Take screenshot of external application

[csKanna]

Hi,

I need to take screenshot of another (third party) application window and save it in a folder.

Can someone guide me on this?
Thanks

[Radjesh Klauke]

Do you already know how to create a screenshot and save it?

[jmcilhinney]

You can use the Graphics.CopyFromScreen method to draw part of the screen onto an Image. I'm sure you'll find examples if you search. As for what part of the screen to draw, you'd have to use the Windows API. the FindWindow function will get the handle of a window and then probably GetWindowPos to get the bounds of that window.

[csKanna]

okay thanks. I somehow managed to get screenshot of the application window. Now there are two problems.

a. if there are other windows on top of that application, it takes the screenshot of that top most window.
b. if i locked my pc, it simply errors and not takes screenshot.

how to fix that?

[Edgemeal]

a. if there are other windows on top of that application, it takes the screenshot of that top most window.

The PrintWindow API can capture windows even if they are behind other windows or off to the sides of the desktop area.
One minor drawback is PrintWindow doesn't support opacity so captured windows are always solid.

Public Class Form1
' Tested on: WinXP-32 and Win7-64.
    Public Structure RECT
        Public left As Int32
        Public top As Int32
        Public right As Int32
        Public bottom As Int32
    End Structure
    Private Declare Function GetWindowRect Lib "user32.dll" (ByVal hwnd As IntPtr, ByRef lpRect As RECT) As Int32
    Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As IntPtr
    Private Declare Function PrintWindow Lib "User32.dll" (ByVal hWnd As IntPtr, ByVal hdcBlt As IntPtr, ByVal nFlags As Int32) As Int32

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        ' get handle of app to capture by the titlebar text
        Dim hWnd As IntPtr = FindWindow(Nothing, "Calculator") '<<< WINDOWS CALCULATOR

        If hWnd = IntPtr.Zero Then
            MessageBox.Show("Window not found!", "No Window Match", MessageBoxButtons.OK, MessageBoxIcon.Information)
        Else
            ' Capture app to Bitmap
            Dim bmp As Bitmap = Capture_hWndToBitmap(hWnd)
            If bmp IsNot Nothing Then
                Try
                    ' save bitmap to a public folder
                    bmp.Save("C:\Users\Ed\Pictures\TEST_CAPTURE.png", Imaging.ImageFormat.Png)                    
                Catch ex As Exception
                    MessageBox.Show(ex.Message, "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error)
                End Try
                bmp.Dispose()
            Else
                MessageBox.Show("Capture failed!", "Capture Fail", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
            End If
        End If
    End Sub

    ' Capture window by handle to bitmap
    Private Function Capture_hWndToBitmap(ByVal WindowHandle As IntPtr) As Bitmap
        Try
            Dim WinRect As RECT
            GetWindowRect(WindowHandle, WinRect)
            Dim bmp As Bitmap = New Bitmap(WinRect.right - WinRect.left, WinRect.bottom - WinRect.top)
            Dim g As Graphics = Graphics.FromImage(bmp)
            Dim hDC As IntPtr = g.GetHdc()
            Dim pwRet As Integer = PrintWindow(WindowHandle, hDC, 0)
            g.ReleaseHdc(hDC)
            If pwRet = 0 Then ' printwindow failed!
                Return Nothing
            Else
                Return bmp
            End If
        Catch
            Return Nothing ' something went wrong!
        End Try
    End Function

End Class

I had posted something similar yesterday but removed it because I was getting an error when run under Win7, turns out I didn't have permission to write the file to the drive/folder I selected!

[bergerkiller]

Using BitBlt is also an option, by passing the Hdc of the Window:

Dim wHdc As IntPtr = GetWindowDC(hwnd)

Remaining code is pretty large, see my Window class for all of the code.
Main idea around it is this:

1. Obtain Window DC
2. Obtain Window bounds or use the DC clip size
3. Obtain bitmap of the size of [2]
4. Make a Graphics object and obtain its Hdc
5. Use BitBlt to copy the data from the source to the destination (graphics)
6. Dispose all Hdc objects (also Graphics)
7. Return Bitmap

In API.DC.vb

Private Declare Function GetClipBox Lib "gdi32" (ByVal hdc As IntPtr, ByRef lprc As WRECT) As Integer
Private Declare Function BitBlt Lib "gdi32" (ByVal hdc As IntPtr, ByVal nXDest As Integer, ByVal nYDest As Integer, ByVal nWidth As Integer, ByVal nHeight As Integer, ByVal hdcSrc As IntPtr, ByVal nXSrc As Integer, ByVal nYSrc As Integer, ByVal dwRop As CopyPixelOperation) As Boolean
        Public ReadOnly Property ClipBox() As Rectangle
            Get
                Dim w As WRECT
                GetClipBox(Me.hdc, w)
                Return w.Value
            End Get
        End Property
        Public ReadOnly Property ClipSize() As Size
            Get
                Return Me.ClipBox.Size
            End Get
        End Property
        Public Function ToBitmap(Optional ByVal operation As CopyPixelOperation = CopyPixelOperation.SourceCopy Or CopyPixelOperation.CaptureBlt) As Bitmap
            Return ToBitmap(Me.ClipSize, operation)
        End Function
        Public Function ToBitmap(ByVal Resolution As Size, Optional ByVal operation As CopyPixelOperation = CopyPixelOperation.SourceCopy Or CopyPixelOperation.CaptureBlt) As Bitmap
            ToBitmap = New Bitmap(Resolution.Width, Resolution.Height)
            Dim g As Graphics = Graphics.FromImage(ToBitmap)
            Dim ghdc As IntPtr = g.GetHdc
            BitBlt(ghdc, 0, 0, Resolution.Width, Resolution.Height, Me.hdc, 0, 0, operation)
            g.ReleaseHdc(ghdc)
            g.Dispose()
        End Function

In Window.vb

Public Function CaptureWindow(ByVal g As Graphics) As Boolean
        Dim DC As New API.DC(g)
        Dim wDC As API.DC = Me.GetWindowDC
        wDC.CopyTo(DC)
        DC.Dispose()
        wDC.Dispose()
    End Function
    Public Function CaptureWindow() As Image
        Dim s As Size = Me.Size
        If s.Width < 1 Or s.Height < 1 Then Return Nothing
        Dim img As New Bitmap(s.Width, s.Height)
        Dim g As Graphics = Graphics.FromImage(img)
        CaptureWindow(g)
        g.Dispose()
        Return img
    End Function