page);
            this.page = null;
        }

        public void Initialize(UILayerInitializeContext context)
        {
            this.page = context.Page;
        }

        public void Update(UILayerUpdateContext context)
        {
            MainWindow.VisiblePagesToViewport[this.page] = context.Viewport;
        }
    }

The next step is to create a custom UILayersBuilder, which will help us to include the newly created ViewportUILayer into the IUILayerContainer.

Example 2: Creating the custom UILayersBuilder

C#

    public class CustomLayersBuilder : UILayersBuilder
    {
        protected override void BuildUILayersOverride(IUILayerContainer uiLayerContainer)
        {
            base.BuildUILayersOverride(uiLayerContainer);

            uiLayerContainer.UILayers.AddLast(new ViewportUILayer());
        }
    }

Using the ExtensibilityManager`s RegisterLayersBuilder() method we will register the CustomLayersBuilder.

Example 3: Registering the custom UILayersBuilder

C#

    public RadFixedDocument document;

    public MainWindow()
    {
        this.InitializeComponent();
        
        CustomLayersBuilder uILayersBuilder = new CustomLayersBuilder();
        ExtensibilityManager.RegisterLayersBuilder(uILayersBuilder);

        PdfFormatProvider pdfFormatProvider = new PdfFormatProvider();
        using (FileStream stream = File.OpenRead("SampleData/SampleDocument.pdf"))
        {
            this.pdfViewer.Document = pdfFormatProvider.Import(stream);
        }
    }

    static MainWindow()
    {
        VisiblePagesToViewport = new Dictionary<RadFixedPage, Rect>();
    }

    public static Dictionary<RadFixedPage, Rect> VisiblePagesToViewport { get; set; }

    private void CreateSnapshot(object sender, RoutedEventArgs e)
    {
        // Implemented in Example 4
    }
		

Now when we have the VisiblePagesToViewport, we can iterate its pages and export the snapshots to the desired image format using the ThumbnailFactory class. For the purpose of the example, we will generate a TIFF image.

Example 4: Exporting the images using the ThumbnailFactory

C#

    private void CreateSnapshot(object sender, RoutedEventArgs e)
    {
        ThumbnailFactory thumbnailFactory = new ThumbnailFactory();
        foreach (KeyValuePair<RadFixedPage, Rect> pair in VisiblePagesToViewport.ToList())
        {
            RadFixedPage page = pair.Key;
            Rect viewport = pair.Value;

            Rect saved = page.CropBox;
            page.CropBox = viewport;
            Size size = PageLayoutHelper.GetVisibleContentBox(page).Size;
            ImageSource imageSource = thumbnailFactory.CreateThumbnail(page, size);
            page.CropBox = saved;

            Image image = new Image();
            image.Source = imageSource;

            Grid container = new Grid();
            container.Background = Brushes.White;
            container.Children.Add(image);
            container.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
            container.Arrange(new Rect(new Point(0, 0), container.DesiredSize));

            RenderTargetBitmap bitmap = new RenderTargetBitmap((int)size.Width, (int)size.Height, 96, 96, PixelFormats.Pbgra32);
            bitmap.Render(container);

            int pageNumber = (page.Parent as RadFixedDocument).Pages.IndexOf(page) + 1;
            string exportedFileName = $"Page_{pageNumber}.tiff";
            using (FileStream fileStream = new FileStream(exportedFileName, FileMode.Create))
            {
                BitmapEncoder encoder = new TiffBitmapEncoder();
                encoder.Frames.Add(BitmapFrame.Create(bitmap));
                encoder.Save(fileStream);
            }

            Process.Start(exportedFileName);
        }
    }