Wednesday, 12 September 2012

Exporting an image from a DirectX 2D Image in Windows 8 C#/XAML Using SharpDX


I’m working on a Windows 8 app which has a drawing element to it. The original WP7 app in Silverlight was fine because a simple drawing rendered in XAML was captured using WritableBitmap.Render and written to a file stream. This feature is missing from the Windows 8 API, so it’s impossible to write a pure C#/XAML app which can export a user created image. To get round this it’s possible to use DirectX/XAML/C++ to create a XAML UI which can draw DirectX images.

DirectX/XAML/C++ offers a number of XAML containers which interface with DirectX and have different behaviours:

I wanted to use a SurfaceImageSource, so I could have my DirectX image in line with other XAML controls and containers.

The big problem is that I don’t want to write a whole app in C++, it would take me a lot longer than C# and it seemed like a sledge hammer to crack a nut using full C++/DirectX for a simple application.

So after much research and stress about what to do, I found SharpDX and thought all my prayers had been answered! SharpDX is a full DirectX to C# interop library which allows DirectX to be brought into C#/XAML apps in the same way as C++/XAML apps.

The major problem was how to save the image you’ve drawn out of the DirectX image? There are a small number of examples of how to do it in C++, so after a lot of cross referencing the SharpDX source and tips from Alexandre Mutel on interfacing with a WICStream, I managed to get it working.

This save method was tested inside the EffectRenderer in the SharpDX lighting effect sample. This is the whole code so you don’t need to paste it back together in sections:

public async void Save()
    // Launch file picker
    Windows.Storage.Pickers.FileSavePicker picker = new Windows.Storage.Pickers.FileSavePicker();
    picker.FileTypeChoices.Add("PNG", new List<string>() { ".png" });
    var file = await picker.PickSaveFileAsync();
    if (file == null)

    // Get stream
    var fStream = await file.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite);

    var factory = new ImagingFactory();

    MemoryStream ms = new MemoryStream(100000);
    ms.Position = 0;

    // Create a WIC outputstream
    WICStream stream = new WICStream(factory, ms);

    var size = this._deviceManager.ContextDirect2D.PixelSize;
    var format = new SharpDX.Direct2D1.PixelFormat(SharpDX.DXGI.Format.B8G8R8A8_UNorm, AlphaMode.Premultiplied);

    // Initialize a Png encoder with this stream
    var wicBitmapEncoder = new SharpDX.WIC.PngBitmapEncoder(factory, BitmapEncoderGuids.Png);

    // Create a Frame encoder
    var wicFrameEncoder = new BitmapFrameEncode(wicBitmapEncoder);

    // Create image encoder
    ImageEncoder wicImageEncoder;
    SharpDX.WIC.ImagingFactory2 factory2 = new ImagingFactory2();
    factory2.CreateImageEncoder(this._deviceManager.DeviceDirect2D, out wicImageEncoder);

    var imgParams = new ImageParameters();
    imgParams.PixelFormat = format;
    imgParams.PixelHeight = (int)size.Height;
    imgParams.PixelWidth = (int)size.Width;
    wicImageEncoder.WriteFrame(_effectGraph.Output, wicFrameEncoder, ref imgParams);

    // Commit changes

    byte[] buffer = new byte[ms.Length];
    ms.Position = 0;
    await ms.ReadAsync(buffer, 0, (int)ms.Length);
    var opStream = fStream.AsStreamForWrite();
    await opStream.WriteAsync(buffer, 0, buffer.Length);
    await opStream.FlushAsync();

    // Dispose

The first section gets a file stream from the user to write the data to once it’s been extracted from the image, then creates an intermediary MemoryStream for the WICStream to interface with (Alexandre pointed out that the Win8 RandomAccessStream will not interface with a WICStream since it needs to perform seek operations) and finally the WICStream itself which WIC will use to write the image to.

The second section creates a Bitmap Encoder, Frame Encoder and Image Encoder and writes the image frame into the stream.

The final section and the bit which caused me a lot of problems, is getting the data from the stream. The encoders all need committing in order, but in many C++ examples the WICStream is also committed which should flush the stream to it’s destination, however it was throwing an exception:

An exception of type 'SharpDX.SharpDXException' occurred in SharpDX.DLL but was not handled in user code

Additional information: HRESULT: [0x88982F50], Module: [Unknown], ApiCode: [Unknown/Unknown], Message: The component cannot be found.

If there is a handler for this exception, the program may be safely continued.

This isn’t particularly helpful, but I was advised that the WIC stream doesn’t need flushing as the underlying stream should take care of this. At this point I could see the memory stream had a size, but when I wrote it to a buffer it was coming out all zeros. This was a simple mistake – the memory stream just needs setting back to the start and it all started magically working!

All I need to do now is work out how to use DirectX to draw my picture! I hope this helps some other people as it’s been causing me a massive headache for a number of days!


  1. Hi Geoff,

    This is really great. I was looking for this solution for a long time.

    Can you maybe help me with using this technique to save an effectRenderer object. It is used in the D2DEffectsHelloWorld Win8 sample.



  2. Hi Fons,

    Thanks, I'll try and take a look tonight. I'm still getting my head around this subject!


  3. Hi Geoff,

    Thanks. My EffectRender has two bitmaps (Direct2D1.Effects) in which the second one (which is partly transparent) is rendered (drawn) on top of the first one. I want to save the result of this Render() must be saved to a file.

    If you want I can send you my project.



  4. Do you have an effect graph in the renderer? I used the _effectGraph.Output as the image. I can take a quick look, but I'm finishing a project for Friday and have another one to do (the DirectX one).

  5. I too face similar issues in my project. For the last two months i was trying to create an image of my canvas. But i failed. Now it seems you found a promising logic to achieve the same but i didn't understand completely the code you provided. Where i can pass my UI control for taking the snapshot. what is this "_deviceManager". and for what it is used for. Can you provide a working sample. Then it would be helpful for me to implement my secondary tile. functionality with a snapshot of my control.

  6. It's not that straight forward, you need to create your drawing in directX not xaml. Then you can export.

    Look at the SharpDX samples for how to do this.

  7. Hey... I tried out your code and the png file that gets created has a security attriubute set (right click on the image -> properties) which states "this file came from another computer and might be blocked..." and you have to unblock it to be able to write to it again.

  8. Sounds strange. Is it saved to local disc?

  9. Yes, it's saved to local disk, just has that annoying security attribute set. Do you see the same behavior when you run it?

  10. Yes, I'm seeing the same thing, don't know why though

  11. Please, can you explain why can't I find "factory2.CreateImageEncoder" in my sharpdx sources?
    and what is _effectGraph?
    I'm hardly new to sharpdx, sorry

    I just want to save to local storage my SurfaceImageSource contents.. but I can't :(

  12. Check out part 2 (link at top) you need to use WIC which is a different API to DirectX but is still included in SharpDX

  13. I'm developing an App that has a Canvas element on XAML, and I drop some images into it. How can I use your code to get the children from the Canvas and save to image?


  14. The short answer use you can't. You need to use a direct2d SurfaceImageSource instead of canvas to do your rendering, then use the same rendering routine to draw to an image as described in the article.

  15. Had the same problem, could not find factory2.CreateImageEncoder method, I am using SharpDX.WIC in my assembly references but still doesn't work.

  16. Looks like this method has been deprecated and ImageEncoder has a constructor with factory parameter. Check out change notes: