Get a bitmap image from a Control view

I would like to "copy to clipboard" what a Control of my WPF app draws on the screen. Therefore, I need to build a bitmap image from my Control current display.

Is there an easy way to do that ?

Thanks in advance.

Answers


I wouldn't call it easy...but the key component is the RenderTargetBitmap, which you can use as follows:

RenderTargetBitmap rtb = new RenderTargetBitmap((int)control.ActualWidth, (int)control.ActualHeight, 96, 96, PixelFormats.Pbgra32);
rtb.Render(control);

Well, that part is easy, now the RTB has the pixels stored internally...but your next step would be putting that in a useful format to place it on the clipboard, and figuring that out can be messy...there are a lot of image related classes that all interact one or another.

Here's what we use to create a System.Drawing.Image, which i think you should be able to put on the clipboard.

PngBitmapEncoder png = new PngBitmapEncoder();
png.Frames.Add(BitmapFrame.Create(rtb));
MemoryStream stream = new MemoryStream();
png.Save(stream);
Image image = Image.FromStream(stream);

System.Drawing.Image (a forms image) cannot interact directly with the RenderTargetBitmap (a WPF class), so we use a MemoryStream to convert it.


If the control you are trying to create a bitmap from is inside a StackPanel it won't work, you will just get an empty image.

Jaime Rodriguez has a good piece of code to get around this on his blog:

private static BitmapSource CaptureScreen(Visual target, double dpiX, double dpiY)
{
    if (target == null)
    {
        return null;
    }
    Rect bounds = VisualTreeHelper.GetDescendantBounds(target);
    RenderTargetBitmap rtb = new RenderTargetBitmap((int)(bounds.Width * dpiX / 96.0),
                                                    (int)(bounds.Height * dpiY / 96.0),
                                                    dpiX,
                                                    dpiY,
                                                    PixelFormats.Pbgra32);
    DrawingVisual dv = new DrawingVisual();
    using (DrawingContext ctx = dv.RenderOpen())
    {
        VisualBrush vb = new VisualBrush(target);
        ctx.DrawRectangle(vb, null, new Rect(new Point(), bounds.Size));
    }
    rtb.Render(dv);
    return rtb;
}

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