The lack of WriteableBitmap.Render in Windows WinRT 8.0 was quite an issue for many apps, but fortunately did WinRT 8.1 (re-)introduce the RenderTargetBitmap class which provides the functionality of rendering the visual tree of the UI to a bitmap. The new update of WriteableBitmapEx makes it even easier to use with a WriteableBitmap by introducing the FromPixelBuffer method.
WriteableBitmapEx is available for 4 platforms: Windows Phone 8 and 7, WPF, Silverlight and Windows Store WinRT .NET XAML 8 and 8.1.
You can download the binaries here or via the NuGet package. The packages contain the WriteableBitmapEx binaries. As usual all samples and the source code can be found in the repository.
How to use
The below code snippet shows how a part of the UI can be rendered into a WriteableBitmap via RenderTargetBitmap, how it can be modified and then finally presented back into the UI by using an Image control.
// Render some UI to a RenderTargetBitmap var renderTargetBitmap = new RenderTargetBitmap(); await renderTargetBitmap.RenderAsync(Panel); // Get the pixel buffer and copy it into a WriteableBitmap var pixelBuffer = await renderTargetBitmap.GetPixelsAsync(); var width = renderTargetBitmap.PixelWidth; var height = renderTargetBitmap.PixelHeight; var wbmp = await new WriteableBitmap(1, 1).FromPixelBuffer(pixelBuffer, width, height); // Modify the WriteableBitmap wbmp.FillEllipse(10, 10, 256, 256, Colors.Salmon); // ... More drawing including writeableBitmap.Blit(...) might go here // Assign WriteableBitmap to an Image control to present it ImgMirror.Source = wbmp;