How to create bitmap from Surface (SharpDX)

Question

I am new to DirectX and trying to use SharpDX to capture a screen shot using the Desktop Duplication API.

I am wondering if there is any easy way to create bitmap that I can use in CPU (i.e. save on file, etc.)

I am using the following code the get the desktop screen shot:

var factory = new SharpDX.DXGI.Factory1();
var adapter = factory.Adapters1[0];
var output = adapter.Outputs[0];

var device = new SharpDX.Direct3D11.Device(SharpDX.Direct3D.DriverType.Hardware,
                                                       DeviceCreationFlags.BgraSupport |
                                                       DeviceCreationFlags.Debug);

var dev1 = device.QueryInterface<SharpDX.DXGI.Device1>();

var output1 = output.QueryInterface<Output1>();
var duplication = output1.DuplicateOutput(dev1);
OutputDuplicateFrameInformation frameInfo;
SharpDX.DXGI.Resource desktopResource;
duplication.AcquireNextFrame(50, out frameInfo, out desktopResource);

var desktopSurface = desktopResource.QueryInterface<Surface>();

can anyone please give me some idea on how can I create a bitmap object from the desktopSurface (DXGI.Surface instance)?

Answer 1

The MSDN page for the Desktop Duplication API tells us the format of the image:

DXGI provides a surface that contains a current desktop image through the new IDXGIOutputDuplication::AcquireNextFrame method. The format of the desktop image is always DXGI_FORMAT_B8G8R8A8_UNORM no matter what the current display mode is.

You can use the Surface.Map(MapFlags, out DataStream) method get access to the data on the CPU.

The code should look like* this:

DataStream dataStream;
desktopSurface.Map(MapFlags.Read, out dataStream);
for(int y = 0; y < surface.Description.Width; y++) {
    for(int x = 0; x < surface.Description.Height; x++) {
        // read DXGI_FORMAT_B8G8R8A8_UNORM pixel:
        byte b = dataStream.Read<byte>();
        byte g = dataStream.Read<byte>();
        byte r = dataStream.Read<byte>();
        byte a = dataStream.Read<byte>();
        // color (r, g, b, a) and pixel position (x, y) are available
        // TODO: write to bitmap or process otherwise
    }
}
desktopSurface.Unmap();

*Disclaimer: I don't have a Windows 8 installation at hand, I'm only following the documentation. I hope this works :)

Answer 2

I've just completed this myself although I am not going to say much about this code!

public byte[] GetScreenData()
    {
        // We want to copy the texture from the back buffer so 
        // we don't hog it.
        Texture2DDescription desc = BackBuffer.Description;
        desc.CpuAccessFlags = CpuAccessFlags.Read;
        desc.Usage = ResourceUsage.Staging;
        desc.OptionFlags = ResourceOptionFlags.None;
        desc.BindFlags = BindFlags.None;

        byte[] data = null;

        using (var texture = new Texture2D(DeviceDirect3D, desc))
        {
            DeviceContextDirect3D.CopyResource(BackBuffer, texture);

            using (Surface surface = texture.QueryInterface<Surface>())
            {
                DataStream dataStream;
                var map = surface.Map(SharpDX.DXGI.MapFlags.Read, out dataStream);
                int lines = (int)(dataStream.Length / map.Pitch);
                data = new byte[surface.Description.Width * surface.Description.Height * 4];

                int dataCounter = 0;
                // width of the surface - 4 bytes per pixel.
                int actualWidth = surface.Description.Width * 4;
                for (int y = 0; y < lines; y++)
                {
                    for (int x = 0; x < map.Pitch; x++)
                    {
                        if (x < actualWidth)
                        {
                            data[dataCounter++] = dataStream.Read<byte>();
                        }
                        else
                        {
                            dataStream.Read<byte>();
                        }
                    }
                }
                dataStream.Dispose();
                surface.Unmap();
            }
        }

        return data;
    }

This will get you a byte[] which can then be used to generate a bitmap.

The following is how I saved to a png Image.

 using (var stream = await file.OpenAsync( Windows.Storage.FileAccessMode.ReadWrite ))
            {
                BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, stream);
                double dpi = DisplayProperties.LogicalDpi;

                encoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Straight,
                    (uint)width, (uint)height, dpi, dpi, pixelData);
                encoder.BitmapTransform.ScaledWidth = (uint)newWidth;
                encoder.BitmapTransform.ScaledHeight = (uint)newHeight;
                await encoder.FlushAsync();
                waiter.Set();
            }

I know this was answered a while ago, and maybe you figured it out by now :3 but if someone else gets stuck I hope this helps!