How do I save all content of a WPF ScrollViewer as an image

Question

I have a WPF window with a ScrollViewer control containing many child controls that extend vertically. When a user clicks a button located at the bottom of the ScrollViewer I would like all the content (currently in view and out of view) to be saved as an image.

I am using the following code which I have adapted from examples showing how to save the content of a Window:

public static void SaveForm(ScrollViewer container, string filename)
{        
    const int dpi = 96;
    var rtb = new RenderTargetBitmap(
        (int)container.ExtentWidth, //width 
        (int)container.ExtentHeight, //height 
        dpi, //dpi x 
        dpi, //dpi y 
        PixelFormats.Pbgra32 // pixelformat 
        );

    rtb.Render(container);
    SaveRTBAsPNG(rtb, filename);
}

private static void SaveRTBAsPNG(RenderTargetBitmap bmp, string filename)
{
    var enc = new System.Windows.Media.Imaging.PngBitmapEncoder();
    enc.Frames.Add(System.Windows.Media.Imaging.BitmapFrame.Create(bmp));

    using (var stm = System.IO.File.Create(filename))
    {
        enc.Save(stm);
    }
}

Currently a PNG is being produced but it only has the currently visible portion of the ScrollViewer. Is there any way I can get the PNG to contain all of the content, including that which needs to be scrolled into view?

Answer 1

Use this with the CONTENT of you scrollviewer as source, not your scrollviewer itself : (It takes a snapshot even if the content is not visible)

    public static void SnapShotPNG(this UIElement source, Uri destination, int zoom)
    {
        try
        {
            double actualHeight = source.RenderSize.Height;
            double actualWidth = source.RenderSize.Width;

            double renderHeight = actualHeight * zoom;
            double renderWidth = actualWidth * zoom;

            RenderTargetBitmap renderTarget = new RenderTargetBitmap((int)renderWidth, (int)renderHeight, 96, 96, PixelFormats.Pbgra32);
            VisualBrush sourceBrush = new VisualBrush(source);

            DrawingVisual drawingVisual = new DrawingVisual();
            DrawingContext drawingContext = drawingVisual.RenderOpen();

            using (drawingContext)
            {
                drawingContext.PushTransform(new ScaleTransform(zoom, zoom));
                drawingContext.DrawRectangle(sourceBrush, null, new Rect(new Point(0, 0), new Point(actualWidth, actualHeight)));
            }
            renderTarget.Render(drawingVisual);

            PngBitmapEncoder encoder = new PngBitmapEncoder();
            encoder.Frames.Add(BitmapFrame.Create(renderTarget));
            using (FileStream stream = new FileStream(destination.LocalPath, FileMode.Create, FileAccess.Write))
            {
                encoder.Save(stream);
            }
        }
        catch (Exception e)
        {
            MessageBox.Show(e);
        }
    }