Rendering WPF Visuals to Bitmap

Sometimes we need to convert a WPF Window or Control (or any other type of Visual) to a plain old GDI+ Bitmap. In WinForms, creating a Bitmap of a Window or Control is quite complex. In WPF it's a piece of cake, at least if you're comfortable with the citizens of the System.Windows.Media.Imaging namespace, like RenderTargetBitmap, and the range of BitmapEncoders. I created a little helper class with some extension methods to Visual to facilitate the process. The class comes with a PngBitmap method that returns a Bitmap (PNG format), and a BitmapSource method for data binding, e.g. to a WPF Image control.

This is a screenshot of a small sample. The textbox and ellipse in the upper part of the window are original WPF Controls. The lower part of the window is a bitmap of the upper part, displayed in an Image control:



The Window has the following XAML content:

    <StackPanel>

        <TextBlock 

            Margin="10"

            Text="Dock of the Bay" />

        <Ellipse 

            Margin="10"

            Height="50" Width="50"

            Fill="DeepSkyBlue" Stroke="MidnightBlue"

            HorizontalAlignment="Left" />

        <Image

            x:Name="ScreenShotImage" />

    </StackPanel>

The screenshot is taken, and displayed in the Image control with the following one-liner:

   this.ScreenShotImage.Source = this.BitmapSource();

Here's the whole extension class:

//-----------------------------------------------------------------------

// <copyright file="VisualExtensions.cs" company="DockOfTheBay">

//     http://www.dotbay.be

// </copyright>

// <summary>Defines the VisualExtensions class.</summary>

//-----------------------------------------------------------------------

namespace DockOfTheBay

{

    using System;

    using System.Drawing;           // Need reference to System.Drawing.dll

    using System.Windows;

    using System.Windows.Interop;   // Need reference to PresentationCore.dll

    using System.Windows.Media;

    using System.Windows.Media.Imaging;

    /// <summary>

    /// Extension Methods for the System.Windows.Media.Visual Class

    /// </summary>

    public static class VisualExtensions

    {

        /// <summary>

        /// Returns the contents of a WPF Visual as a Bitmap in PNG format.

        /// </summary>

        /// <param name="visual">A WPF Visual.</param>

        /// <returns>A GDI+ System.Drawing.Bitmap.</returns>

        public static Bitmap PngBitmap(this Visual visual)

        {

            // Get height and width

            int height = (int)(double)visual.GetValue(FrameworkElement.ActualWidthProperty);

            int width = (int)(double)visual.GetValue(FrameworkElement.ActualHeightProperty);

            // Render

            RenderTargetBitmap rtb =

                new RenderTargetBitmap(

                    height,

                    width,

                    96,

                    96,

                    PixelFormats.Default);

            rtb.Render(visual);

            // Encode

            PngBitmapEncoder encoder = new PngBitmapEncoder();

            encoder.Frames.Add(BitmapFrame.Create(rtb));

            System.IO.MemoryStream stream = new System.IO.MemoryStream();

            encoder.Save(stream);

            // Create Bitmap

            Bitmap bmp = new Bitmap(stream);

            stream.Close();

            return bmp;

        }

        /// <summary>

        /// Returns the contents of a WPF Visual as a BitmapSource, e.g.

        /// for binding to an Image control.

        /// </summary>

        /// <param name="visual">A WPF Visual.</param>

        /// <returns>A set of pixels.</returns>

        public static BitmapSource BitmapSource(this Visual visual)

        {

            Bitmap bmp = visual.PngBitmap();

            IntPtr hBitmap = bmp.GetHbitmap();

            BitmapSizeOptions sizeOptions = BitmapSizeOptions.FromEmptyOptions();

            return Imaging.CreateBitmapSourceFromHBitmap(

                                hBitmap,

                                IntPtr.Zero,

                                Int32Rect.Empty,

                                sizeOptions);

        }

    }

}

By the way, if you prefer to screen capture to XPS instead of to a Bitmap, then I suggest this article.