Saving Surface to Bitmap and optimizing DirectX screen capture in C#

Question

after a whole day of testing I came up with this code, which captures current screen using DirectX (SlimDX) and saves it into a file:

Device d;

public DxScreenCapture()
{
    PresentParameters present_params = new PresentParameters();
    present_params.Windowed = true;
    present_params.SwapEffect = SwapEffect.Discard;
    d = new Device(new Direct3D(), 0, DeviceType.Hardware, IntPtr.Zero, CreateFlags.SoftwareVertexProcessing, present_params);
}

public Surface CaptureScreen()
{
    Surface s = Surface.CreateOffscreenPlain(d, Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height, Format.A8R8G8B8, Pool.Scratch);
    d.GetFrontBufferData(0, s);
    return s;
}

Then I do the following:

   DxScreenCapture sc = new DxScreenCapture();

..code here

    private void button1_Click(object sender, EventArgs e)
    {

        Stopwatch stopwatch = new Stopwatch();

        // Begin timing
        stopwatch.Start();

        Surface s = sc.CaptureScreen();
        Surface.ToFile(s, @"c:\temp\test.png", ImageFileFormat.Png);

        s.Dispose();

        stopwatch.Stop();

        textBox1.Text = ("Elapsed:" + stopwatch.Elapsed.TotalMilliseconds);
    }

The results are:

0. when I don't save surface: avg. elapsed time: 80-90ms

1. when I also save Surface to BMP file: format: ImageFileFormat.Bmp , avg. elapsed time: 120ms, file size: 7mb

2. when I also save Surface to PNG file: format: ImageFileFormat.Png , avg. elapsed time: 800ms, file size: 300kb

The questions are:

1. Is it possible to optimise current image capture? According to this article - Directx screen capture should be faster than GDI. For me, GDI usually takes 20ms to get a "Bitmap", whereas it takes 80ms to get "Surfare" using DX (both without saving).

http://www.codeproject.com/Articles/274461/Very-fast-screen-capture-using-DirectX-in-Csharp

2a. How to save Surface to PNG image format faster? When I save surface to 7mb BMP file it takes almost 6 times less time, than when I save the same surface to 300kb PNG file..

2b. Is it possible to save Surface directly to Bitmap so I don't have to create temporary files?

So I don't have to do following: Surface -> image file; image file open -> bitmap;, but instead: Surface -> bitmap

that's all for now. I'll gladly accept any tips, thanks!

Edit:

Just solved 2b by doing:

Bitmap bitmap = new Bitmap(SlimDX.Direct3D9.Surface.ToStream(s, SlimDX.Direct3D9.ImageFileFormat.Bmp));

Edit2:

Surface.ToFile(s, @"C:\temp\test.bmp", ImageFileFormat.Bmp);
Bitmap bitmap = new Bitmap(@"C:\temp\test.bmp");

is faster than:

Bitmap bitmap = new Bitmap(SlimDX.Direct3D9.Surface.ToStream(s, SlimDX.Direct3D9.ImageFileFormat.Bmp));

by 100 ms!!! Yeah, I couldn't believe my eyes too ;) I don't like the idea of temporary file creation, but a 50% performance increase (100-200ms instead of 200-300+) is a very good thing.

Answer 1

If performance really is an issue, you should consider writing your code in C++ instead. Therefor you dont need an external library but can directly access the backend-buffer of your video card via Windows-API + DirectX.

Accessing the backend(-video)-buffer is a lot faster than reading from the frontend-buffer.

To optimize performance (which also awnsers your question 1) use multithreading (see TPL or threading depending on your needs).

Here is an inside of how to do it in C++ CodeProject examples in C++. From my personal experience, DirectX was by far the fastest.

These steps

1. reading backend-buffer into a bitmap to process the data
2. spawning new thread to repeat step 1 while previous thread is still busy

take about 10-40ms (together) - implemented in C++ (on NVIDIA GeForce GTX 970M) and depending on the current workload of the hardware

Possible middle course

If you want to stick with C# but also need the performance, writing a C++-dll for .NET (see .NET Programming with C++/CLI (Visual C++)) which reads the video buffer and returns the data to your C#-Code will do the trick.

Answer 2

If you don't want to use SlimDX library you can also try

public Bitmap GimmeBitmap(Surface s)
{
    GraphicsStream gs = SurfaceLoader.SaveToStream(ImageFileFormat.Bmp, s);
    return new Bitmap(gs);
}

and try the same for .png - I did not test performance but it have to be faster than using disc temporary file :)

and as for 1st question - try to only once create surface and then on every screenshot only put into it device's buffer data and create the bitmap

d.GetFrontBufferData(0, s);
return new Bitmap(SurfaceLoader.SaveToStream(ImageFileFormat.Bmp, s));

this should save you some time :)