[F#] Screen Capture

capture.fsx

#if NETF
#r "System"
#r "System.Drawing"
#r "System.Windows.Forms"
#else
//#r "nuget: System.Drawing.Common, 5.0.2"
#r @"C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App\6.0.4\System.Drawing.Common.dll"
#r @"C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App\6.0.4\System.Windows.Forms.dll"
#r @"C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App\6.0.4\System.Windows.Forms.Primitives.dll"
#r @"C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App\6.0.4\Microsoft.Win32.SystemEvents.dll"
#endif

open System.Runtime.InteropServices

[<DllImport("user32.dll")>] extern nativeint GetDesktopWindow()

let SRCCOPY = 0x00cc0020
[<DllImport("gdi32.dll")>] extern bool BitBlt(
    nativeint hdcDest, int nXDest, int nYDest, int nWidth, int nHeight,
    nativeint hdcSrc, int nXSrc, int nYSrc, int dwRop)

open System.Drawing

let captureScreen (r: Rectangle) =
    if r.X > 10000 || r.Y > 10000 || r.Width > 5000 || r.Height > 5000 || r.Width < 1 || r.Height < 1 then new Bitmap(1, 1) else
    let ret = new Bitmap(r.Width, r.Height)
    let desktop = GetDesktopWindow()
    use g1 = Graphics.FromImage ret
    use g2 = Graphics.FromHwnd desktop
    g1.Clear(Color.Black)
    let hdc1 = g1.GetHdc()
    let hdc2 = g2.GetHdc()
    ignore <| BitBlt(hdc1, 0, 0, r.Width, r.Height, hdc2, r.X, r.Y, SRCCOPY)
    g1.ReleaseHdc(hdc1)
    g2.ReleaseHdc(hdc2)
    ret

open System.Drawing.Imaging
open System.Windows.Forms

do
    use bmp = captureScreen(Screen.PrimaryScreen.Bounds)
    bmp.Save("screen.png", ImageFormat.Png)