Screen Share

Motivation

I wanted to learn more about COM interop with Go and create a somewhat usable screen sharing tool

Libaries used

This application uses D3D11 IDXGIOutputDuplication to create a somewhat realtime desktop presentation

• github.com/mattn/go-mjpeg for mjpeg streaming
• github.com/kbinani/screenshot for comparison with GDI BitBlt (slightly modified source, to support re-using image.RGBA)
• golang.org/x/exp/shiny/driver/internal/swizzle for faster BGRA -> RGBA conversion (see shiny LICENSE)
• github.com/pixiv/go-libjpeg/jpeg for fast jpeg encoding
  • enable with go build -tag jpegturbo

Demo

Just build the application and run it. It should serve all your monitors on an URL like http://127.0.0.1:8023/watch?screen=N
where screen=N <- N is the monitor index, starting at zero (0).

By changing the lines in main.go regarding the streaming, you can switch between GDI BitBlt or IDXGIOutputDuplication

// ...
framerate := 10
for i := 0; i < n; i++ {
    // ...
    // streamDisplay(ctx, i, framerate, stream)  // <= USE GDI BitBlt
    streamDisplayDXGI(ctx, i, framerate, stream) // <= USE IDXGIOutputDuplication
    // captureScreenTranscode(ctx, i, desiredFps)
    http.HandleFunc(fmt.Sprintf("/mjpeg%d", i), stream.ServeHTTP)
}
// ...

screen recording with ffmpeg

The code contains the function captureScreenTranscode which allows you to record the selected screen directly into ffmpeg and transcode it to h264 in an mp4 container.

Performance

Performance is not optimized to 100%, there are still thing that could be improved.

• only copying the dirty-rectangles (less GPU<->CPU communication)
• faster swizzle implementation using AVX/2 (less time for converting the BGRA texture)
• profile ... profile ... profile

Overall the current implementation is about 2-5x faster than GDI BitBlt (depending on the resolution, the higher the bigger the difference) and uses a lot less resources for cases where there arent any changes to the screen.

app.manifest

To make use of IDXGIOutput5::DuplicateOutput1, an application has to provide support for PerMonitorV2 DPI-Awareness (Windows 10 1703+) This is usually done by providing an my-executable.exe.manifest file either next to the executable, or as an embedded resource.

In this application there are calls to IsValidDpiAwarenessContext and SetThreadDpiAwarenessContext which circumvent the requirement.